One hundred twenty subjects were tested on a verbal dichotic listening task in order to assess the influence of sex and reading ability on lateralization of speech. All subjects were right-handed, with no familial sinistrality. Forty of the subjects were nine years old, forty were thirteen years of age, and forty were seventeen years of age. Half of the subjects at each age level were male, and half were female. Half of each age-sex group were good readers (who were reading at least two grade levels above their current grade) and half were poor readers (who were reading at least two grade levels below their current grade). Results indicated that older subjects and better readers accurately identified more stimuli than did the younger and poor readers. In general, as the males increased in age they exhibited increasing lateralization. Although male good readers showed stronger lateralization for speech at an earlier age as compared to male poor readers, reading ability had no effect on lateralization for males by late adolescence. Females demonstrated significantly greater lateralization for speech than did males at the youngest age tested. The influence of reading ability on lateralization was variable in the female groups. This precludes a definitive statement concerning the effect of reading ability on hemispheric lateralization in females. In addition to assessments of handedness, all subjects were also evaluated as to eye dominance. A surprising finding of the present study is that eye dominance is a highly significant variable with regard to the lateralization of language functions, and may prove to be a more reliable indicator of lateralization than such variables as sex or cognitive abilities. However, this finding is preliminary and must be investigated more fully.
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