Effect of age on horizontal eye movement latency

Reaction time to initiate an eye movement to a target which suddenly appeared 2.8 degrees from fixation was measured for older and younger adults. Healthy men and women were tested in a series of trials; on one-half of these trials prior knowledge of the target's location was given (simple reaction time), whereas on the remaining trials the target could appear to left or right of fixation with equal probability (choice reaction time). For both simple and choice trials, the mean reaction times for younger adults were significantly faster than for older adults. Simple reaction time trials were no faster than choice trials for either age group. In addition to mean reaction times, the distribution of the response times were examined for each age group. The shapes of the two distributions were symmetric; however, the SD of the older adults' scores was greater than that of the younger adults.