Perceptual load vs. dilution: the roles of attentional focus, stimulus category, and target predictability

Abstract

Many studies have shown that increasing the number of neutral stimuli in a display decreases distractor interference. This result has been interpreted within two different frameworks; a perceptual load account, based on a reduction in spare resources, and a dilution account, based on a degradation in distractor representation and/or an increase in crosstalk between the distractor and the neutral stimuli that contain visually similar features. In four experiments, we systematically manipulated the extent of attentional focus, stimulus category, and preknowledge of the target to examine how these factors would interact with the display set size to influence the degree of distractor processing. Display set size did not affect the degree of distractor processing in all situations. Increasing the number of neutral items decreased distractor processing only when a task induced a broad attentional focus that included the neutral stimuli, when the neutral stimuli were in the same category as the target and distractor, and when the preknowledge of the target was insufficient to guide attention to the target efficiently. These results suggest that the effect of neutral stimuli on the degree of distractor processing is more complex than previously assumed. They provide new insight into the competitive interactions between bottom-up and top-down processes that govern the efficiency of visual selective attention.

Keywords: attentional focus; dilution; distractor interference; perceptual load; selective attention.

Figure 1

Examples of cue displays and target displays from Experiment 1. The cue display consisted of 4 frames. The locations of the target, which was either an H or an S, were indicated by 2 or 6 figure-8 place-holders increasing in luminance. The target display consisted of 2 letters or 6 letters, excluding the critical distractor, which always appeared at the center. The 2-letter display is an example of an incongruent trial. The 6-letter display is an example of a congruent trial. Note that the appearance of the target display is signaled by luminance increment.

Figure 2

The congruency effect (incongruent RT–congruent RT) across the different conditions of Experiment 1. Error bars show the standard error of the mean.

Figure 3

Examples of cue displays and target displays from Experiment 2. Note that the appearance of the target display is signaled by luminance decrement.

Figure 4

The congruency effect for Experiment 2.

Figure 5

The congruency effect for Experiment 3.

Figure 6

The congruency effect for Experiment 4.