Library of Excerpts

Lateralization and Language: Part I

"Among subjects participating in 14 placebo-controlled drug cross-over studies, left-handers showed a greater drug-related change in their electroencephalograms (EEGs) than did right-handers. Response differences between left- and right-handers were not hemisphere-specific. Further, the magnitude of EEG changes correlated with handedness scores. A greater effect of centrally active substances in left-handers may, in part, explain the high incidence of left-handers among those with certain brain-related pathologies and the evolution of right-hander predominance in the general population." (Irwin P (1985) Greater brain response of left-handers to drugs. Neuropsychologia 23(1):61)

"Bianki concluded that "in animals the parallel processor of information processing is localized in the right hemisphere and the sequential processor in the left one...The spatial processor, (and) the parallel one, is located in the right hemisphere and the temporel processor, like the sequential one, in the left." "(Ornstein, R. (1997) The Right Mind. Harcourt Brace & Co: San Diego p. 23)

“Area of the midsagittal section of the corpus callosum, particularly in the region of the isthmus, was found previously to be greater in non-consistent-right-handed than consistent-right-handed men in a sample of 15 postmortem cases. Seven cases were obtained subsequent to this analysis. The new cases showed the same association previously observed between hand preference and area of the corpus callosum and its isthmus. In addition, a high negative correlation was found between isthmal area and a quantitative score of the direction and magnitude of hand preference. In the new cases, handedness was predicted better than chance using statistical functions of callosal anatomy derived from the previous group of 15 cases. These results support a relationship between variation in callosal anatomy and handedness in men and the hypothesis of a relationship between callosal morphology and functional asymmetry. The lack of such a relationship among women suggests that the developmental mechanisms leading to callosal anatomical variation in relation to lateralization are influenced by sex hormones. Methodological issues in the use of magnetic resonance imaging for the quantitative study of callosal anatomy are discussed.” (Witelson SF, Goldsmith CH (1991) The relationship of hand preference to anatomy of the corpus callosum in men. Brain Res 545(1-2):175)

"It [the right side of the brain] handles the large movements of the limbs, and the larger emotional reactions such as anger and disgust. And the left side handles the small, precise links that carry the smaller, more precise meanings and movements. ... text and context" (Ornstein, R. (1997) The Right Mind. Harcourt Brace & Co: San Diego p. 175)

"It is when the hemispheres become competent at dealing with the world that matters. A preview of the idea: The right hemisphere matures and becomes responsive to the effects of the outside world at the time in the infant's life when spatial abilities, such as finding the mother and control of the large limb movements, are getting wired up. These are obviously so necessary for survival. And the left hemisphere begins to become more and more mature, and comes on-line at that time, an era of life when the baby is exposed to spoken language and learning the more refined movements of infancy." (Ornstein, R. (1997) The Right Mind. Harcourt Brace & Co: San Diego p. 150)

"There needs to be a connection in our hidden framework for a joke to be perceived as humorous. The first stage of joke processing is usually a mild surprise caused by an incongruity that slightly upsets our anticipation. The second stage consists of solving this incongruity by reinterpreting all of the information in a new context. The pleasure of a joke depends on the individual's ability to solve the incongruity, the joke being all the more funny or subtle as the level of complexity of the problem to be solved is greater. Not everyone gets the joke, no matter how intact their brains may be. Going to another country, or hearing a comedian from a different tradition, often leaves first-time listeners cold, since they don't have the same set of associations as the comic and the crowd. This complexity that comes from the network of possible meanings of words is the province of the right side of the human brain. A long line of research shows that this hemisphere selects words very differently than the left does. The right hemisphere has a ability to hold lots of different meanings of a word available for use while, by contrast, the left hemisphere quickly selects a single meaning. People with damaged right hemispheres, then, have difficulty with jokes because they cannot hold the different meanings of a word or phrase in mind for comparison." (Ornstein, R. (1997) The Right Mind. Harcourt Brace & Co: San Diego p. 108)

"There's a strong sex difference connected to the hands. Males are much more likely to be affected by complications at birth and are more likely to be left-handed as a result of prolonged labor, breeh birth, low birth weight, cesarean delivery, multiple births, or RH incompatibility (mother and baby being of a different blood group). Females are likely to switch to left-handedness if they experience premature birth, prolonged labor, breathing difficulty, or being part of multiple births. ... Men are not only more likely than women to be lefties but also more susceptible to immune disorders such as allergies, asthma, and hay fever and to autoimmune disturbances. Strong left-handers (those who use the left hand for everything) are 2 1/2 times more likely to suffer one of these than strong right-handers." (Ornstein, R. (1997) The Right Mind. Harcourt Brace & Co: San Diego p. 85)

"For gatherers, the situation was different. Those women with the largest repertoire of communicable images of foods and their sources and secrets of perparation were unquestionably placed in a position of advantage. Language may well have arisen as a mysterious power possessed largely by women -- women who spent much more of their waking time together -- and, usually, talking -- than did men, women who in all societies are seen as group-minded, in contrast to the lone male image, which is the romanticized version of the alpha male of the primate group." (McKenna, T (1992) Food of the Gods. Bantom Books: New York p. 55)

"Our review of the Halpern and Coren (1988) data confirmed the fact that left-handers are expiring at an earlier age. Sinistrals were found to have an elevated chance of mortality between 1-2% higher than that of right-handers in any given year, at least beyond the age of 33. Much more powerful confirmation of this higher mortality was provided by Halpern & Coren (1990) who showed that in an unselected sample of death records left-handers die, on average, about 8 years earlier than do right-handers. When we considered the reasons for this elevated mortality, four possibilities were suggested: (a) elevated environmental risk, due to negative interactions with the contructed world biased toward dextrality; (b) covert neuropathology or irregular physiologicala development due to disruptions of the immune system due to in utero exposure to elevated hormonal levels." (Coren, S. & Halpern, D.F. (1991) Left-handedness: A marker for decreased survival fitness. Psychological Bulletin 109: 103)

"For instance, Corballis and his associated (Corballis, 1983; Corballis & Beale, 1983; Corballis & Morgan, 1978; Morgan & Corballis, 1978) have suggested that both cerebral laterality and handedness are under the control of a maturational gradient." (Coren, S. & Halpern, D.F. (1991) Left-handedness: A marker for decreased survival fitness. Psychological Bulletin 109: 99)

"If right-sidedness occurs as a function of the normal maturation of the nervous system, it would seem reasonable to assume that any disruption of delay in physical maturation in a sub-group of the population could result in an increased proportion of left-sidedness. Several lines of evidence support this notion. For instance, Porac, Coren, and Duncan (1980b) compared the lateral preferences (hand, foot, eye, and ear) of a group of mentally retarded individuals with a group of individuals of equivalent chronological age (mean age approximately 17 years) and with a group of equivalent mental age (mean age approximately 4 years). The retarded group had significantly more left-sided preferences than their age peers, replicating earlier work by Gordon (1921) and Mintz (1947). To account for this finding, these researchers suggested that, when retardation in not caused by specific injury, cognitive development in the retardate is simply slower or arrested at a level below that achieved normally. If this hypothesized maturational lag affects more than the retardates' mental ability (Achenbach, 1970), then it might extend also to handedness. Thus one can predict that the retardates' pattern of handedness should be similar to that shown by the more immature preschool group who served as their mental-age controls, showing the decreased proportion of right-sidedness commonly associated with the young. This prediction was confirmed by the data. Additional evidence that left-handedness may be associated with maturational lag comes from some other clinical groups. There is evidence that males with 47,XXY Klinefelter's Syndrome have slower than normal maturational growth rates (Stewart et al., 1979, 1982). Netley and Rovet (1984) have also found that the incidence of nonright-handedness was more than twice as large in a sample of 47,XXY males when compared with age-matched controls. Coren et al. (1986) extended these results to demonstrate that sinistrality is associated with maturational delays in nonclinical samples. They tested 713 females and 467 males and assessed their relative rate of physical maturation using the onset of secondary sexual characteristics, age of menarche, and relative body size as their indicators. They were able to demonstrate that delayed rates of maturation were associated with an increased incidence of left-handedness for both the males and females in their samples. Also consistent with the notion that left-handers have delayed maturation is Coren's (1989b) observation that left-handedness is associated with somewhat smaller body size in terms of both height and weight." (Coren, S. & Halpern, D.F. (1991) Left-handedness: A marker for decreased survival fitness. Psychological Bulletin 109: 99)

"Bakan (1987) further supports it with the observation that offspring from mothers who smoke are more apt to be left-handed." (Coren, S. & Halpern, D.F. (1991) Left-handedness: A marker for decreased survival fitness. Psychological Bulletin 109: 98)

"This was the conceptualization used by Hicks, Dusek, Larsen, Williams, and Pellegrini (1980) and Coren et al. (1982) who proposed that birth stress causes only a shift in the continuum from right-to left-sidedness, not a discrete or abrupt change to full sinistrality." (Coren, S. & Halpern, D.F. (1991) Left-handedness: A marker for decreased survival fitness. Psychological Bulletin 109: 98)

"Parac et al.(1980a) provided a much more detailed analysis of a more contemporary span of time to see if shifts in societal attitudes toward left-handedness are reflected in shifts in the population distribution of this phenotype. ... Their sample consisted of 34 published studies, spanning the period from 1913 to 1976, all of which were based upon North American and Western European samples. Figure 2 shows a scatter plot of the percentage of right-handed subjects plotted against the date of publication. Although there is some suggestion that the percentage of left-handededness is greater for more recent studies, the obtained correlation (r= -0.28) is not statistically significant. Even if it were significant, the slope of the trend would only account for a change of 0.05% per year, or an expected shift in the population of 3.5% over a 70-year period, which is far below the 15% shift toward dextrality observed in Figure 1." Coren, S. & Halpern, D.F. (1991) Left-handedness: A marker for decreased survival fitness. Psychological Bulletin 109: 91)

“Nonright-handedness (NRH) has been attributed to hypoxia-induced brain changes in the fetus and associated pregnancy and birth complications (PBCs). Maternal smoking during pregnancy is known to produce prenatal hypoxia for the fetus, which may result in low birth weight and other PBCs. It was hypothesized that maternal smoking during pregnancy results in a leftward shift of handedness in the offspring. This study compared the distribution of handedness in the offspring of mothers who did and did not smoke cigarettes during pregnancy. Information on maternal smoking, handedness, and PBCs was analyzed for 803 university students. There was a significant shift to the left in the distribution of handedness scores for the offspring of smoking mothers (N = 216), as compared to those of nonsmoking mothers (N = 587). Offspring of smoking mothers also reported significantly more PBCs. Results are consistent with the hypothesis that NRH is associated with pathological neurodevelopment.” (Bakan P (1991) Handedness and maternal smoking during pregnancy. Int J Neurosci 56 (1-4): 161)

“Asymmetry of the planum temporale, a language-related intrasylvian area on the superior temporal gyrus, is the most remarkable anatomical left-right asymmetry of the human brain. The in vivo application of magnetic resonance morphometry in 52 healthy volunteers (26 dextrals and 26 sinistrals) revealed that planum temporale asymmetry is correlated with hand dominance. Left-handers had a significantly lesser degree of leftward planum temporale asymmetry than right-handers. Thus, a structural-functional relation exists in cerebral asymmetry. The correlation is likely to reflect language representation. Because familial sinistrality influenced the anatomical pattern in left-handers and planum temporale asymmetry is already present in the newborn, prenatal factors must play an important role in the development of functional laterality.” (Steinmetz H, Volkmann J, Jancke L, Freund HJ (1991) Anatomical left-right asymmetry of language-related temporal cortex is different in left- and right-handers. Ann Neurol 29 (3): 315)

“Variations in the size of the human corpus callosum were examined as a possible morphological substrate of functional asymmetries of the cerebral hemispheres, such as cerebral speech dominance. The midsagittal surface area of the corpus callosum, obtained by magnetic resonance imaging, was measured in 50 patients with epilepsy and 50 neurologically normal control subjects. The mean callosal area did not differ significantly between patients and control subjects, between left-handed and right-handed subjects, or between men and women. When measurements were compared among 44 patients, whose cerebral speech dominance had been determined by the intracarotid injection of sodium amytal, the area of the corpus callosum was significantly greater in patients with right-hemisphere cerebral speech dominance. The mean callosal area was greater by 109 to 159 square millimeters (18-28%) when compared to that of patients with either left-hemisphere speech dominance or bilateral speech representation. This difference in midsagittal surface area could represent as many as 37 to 54 million additional callosal axons in subjects with right-hemisphere cerebral speech dominance.” (O'Kusky J, Strauss E, Kosaka B, Wada J, Li D, Druhan M, Petrie J (1988) The corpus callosum is larger with right-hemisphere cerebral speech dominance. Ann Neurol 24 (3): 379)

“The neural processing of emotion and the differential processing of affect and cognition are thus far poorly understood. Complex results across studies suggest involvement of the left hemisphere, the right hemisphere, or both. Since handedness is related to cerebral dominance, the present study undertook a comparative analysis of neural processing in strongly lateralized left- and right-handed populations. Parietal EEG and bilateral electrodermal activity were recorded while carefully selected subjects were exposed to emotional stimuli under cognitive, affective, and neutral conditions. Results showed greater lateral differentiation and differentially greater left-hemisphere activation in dextrals but greater overall activation in sinistrals. These findings are consistent with the common observation that cerebral organization is more diffuse in left-handed populations. It seems clear that the comparative study of sinistrals and dextrals can help us to better understand how emotion is processed in the brain.” (Smith BD, Kline R, Meyers M (1990) The differential hemispheric processing of emotion: a comparative analysis in strongly-lateralized sinistrals and dextrals. Int J Neurosci 50 (1-2): 59)

[abstract only? “Two hundred seventy children of school age, 135 of whom were left-handed and an equivalent number of whom were right-handed, have been examined in the present study using a test battery of nine language ability measures: Vocabulary, Similarities, Comprehension (WISC-R), Deductive Reasoning, Inductive Reasoning, Sentence Completion, Comprehension of Sentential Semantics, Comprehension of Syntax, and Text Processing. The data analysis has indicated that: (1) One-factor solution applies both to the right- and left-handed population according to Standard Error Scree Method (Zoski & Jurs, 1996) with regard to language ability measures. (2) Handedness discriminates between right-handers (superior) and left-handers (inferior) in language ability. (3) There have been subgroups of left-handed children who differ in language ability distribution compared with right-handed children according to Hierarchical Cluster Analysis. (4) Extreme versus mild bias to hand preference and hand skill do not differentiate performance subgroups neither within the left-handed nor within the right-handed main group. (5) Sex and familial sinistrality do not affect performance. The results are discussed in relation to (a) "human balanced polymorphism" theory advocated by Annett (mainly Annett, 1985, 1993a; Annett & Manning, 1989), (b) potential pathology (mainly Bishop, 1984, 1990a; Coren & Halpern, 1991; Satz, Orsini, Saslow & Henry, 1985) and "developmental instability" (Yeo, Gangestad & Daniel, 1993), and delay of left-hemisphere maturation in left-handed individuals (Geschwind & Galaburda, 1985a,b, 1987), by pointing out the strength and weaknesses of these theoretical approaches in accounting for the present data.” (Natsopoulos D, Kiosseoglou G, Xeromeritou A, Alevriadou A (1998) Do the hands talk on mind's behalf? Differences in language ability between left- and right-handed children. Brain Lang 64 (2): 182)

“A clinical syndrome of pathological left-handedness (PLH) is proposed to identify the pattern of correlative changes in lateral development associated with early brain injury in some manifest left-handers. This syndrome is believed to be caused by a hemispheric lesion that is predominantly left-sided (or bilateral asymmetric), which onsets before Age 6, and which encroaches upon the critical speech zones of the frontotemporal/frontoparietal cortex. The pattern of changes may include any or all of the following features: shifts in manual dominance, trophic changes in the extremities, transfer of hemispheric speech, and/or intrahemispheric reorganization of visuospatial cognitive functions. Although some of these correlates of PLH have long been known, they have not been recognized as an interrelated pattern of traits that constitute a clinical syndrome. Identification of these individuals, all manifest left-handers, will be shown to have implications for diagnosis/remediation and for models of recovery of function.” (Satz P, Orsini DL, Saslow E, Henry R (1985) The pathological left-handedness syndrome. Brain Cogn 4(1):27)

"In an auditory or musical task, subjects made pitch recognition judgments when the tones to be compared were separated by a sequence of interpolated tones. The left-handed subjects performed significantly better than the right-handed and also had a significantly higher variance. Further analysis showed that the superior performance was attributable largely to the left-handed subjects with mixed hand preference." (Deutsch, D. (1978) Pitch memory: An advantage for the left handed. Science 199: pp. 5590

“The relationship between the strength of left-handedness and spatial reasoning ability was studied in left-handed male and female subjects with and without familial sinistrality (FS). The degree of left-handedness was assessed by the Edinburgh Handedness Inventory. The spatial reasoning ability was measured by Cattell's Culture Fair Intelligence Test. It was found that there was a negative linear correlation between nonverbal IQ and the strength of left-handedness in females with and without FS, a quadratic relationship in male left-handers without FS and a positive linear correlation in male left-handers with FS. These results indicate that the brain may exhibit different patterns of cerebral organization in left-handers to sex and FS. It was concluded that the "crowding" hypothesis may apply only to a subgroup of left-handers, i.e., females with a greater bilaterality of cognitive functions than males.” (Tan U (1991) The relationships between nonverbal intelligence and the strength of left-hand preference in left-handers to sex and familial sinistrality. Int J Neurosci 58 (3-4):151)

“The midsagittal area of the corpus callosum was measured in its entirety and in seven subdivisions in a sample of 50 brains consecutively obtained from autopsies of individuals who had neuropsychological testing before death. A 12-item test of hand preference was used as an index of the pattern of interhemispheric functional asymmetry. Callosal size was analysed for two factors: hand preference, classified as consistent-right-hand preference (CRH) versus non consistent-right-hand preference, and sex. The group of nCRH (n = 18) was found to have a larger overall callosal area, with the greatest difference occurring in the posterior body segments, especially the isthmus. The isthmus probably includes interhemispheric fibres from posterior parietal and superior temporal cortex which involves cortical regions related to functional asymmetry. The results of variation in callosalmorphology are discussed as part of a possible substrate of functional asymmetry and due to variation in axonal elimination in early brain development. Sex differences were found in several aspects of callosal anatomy. (1) The difference between hand groups in the posterior body occurred in interaction with sex:handedness was a factor in callosal size in males (n = 15), but not in females (n = 35). This result is consistent with the general hypothesis of females having less clear lateralization than males. (2) Females did not have a larger overall callosum or a larger splenium, either in absolute size or size proportional to brain weight. The latter measure was considered since callosal area correlated with cerebrum weight (r = 0.48). In contrast, female of both hand groups were found to have a larger proportional isthmus compared to CRH males. (3) Of all callosal regions, only the genu and a part of the anterior body were found to be larger in absolute size in males than females. (4) Callosal size decreased with chronological age in males, but not in females.” (Witelson S (1989) Hand and sex differences in the isthmus and genu of the human corpus callosum. A postmortem morphological study. Brain112 ( Pt 3): 799)

“The relationship between serum testosterone level and visuomotor of learning of hand skill was studied in right-handed young men. Hand skill was assessed by a peg moving task. Peg moving times for the right and left hands linearly decreased at each successive trial (visuomotor learning). The peg moving times for the right and left hands were found to be negatively linearly related to serum testosterone levels: there was a direct relationship between hand skill and testosterone, which was more prominent for the right than the left hand. The slopes of the learning curves for the right hand were found to be equal in subjects with low, normal, and high testosterone. The intercepts of these curves exhibited a shift toward a better hand skill from low- to high-testosterone subjects. The visuomotor learning for the left hand was found to be better in subjects with normal and high testosterone than those with low testosterone. It was concluded that testosterone would favor the visuomotor development especially of the left cerebral hemisphere, probably at puberty; the motor learning of this hemisphere does not seem to be associated with testosterone. Testosterone seems to be advantageous for the visuomotor performance as well as for the motor learning of the right cerebral hemisphere. “ (Tan U(1991) The relationship between serum testosterone level and visuomotor learning in right-handed young men. Int J Neurosci 56(1-4):19)

“Reviews the literature examining the relationship between birth order, birth stress, and lateral preferences in nonclinical samples, with special emphasis on reports since 1971. The review found no evidence to relate birth order position to deviations from right-sidedness for either sex. More direct measures of birth stress indicated that deviations from right-handedness (particularly for male subjects), and also right-eyedness, were statistically related to specific birth stressors. It should be stressed, however, that all the relationships, including the significant ones, were very weak, accounting for less than 1% of the variance. When statistical significance was achieved, it was largely due to the huge sample sizes used in the meta-analyses. Methological and theoretical problems exist in the current literature, and we offer some suggestions to resolve them.” (Searleman A, Porac C, Coren S (1989) Relationship between birth order, birth stress, and lateral preferences: a critical review. Psychol Bull 105 (3):397)

“This paper is the first large-scale attempt to test Geschwind and Galaburda's (1985a, 1985b, 1985c) hypothesis that there should be a four-way association among neurodevelopmental disorders (NDs), special talents, non-right handedness, and immune disorders. In a sample of 11,578 children, several two-way associations were found, but not those most strongly predicted by the theory. For example, non-right handedness was not associated with NDs considered to be secondary to left hemisphere dysfunction (e.g., articulation disorder, reading disability, verbal aptitude deficits). Instead, non-right handedness was associated with NDs that involve generalized brain damage (e.g. cerebral palsy, mental retardation, and seizures). One immune disorder (asthma) was associated with one ND (attention deficit disorder); immune disorder was not associated with non-right handedness. Less than 1% of this sample manifested the co-occurrence of any three or four of these markers. In sum, there was little evidence in support of the syndrome suggested by Geschwind and Galaburda (1985a, 1985b, 1985c).” (Flannery KA, Liederman J (1995) Is there really a syndrome involving the co-occurrence of neurodevelopmental disorder talent, non-right handedness and immune disorder among children? Cortex 31(3):503)

“Serum testosterone levels were determined in female and male subjects. Hand preference was assessed by the Edinburgh Handedness Inventory. Subjects with anomalous dominance (left-handers, mixed-handers, and right-handers with familial sinistrality) were compared to subjects with standard dominance (right-handers without familial sinistrality). The mean serum testosterone levels were found to be significantly higher in subjects with anomalous dominance than those with standard dominance. It was concluded that the results are in accord with the testosterone hypothesis of cer bral lateralization.” (Tan U(1991) Serum testosterone levels in male and female subjects with standard and anomalous dominance.Int J Neurosci 58(3-4):211)

“The relationship between serum testosterone level and motor learning in hand skill was studied in right-handed young women. Hand skill was assessed by a peg moving task. Subjects were required to shift 25 pegs from one of two parallel rows to the corresponding holes as fast as possible, first with right and then with left hand. One trial consisted of the time elapsed to move 25 pegs with one hand. Ten trials were performed by each hand. Peg moving times for the right and left hands linearly decreased at each successive trial (visuomotor learning). Subjects were divided into two subgroups as those having serum testosterone concentrations below and above the mean. The right hand skill and its motor learning was found to be better in subjects with low testosterone than those with high testosterone. The left hand skill was better in subjects with low testosterone than those with high testosterone; there was no significant difference in the left-hand learning in subjects with low and high testosterone (parallel regression lines). Motor learning linearly decreased with testosterone for the right hand, not for the left hand. These results seem to be in accord with the testosterone theory of cerebral lateralization (Geschwind & Behan, 1982).” (Tan U (1991) The relationship between serum testosterone and visuomotor learning in hand skill in right-handed young women.Int J Neurosci 56(1-4):13-8)

“The relationship between serum testosterone level and nonverbal intelligence was studied in right-handed young adults with regard to handedness. Hand preference was assessed by the Edinburgh Handedness Inventory. Hand skill was measured by a peg moving task. Serum testosterone level was determined using tritium-marked-radioimmunoassay. Visual-spatial performance (nonverbal intelligence) was measured by Cattell's Culture Fair Intelligence Test. In men with consistent right-hand preference (GSs: 80 to 100), IQ was found to be positively linearly related to serum testosterone, which exhibited two regression lines belonging to low and high difference in skill between hands. In females with consistent right-handedness, there was a negative linear correlation between IQ and serum testosterone, which also exhibited two different regression lines according to difference in skill between hands. In males with moderate right-hand preference (GSs 50 to 75), IQ was found to be positively linearly related to serum testosterone, exhibiting two different (same slopes) regression lines according to difference in skill between hands. In females with moderate right-hand preference, IQ first increased and then decreased with serum testosterone, exhibiting a quadratic relationship. These results suggested that serum testosterone in young adults may be associated with visual-spatial performance depending upon sex, hand preference, and hand skill.” (Tan U (1990) Relationship of testosterone and nonverbal intelligence to hand preference and hand skill in right-handed young adults. Int J Neurosci 54(3-4): 283)

“The relationship between serum testosterone level and hand performance was studied in right-handed young adults without familial sinistrality. Hand performance was measured by a dot-filling task, which was found to be associated with serum testosterone depending upon sex. In women, the right- and left-hand performance was found to be negatively linearly related to testosterone; there was no significant correlation between the right- minus left-hand performance and testosterone. In men, right- and left-hand performance were found to be directly and inversely related to testosterone, respectively. This pattern exhibited some variations depending on eye and foot preferences. The difference in performance between hands was found to be positively linearly related to serum testosterone levels in men.” (Tan U(1990) Testosterone and hand performance in right-handed young adults. Int J Neurosci 54 (3-4): 267)

“The relationship between serum testosterone level and the degree of hand preference was studied in right-handed young adults. Hand preference was assessed by the Edinburgh Handedness Inventory. Serum testosterone level was determined using tritium-marked-radioimmunoassay. There was no significant correlation between these variables in males without FS. In males with FS and in females with and without FS, the serum testosterone levels were found to be negatively linearly correlated with the degree of the right-hand preference. Similar results were obtained with respect to foot and eye preferences. It was concluded that not only prenatal testosterone but adult testosterone also may exert a life long influence on cerebral lateralization; this effect seems to be much more pronounced in the female than male brain, which may exert a female-like pattern under genetic control.” (Tan U(1990) Relation of testosterone and hand preference in right-handed young adults to sex and familial sinistrality. Int J Neurosci 53(2-4): 157)

“An important basic question is whether it is at all reasonable to suggest that Nature might give us a mechanism which aids the development of speech, but at the cost of total brain power. I believe the answer to this question is ‘yes’. Speech is a unique human species characteristic, of great value for cooperative group living and the transmission of culture. However, as a communication medium, speech has problems for both the speaker and the listener because it is prone to confusion. All humans learn to talk, but those who talk more clearly, decode speech more accurately, and perhaps those who learn to talk earlier, may have an advantage. This is the benefit which I believe is conferred by having speech lateralized. If input and output are controlled by the same side of the brain, speech learning can proceed in infancy without the need to transmit information across the immature corpus callosum (Annett, 1985, Chapter 20). It may not mater which side is chosen, left or right, but nature happens to have chosen the left for most of us. In the human primate with an espeically large brain, there was probably sufficient spare capacity for some reduncancy. It is only recently that humans have been expected to read, and to have high levels of competence in written language and technological skills.” (Annett M (1991) Right hemisphere costs of right handedness in Vision and Visual Dyslexia, Stein JF (ed.) CRC Press, Boca Raton pp. 84)

“Geschwind and Levitsky (1967) reported that in 100 postmortems, a larger planum was found on the left side in 65 brains, on the right side in 11 and in the remaining 24 the two sides were about equal. Galaburda et al. (1987) looked at the actual sizes of the plana on each side in this same series. They found that in symmetrical brains, both plana were large, while in asymmetrical ones (the typical pattern) the size of the planum on the right side was reduced, while the left stayed about the same. Thus, the typical pattern of asymmetry seems to be associated with a reduction on the right side, rather than expansion on the left; and symmetrical brains show no reduction on either side. Similarly, for the right and left hands, it looks as though bias to the right hand depends on loss of left hand skill, rather than increased skill on the right.” (Annett M (1991) Right hemisphere costs of right handedness in Vision and Visual Dyslexia, Stein JF (ed.) CRC Press, Boca Raton pp. 87)

“The Chinese Hakka, Katanganese, Temne agriculturalists and Hong Kong Chinese University students have, as expected, not only more conforming Asch scores, stricter discipline, but also the expected lower incidence of “left-handedness” (3.4%, 1.5%, 0.59% and 0.83%, respectively). In contrast, the more independent Australian Arunta hunters, Chinese Boat-People, and Alaskan Eskimo have left-hand percentages of 10.5%, 9.4%, and 11.3%, respectively, thus confirming Hy. II. The sex differences in left-handedness also supported Hy. III, with the Hakka, Temne, Katanga and Chinese agricultural males being, respectively, 3.8%, 2.5%, 0.79%, and 2.7% left-handed, while the female incidence for these societies is, 0% of a total of 330 Ss.” (Dawson, J.L.M. (1974) Ecology, cultural pressures towards conformity and left-handedness: a bio-social approach. in J.L.M. Dawson , W.J. Lonner (eds.) Readings in Cross-cultural Psychology. Hong Kong: Hong Kong U. Press. p. 136)

"The hypothesis is proposed that these problems are related both to each other and to the speciation event that gave rise to modern Homo sapiens 137,000 or more years ago. A genetic change allowed the two hemispheres to develop with a degree of independence: the capacity for language (with a dominant focus in one hemisphere) evolved as a result of selection acting upon a dimension of variation generated by a single polymorphism plus a random component. Psychosis is the element of the variation associated with failure to establish dominance for language in one or other hemisphere (hemisphere indecision')" (Crow TJ (1996) Language and psychosis: common evolutionary origins. [received from author without publisher name on document] p. 105-109)

"Population variation in handedness (a correlate of cerebral dominance for language) is part genetic and, it has been suggested, its persistence represents a balanced polymorphism with respect to cognitive ability. This hypothesis was tested in a sample of 12,770 individuals in a UK national cohort (the National Child Development Study) by assessing relative hand skill (in a square checking task) as a predictor of verbal, non-verbal, and mathematical ability and reading comprehension at the age of 11 years. Whereas some modest decrements were present in extreme right handers the most substantial deficits in ability were seen close to the point of equal hand skill ('hemispheric indecision'). For verbal ability females performed better than males, but the relationship to relative hand skill was closely similar for the two sexes; for reading comprehension males close to the point of equal hand skill showed greater impairments than females. Analysed by writing hand the relationship of ability to hand skill appeared symmetrical about the point of 'hemispheric indecision'. The variation associated with degrees of dominance may reflect the operation of continuing selection on the gene (postulated to be X-Y linked) by which language evolved and speciation occurred." (Crow TJ, Crow LR, Done DJ, Leask S (1998) Relative hand skill predicts academic abiltity: global deficits at the point of hemispheric indecision. Neuropsychologia : )

[abstract only?] "The relationship between measures (of size or function) on one side of the brain, in relation to the difference between the two sides on that measure, are important components of theories of hemispheric asymmetry. For example, it has been concluded that increasing lateralization (e.g., of hand skill or planum temporale area) occurs at the expense of the non-dominant hemisphere. Here it is demonstrated that such relationships could merely be a necessary consequence of relating components of a laterality index to the index (L - R)/(L + R) itself, or indeed to L - R. An alternative approach (using random data to exemplify the null hypothesis) is presented together with an application to data on hand skill from 12,782 11-year-olds in a cohort study. This demonstrates a symmetry hitherto undocumented of maximal hand skill in left and right hands in left- and right-hand writers respectively, the point of the maximum falling short of the population mean for relative hand skill in either case. If degrees of laterality are what is genetically determined, this suggests that selection is present for a function (perhaps language) associated with a greater magnitude of lateralization than is represented by hand skill." (Leask SJ, Crow TJ (1997)How far does the brain lateralize?: an unbiased method for determining the optimum degree of hemispheric specialization. Neuropsychologia 35(10):1381-7)


"Regardless of sex, early maturing adolescents performed better on tests of verbal than spactial abilities, the late maturing one showed the opposite pattern. Those maturing late were more lateralized for speech than those maturing early. Sex differences in mental abilities, it is argued, reflect differences in the oranization of cortical function that are related to differential rates of physical maturation." (Waber, D.P. (1976) Sex differences in cognition: A function of maturation rates. Science 192: pp. 572)

"The striking relation between rate of physical maturation (independent of sex) and spatial ability, verbal-spatial patterns and lateralization has several important implications. First, sex accounted for only a very small proportion of the variance in comparison to maturational rate. Therefore, reported sex differences in these behaviors probably reflect the differential distribution of the sexes along a physiologicall continuum more than a categorical difference between male and female. This concept might also apply to other behaviors not examined in this study. Second, since matuational rate was shown not to be related to verbal ability, the sex differences in verbal and spatial abilities may have very different etiologies and cannot be explained by a common set of causes, whether environmental or constitutional. Finally, rate of maturation (or its implicit physiological correlates) may play an important role in the organization of higher cortical functions." (Waber, D.P. (1976) Sex differences in cognition: A function of maturation rates. Science 192: pp. 573)

"Evidence that the rs - - might have advantages in motor skills has been found in the discovery that in the large control samples of students and school children to be used below, left handers were faster than right handers for absolute peg moving times, and mixed handers were of intermediate skill. (Kilshaw and Annett, 1983). (Annett, M. & Kilshaw D. (1984) Lateral preference and skill in dyslexics: Implications of the right shift theory. J Child Psychology and Psychiatry 25: 358)

"The Mark II predictions (post hoc in the present case) depend on a more general interpretation of the balanced polymorphism hypothesis explained above. This suggests that there are risks to intellectual development for those at both extremes of the asymmetry distribution. Problems in learning to read may be associated with overexpression as well as with underexpression of the rs + gene. Support for the view that the rs + + risk intellectual deficits beyond the visuospatial and practical ones hypothesized above comes from two sets of observations. First, the analysis of absolute hand speeds in hand preference groups (Kilshaw and Annett, 1983) suggested that hemisphere specialization might be achieved not be some boost to the left hemisphere but rather by some handicap to the right hemisphere. Among those of rs + + genotype there could be some who risk significant impairment of right hemisphere efficiency and who must rely, therefore, on the left hemisphere for all major intellectual skills." (Annett, M. & Kilshaw D. (1984) Lateral preference and skill in dyslexics: Implications of the right shift theory. J Child Psychology and Psychiatry 25: 360)

"Female dyselics, however, tended to be slow with he non-preferred hand." (Annett, M. & Kilshaw D. (1984) Lateral preference and skill in dyslexics: Implications of the right shift theory. J Child Psychology and Psychiatry 25: 362)

"Dyslexics favouring the left hand (<0) tended to be slower than controls with both hands, but the slowness of the right hand was very much less marked than the slowness of the left hand for extreme right-handers." (Annett, M. & Kilshaw D. (1984) Lateral preference and skill in dyslexics: Implications of the right shift theory. J Child Psychology and Psychiatry 25: 367)

"For enjoyment in making things the reduction of L-R time was significant. Children who did not enjoy making things were more dextral than controls ... and also more dextral than dyslexics who did not enjoy making things..." (Annett, M. & Kilshaw D. (1984) Lateral preference and skill in dyslexics: Implications of the right shift theory. J Child Psychology and Psychiatry 25: 370)

"For example, when 60% or dyslexic males were assumed to be rs - - and 40% of rs + +, with means as for controls and standard deviation 8 for both genotypes, the D value was 0.035. The L-R distribution of the dyslexic sample is consistent with the Mark I predictions of the model that the rs - - genotype is overrepresented (perhaps 50-60% in comparison with about 18% in the general population). the unexpected finding, which led to the Mark II interpretation of the model, is that the rs + + genotype is also overrepresented (perhaps 40-50% compared with about 32% for the general population). There were too few female dyslexics to repeat this comparison with control females." (Annett, M. & Kilshaw D. (1984) Lateral preference and skill in dyslexics: Implications of the right shift theory. J Child Psychology and Psychiatry 25: 370)

"If there are two subgroups in the present sample, associated with each extreme of the L-R distribution, is it possible to distinguish the groups for other characteristics? It was anticipated that a subgroup including more rs - - genotypes would be likely to have advantages in practical skills and in mathematics, to have more affected relatives and to be less likely to have a history of perinatal stress than other dylexics. This last assumption depended on the possibility that some dyslexias might be associated with reduced expression of the rs + gene following pathological influence on early development. Trends toward a reduction of L-R mean were found for all these variables (Table 8), provided 'affected relative' is redefined as 'affected female relative'. The variable which most clearly separated the sinistral and dextral groups was 'enjoys making things'. Although it was expected, as explained above, that the rs + + risk deficits in practical skills, it was surprising to find that an assessment of clumsiness based on the simple question "Do you like making things?" would identify a small subgroup of males (16) who were significantly more dextral for L-R time than controls. The remaining males (93) were significantly less biased to the right than controls. This main group of males fulfilled the initial prediction for the whole sample of a reduction of right shift." (Annett, M. & Kilshaw D. (1984) Lateral preference and skill in dyslexics: Implications of the right shift theory. J Child Psychology and Psychiatry 25: 374)

"Reduced shift implies that twins are slightly less biased toward dextrality than nontwins such that, when the incidence of left-handedness in the general population is 7 or 8%, about 11 or 12% is expected in twins." (Annett, M. (1996) In defence of the right shift theory. Perceptual Motor Skills 82 (1): pp. 119)

"There are sex differences in R-L hand skill such that females are slightly more right shifted than males. Females tend to be more mature at birth than males. This observation, together with the finding of a lesser shift in twins than in nontwins, suggested the important hypothesis that cerebral asymmetry depends on rate of hemispheric maturation in fetal life." (Annett, M. (1996) In defence of the right shift theory. Perceptual Motor Skills 82 (1): pp. 120)

"This theory lead to the paradoxical suggestion that strong right-handers should resemble left-handers in having an elevated incidence of left-handedness in parents. This idea was tested by asking the 224 undergraduates in the two studies mentioned above to report their parents' handedness. Scores 0, 1, or 2 were assigned for number of left-handed parents. Gangestad and Yeo (1994) described the regression of parental handedness scores on the peg-moving asymmetry of children. A curvilinear relationship was found, which was interpreted as support for the DI model." (Annett, M. (1996) In defence of the right shift theory. Perceptual Motor Skills 82 (1): pp. 129)

"Tests of the RS model were made in several stages. First, it was shown that the handedness of children of two left-handed parents (L X L families) was as expected for a chance distribution without right shift, about equal numbers of children with the right and left hand superior for skill (Annett, 1974, 1983). However, where one of these parents had a history of birth stress or other early pathology, the children were shifted to dextrality as controls." (Annett, M. (1996) In defence of the right shift theory. Perceptual Motor Skills 82 (1): pp. 116)

"Among children experiencing specific and unexplained problems in learning to read and spell (dyslexics), one type is expected to have weak phonological processing because the cerebral representation of speech is insecure. The second type should have no problems with speech-based processing, but other difficulties probably due to the weak representation of words in visual memory. Handedness and the lateral asymmetries in the first type are random with only accidental biases to either side, while in the second type random asymmetries are strongly displaced toward dextrality such that almost all should be right-handed." (Annett, M., Eglinton, E., Smythe, P. (1996) Types of dyslexia and the shift to dextrality. J Child Psychology and Psychiatry 37 (2): 167)

"The term 'visuospatial' is used to refer to the types of cognitive processing which are at risk in those with weak right hemisphere function, but the nature of the risk is at present underspecified. Evidence for a decline of spatial ability with increasing probability of the presence of the rs + gene was found in two large samples (Annett, 1992c). Mathematical ability is probably at risk in the rs + + genotype (Annett & Kilshaw, 1982; Annett & Manning, 1990b; Benbow, 1986) as is nonverbal reasoning (Annet & Manning, 1989 corrections by Annett, 1993b). There is evidence for weak visual processing in some dyslexics (Benton, 1991; Stein, 1991; Watson & Willows, 1993)." "Handedness is not a discrete variable, but rather a continuous one, with several possible levels of expression, along the continuous R-L distribution. The notorious inconsistency of studies of handedness arises from the treatment of a continuous variable as if it were discrete." (Annett, M., Eglinton, E., Smythe, P. (1996) Types of dyslexia and the shift to dextrality. J Child Psychology and Psychiatry 37 (2): 169)

"Annett and Turner (1974) pointed out that there is a very great difference between predictions for reading and handedness when handedness is treated as the independent variable than when it is the dependent variable. That is, when school samples are classified for handedness and the classes are compared for reading ability no differences are expected, nor are they found (Annett & Turner, 1974; Clark, 1970). However, groups of children with specific reading disability in clinic samples may include an excess of rs - - genotypes so that such groups are likely to include more mixed and left handers than unselected samples. If some dyslexics are of rs + + genotype, strong dextrals could be present in clinic samples also, so the overall effect for handedness would be small." (Annett, M., Eglinton, E., Smythe, P. (1996) Types of dyslexia and the shift to dextrality. J Child Psychology and Psychiatry 37 (2): 169)

"It is important to notice that the rs + gene does ot cause speech but merely aids the development of speech in most people." (Annett, M., Eglinton, E., Smythe, P. (1996) Types of dyslexia and the shift to dextrality. J Child Psychology and Psychiatry 37 (2): 168)

"As the main interhemispheric track, the corpus callosum plays an important role in hemisphere integration and possibly in hemispheric specialization." (Witelson, S.F. (1985) The brain connection: the corpus callosum is larger in left-handers. Science 229: pp. 665)

"Absolute brain weight and volume are significantly larger in males by about 10 to 15 percent, although the sexes do not differ in brain weight relative to body height." Witelson, S.F. (1985) The brain connection: the corpus callosum is larger in left-handers. Science 229: pp. 666)

"Mixed-handers showed significantly larger callosal areas for all measures except for posterior fifth..." Witelson, S.F. (1985) The brain connection: the corpus callosum is larger in left-handers. Science 229: pp. 666)

"...there may be no sex difference in right-handers, but there may be in mixed-handers, with males tending to have a relatively larger posterior half." Witelson, S.F. (1985) The brain connection: the corpus callosum is larger in left-handers. Science 229: pp. 666)

"Such a model would predict that consistent left-handers, like mixed-handers, have a larger callosum than do consistent right-handers. To this end, MRI scans of the midsagittal section were obtained for two consistent left-handed men. Albeit measures from MRI scans and postmortem examinations are not perfectly comparable, for both men the total callosal area was greater than 3, standard deviations above the mean and greater than each individual score of the male right-handed group." Witelson, S.F. (1985) The brain connection: the corpus callosum is larger in left-handers. Science 229: pp. 667)

"Less gray matter was observed in right-handers than in left-handers, inferred from perfusion and clearance rates in regional cerebral blood flow studies." Witelson, S.F. (1985) The brain connection: the corpus callosum is larger in left-handers. Science 229: pp. 668)

"The results for one left-handed subject who wrote with an inverted posture (subject 1) support the hypothesis of an association between callosal size and degree of hemispheric specialization. It has been suggested (J. Levy, Psyhcol Bull. 91 589 (1982)) that inverted left-handed writers have greater functional bilateralization, at least for written language, than do left-handed writers with noninverted posture. The callosum of subject 1 was larger than that of any of the other four left-writing females, as well as being the largest of all 30 female subjects. One left-inverted male was available (one of the subjects who had magnetic resonance imaging). His callosal area was not only 5 standard deviations above the mean of the male right-handers, but was the largest of all the non-right-handed males." Witelson, S.F. (1985) The brain connection: the corpus callosum is larger in left-handers. Science 229: pp. 668)


“The relationship between serum testosterone level and hand skill was studied in right-handed young adults. Hand preference was assessed by the Edinburgh Handedness Inventory. Hand skill was assessed by the peg moving task. Serum testosterone level was determined using tritium-marked-radioimmunoassay. In the total sample, only the right-hand skill showed a direct correlation and an inverse correlation with serum testosterone for men and women, respectively. In male subjects with right-eye preference, both hand skills exhibited a direct relation to serum testosterone. In the total sample, there was a direct and and inverse relationship between the difference in skill between hands and serum testosterone in men and women, respectively. This was, however, affected by right-eye and right-foot preference. It was concluded between men and women; the left cerebral hemisphere seems to be the main target of testosterone.” (Tan, U. (1990) Testosterone and hand skill in right-handed men and women. International Journal of Neuroscience 53: 179) [subjects were 42 male and 17 female right-handed students]

“The results of the present work indicated a different organization within the human brain with respect to relation of testosterone to skilled movement compared to hand preference. Namely, the serum testosterone was found to be associated mainly with right-hand skill in men and women. However, there were fundamental differences in the male and female patterns. Except for male right-handers with right-eye preference, the right hand skill was found to be directly related to serum testosterone in men, and inversely related to serum testosterone in women. In other words, the right-hand skill increased with serum testosterone in men, which contrasts with the Geschwind-Behan hypothesis. In women, the right-hand skill decreased with serum testosterone in accord with the Geschwind-Behan hypothesis. It is, however, interesting that mainly the left-cerebral hemisphere is involved in testosterone actions, except for men with right-hand and right-eye preference exhibiting involvement of both cerebral hemispheres. As expected form the above presented results, there was a direct relationship between the difference in skill between hands and serum testosterone in men. That is, as testosterone increased, the right-hand skill with testosterone causes an increase in L-R hand skill depending upon improvement in the left hemisphere functions for skilled movments with testosterone. In contrast, as testosterone increased, the difference in skill between hands decreased in women. This result was also expected, since right-hand skill deceased with testosterone in these subjects. Thus, testosterone seems to exert a negative effect on the left cerebral hemisphere for skilled movements. However, these effects were found to be also dependent on eye and foot preferences. Here again, men and women showed different patterns. In right-handed men with right-eye preference, the difference in skill between hands was found to be directly related to serum testosterone, but there was not a significant relationship between these parameters in women with right-eye preference. On the contrary, there was not a significant correlation between serum testosterone and L-R hand skill in men with right-foot preference, but there was a marginally significant inverse correlation between these two parameters in women with right-foot preference. In summary, the results of the present work showed that serum testosterone levels are associated with hand skill in right-handed yound adults without FS. There were, however, fundamental sex-related differences in this organization, which were also associated with eye and foot preferences. Testosterone seems to be advantageous for the male brain, but detrimental for the female brain with regard to skilled movements. Moreover, testosterone seems to create a more asymmetrical brain in men, and a more symmetrical brain in women.” (Tan, U. (1990) Testosterone and hand skill in right-handed men and women. International Journal of Neuroscience 53: 188-9)


"In this study five subjects in the HM group reported altered hand preference from left to right as the result of childhood training, whereas there was only one report of change from right to left, which suggest that later influences act ot reduce rather than increase any tendency to left-handedness in the homosexual population." (Lindesay, J. (1987) Laterality shifts in homosexual men. Neuropsychologia 25: 967)

"Studies indicated that musicians differ from nonmusicians in functional hemispheric lateralization (Gordon, 1983; Hassler & Birbaumer, 1988; Witelson, 1980) in that musicians are less left-lateralized than nonmusicians for language functions." (Hassler & Birbaumer, 1988) at each stage of the study." (Hassler, M & Nieschlag, E. (1991) Salivary testosterone and creative musical behavior in adolescent males and females. Developmental Neuropsychology 7: 518)

"Assessments of hand preference and skill in pupils attending a dyslexia clinic (Annett & Kilshaw, 1984) found higher incidences of left- and mixed-handedness, in proportions expected for a distribution of right-left (R-L) skill which was less shifted to the right. However, the R-L mean did not differ from that of controls because some dyslexics were very strongly right-handed. That is, there was an excesss of clinic children at both ends of the R-L continuum and a relative deficit in the centre." (Annett, M. & Manning, M. (1990) Reading and a balanced polymorphism for laterality and ability. J Child Psychology and Psychiatry 31 (4): pp. 511)