The control of movement in the preferred and non-preferred hands.
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Female↗
Biomedical subjects
M Annett
Publications and source records attributed to M Annett.
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↗
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↗
Genetic and nongenetic influences on handedness.
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Female↗
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↗
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↗
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↗