Estimation of the sizes of inhibitory areas in crowding effect in the periphery

Abstract

The influence of the surrounding images on recognition of test objects was studied in psychophysical experiments. Low-contrast Landolt C’s with sizes of 1.1, 1.5, and 2.3 angular degrees whose centers were located at 13.2 angular degrees away from the fixation point were used as test objects. Similar Landolt C’s or rings without gaps were the surrounding objects. The distance between the centers of the test and the additional objects varied between 2.2 and 13.2 angular degrees. In one experiment, the observer’s task was to identify simultaneously both the test and the surrounding objects; in the other experiment, recognition of only the test stimuli was required. In both experiments, deterioration of recognition of the test stimuli was found at all distances between the test objects and the additional images, which was stronger when the observer performed the dual task. The data give evidence of the size of the inhibitory areas exceeding those predicted by the Bouma law and show the contribution of the attention to peripheral crowding effect.