Do you believe that the mind can detect things beyond the conscious realm of sensory perception? Can the blind "see" without vision? A new study provides strong support for these intriguing questions.
This hypothesis was tested in a clever way in a new study by psychologists Bertini, Cerere and Ladavas from the University of Bologna, Italy publishing in the journal Cortex. The researchers analyzed people who were blind in one eye by measuring the subjects' reaction time in identifying images flashed on a computer screen to their good eye. The researchers discovered that when an image was simultaneously flashed to the blind eye, the subjects identified the object seen through the sighted eye much faster.
Interestingly, not any image slipped to the blind eye boosted the reaction time -- only when fearful faces were presented to the blinded eye while happy faces were shown to the sighted eye was their reaction time accelerated. Fear or alarm on the faces of others, even though it is impossible to see consciously through the blind eye, somehow alerted their mind to danger and elevated their mental performance to a heightened state of vigilance.
This may sound like pseudoscientific nonsense, but this is pure neurophysiology.
I've left out one important fact--how these individuals were blinded. The eye itself was intact and perfectly functional; these people were blinded when they suffered a stroke or traumatic injury to the part of the brain that is responsible for vision -- the visual cortex located near the back of the skull. However, neuroscientists studying fear have provided evidence that the eyes also transmit information through a "subcortical" pathway to reach the part of the brain that is critical for vigilance and fear, the amygdala. This short-circuit pathway transmits unconsciously to the part of the brain that is always on guard for life-threatening dangers. Vision -- that is the conscious perception of vision -- takes a different route from the eyes to the cerebral cortex, and the comparatively long processing time required to deliver the sense of vision to our conscious mind could take too long to respond to a sudden threat.
So while these patients were unable to see anything from the eye that could no longer send signals to the visual cortex, the deeper brain circuits responsible for threat detection were preserved and they alerted the amygdala at a subconscious level to the possible threat in the environment gleaned from the fearful expressions on the face of other people. When a split-second response could determine whether you get hit by a car or not, the conscious route to the visual center of the brain may be too slow. Instead we leap out of the path of an on-rushing car and exclaim in panic and fear "What was that!"
There is far more information about the world entering our brain than we are consciously aware, and much is going on in the mind beneath the surface of consciousness.
Bertini, C., Cecere, R., Ladavas (in press) I am blind, but I "see" fear. Cortex, online in advance of press.