Vision

Vision is the sense which allows us to convert the flux of photons into biologically useful information. In these notes, we shall consider experiments (and gedanken experiments) in which the flux is modulated according to mathematical rules. One studies physical and mathematically defined activity patterns in the central nervous system (both directly and through behavior) as the dependent variable. Here is a brief outline of some aspects of vision. In these notes, we only consider vision in humans. Some animal types of vision are quite different. By all means, use whatever resources are convenient to begin to familiarize yourself with some of the topics mentioned below. These notes will be revised from time to time.


I. Much worse than a camera

A. The eye has a ``blind spot'' (which corresponds to the optic nerve);
the corresponding portion of the visual field is blank spot, into which
objects can be made to disappear.

B. The eye has only limited temporal and spatial resolution.  The
image reaching the retina goes through a lens (made of protoplasm and
so not rigid) and the actual transduction occurs via irregularly
distributed cellular processes.

C. Images formed by the eye are constantly subjected to movement, including,
among others,

  1. induced by head and body movements 
  2. saccades (small ``flicks'' in the direction of gaze), around 3/sec.
  3. ocular microtremor (OMT), around 90/sec

II Much better than a camera

A. Overlaps different detection strategies:

  1. foveal for fine detail and color (the fovea is a region of the 
      retina in which the color-sensitive cells are concentrated)
  2. peripheral for movement and light detection (falling meteors
      and dim stars are more easily seen ``from the corner of the eye'')
  3. color vs. form brain region activity show multiple representations
  4. includes output formating for memory and symbolic routines

B. Object-oriented (blind-spot is filled in through object dynamics)

C. Can achieve hyperacuity (resolution exceeds that possible with the
passive use of sensors, i.e., below the cell-spacing)

D. Can determine color even under sharply varying illumination



III How to test and explore?

A. What to study?  E.g., are hyperacuity and texture detection related
to the high-speed, low amplitude eye movement OMT?  Why is color stable? 

B. How to observe patterns in CNS? 

C. What can we learn from clinical studies?

D. Psychophysical experiments - e.g., the Butterfield effect (color
on a black-and-white-only TV)

E. Noninvasive neuroimaging

F. Mathematical simulations


IV Relation between vision and cognition (Pylyshyn, Brain and Behavioral Sci)

V AI, selectionist, connectionist and neural network models

VI Comparison of various depth perception channels

VII Design of ``terminal of the future''

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pck; 1-16-01