Abstract
When people are performing a goal-directed task, they are often subject to interference by task-irrelevant distractors. We investigated how attention is distributed between the target and distractors under varying task loads. In the experiment, in half of trials, participants performed a letter-identification task, under three conditions. In the low load condition, only a target and a distractor, whose colors were green, were displayed. The distractor could be the same as or different from the target letter, presented to the left or right of the target. In the high load condition, the target was surrounded by 5 green, non-targets letters. In the dilution condition, the stimuli were identical to high load except that each non-target letter had distinct colors. In the remaining half (probe-discrimination trials), the 200-ms presentation of the letter task stimuli were followed by the presentation of a visual probe stimulus. The probe appeared at the target, non-target, or distractor location, 50,180,250 or 400 ms after the onset of the search task. As results, the magnitude of distractor interference was greater for the low load than for the high load and dilution conditions, p’s < .01. The analysis of probe data revealed that in the low load and high load conditions, probe responses were significantly slower when the probe was at the distractor location than at the target and non-target location, p’s < .01, with no difference between these two throughout all the SOAs. However, in the dilution condition, probe responses were significantly faster for the target location than for other locations at the 180-ms SOA, p’s < .01. These results suggest that in the dilution condition, attention is solely focused on the target, decreasing distractor interference. By contrast, in the high load condition, rather than attentional focusing, the exhaustion of perceptual load seems to eliminate distractor interference.