Blind sight and its divergent illustrations
Ever since the late nineteenth century, the occipital lobe of brain has been recognized as the primary interpretation centre for a variety of visual stimuli.
For any lesion targeting the visual pathway, there is a strong likelihood that it would lead to the development of blindness i.e., a complete loss of visual stimulus perception and interpretation. However, when the occipital lobe is directly impacted as in case of a traumatic brain injury (TBI) or a stroke, an individual may retain the capability to identify and react towards certain visual stimuli despite being oblivious of their presence.
This rare and bizarre medical condition is better known as blindsight and has been the topic of great interest in the field of neuro-ophthalmology.
Some neuroscientists firmly believe that blindsight is caused by the residual neuronal cells in the occipital cortex that survive the catastrophic changes due to a stroke or TBI. Since the primary visual cortex of the occipital lobe (designated as V1) is an essential prerequisite for the conscious interpretation of visual stimuli, any damage here would definitely result in an inability to comprehend the nature of visual stimuli.
Such patients merely identify any rapid-onset stimulus as something moving in their respective visual field but they can never appreciate what the object actually was while sometimes, they would plainly deny seeing any visual stimulus. In addition, an interesting finding among a few patients has been their ability to perform an accurate colour differentiation without having any conscious perception of the colour.
A classical viewpoint of blindsight classifies this condition into two types; Type I and Type II.
Type I blindsight is said to occur when a lesion in the V1 area would allow a person to detect a “visual” stimulus.
On the contrary, patients having type II blindsight report that instead of seeing any visual stimulus, they have a feeling of some random object moving within their visual field. Still, however, controversy exists in the milieu of blindsight as some researchers have put forward an alternative narrative.
It has been suggested that rather than being a failure of conscious interpretation, blindsight arises due to a faulty or distorted perception of the visual input. Some newer studies have even negated the role of surviving islands of vision within the occipital cortex in the development of blindsight. This depicts the peak of conflicting opinions which surround this particular aspect of neuro-ophthalmology.
While it has been over a century since the discovery of this rare phenomenon, blindsight continues to be an intriguing concept for the medical community and there is still room for extensive research into this subject before any final opinion can be established.