Non-synesthetic people tend to systematically associate certain shapes with particular colors (i.e., circle–red, triangle–yellow, square–blue). In the present study, we investigated whether such color–shape associations influence illusory conjunctions. Two letters were centrally presented, while two colored-shape stimuli were presented in the periphery. Participants were asked to report: (1) whether the letters were identical, (2) the color of a specific shape, and (3) the confidence of the color choice. The colored–shape stimuli were either congruent or incongruent with the color–shape associations. Results showed that participants reported more illusory conjunctions in the incongruent condition. Thus, color–shape associations might precede and subsequently affect feature binding, and/or affect binding via top-down feedback.
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