Blind, Yet Seeing: The Brain’s Subconscious Visual Sense

Intact navigation skills after bilateral loss of striate cortex

de Gelder, B., Tamietto, T., van Boxtel, G., Goebel, R., hahraie, S., Van den Stock, J., Stienen, B.M.C., Weiskranz, L. & Pegna, A. (2008). Intact navigation skills after bilateral loss of striate cortex. Current Biology, 18 (24), R1128-R1129.

TN usually walks with a cane, but researcher Beatrice de Gelder convinced him to put it aside and to try to navigate the obstacle course without its help. He was able to do so flawlessly, despite being unable to consciously see any of the obstacles. Head down and hands loose by his side, he twisted his body to slalom slowly but surely between a camera tripod and a swingbin, and neatly stepped around a random series of smaller items. “At first he was nervous,” says de Gelder. “He said he wouldn’t be able to do it because he was blind.” The scientists broke into spontaneous cheers when he succeeded [Nature News].


Extrageniculate mediation of unconscious vision in transcranial magnetic stimulation-induced blindsight


Ro and his research team studied what could be sensed by volunteers who were temporarily blind. Their findings are reported Monday in the online edition of Proceedings of the National Academy of Sciences.

In the study, temporary, reversible blindness was induced in volunteers by using magnetic pulses that affected the visual cortex, the area in the back of the brain that processes what the eyes are seeing.

A computer screen was in front of the volunteers. In one test, during their momentary blindness the screen flashed with either a vertical or horizontal line. In a second test a red or green ball was shown on the screen.

When the volunteers were asked what they had seen during the temporary blindness, they said they saw nothing, the researchers reported.

But, the researchers said, when the patients were told to guess which way the line was oriented, they were right 75 percent of the time. And they got the color of the ball right 81 percent of the time. Random guessing would be expected to result in a 50 percent correct rate.

Some of the participants said they were guessing randomly and were surprised with their high success rates, the researchers said. Others reported they had a "feeling" about what had been there.

Asked to rate the confidence of their guesses, the higher confidence ratings tended to correspond with more accurate guesses.

Blind man detects emotional facial expressions

Nature Neuroscience 8, 24 - 25 (2004) doi:10.1038/nn1364

  • Blind person 59% success in detecting facial emotions.
  • Activation of right amygdala

Prime-sight in a blindsight subject

Nature Neuroscience February 2002 Volume 5 Number 2 pp 101 - 102 doi:10.1038/nn793

Lawrence Weiskrantz, Alan Cowey & Iona Hodinott-Hill

  • DB retested at age 61.
  • DB reported visible after-images of stimuli in the blindfield when they were turned off ('prime-sight').
  • Can also guess static facial expressions in blindfield.

Non-conscious recognition of affect in the absence of striate cortex.

de Gelder B, Vroomen J, Pourtois G, Weiskrantz L. Neuroreport. 1999 Dec 16;10(18):3759-63.

Patient GY recognizes facial expressions presented in blindfield.

Attention without awareness in blindsight

Kentridge, R.W., Heywood, C.A., & Weiskrantz, L. (1999). Attention without awareness in blindsight. Proceedings of the Royal Society of London, Series B, 266, 1805-1811