WHEN DOES NO REALLY MEAN YES - A CASE-STUDY IN UNILATERAL VISUAL NEGLECT

A patient with unilateral visual neglect indicated whether a dot was o r was not present in a display. When present, the dot appeared equally often in the left and right visual fields. Although he typically deni ed having seen dots in his left visual held, he was able to make this judgment much more quickly than when no dot was in fact present. The m ean response times when the dot was present (1135 and 1004 msec, for l eft and right) were almost twice as fast as the response times when no dot was present (2025 msec). This result suggests that the patient se arched the visual fields individually, and in fact generated a ''No'' response based on detecting the dot in his neglected field. Thus, the mechanisms used to detect stimuli apparently are not rigidly linked to those used to classify them or to produce a response.