VERBAL AND MUSIC DICHOTIC-LISTENING TASKS REVEAL VARIATIONS IN FUNCTIONAL CEREBRAL ASYMMETRY ACROSS THE MENSTRUAL-CYCLE THAT ARE PHASE AND TASK-DEPENDENT

Two dichotic listening tests, one a verbal consonant-vowel identificat ion task, the other a musical chord recognition task, were administere d to 32 women at two points during the menstrual cycle, menses (when o estrogen is low) and the midluteal phase (when oestrogen is high), in a counterbalanced repeated measures design. The degree of asymmetry ch anged across the cycle for both syllables and music. The right ear adv antage recorded for the verbal task was greater during the midluteal p hase than during menses. The left ear advantage recorded for the music task was greater during menses than during the midluteal phase. These reciprocal changes in asymmetry were the result of consistent changes in ear performance. From menses to the midluteal phase, left ear (rig ht hemisphere) performance fell significantly for both tasks whereas r ight ear (left hemisphere) performance showed a small, but non-signifi cant, increase. The findings are discussed in the light of evidence fo r phasic activational effects of gonadal steroids on both asymmetry an d cognition which provide an explanation for the sometimes elusive nat ure and small effect size of sex differences in these characteristics. The relationships between sex differences in asymmetry and cognition are re-examined. (C) 1998 Elsevier Science Ltd. All rights reserved.