MacDonald, J.; (2008) Load induced blindness. Doctoral thesis , University of London.

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Abstract

This thesis has established the effects of perceptual load and working memory load on the conscious awareness of an expected task-unrelated stimulus. Participants performed a visual search task, in which perceptual load was manipulated, while attempting to detect the presence of a meaningless task-unrelated figure, referred to as the critical stimulus (CS). The results showed a consistent reduction in CS detection rate and detection sensitivity (with no accompanying change in response criterion), when the search task was of high perceptual load, compared to a low perceptual load condition. Alternative accounts of the results in terms of memory failure rather than the absence of conscious awareness, the differential search task reaction times in the low and high conditions of perceptual load, goal-neglect, and strategy were ruled out. The effects of perceptual load were generalised to a CS presented directly at fixation, while demonstrating that detection performance was superior for fixated stimuli than for stimuli in peripheral vision, despite size-scaling to account for cortical magnification. Furthermore, the experiments established a dissociation between the effect of perceptual load and the effect of working memory load on conscious awareness, and a second dissociation between the effect of working memory load on awareness and its effect on distractor interference: whereas detection sensitivity and distractor interference were both reduced alike under high perceptual load, working memory load led to increased distractor interference but had no effect on detection sensitivity. Overall, the results generalised perceptual load theory (e.g., Lavie, 1995) to measures of conscious perception, and established a contrast between the effect of working memory load on awareness and on distractibility.

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