The prediction of cerebral speech lateralization and cognitive ability in left and right handers on the basis of manual skill
Date
1977
Authors
Brennan, Valerie Gail
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Abstract
Relationships were investigated between handedness, speech lateralization and verbal and spatial cognitive abilities. The subject sample consisted of 3O male and 3O female adults. Handedness was measured by: a) subject's self classification (SC), b) Hand Preference Questionnaire data, and c) right minus left hand difference scores on five manual skill tests (MS). Speech lateralization was measured by ear advantage (EA) on a verbal dichotic listening task: Right ear advantage was considered representative of speech lateralization to the left hemisphere. Verbal and spatial cognitive abilities were measured by selected subtests from the Wechsler Adult Intelligence Scale (Wechsler, 1955). Three-handedness speech lateralization hypotheses and two handedness-cognitive abilities hypotheses were tested.
Left hemisphere control of speech processing was demonstrated to be greater for right handers than for lefthanders. The SC right handed group had a higher mean right EA than the SC left handed group. Manual skill was shown to be related to speech lateralization. The greater the right hand superiority on manual skill tests, the larger the right EA tended to be. The relationship between subjects' self classification as right or left handed and speech lateralization was shown to be associated with manual skill. When the influence of MS on the SC-EA correlation was held constant, the correlation was reduced to nonsignificance. The conclusion was reached that the manual skill method of measuring handedness is more accurate and has more exploratory power than the self-classification method for investigation of handedness speech lateralization relationships.
Handedness-cognitive abilities hypotheses were not supported. Handedness, defined by manual skill scores, was related to spatial ability such that the greater the tendency toward right hand superiority, the lower the spatial score tended to be. Partitioning subjects according to Leyy's (1969) operational definition of handedness resulted in no significant differences between right and left handed subjects' spatial ability. The Male group had a significantly higher mean spatial score than the Female group. No reliable relationship was found between either of the two measures of handedness and verbal-spatial discrepancy scores. It was concluded that the investigation of posited relationships between handedness and cognitive abilities should await the development and validation of a model of hemispheric specialization which would account for variation in the Jateralization of speech processing and manual skill.