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Blindsight and visual awareness

P Azzopardi¹, A Cowey

¹Department of Experimental Psychology, University of Oxford, Oxford OX1 3UD, UK. paul.azzopardi@psy.ox.ac.uk

Consciousness and Cognition

|October 27, 1998

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Blindsight, a phenomenon where patients with visual cortex damage can detect unseen stimuli, may be explained by differing response criteria in testing. This study suggests response bias, not just awareness, influences blindsight performance, especially for moving targets.

Area of Science:

Neuroscience
Visual Perception
Cognitive Psychology

Background:

Blindsight describes the ability of individuals with striate cortex damage to discriminate stimuli in their blind visual field when using forced-choice methods.
This phenomenon suggests a dissociation between visual performance and awareness, but its interpretation is debated.
Signal detection theory proposes that apparent blindsight dissociations might arise from differing response criteria in yes-no versus forced-choice tasks, particularly near the threshold of conscious vision.

Observation:

A hemianopic subject was tested using yes-no and forced-choice detection for static and moving targets.
The subject exhibited significant differences in response criteria between the two task types.
These criterion differences were sufficient to create a blindsight-like dissociation when using bias-sensitive performance measures.

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Findings:

When bias was accounted for, the subject's sensitivity to static targets was higher in the forced-choice task compared to the yes-no task, deviating from normal control subjects.
Sensitivity to moving targets, independent of bias, did not differ between the yes-no and forced-choice tasks.
Response criteria differences explained the dissociation for motion detection but not for static pattern detection.

Implications:

The findings suggest that response bias plays a role in the observed blindsight phenomenon, potentially explaining why moving stimuli are more frequently reported as perceived than static stimuli.
Blindsight may differ from normal vision near the perceptual threshold.
The study implies that neural mechanisms underlying pattern and motion detection in blindsight might vary depending on whether yes-no or forced-choice tests are employed.