A Study of Handedness and its Relation to Verbal and Spatial Ability

Abstract

The concept of handedness is reviewed, encompassing environmental, developmental and genetic aspects. Particular attention is paid to the measurement of laterality variables and the clarification of techniques involved in handedness assessment. Following a study of previous work pertaining to cerebral dominance, an attempt is made, through the literature, to establish a relationship between handedness and cerebral dominance. The clarification of such a relationship is a prerequisite for the association of specific ability levels with patterns of cerebral dominance, where handedness is employed as an index of such patterns. Subsequently a model relating mixed-handedness to good visuo-spatial ability is envisaged. This contrasts with earlier studies which reveal inferior 'performance' abilities for left or mixed-handers. Three investigations bearing on this model are reported. First a laterality survey was conducted amongst Artists, Engineers and Linguists, to test the hypothesis that more mixed-handedness would be found in Artists and more strong handedness in Linguists. Results upheld both this hypothesis and further predictions concerning other laterality variables. Secondly an experiment was conducted which sought to relate various questionnaire and performance measures of handedness, and which produced handedness distributions for 144 subjects. Thirdly, a further experiment employed this data to select independent groups on stringent handedness criteria. In this experiment, male and female groups of left, mixed and right-handers were compared over a series of tests. Males, in particular, tended to produce significant results in the expected directions. A possible relationship was demonstrated between, on the one hand, mixed-handedness and good performance on a test of spatial ability, and, on the other hand, strong handedness and relatively superior performance in sequencing aspects of linguistic ability. Females, however, performed somewhat differently and reasons for this are suggested. The final discussion, in addition to summarising the main findings, sets the results in the context of the probable relationship between handedness and specific reading retardation (dyslexia). An overview of sex differences in handedness found in the experiments is also presented.