Age-Related Changes in Sensitivity to Global Speed

We examined the effect of speed magnitude and range on the sensitivity to global speed in two different age groups. Stimuli consisted of band-pass dots whose speeds were perturbed by time-correlated or -uncorrelated random noise. The observer discriminated which of two sequentially presented stimuli moved faster. We found that the Weber fractions significantly diminished with increasing the speed of standard. The older observers had higher discrimination thresholds in all experimental conditions. The noise level did not significantly affect sensitivity to global speed differences, except for older observers' performance at the highest noise level. The temporal noise correlation differently impaired the performance of the younger and the older observers. The results are discussed in relation to speed-coding mechanisms and age-related changes in motion perception.