Loads of unconscious processing: The role of perceptual load in processing unattended stimuli during inattentional blindness

Pugnaghi, Giulia; Memmert, Daniel; Kreitz, Carina · 2020 · Crossref

DOI: 10.3758/s13414-020-01982-8

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Summary

This study investigates whether perceptual load modulates the preconscious processing of unattended stimuli during inattentional blindness. While it is well-established that high perceptual load increases the likelihood of failing to detect unexpected objects, it remains unclear if this load also restricts the degree to which undetected stimuli are processed unconsciously. Guided by Lavie’s perceptual load model, the authors hypothesized that high perceptual load would prevent task-irrelevant stimuli from interfering with primary task performance, whereas low load would allow such interference. The researchers conducted two experiments using an inattentional blindness paradigm where participants categorized target numbers while ignoring unexpected, unattended numbers presented in a central array. Interference was measured by comparing reaction times and accuracy when the unattended number was congruent or incongruent with the target’s category. In Experiment 1, perceptual load was manipulated by adding distractor letters to the display in high-load trials. In Experiment 2, load was manipulated by placing distractors in close spatial proximity to the target. Both studies excluded participants who reported noticing the unattended stimuli to ensure processing remained unconscious. The results consistently showed significant main effects of perceptual load, with slower reaction times and lower accuracy in high-load conditions, confirming the manipulation was effective. Experiment 1 replicated previous findings of an interference effect, where incongruent unattended stimuli slowed responses. However, contrary to the hypothesis, there was no significant interaction between perceptual load and condition in either experiment. Bayesian analyses provided moderate evidence for the null hypothesis, indicating that the interference effect did not diminish under high load. Experiment 2 failed to replicate the reaction time interference effect entirely, though accuracy data mirrored Experiment 1’s pattern of no interaction. These findings suggest that high perceptual load does not prevent the preconscious processing of unattended stimuli to an extent that influences primary task performance. The authors conclude that the factors determining whether a stimulus crosses the threshold of awareness may not linearly determine the degree of sub-threshold processing. This challenges the generalizability of the perceptual load model to unconscious processing contexts, implying that even when attentional resources are fully occupied, unexpected stimuli can still be processed sufficiently to cause interference.

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Topics

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• inattentional change blindness
• peripheral attention