Color-shape associations affect feature binding.

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.