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‘Riddoch Phenomenon’: When Blind Persons Can See Moving Objects

The century-long mystery has resurfaced again in a study that confirmed visual processing of motion by the brain of a visually impaired patient.
riddoch phenomenon

Jody Culham’s study opens up new possibilities of investigating the evolutionary aspects of our brain in separating signals from the eye to different brain region.

Can a person, who is otherwise blind, perceive moving objects?  Yes, it is possible. People suffering from the rarer visual problem ‘Riddoch phenomenon’ can perceive objects in motion, but are blind to other visual stimuli.

A century-long mystery, Riddoch Phenomenon, has resurfaced, hinting some of the underlying neural mechanisms involved in it. In a decade-long study, Jody Culham of Western University in Ontario and her team confirmed the presence of the Riddoch Phenomenon in one of the patients, as reported in their paper recently.  She confirmed that their patient could see a hand approaching towards her; she could also catch a ball thrown at her. Initially thought to be hallucinations, the motion perception of the blind patient has been confirmed with the help of psychophysical and neuroimaging techniques.

The facts that emerged in the study revealed the existence of the different routes taken by the signals from the retina to different regions, which opens up new paradigms to better understand visual processing by the brain. This also opens up new possibilities of studying the evolutionary aspects of our brain in separating signals from the eye to different brain regions for giving different effects.  

The patient referred here was a 29-year-old lady whose entire occipital lobe was destroyed by a stroke. The occipital lobe is the brain region that contains the visual system. The incident made her sightless. But she could perceive the movement of objects, which left ophthalmologists perplexed. They were of the view that this was her hallucination. Finally, she was ably diagnosed with Riddoch Phenomenon.

Culham and her team scanned the brain of the patient and detected a hole of the size of an apple in the area of the visual cortex. Visual cortex is where the vision processing takes place in our brain. A hole of this size is a significant one from the perspective of brain functioning. Interesting enough, the stroke didn’t harm the Middle Temporal (MT) region of the brain where motion processing takes place. The MT region has a greater concentration of specialised neurons, the direction selective neurons. The specialised functioning of these neurons confers the MT region with its ability of motion perception of the brain. Leaving the MT region unharmed, according to Culham, is the reason the patient could perceive motions while the lesion in the visual cortex made her sightless for still objects.

The next important question before Culham and  team was to find out how the visual inputs from the eye bypass the visual cortex and go directly to the MT.  The idea put forward by them is that there exist alternate nerve paths that take information from the eye to different areas for differential processing. But this idea still needs robust investigation.

In the human brain, the phenomenon of vision takes place through a much complicated process that involves a variety of organs. Light emanating from any object first hits the eyes. The light particles, the photons, are absorbed by the retina. Absorption of photons brings out changes in the retina cells, which can trigger an electric signal. The electric signal generated rapidly travels to the visual cortex through the routes of optical nerves. It is the visual cortex that further processes the signal from the retina to bring out the visual sensations of any object.

The Riddoch Phenomenon, the strange visual problem, was first reported by George Riddoch in 1917. Riddoch was a neurologist engaged in handling  brain injuries of the soldiers during World War I. His report was further extended by Gordon Holmes, another neurologist who was also treating soldiers with brain injuries during World War I. Holmes also reported in his 1918 paper about the different brain regions functioning differently that give rise to the phenomenon where people can see the motion in object, but fail to see everything static.

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