The effects of ageing on reaction times to motion onset

We have measured reaction time (RT) to motion onset in two groups of subjec ts (average ages: 70 and 29 years), for horizontal gratings of 1 c deg(-1), modulated in either luminance or colour (equiluminant red-green), for vari ous contrasts and speeds. For both old and young subjects, RTs depended on both speed and contrast, being faster at high speeds and high contrasts, an d showed a stronger contrast dependency for chromatic gratings. The older s ubjects were systematically slower than the younger subjects. The differenc e between old and young RTs varied with condition, being 30-40 ms more at t he slow than at the fast speed. The relative difference in RTs in different stimulus conditions shows that at least some of the increase in response t ime with age has a sensory origin. The results relate well to previous work on visual evoked potentials. (C) 1999 Elsevier Science Ltd. All rights res erved.