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Maria Olkkonen, Geoffrey K Aguirre, Toni P Saarela; Robust behavioral and neural integration of color and gloss cues for object classification. Journal of Vision 2020;20(11):517. doi: https://doi.org/10.1167/jov.20.11.517.
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© ARVO (1962-2015); The Authors (2016-present)
Background. Different material attributes may be used as cues to identify object properties, but little is known about cue integration in material perception. We studied the behavioral and neural integration of color and gloss cues for ripeness judgements.
Methods. 11 observers participated in four sessions of psychophysics and fMRI. Stimuli were fruit-like, computer-rendered 3D shapes that varied in color, glossiness, or both. We created a "ripeness space", ranging from unripe (green and/or matte) to ripe (red and/or glossy) stimuli, scaled for each observer with their discrimination thresholds for the individual cues. To quantify integration, we measured discrimination in a joint color-and-gloss condition. A fourth, mixed condition, interleaved the single-cue and joint conditions to investigate the effect of external uncertainty. Thresholds were measured using a single-interval classification task and defined as the standard deviation of a cumulative Gaussian fit to the probability of responding “ripe”. BOLD responses for the four conditions were collected while observers performed the same task in an fMRI scanner. We extracted linear adaptation effects and neural integration from occipito-temporal regions of interest (ROIs: V1-V4, LOC, FFA, control region PPA), localized with a combination of anatomical and functional methods.
Results. Observers integrated color and gloss cues for ripeness judgments, evidenced by decreased thresholds in the joint, compared to single-cue, conditions. External uncertainty adversely affected performance in single-cue (but not joint) conditions, consistent with an optimal task strategy. All ROIs except PPA showed linear adaptation for color and gloss. Most of these areas showed significant cue integration, especially with no external uncertainty. Behavioral and neural integration correlated significantly in functionally defined color- and gloss-selective areas, but not in early visual cortex.
Conclusions. Observers are able to integrate cues over two material attributes in a real-world task. This integration seems to be mediated by mid-level visual cortex.
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