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 tem poral area (MST) and the upper part of the superior temporal polysenso ry area (STPp) of the monkey's brain were recorded during the discrimi nation of direction of visual motion near contrast threshold. In addit ion to stimulus-related decisions the monkeys often made stimulus-inde pendent decisions while stimuli were well below detection threshold (c ontrast <0.01%), or totally absent. During this condition MT neurones showed no systematic changes in their ongoing activity while in the MS T and STPp stimulus-independent decisions in the preferred direction o f a given neurone were accompanied by the highest ongoing activity. We take this as evidence for internally generated representations of dir ection of motion in higher visual areas of the superior temporal sulcu s. Neurones involved in the initiation of a decision or action are des cribed for the first time in area STPp.