Modified signal detection procedures were used to analyze the effects of inferotemporal cortical resections. The results demonstrated (a) a severe difficulty in responding to differences in luminance; (b) a severe difficulty in responding to differences in luminance; (b) a small but consistent change in sensitivity (d'), which is attributed to an increased sensitivity to noise or a deficiency in the suppression of irrelevant aspects of the environment; and (c) an enhanced bias to respond to a nonrewarded stimulus (a lowering of criterion). This altered bias contrasts with the results obtained from limbic resections in a previous experiment which produced a marked increase in bias to a rewarded contingency without influencing discrimination or detection.