Estimating the velocity of briefly presented moving stimuli.

The ability of human subjects to estimate the velocity of briefly presented moving stimuli was studied in a prediction-of-collision experiment. After the disappearance of the moving target the subject had to press a button at the moment the target would reach a predetermined position in the visual field. Four velocities of the moving target were used -6 degrees/s, 10 degrees/s, 14 degrees/s, and 20 degrees/s. For each velocity there were five exposure distances: 0.5, 1.0, 2.0, 3.0 and 4.0 degrees and four concealment distances: 6, 8, 10 and 12 degrees. For the large exposure distances a linear dependence of the response time on the concealment time was observed. This dependence was not linear for exposure durations less than 100 ms. The response time increased in these cases. Despite the common character of the results obtained with different subjects there were clear individual differences most probably due to differences in subjective velocity scales and individual mechanisms of motion extrapolation and organization of motor responses.