Blindsight - Theories of Causation

Theories of Causation

There are three theories for the explanation of blindsight. The first states that after damage to area V1, other branches of the optic nerve deliver visual information to the superior colliculus and several other areas, including parts of the cerebral cortex. These areas might control the blindsight responses, but still many people with damage to area V1 don’t show blindsight or only show it in certain parts of the visual field.

Another explanation to the phenomenon is that even though the majority of a person’s visual cortex may be damaged, tiny islands of healthy tissue remain. These islands aren’t large enough to provide conscious perception, but nevertheless enough for blindsight. (Kalat, 2009)

A third theory is that the information required to determine the distance to and velocity of an object in object space is determined by the lateral geniculate nucleus before the information is projected to the cerebral cortex. In the normal subject these signals are used to merge the information from the eyes into a three-dimensional representation (which includes the position and velocity of individual objects relative to the organism), extract a vergence signal to benefit the precision (previously auxiliary) optical system (POS), and extract a focus control signal for the lenses of the eyes. The stereoscopic informantion is attached to the object information passed to the cerebral cortex.

Evidence of blindsight can be indirectly observed in children as young as two months, although there is difficulty in determining the type in a patient who is not old enough to answer questions.