Hormones and dichotic listening: evidence from the study of menstrual cycle effects.

This report presents evidence for changes in dichotic listening asymmetries across the menstrual cycle, which replicate studies from our laboratory and others. Increases in the right ear advantage (REA) were present in women at phases of the menstrual cycle associated with higher levels of ovarian hormones. The data also revealed correlations between hormone levels and behavioural measures of asymmetry. For example, the pre-ovulatory surge in luteinising hormone (LH) was related to a decrease in left ear scores, which comprised a key part of the cycle related shift in asymmetry. Further analysis revealed a subgroup of women who had not reached postovulatory status by days 18-25 of the cycle, as verified by low progesterone levels. These women showed laterality profiles at days 18-25 that looked more like the other women when measured at the periovulatory phase (i.e., days 8-11). Data were combined with those from a previous study to highlight the stability of effects. Results showed a distinct menstrual cycle related increase in asymmetry in the combined sample. This final comparison confirmed the nature of sex differences in dichotic listening as being dependent on hormone status in women.