Chain link illusion

From an email from Dr. Kabrisky…

I just remembered another disconcerting illusion I noticed when I went to root

for Kathy’s softball team. There was a chain link barrier around the infield

to keep fouled balls from bashing the spectators. I noticed, sitting in the

stands, at various distances from the mesh, that it was easy to get your eyes

converged at several different convergence angles.

The fence mesh is  periodic, of course, and the correlation computer in the

lateral geniculate, which gets registered overlapped data from each retina in

order to converge the eyes appropriately for distance variation, can easily

lock up the eyes at the wrong convergence angle.

The correlation function of a periodic function is periodic, and so the

correlation computation generates multiple peaks, any one of which can cause

lock up. But only one lock-up angle is correct. So every once in a while, the

apparent position of the fence can jump closer than it is and the MESH HOLES

LOOK LARGER, For homework, suggest why they look larger. Explain why the fence

never seems to jump away.

For extra credit, suggest an expiation of how the brain can cause the

appearance of the holes in the mesh to be larger than their subtended optical

angles would define. Does this have anything to do with context and/or the

distance the brain computes the fence to be at.

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