Age-related changes in smooth pursuit initiation.

Quantitative analysis of eye movements is a useful tool for examining the behavioural effects of ageing. Although the effect of ageing on saccadic eye movement has been examined in some detail, the effect of ageing on a second class of eye movement, smooth pursuit (SP), has received less attention. We examined the initiation of SP in a group of fifteen healthy older people (mean age 72 years) and compared their performance with that of ten young controls (mean age 21 years). Although their performance was qualitatively similar, pursuit latency was increased in the older group. Investigation of the gap effect on pursuit revealed that, while the gap effect was present in the older group, it seemed to be directionally asymmetrical. When the longer absolute latencies were taken into account, although the gap effect in the two groups was identical for leftward tasks, for rightward tasks it was reduced in the older group, although this did not reach statistical significance. The difference between the old and young groups was driven by some of the older subjects. At the longest gap duration employed (400 ms), while there was a clear gap effect for leftward tasks in these subjects, there was no reduction in latency, or increases in latency, for rightward tasks. This asymmetry was not related to chronological age within the older group. These results suggest an age-related alteration in SP initiation that is more complex than general slowing of information processing in ageing. They may be indicative of additional ageing effects specific to the oculomotor or closely related systems.