Neuronal activity in MST and STPp, but not MT changes systematically with stimulus-independent decisions

SINGLE units in the middle temporal area (MT), the middle superior temporal area (MST) and the upper part of the superior temporal polysensory area (STPp) of the monkey's brain were recorded during the discrimination of direction of visual motion near contrast threshold. In addition to stimulus-related decisions the monkeys often made stimulus-independent decisions while stimuli were well below detection threshold (contrast <0.01%), or totally absent. During this condition MT neurones showed no systematic changes in their ongoing activity while in the MST and STPp stimulus-independent decisions in the preferred direction of a given neurone were accompanied by the highest ongoing activity. We take this as evidence for internally generated representations of direction of motion in higher visual areas of the superior temporal sulcus. Neurones involved in the initiation of a decision or action are described for the first time in area STPp.