Capacity limits for the detection of changing visual features

Abstract

Evidence that visual perception is subject to various forms of induced blindness has been taken to suggest that observers do not build a complete, spatio-topic representation of their visual environment. Instead, it has been suggested that induced blindness and other phenomena related to selective processing are indicative of capacity limits acting at one or more levels in the visual system. Capacity limits in visual attention have traditionally been studied using static arrays of elements from which an observer must detect a target defined by a certain visual feature or combination of features. In the current study, we use a visual search paradigm, with accuracy as the dependent variable, to examine capacity limits for different visual features undergoing change over time. Stimuli used in these experiments were gabor gratings placed in a circular ring around a central fixation point. In Experiment 1, detectability of a single changing target was measured under conditions where the type of change (size, speed, color), the magnitude of change, the set size and distractor homogeneity were all systematically varied. Psychometric function slopes were calculated for different experimental conditions and 'change thresholds' extracted from these slopes were used in Experiment 2, in which multiple supra-threshold changes were made, simultaneously, either to a single or to two or three different stimulus elements. Together, these experiments examined the interactive effects on processing capacity of changing different stimulus features one at a time and changing several (which are distributed either within a single object or across objects) simultaneously.