Optical Illusions
The description of the human visual system presented above is couched in
standard engineering terms. This could lead one to conclude that there is
sufficient knowledge of the human visual system to permit modeling the visual
system with standard system analysis techniques. Two simple examples of optical
illusions, shown in Figure 15, illustrate that this system approach would be a
gross oversimplification. Such models should only be used with extreme care.
Figure 15: Optical Illusions
The left illusion induces the illusion of gray values in the eye that the brain
"knows" does not exist. Further, there is a sense of dynamic change in the
image due, in part, to the saccadic movements of the eye. The right illusion,
Kanizsa's triangle, shows enhanced contrast and false contours neither of
which can be explained by the system-oriented aspects of visual perception
described above.