Abstract
Older adults' performance is known to be impaired when they perform secondary or interleaved tasks, compared to performing those tasks alone. It is not known, however, whether this impairment extends to simple low-level motion discriminations. We investigated whether performing a secondary task would affect motion coherence thresholds in both older and younger participants. Coherence thresholds (79% correct) were measured for judging the direction of translational global motion (3.4% contrast) in young (<25 yrs) and elderly (>65 yrs) participants. Simultaneous with the motion stimulus up to four, high contrast (34% contrast) squares flashed briefly either at fixation or peripherally at the edges of the motion stimulus. Participants either attempted to ignore these distracters or count them. Older adults' overall performance was similar to the younger adults. Thresholds were significantly higher when performed the counting task and under these conditions older adults were much more impaired than younger adults. Counting peripheral distracters was more detrimental to performance than counting at fixation but there was no correlation between motion coherence thresholds and counting task performance. Thus older adults are impaired when attention is divided and this extends to relatively low-level visual judgements. This pattern of findings is consistent with attentional modulation of global motion perception and models of age related cognitive decline.