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Biomedical subjects

M Annett

Publications and source records attributed to M Annett.

At least 19 recordsLinked to original sources
PubMed1992

Parallels between asymmetries of Planum temporale and of hand skill.

Relationships between the skill of each hand and differences between the hands are described for a sample of 14-15-year-olds representative of the general population. The description is modelled on the account of Galaburda et al. (Neuropsychologia 25, 853-868, 1987) of relationships between asymmetries of the Planum Temporale (PT) and measures of PT area on each side, in order to show parallels between findings for the two types of asymmetry. For both PT and hand skill, the extent of asymmetry appears to depend on the greater variability of the weaker side rather than of the larger or "better" side. The findings are also described as a replication of the study of hand skill in children by Annett and Manning (Br. J. Psychol. 80, 213-226, 1989). As no score transformations were needed in the present sample, the grounds for doubt raised by Bishop (Handedness and Developmental Disorder, Blackwell, Oxford, 1990) about the earlier sample are removed. Repetition of the analyses for right-handed and left-handed writers separately demonstrates very close similarities for findings in the two hand preference groups. Theories about the mechanisms responsible for asymmetries appear to require the presence of factors which reduce brain area and hand skill on one side. For most people the reduction is to the right PT and to the left hand.

Adolescent↗
PubMed1992

Five tests of hand skill.

Four group tests of hand skill, square marking (SQUARES), dotting between targets (DOTS), line drawing between targets (LINES) and punching holes through targets (HOLES), were given to samples of undergraduates and schoolchildren, most of whom were also tested individually on a peg moving task (PEGS). Findings for PEGS were shown to be comparable to those of previous samples. Each new task was compared with PEGS for a standard measure of hand skill asymmetry (R-L%) using 4 criteria of comparison. For 3 criteria there was good agreement: correlations were statistically significant, hand preference subgroups were similar for rank order and the extent of asymmetry was more strongly associated with left hand scores than with right hand scores. This last finding was true for all of 12 comparisons for differing tests and samples, indicating that the finding is unlikely to be an artefact of score transformations as suggested by Bishop (1990a, 1990b). The fourth criterion of comparison, the distribution of R-L% scores, differed between the tasks. All of the new tasks found larger differences between the hands than PEGS. Whereas the shape of the distribution was unimodal for PEGS, as in previous studies, the distributions for DOTS and HOLES were clearly bimodal. Possible reasons for the larger between hand differences for some tasks are considered. It is suggested that the main difference between PEGS (and also to a lesser extent LINES) in comparison with DOTS and HOLES lies in the demand characteristics of the testing situation. Tasks which merely invite subjects to mark as many targets as possible in a unit of time may underestimate the skill of the nonpreferred hand.

Adolescent↗
PubMed1992

Spatial ability in subgroups of left- and right-handers.

Two tests of spatial ability, mental paper folding given to 459 14-15-year-olds representative of the secondary school population, and recall of the Rey figure given to 428 undergraduates, found significant relationships between ability and hand preference when preferences were classified in subgroups of left- and right-handers (Annett, 1970a). In 14-15-year-olds and in female undergraduates there was a W-shaped relation between hand preference and spatial ability. The highest scores were in the centre for right-handers with strong sinistral tendencies. Male undergraduates showed a linear trend, with spatial ability highest in strong left-handers and declining from left to right across levels of hand preference. When spatial test scores were considered in relation to differences between the hands in skill a decline of ability with increasing dextrality was found in right-handers and in left-handers. In terms of the right shift theory (Annett, 1972, 1985), the evidence suggests that there are costs for spatial ability associated with the presence of the rs+ gene, even in single dose (rs+ - genotypes), and that those who lack the gene (rs- - genotypes) have advantages for spatial ability (Annett, 1991 c).

Adult↗
PubMed1991

Speech lateralisation and phonological skill.

A phoneme segmentation task requiring Ss to produce deliberate spoonerisms was performed by 78 undergraduates, along with a dichotic monitoring task and tests of hand preference and hand skill. The hypothesis that those performing badly on the speech task would include a higher proportion of individuals with left ear advantage on the dichotic task was supported. The distribution of cases was consistent with other findings for relationships between cerebral speech lateralisation and side of ear advantage and also consistent with predictions of the right shift theory of handedness and cerebral speech (Annett, 1972, 1985).

Adolescent↗
PubMed1991

Handedness for eating in gorillas.

Observations of spontaneous reaching for food in 31 captive lowland gorillas found a full range of hand preferences between strong left and strong right, with most animals showing intermediate levels of preference. There was a high degree of consistency between observations made on different occasions for the same animal, showing that degrees of relative preference tend to be stable in individuals. The findings agree with the majority of previous studies of apes and other primates in showing no species bias to one side, with about half the animals left and half right preferent.

Animals↗
PubMed1990

Arithmetic and laterality.

Relationships between arithmetic ability, hand preference and hand skill were investigated in a general population sample of schoolchildren, aged 9-11 years. Incidences of non-right-handedness were highest in the children best at arithmetic and fell progressively through average and below average groups. Strong effects were found for hand skill; level of ability declined linearly from left to right across the R-L continuum in both sexes. Strong dextrality was associated with poor left hand skill and not superior right hand skill. Arithmetic ability was positively associated with left hand skill but not with right hand skill.

Child↗
PubMed1990

Reading and a balanced polymorphism for laterality and ability.

The idea that reading ability might vary with right-left hand skill, such that children with mild biases to the right hand have advantages for learning, while children at both left and right extremes have disadvantages, was supported by findings for a large sample of primary schoolchildren. Poor readers tended to have weak left hand skills, giving strong right hand preferences in many cases. Those with additionally poor right hand skills tended to be of low intelligence. Good left hand skills and raised incidences of mixed and left hand preference were found only in a small subgroup, "bright dyslexics".

Aptitude↗
PubMed1989

The disadvantages of dextrality for intelligence.

The right shift (RS) theory of handedness suggests that the human bias to dextrality has costs as well as benefits. Samples of children from six primary schools were individually tested for hand preference, hand skill and Raven's Matrices. Scores on standardized educational tests recently given by teachers were available for three schools. When children were stratified for ability, the distributions of hand preference and of right minus left (R-L) hand skill were as expected if extent of RS is inversely related to ability. When children were classified for R-L score, the most strongly dextral children were poorer than all others for Matrices, English and several other tests. The trend for ability to decline from left to right across the laterality continuum was consistent for all scores available. Strong dextrality is associated with weak left-hand skill, not good right-hand skill, in accord with the hypothesis that the costs of RS are to the right hemisphere. The findings and their interpretation are discussed in comparison with Geschwind's theory of developmental pathology, and for their implications for theories of hemisphere specialization.

Cerebral Cortex↗
PubMed1988

Comments on Lindesay: laterality shift in homosexual men.

The raised incidences of strong left-handedness and of mixed-handedness in homosexual men, as in dyslexics, are mutually consistent under the normal distribution function, as expected by the right shift theory of handedness. It is argued that atypical laterality in these groups is better described as a "reduction of right shift" than as a "left shift".

Differential Threshold↗
PubMed1984

Lateral preference and skill in dyslexics: implications of the right shift theory.

The lateral preferences and L-R skill of 109 male and 20 female dyslexics were as expected if the distribution of lateral asymmetry is shifted less far to the right in dyslexics than in controls. Several aspects of the data were consistent with Annett's hypothesis that some dyslexics lack the left hemisphere speech-organising factor postulated by the right shift theory of handedness and that this would be sufficient to account for the proportion of affected relatives. Some dyslexics were strongly dextral and these differed from the less dextral cases in several ways which resembled the distinction between backward and retarded readers.

Child↗
PubMed1983

Individual variation in directional bias in visual perception.

Directional biases in visual perception were examined for individual differences in sixty-five subjects on two tasks. One task required judgments of the onset asynchrony of pairs of dots presented at random, either one dot in each visual field, or both in the left visual field (LVF), or the right visual field (RVF). The second task required the recall of four letter strings presented randomly in either visual field. Dot-asynchrony judgments were influenced by two main biases: first, an outward from the centre bias in both visual fields, and second, a lateral bias which was significantly from left to right (L-R) in the total sample. A substantial minority of subjects were biased to judge the dots as occurring in right to left (R-L) order. Accuracy of letter report decreased fairly consistently from L-R in the RVF but varied in the LVF. Some subjects showed a L-R report gradient, some a R-L gradient, and some a U-shaped recall pattern. Significant correlations between measures of L-R and R-L biases on the two tasks show that the biases have some stable foundation. The findings suggest that there are directional biases affecting visual perception which are due neither to learned reading habits, nor to cerebral specialization of function.

Female↗
PubMed1983

Right- and left-hand skill I: Effects of age, sex and hand preference showing superior skill in left-handers.

Hand preference and hand skill were examined in relation to sex and age from 3 1/2 to 50+ years. The data were drawn from several samples which avoided volunteer bias, either by selecting children according to birth-date or by taking complete class groups. The distribution of hand preference and of asymmetry of skill gave no evidence of systematic changes with age. Younger children were more variable and showed larger absolute differences in favour of the right hand than older children but L-R times were similar over most of the age range. Time for peg moving decreased with increasing age to a minimum in the late teens, remained stable for the next three decades and increased slightly in the 50+ age group. Males were faster than females with the left hand in almost all age groups. Females tended to be faster than males with the right hand up to 10 years of age but males then equalled and surpassed females, to be faster in most older groups. Correlations between hands did not vary systematically with age or sex. Left-handers were faster than right-handers and right mixed-handers were intermediate for peg-moving time by the non-preferred hand, in both sexes and both sets of samples. Differences for the preferred hand were less clear but still favoured left-handers in several comparisons. The findings raise the possibility that left hemisphere specialization for language is achieved through a right hemisphere handicap and that left-handers escape this risk to cerebral efficiency.

Adolescent↗
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↗
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↗