Impairment in motion discrimination tasks is unrelated to amount of damage to superior temporal sulcus motion areas.

The behavioral role of the middle temporal (MT/V5) area and its satellites in motion processing is still unclear, particularly the degree to which MT/V5 proper is critical for different types of motion processing. Therefore, effects of small and large lesions in the caudal part of the superior temporal sulcus of macaque monkeys were compared for two tasks requiring different types of motion processing: a direction and a kinetic orientation discrimination. The small lesion was restricted to the peripheral representation of MT/V5 but included V4t, whereas the large lesion included all of MT/V5 and the medial superior temporal (MST) area as well as substantial parts of the floor of the superior temporal (FST) area. Both lesions resulted in significant and long-lasting impairment of direction discrimination but had a lesser effect on kinetic orientation discrimination. Thus the effects of small STS lesions on motion perception are much stronger than expected.