Spatial channels of visual processing in cortical blindness

Arash Sahraie, Ceri T Trevethan, L. Weiskrantz, John Olson, Mary Joan MacLeod, Alison Dorothy Murray, R. S. Dijkhuizen, Carl Edward Counsell, R. Coleman

Research output: Contribution to journalArticle

38 Citations (Scopus)

Abstract

Blindsight is the ability of some cortically blind patients to discriminate visual events presented within their field defect. We have examined a fundamental aspect of visual processing, namely the detection of spatial structures presented within the field defect of 10 cortically blind patients. The method outlined is based on the detection of high-contrast stimuli and is effective in flagging a 'window of detection' in the spatial frequency spectrum, should it exist. Here we report on the presence of a narrowly tuned psychophysical spatial channel optimally responding to frequencies less than 4 cycles/degrees in eight out of 10 patients tested. The two patients who did not show any evidence of blindsight appear to have intact midbrain structures, but have lesions that extend from the occipital cortex to the thalamus. In addition, we have recorded subjective reports of awareness of the visual events in each trial. Detection scores of eight blindsight patients were subsequently subdivided based on the subjective reports of awareness. It appears that the psychophysical spatial channel-mediating responses in the absence of any awareness of the visual event have a narrower frequency response than those involved when the patients report some awareness of the visual event. The findings are discussed in relation to previous reports on the incidence of blindsight and performance on tasks involving spatial processing.

Original languageEnglish
Pages (from-to)1189-1196
Number of pages7
JournalEuropean Journal of Neuroscience
Volume18
Issue number5
DOIs
Publication statusPublished - Sep 2003

Keywords

  • awareness
  • blindsight
  • damaged visual pathway
  • visual discrimination
  • CONTRAST-SENSITIVITY FUNCTIONS
  • RESIDUAL VISION
  • CEREBRAL LESIONS
  • FIELD DEFECTS
  • BLINDSIGHT
  • FREQUENCY
  • RESPONSES
  • ABSENCE
  • EXTRAGENICULOSTRIATE
  • DISCRIMINATION

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