Abstract
It is unclear how shadows are processed in the visual system. Whilst shadows are clearly used as an important cue to localise the objects that cast them, there is mixed evidence regarding the extent to which shadows influence the recognition of those objects. Furthermore experiments exploring the perception of shadows per se have provided evidence that the visual system has less efficient access to the detailed form of a region if it is interpreted as a shadow. The current study sought to clarify our understanding of the manner in which shadows are represented by the visual system by exploring how they influence attention in two different object-based attention paradigms. The results provide evidence that cues to interpret a region as a shadow do not reduce the extent to which that region will result in a within-‘object’ processing advantage. Thus, whilst there is evidence that shadows are processed differently at higher stages of object perception, the present result shows that they are still represented as distinctly segmented regions as far as the allocation of attention is concerned. This result is consistent with the idea that object-based attention phenomena result from region-based scene segmentation rather than from the representations of objects per se.
Highlights
The pattern of stimulation that falls upon the retina is not informative
This article seeks to build on the fact that the interpretation of a region as a shadow can alter the accessibility of the form of that region by testing whether cues that alter the interpretability of a region as a shadow influence the allocation of attention to that region, using ‘object’-based attention paradigms
The results provide consistent evidence that increasing the extent to which a region could be interpreted as a shadow had no effect on the extent to which that region could be selected as an ‘object’ of attention
Summary
The pattern of stimulation that falls upon the retina is not informative. The limited capacity of the visual system can be employed most effectively if it is focused on those aspects of visual structure that most effectively enable us to recognise objects and to act upon them. Shadows pose an interesting representational challenge in this context because on the one hand, they do not represent inherent structure in the environment, but on the other, they are potentially informative with respect to the objects that cast them. Reviewing the status of shadows in the human visual system reveals a somewhat mixed picture, in which inconsistencies in the pattern of illumination implied by shadows are hard to identify (Ostrovsky et al 2005) and in some contexts have no measurable influence on object recognition (Braje et al 2000; Bonfiglioli et al 2004), but in other contexts shadows clearly aid and/or interfere with object recognition (Tarr et al 1998). This article seeks to build on the fact that the interpretation of a region as a shadow can alter the accessibility of the form of that region by testing whether cues that alter the interpretability of a region as a shadow influence the allocation of attention to that region, using ‘object’-based attention paradigms
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