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Biomedical subjects

M Annett

Publications and source records attributed to M Annett.

At least 55 records · Page 3Linked to original sources
PubMed1983

Right- and left-hand skill II: Estimating the parameters of the distribution of L-R differences in males and females.

The distribution of differences between the hands (L-R) in skill, as measured by a peg-moving task, was examined for several samples in which volunteer bias was absent or minimal. After comparing the main samples for hand preference and L-R times, they were combined to give 617 males and 863 females, aged 12-63 years. There was also a smaller sample of 122 males and 156 females, aged 6-15 years. The L-R distributions were negatively skewed and leptokurtotic. They were not compatible with the sum of two normal distributions, one of right-handers and one of left-handers. They were compatible with the sum of two or three normal distributions when one was unbiased to either side and the others were shifted to the right, as expected for the dominant or additive versions of the single gene interpretation of the right shift theory of handedness (Annett, 1978b, 1979). Sex differences in L-R scores confirmed that females tend to be more dextral than males. This was true of right-handers but not of left-handers, as expected if the sex difference is due to stronger expression of the rs+ gene in females than males and if this gene is absent in the majority of left-handers. There were trends suggesting that L-R asymmetry differs with educational status, undergraduates being less shifted toward dextrality than the general population.

Adolescent↗
PubMed1982

Mathematical ability and lateral asymmetry.

The hypothesis that special ability in mathematics is associated with a reduction in bias to dextral preference and skill was examined in several samples of students and in 97 male and 27 female teachers of mathematics, mainly in Universities and Polytechnics. The math students and math teachers differed from controls, both general and academic, in the direction predicted and several comparisons were statistically significant. Differences were in most cases clearer for males than females. An analysis of the findings in relation to the right shift (RS) theory of handedness (Annett, 1972, 1978) suggests that the incidence of left preference and skill is slightly raised in mathematicians not because of any intrinsic advantage of left preference but rather because extreme bias to the right, as expected in those carrying a hypothesised rs++ genotype, is disadvantageous for mathematical thinking. If the role of mathematics can be regarded as one of developing languages to describe those aspects of human experience which otherwise could be understood only in visuo-spatial images, it can be seen to require a coordination of those aspects of human intelligence which have been distinguished as depending differentially on the left and right cerebral hemispheres. The present findings suggest that this process might be impeded by a double dose of a gene which promotes left hemisphere language specialisation.

Adolescent↗
PubMed1980

Birth order, birth stress and handedness.

Left-handed and right-handed parents in personally visited families were asked about the perinatal history of themselves, and their children. Reported birth stress (RBS) was as frequent for right-handers as for left-handers. The children of left-handed mothers were not more likely to have RBS than the children of right-handed mothers. The incidence of RBS was greater for first borns than children of later birth rank. A weak trend to a higher proportion of birth ranks 1st and 4th + among left- than right-handers was found for daughters, but not for fathers, mothers or sons. Empirical and theoretical objections to the hypothesis that pathology of the left hemisphere is a major determinant of left-handedness are reviewed.

Birth Order↗
PubMed1979

Family handedness in three generations predicted by the right shift theory.

The hand preferences of Open University (OU) students and their relatives, including children, are described. As in earlier series, estimates of heritability are higher for mothers than fathers. There is no evidence of smaller heritability for paternal than maternal grandparents. The distribution of left-handedness in families is examined in the light of predictions of the right shift theory and on the assumption that the shift depends on a single gene. Good agreement is found between the observed and expected numbers of R x R, L x R and L x L families. Predictions are successful for both strict and generous criteria of sinistrality. Generation differences are found between OU students and their parents and between the students and their children. These are discussed from the viewpoint of a possible heterozygote advantage in intelligence. The higher proportion of sinistral children born to sinistral mothers than fathers can be partly accounted for by supposing that the right shift is more effective in females than males.

Adult↗
PubMed1979

Individual differences in right and left reaction time.

Experiments designed to check the absence of effects for hands and handedness in simple and two-choice reaction time found unexpected individual differences related to stimulus laterality. The majority of subjects responded faster to the stimulus on the left and a substantial minority responded faster to the stimulus on the right in any choice pair. The right index finger was slower than the left index or the middle fingers. Choices tended to be faster between fingers on different hands than on the same hand and same-hand choices were faster with the left hand than the right hand. There were no effects attributable to hand preference or sex.

Choice Behavior↗
PubMed1976

Handedness and the cerebral representation of speech.

Hand preferences vary not discretely but continuously and the continuum of preference is closely and reliably linked with a continuous roughly Normal distribution of differences between the hands in skill. Questions about handedness can be usefully formulated in terms of the distribution of differences in skill and in terms of the theshold or criterion which divided those likely to be classified as right handers from those likely to be classified as left handers. A theory of the origin of hand preferences suggests that three factors are involved. The first in non-genetic accidental variation in the development of the two sides of the body in all bilaterally symmetrical species showing limb preferences. The second in a systematic bias to the right hand in man, probably linked with the tendency for the left hemisphere to serve speech. The third is socio-cultural factors affecting the expression of sinistrality. An explanation of the relation between hand preference and cerebral speech laterality requires the assumption that in some individuals the factor biasing speech to the left hemisphere is absent. This would imply that the bias is not a universal species character but that it is subject to genetic variation. Making the simplest possible further assumptions that in the absence of bias, the laterality of handedness and of cerebral speech are independent and each governed by chance, it is possible to account for the distribution of right and left handers with dysphasias following right and left unilateral cerebral lesions.

Aphasia↗
PubMed1976

A coordination of hand preference and skill replicated.

Annett (1970a) described 283 subjects classified for hand preference and measured for the movement time of each hand on a peg moving task. A new sample of 804 subjects has been examined and classified as before. The mean differences between hands for each preference group are very similar in both samples. Hand preference can be regarded as anchored to an objective measure of manual skill. Both preference and skill are continuously distributed variables, not discrete ones. The quest for the 'essence' of left handedness should be replaced by studies of the characteristics of the distributions involved and of the criteria used to identify segments of the distributions.

Functional Laterality↗
PubMed1975

Hand preference and the laterality of cerebral speech.

A theory of the origins of hand preferences (Annett, 1972) is outlined and its implications for the distribution of cerebral speech in handedness groups are examined. Five studies of dysphasia in right and left handers with unilateral cerebral lesions are compared and found surprisingly consistent. Data from three series found alike in all essential respects are combined to give a substantial number of cases with which to test the expectations of the theory. The agreement is close enough to justify a reconsideration of the model in the light of the evidence and also an analysis of possible reasons for the main differences between series. In spite of the many uncertainties involved in inferences from dysphasia to cerebral speech laterality, it is concluded that the evidence is strong enough to offer a useful test of hypotheses as to the distribution of cerebral speech in handedness groups. Other questions bearing on handedness and cerebral speech are briefly considered in order to show the explanatory range and power of the theory.

Aphasia↗