Matchmaking: Sex, conflict, and the cerebral hemispheres

Abstract

Three experiments examined how humans make same-different judgments of simultaneously presented letter pairs using the entire English alphabet, in two tasks: a letter category task in which pairs of letters in different letter cases (instances) belonged to the same (e.g., "X x") or different (e.g., "X o") letter category; and a letter instance task in which pairs of letters in the same letter category belonged to the same (e.g., "X X") or different (e.g., "X x") letter instance. Three experiments used these two tasks to present letter pairs in different arrangements: Experiment 1, centrally to both cerebral hemispheres; Experiment 2, laterally to either the left or right cerebral hemisphere; Experiment 3, laterally to either different hemispheres or to the same hemisphere. The roles of nominal identity (letter names), orthographic identity (how letter graphemes correspond to letter phonemes), and abstract visual-form identity (letter categories) were investigated by examination of letter confusability. The results indicate that visual and not nominal identity is used to perform the letter category task. In addition, women (but not men) used orthographic identity to solve the letter category task during some conditions of all three Experiments. A new kind of analysis indicates that, across-sex, letter category predicts 82% of the variance in response latency to same-category judgments, but only 14% of the variance in response latency to same -instance judgments, functionally dissociating form-invariant (category) and form-variant (instance) visual information. Women (but not men) use form-invariant (category) information when making different-instance judgments--even when such information is insufficient for solving that task--and consequently, women's cerebral asymmetries are shifted and their interhemispheric communication of information is selectively impaired (relative to men) when this information conflicts with that necessary to solve the task. Thus, the kind of information, rather than the number of cognitive processes , determines how processing is lateralized and integrated across the cerebral hemispheres in letter matching tasks. Comparisons of presentations to both and single hemispheres indicate that hemispheric dominance is dissociated from hemispheric asymmetry as a function of sex-dependent attentional strategy and informational conflict in interhemispheric interaction.