A blindsight conundrum: how to respond when there is no correct response.

Area of Science:

• Neuroscience
• Visual Perception
• Cognitive Science

Background:

• Blindsight research typically assumes correct responses to all visual stimuli in the cortically blind field.
• The current study introduces 'no stimulus' (blank) trials to probe responses in blindsight conditions.

Observation:

• Subjects included hemianopic and normal monkeys, and a human hemianope aware of some blind-field targets.
• Stimuli were presented in the blind field (hemianopes) or both hemifields (normal subjects).
• Blank trials were introduced to assess responses in the absence of visual stimuli.

Findings:

• Monkeys often responded to blank trials, typically by indicating a target in their blind field.
• Human subjects were less likely to respond to blank trials.
• Reaction times for false responses to blank stimuli were longer than for blind field targets in monkeys.
• Human confidence reports correlated with stimulus awareness, but not with response accuracy.

Implications:

• Blindsight may involve implicit or explicit registration of stimulus differences, even in the absence of conscious awareness.
• Response patterns in blindsight can differ between species and depend on task demands.
• Investigating responses to 'catch' trials offers new insights into the processing of visual information in cortically blind individuals.