Differences in response criterion and sensory sensitivity to visual flicker among major depressive patients, dysthymic patients, and normal controls were investigated. Also, signal detection confidence ratings and response times were compared. The results indicated that major depressive patients responded more conservatively (i.e. were less willing to respond ‘flicker’) than either of the other groups. The groups did not differ significantly on a criterion free measure of flicker sensitivity. The major conclusions are: (1) previously reported visual flicker differences between depressed patients and normal controls were probably due to the more conservative response criterion of the patients and not to flicker sensitivity differences between groups; and (2) confidence ratings and response times yield similar conclusions with respect to visual flicker sensitivity and response criterion. Therefore, interpretations concerning a sensory or perceptual deficit in depression must take into account the differences in response criterion between depressed patients and normal controls.