Speed perception during acceleration and deceleration.

We have recently shown that stimulus acceleration affects subsequent preferred speed and tuning widths of macaque area MT neurons (A. Schlack, B. Krekelberg, & T. D. Albright, 2007). Given the close link between area MT and speed perception, this predicts that speed perception should depend on the acceleration context. Here, we show that this is indeed the case for both speed discrimination and speed perception. Specifically, speed discrimination thresholds improve in an acceleration context but absolute speeds are more underestimated than in a deceleration context. In line with our physiological data, these changes can be understood in terms of speed-dependent adaptation mechanisms in MT and do not require an explicit acceleration dependence of speed perception.