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OPTICAL ILLUSIONS have once been the key to the 
psychology of vision - many configurations are known to 
effect our normal perceptual mechanism of straightness, 
parallellity, length, size, circularity, etc. (See 
Davson (1962, p. 228) who collected a dozen examples, 
Vernon (1962, title-page and p. 55, 56), and Tolansky 
(1964), a book full of Illusions). The disturbing effect 
of the simple figures and patterns are merely of 
physiological nature, as if the sloping of curved lines 
guide the eyes-to make unwanted scanning movements, or 
that the retinal image processing mechanism is activated 
in an unusual manner. 
Most illusions are rather common as to the qualitative effect, the 
quantitative aspect is probably cultural bound and varies considerably 
(Hempenius et al, 1967). 
Illusions attract attention, or is it the other way around? 
Some illusions are rather attractive as patterns, fit for fashion, 
whereas other patterns work provocating and even repulsive (Op-Art). 
I is not clear in how far the optical illusions are of relevance 
to photo-interpretation. Do the cleverly man-made patterns have 
equivalent or vague analogues in our natural environment? It would 
be interesting to hear of interpretors who discovered illusions of 
this simple physiological type in aerial photographs. If they occur, 
it is good to know the remedy against false interpretation: measure 
the wanted property! Tolansky concludes his book with: "Not "Seeing", 
but "Measuring" is believing"! (1964, p.155). See also Pseudo and 
False Vision at the end of this paragraph, where it is combined with 
these pure optical illusions.| 
The remaining cards on the yellow square are selected SHAPE + 
and arranged thus that the five facets reflect an PATTERN 
Perception 
increasing physiological influence from top to bottom: 
Perception of Space & Movement, of Shape & Patterns, of DEPTH + 
Depth & Heights, of Colour, and Pseudo & False Vision. 
Obviously, any other arrangement has its advantages and 
will also have chances to imprint the reader completely 
wrong relations. 
  
  
  
  
  
  
HEIGHT 
Perception 
  
  
  
  
COLOUR 
Perception 
  
  
  
ILLUSIONS 
Optical 
+ Pseudo