Cite as:
Porter G, Tales A, Wilcock G K, Trościanko T, Leonards U, 2005, "The effects of ageing on processing load in feature and conjunction search: A pupil-size and eye-movement study" Perception 34 ECVP Abstract Supplement

The effects of ageing on processing load in feature and conjunction search: A pupil-size and eye-movement study

G Porter, A Tales, G K Wilcock, T Trościanko, U Leonards

The pupil of the eye dilates with processing load. We have previously shown that this measure is sensitive to subtle difficulty manipulations during performance in an inefficient feature-search task (eg Porter et al, 2004 Perception 33 757). Here, to investigate ageing effects on load during search, we compared a conjunction with two feature-search tasks for younger (age 18 - 30 years) and elderly (age 60 - 85 years) participants, matching tasks as well as possible for response speed and accuracy. For both age groups, the patterns of pupillary dilation during performance were indistinguishable for the three tasks, suggesting similar processing load for the different searches. Moreover, pupillometry measures seemed unaffected by minor differences in eye-movement indices between tasks. Conjunction search involved more saccades and longer overall scan paths than feature searches, mirroring slightly longer reaction times. Additionally, conjunction-search-based saccade amplitudes were reduced and fixation durations increased, the latter for elderly subjects only. On directly comparing results for younger and older participants, a general slowing of both performance and pupil response was evident in the elderly. Older participants showed delayed pupil reflexes on stimulus onset and slower recovery from these compared with the young. Fixation durations were also longer, with more saccades made per search trial by the older group. However, the pupils' dilatory patterns towards response were equivalent in shape and amplitude for both age groups. Given that pupil dilation patterns were identical for the different tasks, they cannot have been influenced by response speed, number of eye movements, or fixation duration. Taken together, these data indicate that the essential processing nature, as measured by pupillary indices of processing load, is preserved for both feature- and conjunction-search tasks in healthy ageing. This processing nature seems unaffected by the occurrence of search-type specific and age-specific changes in strategy as implied by eye-movement data.

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