One of the Cognitive ghosts discussed in the The Rest Is Science episode “Cognitive Ghosts”.
What it is
Blindsight is the astonishing condition in which someone who is genuinely, consciously blind — because the part of the brain that creates visual awareness is destroyed — can still respond accurately to things they cannot see. They’ll correctly guess the location or movement of objects, dodge obstacles, even read emotions on faces, all while sincerely insisting they see nothing. Asked how they did it, they confabulate — “I just guessed” — because the conscious mind was never told.
What’s happening in the brain
Damage to the primary visual cortex (V1) — usually from stroke or a tumour — removes conscious sight. But visual information also travels along older, parallel pathways (via the superior colliculus and other subcortical routes) that bypass V1 and still feed motor and emotional systems. So the body acts on visual data the conscious self has no access to: the lights are on, but the part of you that “watches” has been disconnected. It’s a striking demonstration that vision and the awareness of vision are separable — a favourite case study in consciousness research.
References from the show
- Quote: “Their body starts reacting to things — even a bump in the road. They’ll avoid it, but won’t tell you how.”
- The classic demonstration the hosts allude to: a cortically blind patient (known in the literature as TN) successfully walking the length of an obstacle-filled corridor without his cane and without hitting anything.
Links
- Blindsight — Wikipedia
- The term was coined by Lawrence Weiskrantz in the 1970s · Looking back: Blindsight in hindsight — BPS
- Blindsight: a conscious route to unconscious vision — Current Biology
Related
- The Third Man Factor — another case of the brain reacting to signals the conscious self can’t place
- The Call of the Void — confabulating an explanation after the fact
- Cognitive ghosts