Seeing pure motion

In our everyday experience, we can see things moving, but seeing the moving without seeing the thing seems to be a meaningless concept. What is motion in vision? Motion appears to be an abstraction of visual experience, but it is in itself not an experience.

Strangely that is not true. In some very unusual condition it is possible to see the moving without seeing the thing. The most intriguing example is what’s called the Riddoch Syndrome (Zeki & ffytche, 1998). George Riddoch was a medical doctor who looked after soldiers wounded by gunshots after WWI. He noticed that some soldiers blinded by damages in the primary visual cortex reported that they could sense “moving things” but they couldn’t characterize the attribute of the stimulus. They described what they saw as “moving something with no shape or color” or “moving shadows”.

Zeki and ffytche characterize the Riddoch Syndrome as “awareness without discrimination”, which interestingly echoes blindsight, “discrimination without awareness”. Both syndromes seem  to be associated with lesion of the primary visual cortex. As a matter of fact, the same subject (namely, the famous GY) can have both.

The Riddoch syndrome used to be the only case of “seeing pure motion” that I was aware of. I am very glad that a recent paper by To et al. discusses a similar phenomenon. Thankfully you don’t have to undergone brain surgery to experience this!

… In his classic paper of 1875, Sigmund Exner claimed that in the outermost part of the lower visual field there was a region where he experienced a pure sensation of motion without form or color. It may seem almost funny (fast komisch), he wrote, that one can see motion without a moving object, but that was the only way to describe his sensation (Exner, 1875, p. 163). His words anticipate the descriptions given by patients who have suffered injuries to the primary visual cortex and who are shown an object moving within their blind field (Azzopardi & Cowey, 1998; Riddoch, 1917)…

References:

Zeki & ffytche (1998) The Riddoch syndrom: insights into the neurobiology of conscious vision. Brain, 121: 25-45.

To, Regan, Wood & Mollon (2011) Vision out of the corner of the eye. Vision Research, 51:203-214.

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~ by hhyu on February 7, 2011.

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