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John Greenwood, Michael Parsons; Dissociable effects of crowding for judgements of colour and motion. Journal of Vision 2016;16(12):234. doi: 10.1167/16.12.234.
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© ARVO (1962-2015); The Authors (2016-present)
In peripheral vision, object recognition is impaired by clutter. This crowding effect disrupts the identification of a diverse range of features including orientation, motion, depth and colour. Although current models depict crowding as a singular object-selective mechanism that affects these features simultaneously, rather than multiple feature-specific instances that operate independently, prior research is equivocal. We examined crowding for colour and motion, two features that allow a strong test of feature independence (e.g. given prior findings for visual search). Cowhide stimuli were presented 15 degrees in the periphery; observers reported either the target hue (blue/purple) or its carrier direction (CW/CCW of upwards). To assess the independence of these judgements, we first established that two key aspects of crowding, shown previously for orientation, are also true for colour and motion. First, crowded errors are systematic: identification errors for both target hue and direction were biased, generally towards the identity of the flankers. Second, crowding is selective for target-flanker similarity: motion crowding was strong when target-flanker directions were similar and weak when they differed, and likewise for colour crowding. These findings allowed us to test the independence of crowding for hue and direction by requiring observers to indicate both features. An object-selective mechanism predicts that when crowding is weak for one feature (e.g. colour) and strong for the other, errors for both features should be either unaffected or reduced (i.e. that crowding is all-or-none). In contrast, our results follow the predictions of independent feature-selective processes: when crowding was weak for colour and strong for motion, errors were reduced for colour but remained for motion. Likewise, colour errors predominated when crowding was strong for colour and weak for motion. Given this double dissociation, we argue that crowding is not a singular process but rather a feature-specific pooling operation that occurs throughout the visual system.
Meeting abstract presented at VSS 2016
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