Schizophrenic patients have serious visual masking deficits which are likely related to the genetic underpinnings of the disease because also unaffected relatives of the patients show masking deficits. We presented a left/right offset vernier followed by an ISI and a masking grating. Observers indicated the offset direction. We determined the SOA (vernier duration plus ISI), to reach 75% correct responses. Analyzing a new sample, we found that patients (n=239) needed SOAs of 127.6ms, relatives (n=125) of 62.4ms, and controls (n=145) of 32.2ms. In addition, we analyzed the data for the groups separately for men and women. We found main effects of Group and Gender but no significant interaction. Female observers needed SOAs of about 15ms longer than the male observers in the control group, 25ms in the relatives group and 37ms in the schizophrenia group. For the control group, hence, females performed by a factor of nearly 2 worse than males. No gender effect was found for executive functions as measured with the WCST. It seems that both gender and the susceptibility for schizophrenia are independent main effects affecting spatio-temporal vision. Our results show that a proper gender balance is crucial in experiments where signal to noise ratio is low.