Blindsight is sensitive to stimulus numerosity and configuration: Evidence from the redundant signal effect

Alessia Celeghin, Silvia Savazzi, Marissa Barabas, Matteo Bendini, Carlo A. Marzi

Research output: Contribution to journalArticleScientificpeer-review

15 Citations (Scopus)


One important, yet relatively unexplored question is whether blindsight, i.e., unconscious visually guided behavior in hemianopic patients, is endowed with basic perceptual properties such as detecting stimulus numerosity and overall configuration. Rather than a forced-choice procedure in which patients are supposed to guess about stimuli presented to the blind hemifield, we used a redundant signal effect paradigm, i.e., the speeding of simple reaction time (RT) when presenting multiple versus single similar stimuli. The presence of an effect of numerosity for the (unseen) stimuli presented to the blind field was indirectly assessed by measuring RT to bilateral versus unilateral stimuli presented to the intact hemifield. Chronic hemianopic patients were tested with unilateral or bilateral black dots, both of which could be either single or quadruple. The latter could either have a fixed spatial configuration representing a diamond or be randomly spatially assembled on every trial. Both configurations covered the same extent of visual field and had the overall same luminance. We found that a numerosity effect as a result of increasing the number of stimuli in the blind field was indeed present but only with the diamond configuration. This is a convincing evidence that this form of blindsight does not depend upon stimulus numerosity per se but is likely to be related to the presence of structured and memorized rather than meaningless changing stimuli.
Keywords: Blindsight Hemianopia Redundancy gain Subcortical visual pathways Reaction time
Original languageEnglish
Pages (from-to)1617-1623
JournalExperimental Brain Research
Issue number5
Publication statusPublished - 2015


  • Blindsight
  • Hemianopia
  • Redundancy gain
  • Subcortical visual pathways
  • Reaction time

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