Darwin, Donders, and Binocular Vision


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Working through my reading bucket list, “From So Simple A Beginning: The Four Great Books Of Charles Darwin” p. 1394:

“The vacant expression of the eyes is very peculiar, and at once shows when a man is completely lost in thought.  Professor Donders has, with his usual kindness, investigated this subject for me.  He has observed others in this condition, and has himself been observed by Professor Englelmann.  The eyes are not then fixed on any object, and therefore not, as I had imagined on some distant object.  The lines of vision of the two eyes even often become slightly divergent; the divergence, if the head be held vertically, with the plane of vision horizontal, amounting to an angle of 2 degrees as a maximum.  This was ascertained by observing the crossed double image of a distant object.  When the head droops forward, as often occurs with a man absorbed in thought, owing to the general relaxation of his muscles, if the plane of vision be still horizontal, the eyes are necessarily a little turned upwards, and then the divergence is as much as … between 6 and 7 degrees. Professor Donders attributes this divergence to the almost complete relaxation of certain muscles of the eyes, which would be apt to follow from the mind being wholly absorbed,  The active condition of the muscles of the eyes is that of convergence; and Professor Donders remarked, as bearing on their divergence during a period of complete abstraction, that when one eye becomes blind, it almost always after a short lapse of time, deviates outwards; for its muscles are no longer used in moving the eyeball inward for the sake of binocular vision.”

Shades of Cooper and Flax redux … when the mind is out, the eye is out: panoramic viewing associated with intermittent exotropia of the divergence excess type, and AD(H)D associated with convergence insufficiency both being exo drifts, the former resulting from (or in) divided attention, and the latter from (or in) inattention.  Planes of disregard …

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One thought on “Darwin, Donders, and Binocular Vision

  1. The observation of the eye being out when the mind is “out” is interesting. As much creative thinking as Darwin did, his mind and eye must have been out a great deal of the time. In our office, when my own mind and eye are out, I’ve also noticed that introversion blunts egocentric stereopsis, or, if you prefer, SILO–the perception of a viewed object getting smaller and coming in through Base In prism and larger and going out through Base Out prism. When a patient, who is perceiving SILO, is asked a question about a stressful area of his life, the SILO perception is often lost. Thus when the mind is out so is the eye, but when the mind is inward the perception of the world flattens. As we work with patients they generally become happier and more extroverted. I’ve hypothesized that this improvement in mood is related to increased egocentric depth perception, but it could as easily be do to improved performance in life. Or both. Or neither. That’s a pretty safe bet.

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