Blinded by the load: attention, awareness and the role of perceptual load

Abstract

What is the relationship between attention and conscious awareness? Awareness sometimes appears to be restricted to the contents of focused attention, yet at other times irrelevant distractors will dominate awareness. This contradictory relationship has also been reflected in an abundance of discrepant research findings leading to an enduring controversy in cognitive psychology. Lavie's load theory of attention suggests that the puzzle can be solved by considering the role of perceptual load. Although distractors will intrude upon awareness in conditions of low load, awareness will be restricted to the content of focused attention when the attended information involves high perceptual load. Here, we review recent evidence for this proposal with an emphasis on the various subjective blindness phenomena, and their neural correlates, induced by conditions of high perceptual load. We also present novel findings that clarify the role of attention in the response to stimulus contrast. Overall, this article demonstrates a critical role for perceptual load across the spectrum of perceptual processes leading to awareness, from the very early sensory responses related to contrast detection to explicit recognition of semantic content.

Keywords: attention; change blindness; conscious visual awareness; contrast response function; inattentional blindness; perceptual load.

Figure 1.

Schematic of the experiment procedures (a,b) and results (c) from [13]. This figure illustrates a load manipulation in which the task varies but the stimuli are identical (a) or the set size of heterogeneous items is increased in a random subset of the trials (b) across low and high loads. A critical stimulus is added on the last trial. Both load (black bars, low load; white bars, high load) manipulations led to a substantial reduction in awareness reports for this stimulus (c). (Online version in colour.)

Figure 2.

Perceptual load and the CRF. (a) Example of high-load displays. (b) Psychometric functions for low- (black curve) and high- (grey curve) perceptual load. The estimated contrast threshold parameter for each psychometric function is also shown in dashed vertical lines (contrast threshold yielding half-maximum performance). Each data point represents the mean across participants. Error bars are ±1 s.e.m.