Effect of Eye Position on Perception

[P3D Jacques Lajoie <lajoie.jacques@xxxxxxx>]

>John Roberts writes

>>It also depends on the direction of the gaze. To ensure that the
>>visual world remains stable as we look around us, in addition to the
>>retinal image, the brain must also take into account the movements of
>>the eyes and head.
=2E..
>>When I shift my eyes or
>>head to the side, I don't think the whole universe has suddenly moved.

>Gabriel Jacob replies

>That is a perfect example of a perfectly known effect. This is no "new
>discovery" and visual researchers know very well that in normal visual
>perception, the universe doesn't move when shifting eyes or head.

You are right. There is a nice demonstrration I use in an undergraduate
course on visual perception:

Just press-push lightly with your index finger on one side of your eye (to
move it laterally) and you will see the visual scene moving laterally on
the opposite side. Explanation: you by-pass the compensation the cortex is
always giving to the visual scene when initiating eye movements.

Moreover, there is a well known symptom in visual neuropathology: when the
subject moves his eyes to the right, the visual field shift also to the
right; this means that the oculomotor nerve directing the movement to the
right is not working properly but the brain will compensate all the same
for the movement to be done by moving the visual field to the right !!!

Jacques Lajoie
http://www.mpsycho.uqam.ca



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