Adaptation in macaque MT reduces perceived speed and improves speed discrimination.

The visual system adapts to its environment. Some adaptive changes are detrimental-perception is no longer veridical. Others are beneficial-the ability to discriminate two stimuli improves. The latter may reflect the visual system's ability to zoom-in on the currently relevant properties of the environment. We studied the neural basis of adaptive changes in the middle temporal area (MT) of macaque monkey visual cortex. Our data show that brief adaptation to a moving stimulus reduces the magnitude of neural responses and reduces the width of speed tuning curves. Comparable with what has recently been reported in the direction domain, the response reduction was largest when the test speed was different from the adaptation speed. Using an ideal observer analysis, we show that these response changes in MT are consistent with a reduction in perceived speed as well as an improvement in speed discrimination. This supports the view that adaptive response changes in MT are not just a consequence of neural fatigue, but an active process that enhances the discrimination of speed.