Discrimination of tone duration was studied as a function of menstrual cycl
e phase. In three phases of their menstrual cycle, 12 women compared the du
rations of 64 pairs of tones. They discriminated the tone durations least w
ell in the premenstrual phase and tended to speed up their responding over
sessions. In contrast, a control group of 12 men tended to improve their pe
rformance over sessions while response time remained constant.