Library of Excerpts

Lateralization and Language II

"For right-handers, the right hand was stonger than the left hand... For the left-handers as a group there was no significant hand difference.....A significant Group X Hand interaction for the left-handers...indicated that the two groups differed in direction of hand strength superiority. For CLH's the man favored the left hand..., while for the ICLH's the mean favored the right hand...(Peters, Michael (1990) Subclassification of non-pathological left-handers poses problems for theories of handedness. Neuropschologia 28: 282)

Consistent left-handers...left hand measures are larger. Inconsistent left-handers....the right hand is larger than the left. Inconsistent left-handers....the right hand was more accurate than the left hand. Consistent left-handers....the left hand was more accurate than the right hand. Tapping performance showed no significant overall group differences....in ICLH's the left hand wa faster...and in CLH's, the left hand was faster as well..." (Peters, Michael (1990) Subclassification of non-pathological left-handers poses problems for theories of handedness. Neuropschologia 28: 283-5)

"However, the two subgroups of left-handers differed in significant ways in terms of the patterns of observed asymmetries. CLH's use their left hand for writing, the measures of left hand thumb and index finger size are larger than the corresponding right hand meaures, they are stronger with the left hand and they throw with the left hand, they throw better with the left than with the right hand and they tap faster with the left than with the right hand. In contrast, those classified as ICLH's show a different pattern. The term "inconsistent" turns out to be a misnomer if one interprets inconsistent to mean that subjects are inconsistent in hand choice within task. Such within task inconsistency in preference has been called "ambiguous handedness" by Satz, et al. The ICLH's show within task consistency but are inconsistent with regard to both preference and performance between tasks. What is of interest is that the inconsistency is by no means random. The ICLH's write with the left hand, they perform better with the left hand on the speed finger tapping task and they do better with the left hand on the Purdue Pegboard task. However, ICLH's are stronger in the right hand, right hand measurements for thumb and index finger size are larger, and they throw better with the right hand. This group of left-handers shows a very clear dissociation in preference and preformance for activities that involve whole arm movements and strength. ... It should be noted that a similar situation applies to statements that left-handers, as a group, do not show significant differences in terms of one hand being stronger than the other. It is true enough, as was the case for the strength data in this study, that left-handers as a group show non asymmetries favoring the right or left hand. That is so because the directional differences for he CLH's and the ICLH's cancel each other out. (Peters, Michael (1990) Subclassification of non-pathological left-handers poses problems for theories of handedness. Neuropschologia 28: 286-7

"We have, then, two contemporary theories that predict associations between handedness and developmental language disorder. Both predict excess non-right-handedness in children with specific language disorders, and Annett and Kilshaw further predict that right-handers with developmental language disorders should have unusually poor left hand skills." (Bishop DVM (1990) Handedness, clumsiness and developmental language disorders. Neuropsychologia 28: 682)

"In line with prediction, a modest (though non-significant) increase in left-handedness was found in this subgroup (20% compared to 12.3% in control children), and there was a particularly high rate of left-handedness among those children who were unusually clumsy with the non-preferred hand (3 our of 6 of these children were left-handed). The numbers of speech-impaired children were too small to prove a convincing test of the hypothesis, but it is interesting to note that insofar as there is evidence for a link between clumsiness of the non-preferred hand and verbal difficulties, this involves children with expressive speech disorders. This suggests that in those subgroups of developmental language disorder where previous studies have reported an excess of left-handedness, brain injury may be implicated." (Bishop DVM (1990) Handedness, clumsiness and developmental language disorders. Neuropsychologia 28: 684)

"This study provided little support for theories that attribute developmental language disorder to weak cerebral lateralization. Left-handedness and mixed-handedness were no more common in language-impaired children than in a control group, and the difference in skill between the two hands was similar for language-impaired and control children. Furthermore, there was no evidence for the excess of strong right-handers with poor left hand performance that was predicted on the basis of Annett and Kilshaw's work. On the basis of previous studies, it had been anticipated that a link with non-right-handedness might be specific to children with severe problems in speech sound production, but this prediction was not confirmed in this sample, regardless of whether or not the speech problems were associated with comprehension difficulties. As in the control sample, poor performance with the non-preferred hand was more common in left-handers than right-handers in the language-impaired sample. The percentages in each group were similar in both samples, although the difference did not reach statistical significance in the smaller language-impaired group. There was no indication from this study that left-handers with very poor right hand scores are particularly common among children with developmental language disorders. Furthermore, the small subset of left-handers with poor right hand skill did not form a homogenous group in terms of profile of language skills." (Bishop DVM (1990) Handedness, clumsiness and developmental language disorders. Neuropsychologia 28: 689)

"Yalom et al. (1973) studied 20 16-year old boys of diabetic mothers, who had received estrogen or progesterone during pregnancy. These boys showed less heterosexuality and less masculinity than 20 control boys. Netley and Rovet (1982) showed that among 33 males with 47,XXY syndrome, 24% were nonrighthanded, compared to 10% of a control group. ... In the present study, as well as in Lindesay (1987), only homosexual men were studied. In Rosenstein and Bigler (1987) and McCormick et al. (1990), both men and women were studied, and in the latter study, a significant increase in lefthandedness (or rather nonrighthandedness) was obtained for women. This was assumed to be related to higher-than-normal levels of prenatal testosterone levels. In their results, the increase in lefthandedness in homosexual women (which have lower occurrence than men in the general population) is much larger than that of homosexual men. It is, therefore, fair to assume that the increase in testosterone, believed to cause both lefthandedness and homosexuality in women, will give a more pronounced effect in women than in men." (Gotestam, K.O., Coates,T.J., Ekstrand, M. (1992) Handedness, dyslexia and twinning inhomosexual men. International Journal Neuroscience 63 (3-4): 184)

"Artistic and mathematical talents were higher in left-handers, as was the frequency of occurence of asthma. Right-handers were higher in musical talent. (Smith, B.D., Meyers, M.B., Kline, R. (1989) For better of for worse: left-handedness, pathology, and talent. Journal Clinical Experimental Neuropsychology 11 (6): 949)

"Geschwind (1976), Kimura (1976), and Zangwill (1976) have all emphasized the role of the left hemisphere in the planning and control of purposive, sequential acts, and it has been argued that sequential aspects of perception are tied to the left hemisphere through its prior involvement with motor sequencing (Corballis 1980; Craig 1980)." ( Corballis, M.C. (1981) Towards an evolutionary perspective on hemispheric specialization. Behavioral and Brain Sciences 4: pp. 69)

"Our principal finding was that of the 11,102 individuals responding to the question of writing hand, 9.5% indicated that they wrote with the left hand, 89.6% with the right hand, and 0.9% with either hadn (Table I). (Perelle, I.B. & Ehrman, L. (1994) An international study of human handedness: the data. Behavior Genetics 24 (3): 219)

"Kimura (1992) concluded that males tend to do better than females on mathematical reasoning, whereas females tend to better than males on arithmetic calculation. ... In our study, the effects of sex and familial sinistrality on spatial functioning varied depending on the type of spatial ability that was examined. Males outperformed females on Rotated Figures and Surface Development, two tasks that require mental manipulation of spatial objects. LHFS+ subjects outperformed LHFS- objects on Hidden Figures and Picture Completion, two tasks that relate to visual closure." (Van Strien JW, Bouma A (1995) Sex and familial sinistrality differences in cognitive abilities. Brain and Cognition 27(2):143-4)

"Cognitive functioning was assessed in 69 left-handed males and females with a positive family history of left-handedness and in 77 left-handed and 55 right-handed males and females without familial left-handedness. Compared to females, males preformed better on numerical reasoning and on two visuaospatial tasks involving spatial manipulations (Figure Rotation and Surface Development). Within the group of left-handers, the multivariate effect for Familial Sinistality was significant. Left-handers with familial left-handedness exhibited better scores on numerical reasoning, on verbal reasoning, and on two visuospatial tasks involving visual closure (Hidden Figures, Picture Completion) than did left-handers without left-handed relatives. The nonfamilial left-handers also exhibited lower scores on both inductive reasoning tasks when they were compared to their right-handed conterparts. The outcome runs contrary to the prevalent conclusion that left-handers with left-handed relatives are more likely to exhibit lower performances on visuospatial tasks than left-handers without such relatives." (Van Strien JW, Bouma A (1995) Sex and familial sinistrality differences in cognitive abilities. Brain and Cognition 27(2):137)

"Of the 136 men, 24 (17.6%) were left-handed. This incidence is significantly higher (p<.001) than that of the approximately 10% of men in the general population who are left-handed (Karpinos and Grossman, 1953; Oldfield, 1971). Of the 48 women, only 8% (N=4) were left-handed. Left-handedness was significantly more frequent in alcohol-abusing men with alcoholic fathers (12/44 = 27%) than in those with nonalcoholic fathers (8/74 = 11%; p=.01) and in first-born (11/31 = 35%) than in nonfirst-born men (9/78 = 12%; p<.004). Of the right-handed men and women, 45% (34/76) had a first-degree relative who was left-handed. Additionally, of the right-handed men with alcoholic fathers, 66% (12/18) had a first-degree relative who was left-handed, compared to the 34% (13/38) of the right-handed men with nonalcoholic fathers (p<.03). ... Of the left-handed men, 60% (17/28) --- vs. 30% (32/107) of the right-handed men --- had an alcoholic father (p<.003). (The frequency of maternal alcoholism in the sample was substantially lower, approximately 13%, and appeared unrelated to handedness.) Of the left-handed men, 46% (12/26) were first born, 15% (4/26) were second born, and 38% (10/26) were later born. Of the right-handed men, 23% (21/90) were first born, 37% (33/90) were second born, and 40% (36/90) were later born. Significantly more of the left-handed men were first born and significantly more of the right-handed than left-handed men were second born (p=.01)" (London WP, Kibbee P, Holt L (1985) Handedness and alcoholism. J Nerv Ment Dis 173(9):570-571)

"It is noteworthy that, in our sample, 42% (20/47) of the women and 28% (37/130) of the men had a first-degree relative who evidenced either attention deficit disorder, learning disability, or stuttering. Family histories of migraine and of thyroid disorders in mothers were also frequently reported, particularly by the women. For example, of the last 62 women and 149 men admitted to the treatment team (April 1982 through July 1984), 38% (24/62) of the women's mothers were described as having suffered migraine headaches, vs. only 15% (22/149) of the men's mothers (p<.001). In addition, of the mothers with migraine, 38% (14/37) had an alcoholic father (the maternal grandfather of our patient) vs 21% (30/143) of the mothers without migraine (p< .04). As for thyroid disorders (both hyperthyroidism and hypothyroidism), Lindemann et al. (1984) have reported their frequency in the general populution to be about 1.4% in women and 0. 22 % in men. In contrast, of the last 41 women and 82 men in our series, 27% (11/41) of the mothers of the women and 15% (12/82) of the men's mothers were described as having thyroid disorder. Finally, of the last 62 women in the series seven were firmly diagnosed as having hypothyroidism (based either on an elevated thyroid-stimulating hormone or an augmented response of thryoid-stimulating hormone to intravenous thyrotropin-releasing hormone and by response to thyroid supplement over a minimum 6-month follow up period). Only one of the last 149 men in the series was so diagnosed." (London WP, Kibbee P, Holt L (1985) Handedness and alcoholism. J Nerv Ment Dis 173(9):570-571)


"Barnes and Richards {12} measured the time it took for newborns to establish normal breathing, and then followed up these Ss to age three when handedness was established. They found that 29 of 30 who became right handed had established breathing in 2 min or less, whereas only 6 of 15 who became either left-handed or ambidextrous had established breating in this time. Hypoxia at birth thus seems to be a good predictor of handedness at age three." (Bakan, P. (1977) Left handedness and birth order revisted. Neuropsychologia 15 (6): 838)

"Thirty pairs of dichotically presented CV syllables were administered to matched samples of Native American Navajo and Anglo subjects. While sex was not a significant factor, significant differences were evidenced in the performance of the Native American Navajo and Anglo subjects. As predicted, the Navajo subjects demonstated a left ear advantage compared to the traditional right ear effect found in the Anglo subjects. These results are discussed as they relate to linguistic processing and neuropsychological theory. ... Cllinical reports of aphasic Japanese subjects have shown them to have considerable variability in their writing of Kana and Kanji characters (6-9). The Kana symbols are phonetic representations of syllables, while the Kanji characters represent the legographic properties of the characters. Recent studies have investigated the capacity of the two cerebral hemispheres in normal Japanese subjects to differentiate and process these two types of written characters {10-12}. The results of these studies have indicated that the two cerebral hemispheres do differentially process Kana and Kanji characters. The Kana (phonetic) symbols seem to be processed in the left cerebral cortex while the Kanji (logograhic) characters are more reliably reported when projected to the right cerebral hemisphere. These results seem to be consistent whth the clinical observations noted in aphasic Japanese patients {6-9} and are intriquing for several reasons. First, reading these symbols in Japanese appears to require a more neurologically integrated effort than reading English, as it seems to involve the processing of symbols in both cerebral hemispheres rather than in the left cerebral cortex, which seems to be the case with English. Second, one could speculate that some mechanism must scan the characters and, based on their stimulus properties, shift attention transcallosally to the appropriate hemisphere. Finally, these studies suggest that cerebral function for written Japanese may be less fully lateralized in Japanese subjects as is traditionally reported in the contempory literature for English-speaking subjects. If this is indeed the case, there may be other populations in which language lateralization differs relative to our current understanding of neuropsychological asymmetries. There is some very limited evidence that lateralization for language in the Native American Hopi differs more dramatically than would be expected {13}. Using an analysis of EEG ratios, these investigators found a significant right cerebral hemisphere specialization for language processing in Hopi Indian children." (Scott, S., Hynd, G.W., Hunt, L. & Weed, W. (1979) Cerebral speech lateralization in the American Navajo. Neuropsychologia 17: 89)

"These findings confirm the view that one sided dominance similar to that in the upper limbs is also to be seen in the lower limbs. However, no correlation has been observed between dominance in the upper and lower limbs." (Chhibber, S.R. & Singh, I. (1970) Asymmetry in muscle weight and one-sided dominance in the human lower limbs. Journal Anatomy 106: pp. 556)

"To Geschwind and Galaburda (1987) it seemed that the biologically and evolutionarily normal situation is of asymmetry, present throughout the mammals (CL, p. 21), but present in some form in invertebrates, and "even single-celled organisms" (CL, p. 20). In man and other mammals this takes the form of predominant left-sided and left-hemisphere advancement. Left-handedness and atypical asymmetry is then a deviant form derived from the standard animal model for which the one particular asymmetry is the norm. This model contrasts with the implicit evolutionary model of Annett (1985), in which random dominance is the norm in nonhuman species, and it is right-handedness and left hemisphere dominance that have evolved recently in evolutionary time." ( McManus, I.C. & Bryden, M.P. (1991) Geschwind’s theory of cerebrel lateralization: developing a formal, causal model. Psychological Bulletin 110 (2): 249)

"This broad category [developmental learning disorders] principally includes developmental dylexia, stuttering, delayed speech, childhood autism, and hyperactivity (CL, p. 83), and Giles de la Tourette syndrome should probably also be included (CL, p. 83). These conditions are linked by having an excess of males, a "rather similar pattern of inheritance" (CL, p. 84), and increased personal and familial left-handedness (CL, p. 84; Bishop, 1983; Boucher, 1977; Colby & Parkinson, 1977; Parac & Coren, 1981). ( McManus, I.C. & Bryden, M.P. (1991) Geschwind’s theory of cerebrel lateralization: developing a formal, causal model. Psychological Bulletin 110 (2): 242)

"Artistic and mathematical talents were higher in left-handers, as was the frequency of occurence of asthma. Right-handers were higher in musical talent. (Smith, B.D., Meyers, M.B., Kline, R. (1989) For better of for worse: left-handedness, pathology, and talent. Journal Clinical Experimental Neuropsychology 11 (6): 949)

"The present study assessed the association between handedness and a variety of disorders, talents, and skills in subjects and their parents and siblings. Results showed that mathematical, artistic, and muscial talents varied systematically as a function of handedness. Verbal skills, stuttering, and asthma were also significant discriminators in some discriminant function analyses, and certain variations in the definition of handedness produced systematic variations in results. Finally, certain disorders, particularly eczema, stuttering, and epilepsy, in the parents were related to handedness in their offspring." [note chart on page 948 showing stuttering 1.6% left handers, 0.5% right handers; asthma 8.5% left handers, 3.8% right handers] (Smith, B.D., Meyers, M.B., Kline, R. (1989) For better of for worse: left-handedness, pathology, and talent. Journal Clinical Experimental Neuropsychology 11 (6): 944)

"Three generations of selection for right- and left paw preference failed to elicit changes in the qualitative indices or dextrality or sinistrality. According, it appears highly doubtful that paw preference variation in C57BL/6J mice is maintained by a residue of heritable genetic variation, or that is is significantly influenced by cultural factors associated with the phenotypes of the parents. (Collins, R.L. (1969) On the inheritance of handedness. 2: Selection for sinistrality in mice. Journal Hered 60: pp. 119)

"Recently, it was reported that breast cancer may be associated with reversed cerebral asymmetry and hand preference. (Olsson and Ingvar 1991; Sandson et al. 1992; Hsieh et al. 1992). Independently, other researchers have suggested that increased levels of estrogens in pregnancy (Trichopoulos 1990), which are associated with higher birth weight (Gerhard et al. 1987; Petridou et al. 1990; Ekbom et al. 1992), may increase the risk of breast cancer in the offspring (Trichopoulos 1990)." (Petridou, E., Flytzani, V., Youroukos, S., Lee, I.M., Yen, Y.Y., Yong, D., Trichopoulos, D. (1994) Birth weight andhandedness in boys and girls. Human Biology 66 (6): 1094)

"The association between selected demographic variables and birth weight on the one hand and a composite hand preference score based on seven hand tasks (each performed twice) on the other was investigated in a sample of 1387 male and female schoolchildren aged 5 to 10 years old. In multiple regression models left-handedness was significantly more common among boys and among children of better educated mothers and tended to decrease with age. No association was found with respect to urban or rural residence or birth order. Increased birth weight was associated with right-handedness in boys but with left-handedness in girls, and the birth weight by sex interaction term was statistically significant (p = 0.037). The demographic associations in the present study are compatible with those reported previously. The different associations of birth weight with hand preference in boys and girls indicate that the pr natal hormonal factors that affect brain lateralization and handedness are qualitatively or quantitatively different in the two sexes and may be differentially associated with birth weight." (Petridou, E., Flytzani, V., Youroukos, S., Lee, I.M., Yen, Y.Y., Yong, D., Trichopoulos, D. (1994) Birth weight andhandedness in boys and girls. Human Biology 66 (6): 1093-1101)

"Several neurological and immune phenomena associated with cerebral laterality also show an atypical season of birth pattern. Alcoholism is also associated with cerebral laterality. In this pilot study (n = 292), 66% of right-handed alcoholic men were born during the summer and fall (expected 52%, p less than 0.001). This finding suggests that at high latitude more right-handed men would become alcoholic because seasonal effects usually intensify with increasing latitude. In addition, in our sample of alcoholic men, left-handedness was associated with having an alcoholic father or with being first-born. Together, these findings suggest that the prevalence of alcoholism should increase with increasing latitude, and that the frequency in alcoholic men of being left-handed, first-born or having an alcoholic father should decrease with increasing latitude. The available literature tends to substantiate these correlations, but more systematic studies of season of birth and correlations with latitude in alcoholism are required." (London, W.P. (1987) Alcoholism: theoretical consideration of season of birth and geographic latitude. Alcohol 4 (2): 127)

<88(389)> "But the most prestigious weapon of the elite class was the dagger which was a routine accoutrement of leading males (usually held in the right hand) found in all the rich tumuli." {includes pictures}

<98(102-3)> "The problem drifts off into even more mystery when we remember that the neurological structure necessary for language exists in right hemisphere as well as the left. In a child, a major lesion of Wernicke's area on the left hemisphere, or of the underlying thalamus which connects it to the brainstem, produces transfer of the whole speech mechanism to the right hemisphere. A very few ambidextrous people actually do have speech on both hemispheres. Thus the usually speechless right hemisphere can under certain conditions become a language hemisphere, just like the left."

{Does physical language use both hemispheres? In attempting to use one hemisphere when speech was invented does handedness then appear?}

"Cognitive functioning was assessed in 69 left-handed males and females with a positive family history of left-handedness and in 77 left-handed and 55 right-handed males and females without familial left-handedness. Compared to females, males performed better on numerical reasoning and on two visuospatial tasks involving spatial manipulations (Figure Rotation and Surface Development). Within the group of left-handers, the multivariate effect for Familial Sinistrality was significant. Left-handers with familial left-handedness exhibited better scores on numerical reasoning, on verbal reasoning, and on two visuospatial tasks involving visual closure (Hidden Figures, Picture Completion) than did left-handers without left-handed relatives. The nonfamilial left-handers also exhibited lower scores on both inductive reasoning tasks when they were compared to their right-handed counterparts. The outcome runs contrary to the prevalent conclusion that left-handers with left-handed relatives are more likely to exhibit lower performances on visuospatial tasks than left-handers without such relatives."
(Van Strien JW, Bouma A (1995) Sex and familial sinistrality differences in cognitive abilities. Brain and Cognition 27(2):137)

"Two Canadian psychologists, Stanley Coren and Clare Porac, examined over a thousand photographs and reproductions of drawings, paintings, and sculptures dating from about 15,000 B.C. to 1950 A. D., and tabulated unambiguous representations of handedness. Over the entire period the incidence of right handedness remained approximately constant at about 90 percent. Coren and Porac concluded that humans have been predominantly right handed, without significant variations in incidence, for at least 50 centuries." (Corballis and Beale 1983: 95, The Ambivalent Mind)

"Writing in 1890, Gabriel de Mortillet suggested that left handedness may have been about twice as prevalent as right handedness in neolithic (late Stone Age) times. His excavations in France and Switzerland yielded 197 stone scrapers adapted to the left hand, 105 adapted to the right hand, and 52 usable by either." (Corballis and Beale 1983: 95-6, The Ambivalent Mind)

"Chimpanzees do not, as a species, display an overall preference for one or other hand, even though observations in the wild suggest that they use tools in a variety of ways." (Corballis and Beale 1983: 97, The Ambivalent Mind)

"There is also evidence that women report a greater tendency to left-right confusion than do men." (Corballis and Beale 1983: 43, The Ambivalent Mind)

"When this inventory was administered to 394 men and 734 women undergraduates at Edinburgh University, 10 percent of the men and 5.92 percent of the women were found to have quotients of less than zero, indicating at least some degree of left handedness.....the same clear difference was apparent in the study of 4,143 Chinese adolescents in Taiwan that we refer to in Chaper 6." (Corballis and Beale 1983: 108, The Ambivalent Mind)

"According to Annett, the majority of people inherit what she calls a "right shift." We may assume that these individuals carry a dominant allele like the one we previously labelled R. Among this majority the right hand is favored overall, but because of environmental influences the degree of right handedness varies, giving rise to a bell-shaped distribution. Because of this variation, some small proportion of this group will actually be classed as left handed. We may include pathological effects under the broad category of environmental influences. Annett suggests that the right shift is more marked for women than for men, perhaps because men are more susceptible to pathological influences at birth. What is especially interesting about Annett's theory is that the alternative to the right shift is not a left shift, but is rather a lack of the right shift. That is, a minority of people inherit no genetic predisposition to be either left handed or right handed. Let us suppose that this is due to a recessive allele which we lable N, for neutral. The distribution of handedness for NN individuals will also be bellshaped, but will be symmetrical about the point of zero handedness. As is the case with rats and mice, half of these individuals will be left handed and half right handed, although a good many may be better classed as of mixed handedness (we do not mean to imply that these people are mouselike in other respects). The two hypothetical distributions are illustrated in Figure 7.3. Barring those who are left handed because of extreme environmental or pathological influences, left handers can thus be seen as falling within the category of NN individuals. This neatly explains why only about half of the children of left-handed couples are left handed. Indeed, Annett herself carried out a study of the children of families in which both parents were left handed, carefully screening out those families in which one or other parent had had birth complications that might have accounted for their left handedness. The children of the remaining families showed no overall difference between the left and right hand on the peg-moving task; of the forty-five chldren, twenty-three were faster with the left hand and twenty-two were faster with the right hand. These children had evidently inherited the lack of any predisposition to be either left or right handed, exactly as the theory would predict." (Corballis and Beale 1983: 122-123, The Ambivalent Mind)

"the most bizarre finding of all, perhaps , is that right handers process the word "right" more quickly than the word "left," while there is no difference among left handers." (Corballis and Beale 1983: 124, The Ambivalent Mind)

"A good example of both local enlargement and changed connectivity is Broca's area in the human brain, which is intimately involved in speech and language. Located in the prefrontal cortex, it is greatly enlarged compared to its homologues in other primates. Functionally, it is involved with the face and mouth movements during feeding in apes. Vocalizations are under limbic control. In contrast, our own vocalizations are integrated into neocortical circuitry including of course the enlarged Broca's area (see Lieberman, 1984, for review). (McKinney, M.L. & McNamara, K.J (1990) Heterochrony: The Evolution of Ontegeny: Plenum Press, New York p. 304)

"Fingerprints, which so often provide crucial evidence, have also furnished useful support for Annett's theory....David C. Rife summarized five studies of fingerprints and handprints in a total of 3,095 right handers and 1,642 left handers, and in each study the asymmetry between the hands was less among the left handers than among the right handers. Since the patterns of fingerprints and handprints areknown to be inherited, presumably genetically, this evidence is sometimes cited in general support of genetic theories of handedness. It favors Annett's theory particularly, since it is again consistent with the notion that most left handers belong to a sub-group of the population that lack consistent asymmetry, while the majority of right handers are genetically prdisposed to be asymmetrical." (Corballis and Beale 1983: 124, The Ambivalent Mind)

"Out of 140 right-handed patients tested at the Montreal Neurological Institute, 96 percent had language represented in the left cerebral hemisphere, while only 4 percent had language represented in the right. Out of 122 left handers or patients with mixed handedness, 70 percent had language in the left hemisphere, 15 had language in the right, while the remaining 15 percent had language represented on both sides." (Corballis and Beale 1983: 134, The Ambivalent Mind)

"Some writers have distingished between familial left handers, those with at least one left-handed parent or sibling, and nonfamilial ones, those from right-handed families. This distinction should correspond roughly to that between left handers lacking the right shift, which is assumed to be an inherited condition, and those who are left handed for pathological reasons. As one might expect from Annett's theory, the evidence suggests that familial left handers show no overall bias in cerebral lateralization. Indeed, individuals in this category often have language skills represented on both sides of the brain. Nonfamilial left handers, on the contrary, seem to show normal left-cerebral dominance for language. To explain this, we must again assume that pathological influences such as birth stress may cause handedness to switch, but have little effect on cerebral lateralization. In the previous chapter, we cited evidence that left handers do show a higher incidence of minor pathologies." (Corballis and Beale 1983: 136, The Ambivalent Mind)

"Some individuals, however, are assumed to lack the right-shift factor. We assume that in these individuals handedness and cerebral dominance for language are established independently and at random. Among the left and mixed handers of the Montreal investigation, 15 percent were right cerebrally dominant and 15 percent had language represented in both cerebral hemispheres. We take it that these individuals belong to the group lacking the right shift. Since this group should display no overall bias in cerebral lateralization, we must add to it another 15 percent with left-cerebral dominance for language. Overall, then, 45 percent of the left and mixed handers belong to the special group lacking the right shift. We must also expect some right handers to belong to this group, which explainss why there is a small proportion of right handers who are right cerebrally dominant for language. However, we still have another 55 percent of left and mixed handers who do not belong to the recessive group lacking the right shift, and who are left cerebrally dominant for language. This may constitute the "pathological" left handers, those who are non-right handed because of birth stress or some other extreme environmental influence." (Corballis and Beale 1983: 137, The Ambivalent Mind)

"So far as we can judge form published accounts and photographs, Koko does not seem to exhibit marked handedness; she is described as left handed in pouring milk into a cup, but is predominantly right handed in typing. We know of no evidence related to functional cerebral asymmmetry, either in Koko or in any other gorilla." (Corballis and Beale 1983: 147, The Ambivalent Mind)

"Yet one can easily reverse the argument and maintain that handedness is a consequence of the lateralized representation of language in the brain. The British neurologist, Lord Brain, argued that because nonhuman animals are equally divided in their preferences for one or other hand (or paw), it must have been the appearance of a "motor speech center" in the left hemisphere of humans that brought about the preference for the right hand. W. W. Roberts, the Scottish neurologist, also argued for the priority of lateralization for speech, not only in evolution but also in the development of the child. "It is not improbably that the infant passes through an earlier, fleeting, simian phase [in which] rudimentary handedness can be detected. But true human handedness occurs only after the beginnings of speech, by which it is directed and to which it is limited. Its essential quality is its determination by speech."' (Corballis and Beale 1983: 148, The Ambivalent Mind)

"Among nonhuman animals such as rats, mice, monkeys and chimpanzees, handedness seems to be determined on a random basis.: (Corballis and Beale 1983: 150, The Ambivalent Mind)

"Indeed, until about 1500 A.D., right-to-left scripts were about as numerous as left-to-right ones, and gradual predominance of left-to-right scripts is probably due to historical factors rather than toany intrinsic superiority associated with right handedness." (Corballis and Beale 1983: 65, The Ambivalent Mind)

"One argument for the priority of cerebral lateralization over handedness is that more people have language represented in the left hemisphere than are right handed. We interpret this to mean that handedness is the more fragile phenomenon, more easily reversed by pathological influences early in life; this very fragility may mean that handedness is the more recent phenomenon in evolution, just as it appears later in the development of the child." (Corballis and Beale 1983: 149, The Ambivalent Mind)

"In certain kinds of specific skills, left or mixed handers seem to be superior at associating verbal with nonverbal symbols, perhaps because the two sides of their brains are less differentiated. This might account for the supposedly high proportion of left handers in the architectural profession. It has also been reported that left handers, and especially those who are weakly left handed, are superior to right handers in acoustic memory for pitch, but we do not know why this should be so." (Corballis and Beale 1983: 151, The Ambivalent Mind)

"It is of interest that most blind people read braille more quickly and accurately with their left hands than with their right hands, again suggusting dominance of the right cerebral hemisphere....Many blind readers use both hands, with the left hand actually running ahead of the right, but it was generally believed that the function of the left hand was simply to locate the ends and beginnings of lines. Yet the testimony of blind readers asserts a much more prominent role for the left hand....Recent experimental studies have confirmed that some three-quarters of blind readers prefer the left hand in reading braille and are more proficient with the left hand than the right." (Corballis and Beale 1983: 156-7, The Ambivalent Mind)

"One unpublished report suggests a right-hemispheric advantage in the recognition of briefly presented handwritten words, which is in contrast with the usual left-hemispheric (i.e., right visual field) superiority in the identification of letters depends on the type face, and the more complex, scriptlike type faces may actually give rise to a right-hemispheric advantage. Finally, Japanese readers show a left-hemsipheric advantage in identifying Hirakana symbols, which resemble the letters of Western alphabets, but a right-hemispheric advantage in identifying Kanji symbols, which are ideographic in the traditional Chinese manner." (Corballis and Beale 1983: 158, The Ambivalent Mind)

"We have already noted the right-hemispheric advantage in the perception of melody, pitch, timbre and harmony, but we also noted in the previous chapter that there is a left-hemispheric advantage in the perception of rhythm." (Corballis and Beale 1983: 158, The Ambivalent Mind) {Why white guys can't dance and why rhythm may have gone early when words began to be sexually selected for?}

"To complicate matters further, there is evidence that while musically naive listeners display a right-hemispheric advantage in the recognition of melodies, musically experienced listeners display a left-hemispheric advantage; we discussed this phenomenon in the previous chapter." (Corballis and Beale 1983: 159, The Ambivalent Mind)

"There seems to be a motor component underlying other left-hemispheric perceptual advantages as well. For instance, we noted earlier that there is a left-hemispheric superiority in the perception of rhythm, but this may be a secondary consequence of the demonstrated left-hemisphere superiority in the production of rhythmic sequences. Similarly, the left hemisphere appears to be superior to the right in judgements of simultaneity, temporal order, and duration, but these is turn may reflect a left-hemispheric advantage in fine motor control. Again, we have seen that trained musicians show a left-hemispheric advantage in recognizing melodies, while musically inexperienced listeners show a right-hemispheric advantage. We might, however, attribute this to the fact that trained musicians are primarily involved in the production of music, so that the motor component is more prominent." (Corballis and Beale 1983: 174, The Ambivalent Mind)

"The simplest explanation of right-hemispheric specialization is simply that it is gained by default. The left hemisphere, having assumed the dominant role in language and in purposeful actions, may have forfeited some of its capacity for functions that would otherwise be represented bilaterally. This interpretation is consistent with the evidence that right-hemisphere advantages are typically rather small, and cover a wide range of nonverbal functions, including very elementary ones as judgments of depth or hue. These functions scarcely suggest a superordinate mode of consciousness. Rather, many of them are functions that one would expect to find represented bilaterally in nonhuman primates." (Corballis and Beale 1983: 174-5, The Ambivalent Mind)

"There is evidence that women are inferior to men in spatial ability, and are more confused about left and right than men are. Consistent with Webster's theory, women also show the lesser degree of cerebral lateralization. We might also note that women appear to be superior to men in verbal ability, despite their more bilateral representation of language." (Corballis and Beale 1983: 175, The Ambivalent Mind)

"Liederman further proposed that maturity of the corpus callosum may be a crucial factor affecting hand preference. Until interhemispheric callosal connections are functional, hand movements that cross the body midline are seldom observed. Young infants, like split brain patients, typically use the left hand to reach for locations on the left side and the right hand to rech to the right. Once the corpus callosum is functional, the child is able to use the preferred hand regardless of the location of an action relative to the body. A mature corpus callosum is also probably important for the inhibition of symmtrical bilateral movements ('mirror movements'). Such inhibition seems necessary to enable asymmetical bimanual actions to occur (Fog and Fog 1963). There have been few studies relevant to the issue of neuromotor maturity and handedness, although Cohen (1966) showed that consistent hand preference at 8 months of age was significantly related to advanced developmental status, and the lack of preference to below average develop. Kaufman et al. (1978) and Tan (1985) confirmed that preschool children with 'unestablished' hand preference (assessed on the McCarthy scales) had lower levels of motor skill than those with consistent handedness, and Tierney et al. (1984) found a link with lower overall scores on the General Cognitive Index." (Bishop, D.V.M. (1990) Handedness and Developmental Disorder. MacKeith, Manchester pp. 67)

"Part of our reason from supposing that left-hemispheric specialization is primary is that right-hemispheric advantages seem relatively slight compared with left-hemispheric advantages. If there is an exception to this rule, however, it is to be found in the very striking right-hemispheric dominance for spatial manipulations to be observed in split-brain patients. As we noted at the beginning of this chapter, the right hand of the split-brain patient is peculiarly inept at arranging blocks to match a pattern, or at drawing a cube in perspective, and the eager and efficient left hand must sometimes be prevented from helping out. This asymmetry rivals in degree the left-hemispheric superiority for verbal skills. It is important to note, however, that the areas of the right hemisphere that mediate these manipulospatial skills are directly opposite language-mediating areas in the left cerebral hemisphere. Morever, the corresponding areas mediating manipulospatial skills are bilaterally represented in nonhuman primates. These considerations prompted the authors of a recent discussion of this problem to reach precisely the conclusion we are advocating here. "...we feel that the superior performance of the right hemisphere of split-brain patients on a variety of manipulospatial tasks may not reflect the overall cognitive style and evolutionary specialization of the right hemisphere, but instead may represent localized processing inefficiencies in the left parieto-temporal junction due to the presence of language." " (Corballis and Beale 1983: 178, The Ambivalent Mind)

"Arthur Benton of the University of Iowa has shown that accuracy in left-right discrimination is higher the more extreme the preference for one or other hand. He has also observed that children with one-sided disabilities are relatively good at telling left from right, while otherwise normal adults who profess to experience frequent left-right confusions tend to be ambidextrous." (Corballis and Beale 1983: 199, The Ambivalent Mind)

"We have already noted that left handers, who are more likely to have bilateral representation of speech than are right handers, may have slightly superior ability in mental rotation, memory for pitch, and in the association of verbal with nonverbal symbols --- a useful aptitude, perhaps, in fields like architecture." (Corballis and Beale 1983: 206, The Ambivalent Mind)

"We shall not claim that the lack of cerebral lateralization invariably causes dyslexia or stuttering, neither shall we contend that these disabilities are always due to lack of lateralizaion. Our claim is simply that these conditions may occur more frequently among those lacking consistent lateralization than among those with the usual left-cerebral dominance for language. (Corballis and Beale 1983: 207, The Ambivalent Mind)

(left handers)"are overrepresented in almost every pathological group,including schizophrenics, epileptics, hyperative children, and disabled learners, not to mention the male sex generally." (Corballis and Beale 1983: 207, The Ambivalent Mind)

"It has been suggested that dyslexia might be specific, not to reading generally, but to the reading of specific languages, notably those of Western culture. There is evidence for instance that reading problems are comparatively rare among Japanese children." (Corballis and Beale 1983: 210, The Ambivalent Mind) {Note: it may be that dyslexia is indemic to western culture genetic proclivities, not the script}

"Finally, there is evidence that dyslexia runs in families, suggesting that it may be genetically inherited. For instance, Richard Masland of Columbia University recently reported to the Orton Society, established in 1949 to further the work pioneered by Orton, on a study of the families of twenty dyslexic children. He claimed that 45 percent of the first-degree relatives of these chldren were also dyslexic. We shall encounter further evidence for the inheritance of at least some kinds of dyslexia in the studies discussed below." (Corballis and Beale 1983: 211, The Ambivalent Mind)

"Not all investigators have found left-right confusion to be a conspicuous characteristic of poor readers. In one study of 429 second graders in Reno, only ten children showed left-right confusions along with severe reading problems, but these were among the forty-three considered by their teachers to be the poorest readers. Other evidence reinforces the idea that left-right reversals occur most frequently among the most severe cases and are more likely to be observed in children referred to clinics for remedial reading than in poor readers picked from the classroom. Two recent studies have shown that poor discrimination of mirror imageis specific to left-right mirror images, and does not apply to up-down mirror images." (Corballis and Beale 1983: 214, The Ambivalent Mind)

"In his monograph of 1960, Oliver Zangwill examined a group of twenty dyslexic patients and noted that thirteen of them showed some manifestation of left-right confusion, either in the form of letter reversals, right-to-left scanning, or confusion over the left and right sides of the body." (Corballis and Beale 1983: 214, The Ambivalent Mind)

"Indeed, in one recent study, poor readers were shown to be deficient in the processing of verbal acoustic information. Clearly, these children were not dyslexic in the strict sense of the word..." (Corballis and Beale 1983: 219, The Ambivalent Mind) {Note: anamoly that runs counter to our thesis!}

"Again, in a restricted sense, the reader who is prone to left-right confusions (or left-right equivalence) might be regarded as a more holistic perceiver than one who is not. However we do not think that these difficulties reflect a right-hemispheric mode of processing so much as a lack of hemispheric asymmetry. (Corballis and Beale 1983: 220, The Ambivalent Mind)

"The capricious nature of reading disability is illustrated by a study carried out by Harold W. Gordon in Haifa, Israel, on twelve dyslexic children and their families. These children were markedly better at what Gordeon called "right-hemisphere" tasks, involving mental rotation, perceptual completion, and block design, than at "left-hemisphere" tasks involving serial processing, word production, and immidiate recall of series of digits. A control group of normal readers showed no overall difference in skill between two kinds of tasks. Gordon concluded that the dyslexic children were "locked" into a right-hemisphere mode of processing. A slightly different interpretation, but one that is more consistent with our own line of reasoning, is that the dyslexic children were essentially unlateralized, and thus lacked the serial skills typical of left-hemispheric specialization, although they evidently compensated in terms of spatial, non-serial skills. But the interesting point is that 90 percent of the first-degree relatives of the dyslexics showed the same profile of skills as did the dyslexics themselves, even though most of them claimed never to have had any difficulty with reading." (Corballis and Beale 1983: 221, The Ambivalent Mind)

"The association between familial left handedness, weak cerebral dominance for speech, and stuttering, was confirmed ina remarkable way by a series of clinical cases described in 1966 by a Philadelphia neurologist, R. K. Jones. Jones described four patients, referred for neurosurgical treatment of brain injury in the region of the presumed speech areas. Three were left handed and one right handed, but all came from families with a high incidence of left handedness, suggesting that they belonged to that subgroup of the population inheriting no consistent predisposition to lateralization (see Chaper 8). Their neurological problems were of recent origin and quite unrelated to their stuttering. The cerebral hemisphere in which speech was represented was determined both pre- and post-operatively by means of Wada's sodiumamytal test. Before the operation, the test showed a most unusual state of affairs; in each patient, speech control was bilaterally represented. Following surgery to the damaged crebral hemisphere each patient was albe to speak without stuttering. The post-operative Wada test now revealed unilateral control of speech by the unoperated hemisphere; in three cases this was the right, in one the left. What is remarkable about Jone's report is that all four patients had familial associations with left handedness, bilateral representation of speech, and remission of stuttering following surgical instatement of unilateral speech control. This must be regarded as strong evidence not only of an association between stuttering, bilateral control of speech, and familial left handedness, but also of a causal relation between bilateral control and stuttering. Since these observations are based on only four cases it would seem unwise to generalize to all or even the majority of stutters, but it may reasonably be taken to indicate the existence of a subgroup of stutterers in whom anamalous cerebral dominance is a significant causal factor." (Corballis and Beale 1983: 231, The Ambivalent Mind)

"Taken overall, there is rather convincing evidence that stutterers often show anomalies of cerebral lateralization. In many cases, however, the anomaly was one of reversal rather than of weak or absent lateralization. Given that nearly all of the subjects who showed reversal were right handed, this might still be taken as evidence of interhemispheric conflict, with one hemisphere specialized for control of the dominant hand and the other for the representation of language. One might even suppose that this inconsistency reflects a switch in handedness---that these subjects were forced to switch to the right hand. In the absence of further evidence that this was so, however, the more cautious interpretation is simply that these stutters were without any strong predisposition toward consistent lateralization, so that different manifestations of laterality were in conflict. The evidence also suggested that, in some stutterers at least, there may be bilateral control over speech, leading to interhemispheric conflict. This was especially striking in the case of the four patients described by Jones and was corroborated to some extent by the results of Sussman and MacNeilage for their dichotic tracking task---one of the few tasks designed to measure lateralization for the production of speech in normal human subjects. The theory advocated by Orton and Travis is therefore given reasonable support." (Corballis and Beale 1983: 235, The Ambivalent Mind)

"We cannot leave our discussion of anomalies of cerebral lateralization without raising an issue that poses a problem for our interpretation of both dyslexia and stuttering. Both afflictions are much more frequent among males than among females, yet the evidence suggests strongly that women are less highly lateralized than men, both with respect to the left-hemispheric representation of langauge and the right-hemispheric representation of spatial functions. How can we explain this disturbing anomaly? Up to a point, it might be attributed to the higher incidence of cerebral pathology in males; recall, for instance, that a higher proportion of men than women are left handed. Again, the lesser degree of lateralization in women compared with men seems to have been firmly established only among adults, and there is even some evidence that boys lag behind girls in the development of lateralization. We suggested earlier that the growth of lateralization may cease earlier in girls than in boys, since girls reach puberty at an earlier age, on average, than boys do. Reading disability and (typically) stuttering develop well before puberty, when lateralization may be if anything more highly developed in girls than in boys." (Corballis and Beale 1983: 235, The Ambivalent Mind)

"At Montreal, where they've probably done more carotid amytal studies than anywhere else, they found that among right-handers, 4 % are right-hemisphere dominant for language. That really is a pretty good confirmation of our idea that right-handers are 99% left-dominant for language, because that 4% figure(different from the 1% for crossed aphasia) is based on a population being prepared for surgery. They would not have had amytal testing if they did not have a history of epilepsy, you understand. So that in a population where we can expect some deviance because of the early brain injuries and long epileptic history, there is still only 4% right-hemisphere speech dominance." (Benson and Zaidel (Bogen) 1985: 34, The Dual Brain)

"In contrast to the greater lateralization of men than women for verbal and perhaps spatial processing, numerous studies indicate that women and girls show greater asymmetries than men and boys in regard to handedness. Females are more likely than males to be right-handed and to show an extreme preference for use of the right hand. It has been suggested that the stronger female preference for the right hand may reflect a tendency for women to endorse extreme responses. This explanation cannot account for the increased incidence of right-handed females and left-handed males, however. In addition, as will be described in detail in the next section of this chapter, asymmetries in laboratory animals that may correspond to human handedness are greater in females than in males. Another type of aymmetry that has been reported to be enhanced in women as compared to men involves performance on dichotic-listening tasks composed of melodies or other nonspeech sound (right-hemisphere stimuli) although data supporting these sex differences are less extensive than those supporting sex differences in hand preferences of verbal processing." (Benson and Zaidel (Hines and Gorski) 1985: 79, The Dual Brain)

"Left-handers are not a homogenous group with respect to patterns of lateralization, however. Clinical and experimental data reveal an important difference between familial and nonfamilial left-handers. Nonfamilial left-handers appear to be more like male right-handers; the incidence of aphasia is consistently associated with lesions to only one side of the brain, the left hemisphere. Initial apahsia can be more severe and recovery from aphasia slow and limited as well. But familial left-handers and those right-handers with left-handedness in the family appear to have greater bilateral control of language and better prognosis for recovery. In experimental data as well, cerebral ambilaterality is more associated with familial sisistrality, while nonfamilial left-handers show more consistent unilateral left-sided dominance for language." (Benson and Zaidel (Curtis) 1985: 105, The Dual Brain)

"The most common subpopulations with disorders of language acquisition---namely. developmentally aphasic children, dyslexics, and autistics---are consistently associated with atypical laterality patterns. Each of these populations comprises more than one subgroup, and the etiology of the disorders is unknown. Yet with each group, we find developmental language dysfunction accompanied by indications of abnormal or atypical cerebral organization. With both developmental aphsics and dyslexics, there is a higher than normal incidence of non-right-handedness; mixed laterality of handedness, footedness, eyedness, and "visual-fieldedness"; and a family history of mixed laterality and developmental language problems." (Benson and Zaidel (Curtis) 1985: 106, The Dual Brain)

"The data considered here suggest that language acquisition---more specifically, the acquisition of the computational component---may be a crucial trigger for the development of lateralization. If language acquisition is prevented, lateral asymmetries may never be established." (Benson and Zaidel (Curtis) 1985: 110-111, The Dual Brain)

"Yet another complication to the simplified handedness-language dominance correlation appears to depend upon the degree of education of the patient prior to the brain injury. In a report of a single well-studied case, Wechsler reported aphasia in a right-handed illiterate secondary to right-hemisphere CVA. Cameron et al. studied65 patients with known left-hemisphere CVAs, divided into three groups based on their premorbid ability to handle written language: literate, semiliterate, and illiterate. Of the literate group, 78% were aphasic and 22% nonaphasic; 64% of the similiterate group became aphasic, while 36% did not. In the totally illiterate group, on the other hand, the findings were reversed---36% became aphasic and 64% did not. Both studies suggest that formal education, even at a minimum level of semiliteracy, may influence the lateralization or at least the degree of hemispheric dominance for language." (Benson and Zaidel (Benson) 1985: 199, The Dual Brain) (text goes on to say another study did not support this position)

"Syntactically, it was initially believed that the disconnected RH could understand simple active or negative sentences, but not tense, plural inflections, or the relationship among subject, verb, and object." (Benson and Zaidel (E. Zaidel) 1985: 209, The Dual Brain)

"It would seem that the RH has a short-term verbal memory with a capacity of 3 plus or minus 1 items, whereas the LH has the normal capacity of 7 plus or minus 2 items. (Benson and Zaidel (E. Zaidel) 1985: 210, The Dual Brain)

"The results may be summarized as follows:
1. The disconnected RH can comprehend not only nouns, verbs, and adjectives, but also a variety of grammatical and syntactic structures extending form functors to tense markers and to simple syntactic transformations such as the passive or negative.
2. Despite a large variability across subjects and linguistic structure, uninflected morphological constructions (free morphemes) are easier for the RH on lexical items involving numbers, adjectives of relatively high error rate in the RH on lexical items involving numbers, adjectives or relative quantity, and quantifiers (such as "four," "many," "middle"). By contrast, the RHs are adept at understanding spatial prepostions )such as "on," "in," "under"). The RHs scored least well on constructions requiring the coordination of subject-object and direct-object-indirect-object relations, which place a premium on order and load on memory.
3. The RH is selectively affected by the length of the message more than by its syntactic complexity or difficulty of vocabulary (Shewan's Test; 90).
4. The RH finds syntactic structures (prediction, complementation, etc.) more difficult than grammatical categories (case, number, gender, tense, etc.), which are in turn more difficult for the RH than morphological constructions (suffixes), with lexical items (nouns, verbs, adjectives, adverbs, and prepositions) being relatively easiest (Carrow's Test; 90,95)." (Benson and Zaidel (E. Zaidel) 1985: 211, The Dual Brain)

"Hemifield tachistoscopic studies in normal subjects suggest that the RH is superior or equal to the LH in physical-identity matches of letters, in recognizing unuasual scripts, or in recognizing cursive script. Many workers found evidence consistent with a selective RH ability to understand concrete, imageable nouns, as against abstract, nonimageable words." (Benson and Zaidel (E. Zaidel) 1985: 216, The Dual Brain)

"The role of the RH is broader aspects of linguistic and paralinguistic communication is highlighted in the work of Gardner and associates. They found that RBD {right brain damaged} patients had difficulty in understanding cartoons, preferred non sequitor ending to jokes, and in general exhibited an inappropriate sense of humor. There is also a corresponding deficit in interpreting metaphors, figures of speech, and idiomatic expressions. Here the literal meaning is preserved, but the use of contextual pragmatic features seems impaired. Similarly, RBD patients are impaired in their comprehension of the overall structure or theme of connected text or discourse: They misinterpret emotions and motivations, fail to get the point of a story, and inject irrelevant personal elements." (Benson and Zaidel (E. Zaidel) 1985: 221, The Dual Brain)

"Females have been shown to be field-dependent relative to males, and non-right-handers to be field-dependent relative to right-handers. While most right-handed persons make most of their speech-related gestures with their right hands, field-dependent persons, who presumably process speech more bilaterally, tend to show more bilaterality in their speech-related gestures." (Benson and Zaidel (TenHousten) 1985: 344, The Dual Brain)

"LaMay and Culebras (1972) have demonstrated asymmetry of the Sylvian fissures in fossil human skulls. Other asymmetries present in modern humans have been found in fossil primate skulls (Holloway and de Lacoste 1982)." (Geschwind & Galaburda 1987: 4, Cerebral Lateralization)

"This suggests that strong right cerebral dominance for language either does not exist or is rare (except after early gross left hemisphere damage) and that in lefthanders cerebral dominance for language is either leftsided or bilateral." (Geschwind & Galaburda 1987: 6-7, Cerebral Lateralization)

"It is conceivable that the figure of 35% may represent the proportion of the population with anomalous dominance for language, this is, without strong left predominace." [referring to relative cerebral planum size] (Geschwind & Galaburda 1987: 33, Cerebral Lateralization)

"The demonstations of asymmetry in animals appear to confirm the belief that biologically determined symmetry has existed throughout vertebrate evolution and that human asymmetries are neither a recent development nor an example of a fundamental feature of neuroanatomy and behavior." (Geschwind & Galaburda 1987: 55, Cerebral Lateralization)

"The occurance of high talents through this mechanism may also help to explain the high frequency of such disorders as childhood dyslexia. The high spatial talents of many of the affected individuals may counteract the evolutionary disadvantage of their disabilities. This would, of course, be even more conspicuously the case in nonliterate societies, in which failure to learn ot read would not be a problem." (Geschwind & Galaburda 1987: 66, Cerebral Lateralization)

"The neurological substrates of these functions probably develop according to different schedules. Certain prenatal retarding influences might be operative to a marked degree during the development of either, or both, of these functions. If the degree of retardation is sufficiently great, the initial anatomical advantage in the left hemisphere will be diminished and the two sides will exhibit a greater degree of symmetry. The more nearly symmetry is achieved in some particular region, the more likely there will be random dominace for the function subserved by that region. In the majority of people both functions will remain left hemisphere dominant, but there will be a majority in whom either, or both, will be randomly determined or occasionally clearly shifted to the right. If either can be shifted independently of the other, it is likely that there is no strong intrinsic linkage. It should be clear that our hypothesis regarding the cause of random dominance differs in some respects form Annett's. She believes that in about 18% of the population dominance is random and that in these people accidental factors determine the lateralization of languge or handedness. The remainder of the population carries a "right-shift" gene that increases the probability of left hemisphere dominace for these functions. By contrast, we postulate that in most humans there is an innate bias toward left hemisphere dominace for both of these functions and that certain influences during fetal life act to diminish this innate bias and thus to create random dominance. Like Corballis and Morgan (1978), we believe in a "left-shift" factor. (Geschwind & Galaburda 1987: 69, Cerebral Lateralization)

"The term anomalous dominance refers to those in whom the pattern differs from the standard form. There is no sharp cutoff point at which one can speak of a shift from standard to anomalous dominance. Our rough estimate is that anomalous dominance will be found in approximately 30% to 35% of individuals, roughly the percentage in whom the planum temporale is not larger on the left side. It is important to stress anomalous dominance rather than left-handedness. According to Annett's formulation, lefthanders comprise about half of those in whom handedness is random. She estimates that random handedness is present in 18% of the population, of whom about half, or 9%, will be lefthanded." (Geschwind & Galaburda 1987: 70, Cerebral Lateralization)

"In our view, the rarity of anomalous dominance of right hemisphere functions reflects the earlier and more rapid development of that side of the brain, which is thus less subject to modulating influences." (Geschwind & Galaburda 1987: 71, Cerebral Lateralization)

"Furthermore, Annett (1970) has stressed that handedness, like height, is a continuous variable. In studying the associations of handedness, the appropriate question is therefore not, "Is lefthandedness more common in condition A than is the general population?" but rather, "Is the distribution of handedness scores different in condition A from that in the general population?" (Geschwind & Galaburda 1987: 75, Cerebral Lateralization)

"An elevated rate of lefthandedness is found among architects (Peterson and Lansky 1974) and among the mathematically gifted (Kolata 1983). " (Geschwind & Galaburda 1987: 82, Cerebral Lateralization)

"It could be the case that although growth of the left hemisphere is slowed to a greater extent in lefthanders than in righthanders, it may attain a greater final size in lefthanders. This could occur with the growth period is prolonged---for instance, when pregnancy is longer than average or when puberty is late, which would allow for further development in childhood." (Geschwind & Galaburda 1987: 98, Cerebral Lateralization)

"Our own formulation in some respects resembles tht of Corballis and Morgan (1978), who postulate the existence of a "left shift" (influences that tend to favor right cerebral dominance), though it also differs from theirs in several ways. We begin with the assumption that cerebral dominance is determined primarily by anatomical symmetry, so that language lateralization will depend to a great extent on the size of the planum temporale, which is larger on the left in about 65% of brains (Geschwind and Levitsky 1968). Although the left side can be even ten times larger than the right, it is unusual for the right side to be massive compared tothe left. The size distribution is markedly skewed to the left; as noted earlier, this appears to be the case even in utero (Wade, Clarke, and Hamm 1975), although the right side develops more rapidly (Fontes 1944). We presume that the basic pattern of most brains includes a larger left side. Certain influences in the course of pregnancy tend to slow development on the left; the greater these influences are, the more likely it is that the brain will be shifted toward symmetry, and in a few cases even to modest asymmetry favoring the right side. Our hypothesis is essentially the mirror image of Annett's; that is, we presume a strongly left-hemispheric basic dominance pattern, along with a set of influences producing a shift to increasing symmetry and thus favoring random dominance. We have already described several genetic factors that might play a role in this process by controlling the levels of hormones, especially testosterone, as well as sensitivity to it. These include the Y chromosome, several major histocompatibility locus genes, and genes on the X chromosome and chromosome 15. There are probably other types of genetic influence; for example, the baseline level of left-sided asymmetry probably varies in the population. (Geschwind & Galaburda 1987: 127-128, Cerebral Lateralization)

"Other features of the familial distributions present problems for any genetic theory, for example, a trend for lefthanded mothers more than lefthanded fathers to have lefthanded children." (Geschwind & Galaburda 1987: 128, Cerebral Lateralization) [Question: do the females come from more familial lefthanded families? Since more males than females are lefthanded, is that a result of higher testosterone levels over and above present male levels causing a shift further back to circle culture laterialization?]

"Injections [intracarotid amytal test] on the left typically produce a depressive reaction, whereas those on the right typically lead to unconcern." (Geschwind & Galaburda 1987: 213, Cerebral Lateralization)

"Thus, too studies (Churchill, Igna, and Seirf 1962; Grapin and Perpere 1968) have shown a strong relationship between birth position and later handedness, with ROA [right occiput anterior] infants having a much higher later frequency of lefthandedness than LOA infants." (Geschwind & Galaburda 1987: 226, Cerebral Lateralization)

"Language and motor dominance may be located in opposite hemispheres, but linkage cannot be excluded with certainty for the reasons just given. On the other hand, it is clear that the typical dominance functions of the right hemisphere rarely shift, even when language is shifted, suggesting that at least one the right brain asymmetries is not linked to language." (Geschwind & Galaburda 1987: 238, Cerebral Lateralization)

"Apes favor the left limb for certain tasks (a mother preferentially cradles an infant with her left arm), while selecting the right limb for others (locomotion is often initiated with the right hand). When comparing data on the bonobos at the Yerkes Primate Center and the San Diego Zoo, William Hopkins, and American expert on brain lateralization, and I were excited to discover that handedness extends to gesticulation. Bonobos wave, beg, wrist-shake, or make threatening gestures predominantly with their right hands. This is the first evidence in a close relative of our that a communicatory capacity other than language may be associated with the left side of the brain. The similarity in brain specialization hints at a shared evolutionary history between gesturing and language." (De Wall & Lanting 1997: 43, Bonobo)

"First it is to be noted that analysis has shown that the early bronze tools and weapons were made for right-handed individuals and that dextrals produced the oldest human artwork. Going back further in time, the examination of stone implements has provided quite convincing evidence that they were made by right-handed individuals. Toth contends that as far back as 2 million years ago hominids were preferentially right-handed. Examination of both the tools and the flakes at dates sites at Lake Turkana, Kenya, indicates that the striking stone was held by the right hand, while the left hand held the fabricated object (core), turning it in a clockwise direction. Hence, Toth suggests that a genetic basis for right-handedness has existed for a least a period of 2 million years." (MacLean 1990: 542, The Triune Brain in Evolution)

"Of the many mental features that are claimed to be different between the sexes, four stand out as repeatable, real, and persistent in all psychological tests. First, girls are better at verbal tasks. Second, boys are bette at methematical tasks. Third, boys are more aggressive. Fourth, boys are better at some visuo-spatial tasks and girls at others. Put crudely, men are better at reading a map and women are better judges of character and mood---on average. (And, interestingly, gay men are more like women than heterosexual men is some of these respects.) (Ridley 1993: 250, The Red Queen)

"When people are asked to rotate a diagram of an object mentally to see if it is the same as another object, only about one in four women scores as highly as the average man." (Ridley 1993: 250, The Red Queen)

"modern primitive peoples may possibly be somewhat less lateralized in terms of brain function than their civilized literate counterparts..." (Bradshaw & Nettleton 1983: 6, Human Cerebral Asymmetry)

Nachshon and Carmon (1975) also successfully demonstrated a double dissociation, a right-hand superiority for a sequential task and a left-hand superiority for a simultaneous one..." (Bradshaw & Nettleton 1983: 106, Human Cerebral Asymmetry)

"It has long been known that Braille may be more easily read by the left hand (for review, see Harris, 1980b). (Bradshaw & Nettleton 1983: 106, Human Cerebral Asymmetry)

"Shanon (1980), using musicians as subjects, found a left hemisphere advantage for performing complex musical tasks. Gates and Bradshaw (1977b) investigated the detection of pitch, rhythm, and harmony changes in music perception. While reaction times did not differ between ears for the detection of a changed note in either a single-line melody or a five-note whole tone sequence, the right ear proved the more accurate. In detecting rhythm changes in a five-note sequence, the left ear proved the faster and the right more accurate. No ear differences were apparent in the detection of harmony changes. The right ear proved more sensitive (d') in recognizing exerpts from unfamiliar melodies, and the left for recognizing excerpts from familiar melodies. We may therefore conclude that, overall musical functions are not strictly lateralized to the right hemisphere, though there may often be a considerable right hemispheric involvement. Varying degrees of right hemisphere mediation may appear for the perception of pitch, harmony, timbre, and intensity, particularly perhaps for more complex, structured, tuneful melodious combinations and as a function of competence and familiarity." (Bradshaw & Nettleton 1983: 157-8, Human Cerebral Asymmetry)

"Problems for the simple verbal-nonverbal dichotomy appear when it is found that the right hemisphere possesses considerable linguistic powers, more strongly receptive perhaps than expressive; that the left hemisphere is superior in certain visuospatial tasks that are best perfomed by a strategy involving an analytic extraction of significant or distinguishing features or elements; and that the right hemisphere is not always, or in all aspects, dominant for music, particularly where the sequential or temporally extended nature of the auditory stimuli are important, as in judgements involving temporal order, durations, simultaneity, rhythm, or categorical perception. Moreover, studies with both clinical patients and normal subjects have indicated that the left hemisphere may be uniquely specialized in terms of temporal order, sequencing, and segmentation, at both sensory and motor levels, in the latter case for the control of rapid sequential changes in limb, hand, finger, or articulator positioning. Thus, the left hemisphere may act as a dynamic, kinesthetic-interoceptive, temporally dependent control system for target acquisition within the body schema while the right acts in terms of static, exteroceptive, visuospatial functions largely outside of body space. Additional and independently derived support for such a concept comes from work with dysphasic and dyslexic children, for whom there now appears to have been a long natural hisory of deficits in perceiving the temporal order of nonverbal auditory stimuli. Accordingly, the left hemisphere mediation of language may possibly not depend on its symbolic or even largely phonological attributes, but rather on the need for analytic, time-dependent, and sequential coding to occur, both at receptive and, more particularly, expressive levels. We are now faced with a major problem. The left hemisphere undoubtedly does mediate language processes: All the evidence from asymmetries in brain morphology and the effects of clinical lesions support such a position. Does it mediate them because of a prior analytic or segmental specializaition of the left hemisphere? (That is, at some time in the evolutionary history of humans or even in the ontogenetic history of the individual, were language mechanisms attracted to and subjected to further neural development in the left hemisphere because of its prior analytic-segmental specialization?) This position would view the left hemisphere as being adapted not for symbolic functions per se, but rather for the execution of some categories of motor activity that happened to lend themselves readily to communication. Alternatively, are all the apparent left hemisphere language superiorities really just manifestations of the left hemisphere's processing analytically and sequentially? Certainly, there seems to be plenty to evidence for analytic or segmental left hemisphere superiorities independent of any phonological or verbal component. However, some (e.g., Studdert-Kennedy, 1970; Springer, 1979) argure strongly for the primacy of speech and verbal processes with respect to left hemisphere dominance, in particular the unilateral motor control of the speech apparatus. Speech, they say, is a species-specific capacity representing a "quantum jump in evolution"; it is therefore mediated by a specialized left hemisphere mechanism to cope both with the limited resolving power of the human ear and the lack of acoutic invariance in the speech signal. Such a mechanism is held to be responsible on the one hand, for the phonological or sound system that specifies the elemental speech sounds and applies rules for their combination into meaningful words and, on the other, for the rules of syntax for combining such words into phrases or sentences." (Bradshaw & Nettleton 1983: 174-5, Human Cerebral Asymmetry)

"In studies employing both clinical patients and normal subjects, a large REA (left hemisphere superiority) is typically found for the discrimination of duration, temporal order, sequencing, and rhythm, leading to the suggestion that there is a fundamental left hemisphere capacity for discriminating between rapidly changing acoustic signals, and that this capacity underlies the traditional verbal superiority of the left hemisphere. Similar studies of normal subjects, brain-damaged individuals, and dyslexia and dysphasic childen have demonstrated an important left hemisphere superiority in controlling fine, sequential, manipulative movements of the limbs, hands, fingers, and articulators, in terms of kinesthetic control towards internalized representations of sequential target positions. Although the right hemisphere may be responsible for an awareness of spatial interrelationships, the left organizes movement into correct sequences. Such considerations may account for the fact that motor sequential or segmental aspects may be more strongly lateralized than the perceptual, particularly if they are the more fundamental." (Bradshaw & Nettleton 1983: 186, Human Cerebral Asymmetry)

"Going back into prehistory, most paleolithic tools and weapons seem to have been made by-and for-the right hand (Wilson, 1885; Mortillet, 1890), and a majority of prehistoric handprintss are those of dextrals (Uhrbrock, 1973). The profiles of human and animal heads in cave paintings typically tend to face left (Wilson, 1885), a characteristic still evident in the work of madern right-handed artists (left-handed artists find it easier to drawprofiles facing right). Likewise Cro-Magnon hand silhouettes are usually of the left hand (i.e. drawn by the right around the left; Magoun, 1966). Earlier still, the stone implements used by Peking man seem to fit the right hand better than the left (Black, Young, Pei, & de Chardin, 1933). Even Australopithiecus seems to have been predominantly dextral, according to Dart (1949). He reached this conclusion form a forensic analysis of the side of injury to fossil baboon skulls found with the remains of this hominid in circumstances suggesting the baboons were prey." (Bradshaw & Nettleton 1983: 190, Human Cerebral Asymmetry)

"Searleman (1980), using a dichotic test with verbal stimuli, found that preferred footedness was the best predictor of language lateralization, compared with handedness, sighting dominance, hand posture used in writing, and strength of handedness. Left-footed subjects had the highest incidence of a LEA, perhaps because cultural bias against left-footedness is less than against left-handedness." (Bradshaw & Nettleton 1983: 192, Human Cerebral Asymmetry)

"Comtempory estimates of the incidence of sinistrality range from 1 to 30 percent, with a mode of around 10 percent (Hardyck & Petrinovich, 1977) and a higher incidence when less stringent criteria are employed." (Bradshaw & Nettleton 1983: 193, Human Cerebral Asymmetry)

"Rasmussen and Milner (1977) assessed speech dominance by intracarotid injection of sodium amytal; in 262 patients without clinical evidence of early damage to the left hemisphere, they found evidence of left hemisphere language dominance in 96 percent of dextrals and 70 percent of sinistrals; evidence of right hemisphere language in 4 percent of dextrals and 15 percent of sinistrals; and evidence of bilaterality in none of the dextrals and 15 percent of the sinistals. (They also studied 134 patients with definite clinical evidence of early left hemisphere injury, and obtained similar results, with a shift towards the right hemisphere in all cases.) Turning to lateralized ECT, McManus (1979) tabulates five studies (from 1970 to 1978) that determined the cerebral speech dominance of dextrals from all five studies, 91 percent had left hemisphere dominance, and of the 48 sinistrals, 71 percent had left hemisphere dominance, figures which are remarkably and reassuringly close agreement with the Wada test results of Rasmussen and Milner. Since the subjects in these ECT studies were psychiatric patients with no evidence whatsoever of local or lateralized brain damage, they may be regarded as being representative of normal people with respect to language lateralization. In summary then, left hemisphere language dominance is more general than dextrality, and reversed dominance less frequent than sinistality (Hecaen & Sauguet, 1971). With respect to clinical records of aphasia, Satz (1979) finds that 70 percent of sinistrals are bilateral for language, 15 percent have right hemisphere language and 15 percent left hemisphere language. While, unfortunarely, similar quantitative data obtained under exactly comparable circumstances for dextrals are not available, the general consensus of clinical opinion (see, e.g., Chapter Eight) is that damage to the left hemisphere in dextrals is far more likely to result in aphasia than with sinistrals." (Bradshaw & Nettleton 1983: 197, Human Cerebral Asymmetry)

"Moreover, an even more serious problem is that, according to the model, homozygosity should breed true, with only dixtral offspring form fully dextral parents and only sinistral offspring form fully sinsitral parents. Unfortunately, Annett's (1973) own data disprove this---84 percent of sinistrals have two dextral parents and 50 percent of children of two sinistral parents are dextrals." (Bradshaw & Nettleton 1983: 204, Human Cerebral Asymmetry)

"A disproportionate number of sinistrals are found among a number of clinical populations, including mental retardates, epileptics, stutterers, and sufferers from dysarthria, cerebral palsy, developmental aphasia, and dyslexia (for reviews, see Carter-Saltzman, 1979; Hicks & Kinsbourne, 1978; Satz, Baymur, & Van der Vlugt, 1979; Springer & Searleman, 1980). There are even said to be more nondextrals among smokers (harburg, Feldstein, & Papsdorf, 1978) and criminals (Andrew, 1978)! Sinistrality is also said to be more common among the first- or late-born, those born of very young or old mothers, twins, males (who are larger at birth), and those known to be the products of complicated pregnancies." (Bradshaw & Nettleton 1983: 206-7, Human Cerebral Asymmetry)

"A resolution to this issue if offered by Annett and Turner (1974), who showed that when a large random sample is classified for handedness, and the resultant groups compared, for example, on reading scores, no significant differences emerge. However, if one then looks only at those with very low scores, more sinistrality is pathological. Confirmation is offred by Bishop (1980), who took an unselected group of preadolescents, tested them on intelligence, reading ability, and manual dexterity, then chose a target group not on the basis of sinistrality but on the basis of very poor performance by the nonpreferrred hand (i.e., usually but not always the left hand). These subjects were impaired in intelligence and reading, and sinistrals in the target group had a lower incidence of fmailial sinistrality than other sinistrals, who were not as impaired in performance on the nonpreferred (right) hand. These target-group (nonfamilial) sinistrals were presumably pathological left-handers, perhaps with mild unilateral brain abnormality leading to a depression of contralateral performance, clumsiness, poor cognitive performance, and sinistrality. In two of our own studies (J.L. Bradshaw et al., 1981a; J.L. Bradshaw & Taylor, 1979), we found in a sample of university students that nonfamilial sinistrals performed significantly more poorly on tachistoscopically presented verbal tasks (naming word-non-word decisions) than either familial sinistrals or dextrals. We must, however, conclude that across the whole population, excluding university students and clinical samples, which between them seem to have attracted an undue degree of research attention to date, there is comparatively little evidence of any obvious deficit in sinistral functioning. Apart from birth stress hypothesis per se, it is also possible that a language invasion into right hemisphere processing space (which, to judge by their possibly reduced asymmetries might seem to be more common among both sinistrals and females), might make sinistrals inferior to dextrals on nonverbal tasks and possibly superior on verbal abilities (J. Levy, 1969). (Such a double dose of language, apart form boosting the faculty, could also account for the reportedly higher incidence of stuttering among sinistrals because of hemispheric competition for the unpaired articulators.) Females are superior to males verbally, and inferior in nonverbal tasks (see Chapter Eleven). Some empirical support is claimed for the Levy hypothesis, though others have found no differences between handedness groups (for detailed reviews, see Carter-Saltzman, 1979; Swanson, Kinsbourne, & Horn, 1980). Since those reviews were published, O. Johnson & Harley (1980) found that strongly sinistral university students were better on verbal and worse on spatial tasks than strong dextrals. J.L. Bradshaw et al. (1981a) found evidence of a significant nonverbal intelligence deficit among sinistral university students, particularly familial, with parental handedness being a better predictor of performance than sibling handedness. Exactly comparable findings in a dichaptic shape discrimination task were reported by Nilsson et al. (1980): very poor performance by familial sinistrals, especially when the relationship was one of parent rather than sibling sinistrality. Such findings suggest that sinistrals have a somewhat different cognitive organization form dextrals, and that both environmental factors (inferior nonfamilial sinistral processing on speeded tasks) and gentic factors (inferior familial sinistral processing on unspeeded intelligence tests) may operate in sinistrality." (Bradshaw & Nettleton 1983: 208-9, Human Cerebral Asymmetry)

"Sinistrality is more common in males. Although sinistrals seem to be less lateralized than dextrals, males are generally more lateralized (at least with respect to languge processes) than females." (Bradshaw & Nettleton 1983: 210, Human Cerebral Asymmetry)

"Compared to boys, girls speak earlier, develop larger volcabularies, can cope with more complex syntactic forms, articulate more quickly and more clearly, are more fluent, and are better readers. (Harris, 1977, 1978). ... Male superiority in nonverbal and visuaspatial functioning may have received greater attention because such superiorities are more diverse and less immediately easy to define, quantify, and observe, though as McGee (1979) notes, male superiority on tasks requiring spatial visualization and spatial orientation is among the most persistent of individual differences in the abilities literature. ... All the various factorial studies agree that spatial visualization involves the ability to mentally manipulate, rotate, twist, or invert a pictorally presented stimulus and to recognize or recall a configuration where there is movement among the internal parts of a configuation or where the object is manipulated in three-dimensional space. Imagery and mathematical ability, especially geometry and algebra, seem to be related to this. (According to Benbow & Stanley, 1980, very substantial sex differences favor boys in mathematical reasoning ability, as opposed to computational competence, in which girls may excel. Their studies showed that this effect could not be ascribed to differential course taking, educational experiences, etc.)" (Bradshaw & Nettleton 1983: 216, Human Cerebral Asymmetry)

"Familial correlations (between parents and children, between siblings, and between identical and nonidentical twins) suggest that both verbal and spatial abilities may have high levels of heritability, and that while verbal ablility may also be influenced by cultural and educational variables, this may be less true of spatial abilities (Vandenberg, 1968; Vandenberg & Kuse, 1979)." (Bradshaw & Nettleton 1983: 217, Human Cerebral Asymmetry)

"Females are more likely to be affected in their speech than males after right hemisphere lesions." (Bradshaw & Nettleton 1983: 221, Human Cerebral Asymmetry)

"As early as 1880 studies of asymmetry of brain anatomy and morphology showed that differences i weight between the two hemispheres are smaller in females (McGlone, 1980). The shape of the Sylvian fissure is symmetrical in a greater percentage of females." (Bradshaw & Nettleton 1983: 221, Human Cerebral Asymmetry)

"Although intelligence tests have been constructed to be free, overall, of sex bias, girls consistently score higher on verbal tasks and lower on visuospatial tasks than boys, especially after puberty. These differences may also be reflected in the distribution of the sexes in certain occupations (e.g., music composition and professional chess), in clinical disorders (developmental dysphasia and dyslexia, stuttering, and autism), in developmental milestones (e.g., learning to speak), and in general behavior in infancy. Two factors in male visuospacial superiority have been isolated: spacial visualization (the ability to mentally manipulate a stimulus configuration) and spatial orientation (the perception of the position and configuration of objects in sapce from the observer's viewpoint). These two factors are almost identical to those isolated in studies on the effects of localized brain damage on nonverbal cognitive performance." (Bradshaw & Nettleton 1983: 225, Human Cerebral Asymmetry)

"Females often show a LVF superiority for lexical decision tasks (but not where vocal naming latencies are measured) early in the task. They resemble sinistral males to some extent in that they demonstrate a verbal contribution from the right hemisphere, suggesting that in females right hemisphere processing areas normally reserved for visuospatial processing have been invaded by secondary speech mechanisms acting in an auxiliary capacity for the comprehension of difficult or unfamiliar material. Moreover, females with right hemisphere injury show depressed verbal intelligence scores but no dysphasia. Thus the right hemisphere in females appears to participate more in comprehensional than expressive speech, hence the absence of any apparent effects when it is suppressed by unilateral amytal injection." (Bradshaw & Nettleton 1983: 226, Human Cerebral Asymmetry)

"It is possible that sex differences in verbal and spatial skills are due to differences in rates of maturation. Early-maturing adolescents (and females generally mature earlier than males) score better on verbal than on spatial tests and are less lateralized. Late maturers might establish hemisphere dominance later, to the advantage of spatial ability if language normally develops before spatial skills." (Bradshaw & Nettleton 1983: 226, Human Cerebral Asymmetry)

"Hemispheric asymmetry is still widely believed to develop slowly during childhood, with speech not fully lateralized to the left hemisphere until puberty. The two hemispheres are said to initially play an active and more or less equipotential role in verbal processes, at least until language is fully established, with the left gradually assuming functional prepotency, possibly by actively inhibiting the right." (Bradshaw & Nettleton 1983: 228, Human Cerebral Asymmetry)

"Familial sinistrality, and especially parental handedness, is an important determinant of performance. Nonfamilial sinistrals appear to be the least lateralized or the most likely to demonstrate abnormal laterization. .... A number of genetic models have been proposed, but all so far have foundered on the twin and sibling data." (Bradshaw & Nettleton 1983: 265, Human Cerebral Asymmetry)

"More directly from the point of view of handedness, Walker and Birch (1970) have observed poorly developed preferences for hand and eye usage, as well as impaired awareness of right-left spatial organization, in a high proportion of 'schizophrenic children'; and Oddy and Lobstein (1972) have reported an increased incidence of crossed dominance between hand and eye in adult schizophrenics." Lishman, W.A. & McMeekan, E.R.L. (1976) Hand preference patterns in psychiatric patients Br. J. Psychiatry 129: pp.158)

"The patients with purely psychotic disorders show a considerable number of left-handers, and this becomes more pronounced among the young psychotics. Thus one-fifth of the young psychotics wre sinistral writers, and all of these were strong left-handers. The sexes are shown separately in the table; male psychotics are seen to account for this excess, the distribution among females being unremarkable. The psychotic patients consisted of 30 manic-depressives, 14 schizoaffectives and 26 schizophrenics. Detailed analyses showed that the excess sinistrality among the psychotics was largely due to manic-depressive and schizo-affective psychoses rather than schizophrenic psychosis. Lishman, W.A. & McMeekan, E.R.L. (1976) Hand preference patterns in psychiatric patients Br. J. Psychiatry 129: pp.162)

"Certain symptoms among the psychotic patients perhaps deserve comment. A crude symptom inventory showed that delusion formation was rather strongly associated with left-handedness. There were 52 patients with delusions and 18 without; the former contained 19 per cent left-handed individuals and the latter none. Among the young psychotics, 34 per cent of those with delusions were left-handed, but none of those without delusions. Hallucinations, by contrast, showed rather the reverse, 8 1/2 per cent of hallucinated psychotics being left-handed compared to 20 1/2 per cent of non-hallucinated psychotics. The figures for young hallucinated and non-hallucinated psychotics were 11 1/2 per cent and 46 per cent respectively. ( Lishman, W.A. & McMeekan, E.R.L. (1976) Hand preference patterns in psychiatric patients Br. J. Psychiatry 129: pp.163)

"Males and females show an identical pattern of familial sinistrality, provided no indication that the excess of left-handedness in male patients was due to genetic influences. Moreover the proportion of patients with a parent, sibling or child left-handed was very similar to that in Annett's normal sample of Open University students (28.3 per cent males and 28.9 per cent females). It can be seen that the proportion of left-handed patients with sinistral first degree relatives is reduced in comparison to right-handed patients; this is the reverse of what would have been expected if the majority of left-handed patients had inherited their sinistral tendencies. Table VI shows the situation in different diagnostic groups. The neurotics show no striking differences from the patients as a whole. The personality disordered patients have an excess of sinistral first-degree relatives, so their slight excess of mixed-handers may have a genetic basis. The psychotics, however, have no excess of left-handed relatives (if anything the reverse), so their excess of left-handedness does not appear to rest on genetic factors. Thus the evidence for an acquired abnormality in hand preference is most strong among the psychotics." (Lishman, W.A. & McMeekan, E.R.L. (1976) Hand preference patterns in psychiatric patients Br. J. Psychiatry 129: pp.163)

"Moreover the left-handers among the patients have shown a reduced incidence of familial sinistrality compared to the right-handers. Altogether this suggests that in some at least of the left-handed patients their sinistrality has been acquired rather than inherited." (Lishman, W.A. & McMeekan, E.R.L. (1976) Hand preference patterns in psychiatric patients Br. J. Psychiatry 129: pp.165)

"There is evidence that the minor hemisphere possesses some minimal ability to express language, but it is difficult to observe because of competition form the major hemisphere for control of the motor mechanisms for the production of language. These interference effects support a rationale for the evolution of a unilateral control of language expression, namely that such lateralization was a adaptation permitting control of the unique vocal apparatus, uncomplicated by the competitive antagonism between hemispheres. (Levy, J. (1969) Possible basis for the evolution of lateral specialization of the human brain Nature 224: 614-615)

"It is therefore not illogical to suppose that during the evolution of the hominids Gestalt perception may have lateralized into the mute hemisphere as a consequence of an antagonism between functions of language and perception." (Levy, J. (1969) Possible basis for the evolution of lateral specialization of the human brain Nature 224: 615)

"In summary, belateral language capacity seems to interfere with abilities usually associated wit the minor hemisphere. Whether it is the presence of language per se, or whether it is some pre-existing brain organization which permits the development of language which is responsible for disfavouring Gestalt apprehension could not be determined from this study. In either case, it is reasonable to conclude that, given a hemisphere laterally specialized for language, the evolution of lateralized perception can be accounted for by the foregoing interpretation." (Levy, J. (1969) Possible basis for the evolution of lateral specialization of the human brain Nature 224: 615)

Further, dyslexic epileptic males had significantly younger age of seizure onset than nondyslexic males, consistent with other epileptic syndromes associated with cortical anomalies. Left-handed epileptic females were also at greater risk for dyslexia---among epileptic dyslexic patients, 15 percent of males versus 45 percent of females wrote with their left hand, possibly the first demonstration of elevated left-handedness in famales compared to males." (Schaehter S.C., Galaburda, A.M. & Ransil B.J. (1993) Associations of dyslexia with epilepsy, handedness, and gender Annals of the New York Academy of Sciences 482: p. 402-3)

"Masculinised females, who by our hypothesis, should have a high rate of personal and familial anomalous dominance, have elevated levels of luteinizing hormone. Since their offspring may have greater exposure to masculinizing effects in utero, they may have an elevated rate of LH. This hypothesis is in conformity with the higher rate of LH in mothers of twins and in the twins themselves." (Geschwind, N. & Galaburda, A.M. (1985) Cerebral Lateralization. Biological mechanisms, associations, and pathology: II. A hypothesis and a progam for research. Archives of Neurology 42(6): pp. 535)

"Another factor, often overlooked in the study of spatial function, may lead to erroneous conclusions. It is often assumed that spatial talent depends only on right-hemisphere function, but in fact each hemisphere contributes. Left-hemisphere lesions affect predominantly the placement of internal details while right-hemisphere lesions tend to affect external configuration. It is possible that some individuals may have high talents in one or the other function, although some are good at both. Tests of spatial function often do not distinguish these capabilities, just as handedness tests may fail to distinguish "pyramidal" and "axial" motor dominance, as was discussed in an earlier section." (Geschwind, N. & Galaburda, A.M. (1985) Cerebral Lateralization. Biological mechanisms, associations, and pathology: II. A hypothesis and a progam for research. Archives of Neurology 42(6): pp. 523)