Some blind people can point at what they cannot see
After damage to the primary visual cortex, some patients report no sight in part of the field and still discriminate location or motion there above chance.
Established2 min read
Weiskrantz studied patient D.B., who had a portion of V1 removed. Shown a light in the blind field, D.B. insisted he saw nothing, then — when forced to guess — pointed at it. Orientation and motion came out the same way: denied experience, better-than-chance performance.
The route is thought to run through older midbrain paths that do not require V1. Blindsight is residual visual computation without the report of seeing.
Caveats
- It follows specific lesions, usually of V1. Most blindness is not blindsight.
- Stray light in the eye has to be controlled. The careful studies did that.
Sources
- 1Weiskrantz L.. Blindsight: A Case Study and Implications. Oxford University Press, 1986.