Shadow processing in ageing and Alzheimer's disease

G Porter, U Leonards, T Troscianko, JMA Haworth, A Bayer, A Tales

Research output: Contribution to conferenceConference Abstract

Abstract

Participants show differences in processing speed between shadow-like image regions and equivalent regions which are not perceived as shadow-like (e.g. Rensink & Cavanagh, 2004, Perception 33, 1339-1358). This indicates that visual processing mechanisms somehow make shadows difficult to perceive, presumably to help minimise light-related noise in visual inputs and facilitate object recognition. Here we examined whether such shadow-specific processing might be altered by ageing and particularly Alzheimer's disease (AD), reasoning that a declining ability to "suppress" shadows would increase visual noise and thus potentially contribute to the visual confusion experienced by some AD patients. We used visual search for a discrepant target among items which appeared as posts with shadows cast by light-from-above when upright, but as angled objects when inverted. Young participants showed the classic effect of slower responses with upright than inverted displays, but only when the shadow-like part was dark, not white (control condition). Crucially, this interaction of shadow colour with item orientation was maintained in healthy older and AD groups, indicating that processing mechanisms specific to light-from-above shadows remain unaltered in healthy ageing and AD. Both older groups were, however, slower when discriminating dark as compared to white shadow-like regions regardless of orientation, in line with altered contrast perception in ageing. More interestingly, AD patients were slower at distinguishing any type of upright items, irrespective of "shadow" colour, in keeping with specific deficits to lower visual field processing in AD. Overall, shadow visibility appears (if anything) reduced in older people due to general, not shadow-specific, changes.
Translated title of the contributionShadow processing in ageing and Alzheimer's disease
Original languageEnglish
Pages1154 - 1154
Number of pages1
Publication statusPublished - 2010

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