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There is an ongoing controversy regarding the role of gender in modulating components of the human visual-evoked potential (VEP) and event-related potentials (ERPs). Our aim was to further characterize the role of gender on VEPs, ERPs and response performance in an object recognition task. We recorded VEPs and reaction time (RT) in a paradigm wherein subjects responded to a randomly presented "Relevant" stimulus, and did not respond when presented with "Irrelevant" or "Standard" visual stimuli. There was no effect of gender on early components of the VEP or RT to Relevant stimuli. Relevant and Irrelevant stimuli evoked distinct VEP components including the P300, N400 and late-positive (LP) ERPs that were well-discriminated from those of the Standard stimulus. Females were characterized by greater P300 and N400 responses than males for the Relevant stimulus, but exclusively greater N400 responses for the Irrelevant stimulus. There were no significant gender differences for the LP, or for the latency of any ERP component. Gender differences were not attributed to hemispheric asymmetry, as there were no significant differences in P300 and N400 VEP amplitudes between lateral occipital or parietal electrode positions. These results indicate that the N400 can be elicited in a task requiring the processing of irrelevant, but not unexpected, stimuli and that females process visual information differently than males, perhaps by increased allocation of attentional resources to distracting stimuli.

Circulating levels of oestrone and progesterone were measured by radioimmunoassays in plasma samles from 5 female owl monkeys on 60 consecutive days. Both steroids exhibited cyclic fluctuations and based on nadir to nadir intervals the ovarian cycle was estimated to be 15.92 +/- 0.26 days. Levels of oestrone and pregnanediol-3 alpha-glucuronide were also measured in daily urine samples. The fluctuations of urinary steroids reflected those observed in plasma. Ketamine sedation had no effect on the length of the cycle. Peak values of plasma progesterone and oestrone were 250.48 +/- 11.37 and 3.59 +/- 0.066 ng/ml respectively. There was no clear hormonal distinction between the follicular and luteal phase of the cycle in these owl monkeys.

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