[Velocity perception for curved motion]

This study examined the effect of direction change of tangential velocity on speed perception using a dot in curved motion. The PSE values were measured for four standard stimuli of different motion curvature. In Experiment 1, semicircular motion was a comparison stimulus. The result showed that the PSE values increased with increasing motion curvature. This implies that direction change of tangential velocity can affect its speed perception. However, in Experiment 2, the effect of direction change of tangential velocity was not clear when a comparison stimulus was replaced with linear motion. In Experiment 3, the motion curvature as a comparison stimulus was set near the threshold level of curvature detection. As the result, the similar trend to Experiment 1 was observed. However, the effect of direction change of tangential velocity remained the same as Experiment 2. These results suggests that direction change of tangential velocity can affect its speed perception, while the effect depends on how much direction change of tangential velocity could be detected for a comparison stimulus.