'Seeing' in the blind hemifield following hemispherectomy

Area of Science:

• Neuroscience
• Visual Perception
• Cognitive Science

Background:

• The striate cortex (primary visual cortex) was traditionally considered indispensable for vision.
• Destruction of this area was thought to cause permanent contralateral blindness.
• However, evidence for blindsight (residual vision in blind fields) has accumulated over decades.

Purpose of the Study:

• To investigate the neural substrates of blindsight.
• To resolve controversy regarding the mechanisms of residual vision after striate cortex damage.
• To identify critical pathways mediating blindsight.

Main Methods:

• Examined hemianopic human and monkey subjects with residual vision in their blind fields.
• Studied patients who underwent hemispherectomy or hemisphere disconnection for epilepsy.
• Analyzed visual processing in subjects with no functional striate or extrastriate cortex on the ablated side.

Main Results:

• Blindsight demonstrates significant residual visual capacities in the absence of the striate cortex.
• Alternative pathways, potentially involving subcortical routes to extrastriate areas, mediate blindsight.
• Patients with hemispherectomy provided crucial evidence for non-striate pathways in blindsight.

Conclusions:

• The striate cortex is not indispensable for all aspects of vision.
• Subcortical pathways and extrastriate visual areas play a critical role in blindsight.
• Understanding blindsight offers insights into visual system plasticity and alternative processing routes.