Fig. 1.

Stimulus presentation in the psychophysical SimChain procedure. a An example of a luminosity trial during Experimental Phase 1, with stimuli biased toward luminosity salience. A blue background also signaled that subjects should sort according to luminosity. The exact stimulus properties and positions were randomly assigned on each trial. b An example of a radius trial during Experimental Phase 1, with stimuli biased toward radius salience. A red background signaled radius responding. c An example of a trial in Experimental Phase 2, in which stimuli varied across the full range possible radius and luminosity values. The arrows show a correct response, given the blue background cue. d Another trial in Experimental Phase 2, in which the red background cue signals radius responding (color figure online)