Perceived size and spatial coding

Abstract

Images of the same physical dimensions on the retina can appear to represent different-sized objects. One reason for this is that the human visual system can take viewing distance into account when judging apparent size. Sequentially presented images can also prompt spatial coding interactions. Here we show, using a spatial coding phenomenon (the tilt aftereffect) in tandem with viewing distance cues, that the tuning of such interactions is not simply determined by the physical dimensions of retinal input. Rather, we find that they are contingent on apparent size. Our data therefore reveal that spatial coding interactions in human vision are modulated by processes involved in the determination of apparent size.

Figure 1.

a, b, Graphics depicting the apparatus used in these experiments. c, d, Graphics depicting the three-dimensional visual frame used in all experiments, and the subjective appearance of the standard and comparison stimuli in experiment 1. e, Bar plot showing the comparison stimulus size matched to the standard stimulus as a proportion of the standard stimulus size. The dotted horizontal line shows a proportion of 1, at which there would be no size illusion. The error bar shows SEM.

Figure 2.

a, Graphic depicting the subjective appearance of adapting stimuli in experiment 2. b, Graphics depicting test stimuli from experiment 2. c, Graphics depicting the physical overlap between test and adapting stimuli. Regions of overlap are depicted by transparent red rings superimposed on depictions of adapting stimuli. d, Bar plots showing the signed magnitude of tilt aftereffects. Negative values signify that test stimuli appeared rotated away from the orientations of gratings within inner sectors of adapting stimuli, and positive values signify that test stimuli appeared rotated away from the orientations of gratings within outer sectors. Error bars show SEM.