BRAIN AND LANGUAGE 65, 356–358 (1998)ARTICLE NO. BL981991

NOTES AND DISCUSSION

Stories about Hands, Brains, and Minds

Marian Annett

University of Leicester, Leicester, United Kingdom

The ‘‘extreme’’ versus ‘‘mild’’ classification of handedness of Natsopoulos etal. (1998) is not comparable to that of Annett (review, 1995) because 50% of theformer sample were left-handers while the samples of the latter were unselected forhandedness. The 20% of the Natsopoulos sample called ‘‘extreme’’ right-handersrepresent nearly 40% of the general population. The possibility cannot be ruled outthat the advantage for right-handers in this sample was due to a small excess ofdisabled children among left-handers because there were no controls for hand skillor for reading ability. 1998 Academic Press

Natsopoulas et al. (1998) compared 135 left-handed and 135 right-handed7- to 12-year-olds on nine language tests and then discussed several hypothe-ses about handedness and hemisphere specialization in the light of the results.I do not doubt the results but suggest some caution about the theoreticalinterpretations, particularly for my right shift (RS) theory (Annett, 1972,1985, 1995). The issues are, first, controls for developmental disabilities and,second, mapping between this sample and others unselected for handedness.

The chief outcome of the Natsopoulos study was a substantial similaritybetween left- and right-handers. Principal components analyses for eachhandedness group separately found a single factor with the same tests havingthe highest (comprehension of syntax) and lowest (sentence completion)loadings for both. Comparisons for each test separately found only one (sen-tence completion) clearly superior in right-handers but others showed trendsin this direction (particularly deductive reasoning) and an overall MANOVAwas reported to give a significant difference in favor of right-handers. Hierar-chical cluster analysis distinguished several subgroups including one (N 5

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NOTES AND DISCUSSION 357

38) with excess right-handers (71% from the base rate of 50%) and another(N 5 22) with excess left-handers (73%). The former was good on mosttests, particularly sentence completion, but the latter was poor on all tests,suggesting the presence of learning-disabled children.

The interpretation of findings depends on questions about methods, partic-ularly subject selection. The children were described as ‘‘unselected’’ butall research has to have a selection rule. I infer that the rule here was thatall left-handers in the age range in six schools were included. Right-handerswere said to be drawn ‘‘randomly’’ from the same population but the proce-dure for ensuring randomness was not described. A footnote explained thatno Ss had neuromotor or mental abnormalities, according to informationobtained from teachers. It may be inferred, therefore, that the sample repre-sented the full range of children in school, except for any with major disabili-ties. The range would include children with problems, including minor pa-thologies and reading difficulties. A new test of hand skill, placing pins ina cork surface for one trial by each hand, was used to classify children forright minus left (R-L) hand skill, but performance was not analyzed so asto reveal children with weak hand skills. Several tasks required the childto read considerable chunks of prose, especially sentence completion anddeductive reasoning. A small excess of disabled children among the left-handers could be responsible for the differences observed for handedness.Because handedness groups were not matched for manual skill or readingability, the causes of differences for ‘‘language’’ tests are unclear.

The comparisons for language that were proposed to test the RS theorydepended on classifying for ‘‘extreme’’ versus ‘‘less extreme’’ handednessfor both preference and skill. No differences were found for strength of pref-erence in either handedness group by either criterion. Contrasts were thentested between extreme left- and extreme right-handers which confirmed thefindings of the main analysis that right-handers tended to be better. This wasinterpreted as contrary to my findings for strong right-handers in severalsamples (cited by Natsopoulos et al.). Natsopoulos et al. classified their sam-ple for R-L pin placing in a manner that appears to match my classificationsfor R-L peg moving (20, 30, 30, and 20% from left to right along the R-L continuum), but whereas my samples were drawn without selection forhandedness (by date of birth or from whole classes), half of the Natsopoulossample were left-handers and these were reported to be 7.5% of the totalpopulation. The right-handers, therefore, were drawn from 92.5% of the pop-ulation and the ‘‘extreme’’ (20%) in the Natsopoulos sample represent justunder 40% of the general population. They are not comparable to the‘‘strong’’ right-handers of my samples.

Graphs of mean scores for each test were given for the hand skill groupsbut no statistical analyses or tests of trend were reported over all four groups.Inspection suggests that the most dextral group tended to be superior on alltests. The main contrasts in this sample were probably not between right-

358 NOTES AND DISCUSSION

versus left-handers but between the most dextral versus all the rest. Thesuperiority of this group on language tests may be due to accidents of sam-pling or to advantages associated with the typical bias to dextrality for speechand speech dependent processing (especially phonological skills for reading).

The puzzle of relationships between individual differences for handednessand individual differences for cerebral specialization has led to many specu-lative theories but until the relevant genetic and brain imaging studies aredone the theories will remain stories. The RS story suggests that left- andright-handedness are primate universals, while speech and language are hu-man universals entirely independent of handedness, except that a gene (RS1)present in some 80% of the population directs speech learning to the lefthemisphere by impairing the relevant control mechanisms of the right hemi-sphere and incidentally weakening the left hand. Among the possible costsand benefits associated with the RS1 gene reviewed by Annett (1995) nonewere for language nor for mind. A surprising development of the RS theorysuggests, however, that there could be costs for both language and mind ifthe RS1 gene mutates to an ‘‘agnosic’’ form, losing its directional codingand giving risks of schizophrenia and autism (Annett, 1997).

REFERENCES

Annett, M. 1972. The distribution of manual asymmetry. British Journal of Psychology, 63,343–358.

Annett, M. 1985. Left, right, hand and brain: The right shift theory, London: Erlbaum.

Annett, M. 1995. The right shift theory of a genetic balanced polymorphism for cerebraldominance and cognitive processing. Cahiers de Psychologie Cognitive, 14, 427–480.

Annett, M. 1997. Schizophrenia and autism considered as the products of an agnosic rightshift gene. Cognitive Neuropsychiatry, 2, 195–240.

Natsopoulos, D., Kiosseoglou, G. Xeromeritou, A., & Alevriadou, A. 1998. Do the hands talkof the mind’s behalf? Differences in language ability between left- and right-handedchildren. Brain and Language, 64, 182–214.