Living in the Present 2

26/08/2008 by admin.

Brain Blogger (here) had a post on predicting the near future based on a paper (paper) by Changizi, Hsieh, Nijhawan, Kenai, and Shimojo called ‘Percieving the Present and a Systematization of Illusions’. The Abstract:

“Over the history of the study of visual perception there has been great success at discovering countless visual illusions. There has been less success in organizing the overwhelming variety of illusions into empirical generalizations (much less explaining them all via a unifying theory). Here, this article shows that it is possible to systematically organize more than 50 kinds of illusion into a 7 x 4 matrix of 28 classes. In particular, this article demonstrates that (1) smaller size, (2) slower speeds, (3) greater luminance contrast, (4) farther distance, (5) lower eccentricity, (6) greater proximity to the vanishing point, and (7) greater proximity to the focus of expansion all tend to have similar perceptual effects, namely, to (A) increase perceived size, (B) increase perceived speed, (C) decrease perceived luminance contrast, and (D) decrease perceived distance. The detection of these empirical regularities was motivated by a hypothesis, called ‘perceiving the present’, that the visual system possesses mechanisms for compensating neural delay during forward motion. This articles shows how this hypothesis predicts the empirical regularity.”

It takes about a tenth of a second for light on the retina to be processed to a conscious perception. A significant distance can be traveled in that time by a person or an object that a person wants to avoid or wants to catch. It is unlikely that we could walk down a crowded street without accident if we had a tenth of a second delay between our ‘now’ and the real ‘now’. By looking at the optic flow regularities of a moving observer going in the same direction as they are looking, it is possible to predict the scene changes in a tenth of a second. This appears to be what the brain does (whether or not we are moving forward). The logic would be that it everything is a little wrong because we are not moving forward, that is a safe mistake. But it would not be safe to have everything a little wrong if we are moving forward. One can do no harm and the other just might be lethal.

This adds more weight to the notion that we do live our lives in a projection into the near future. Also pointing in this direction are investigations of the flash-lag illusion (as described below by Chappell and Hine).

“The flash-lag effect occurs when an object is flashed adjacent to the path of a smoothly moving object, and abreast of the moving object. The flashed object appears to spatially lag the moving object in the direction of motion…”

In other words, the moving object is seen to be ahead of its position at the time of the flash. It has been projected into the future in our consciousness. This trick of foreseeing the probably future about a tenth of a second ahead is either a sophisticated calculation of the trajectories of objects depending on their bearing and speed or it is a collection of little ‘rule of thumb’ corrections that are ‘good enough’ for the purpose most of the time.

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