PSEUDO and FALSE PERCEPTION is the label for a series of perceptual 
mistakes and complex illusions, which should not occur in professional 
photo-interpretation. They can be minimized and compensated for by 
education and experience, but not completely avoided. 
page 88 
Therefore we will mention them here, as it is felt that if the 
operator knows the traps and pitfalls, he may avoid big errors. 
We distinguish three categories of false or pseudo perceptional 
effects. 
n. 
First, there is a group caused by the limitations of the photo- 0 % 
graph, with respect to the small detail reproduction. Very small 
details are not visible in the record, due to spread and low contrast, 
but the operator should not conclude that the terrain does not 
contain such small objects, Also two white lines on the ground may be 
blurred into one line in the print; the senior photo-interpretor 
gained this knowledge by experience, a student has to be told that 
photos do not always be a true representation of the terrain. 
Examples for the second category are easily found in the domain of 
depth and height perception, where the operator may see things in an 
unusual but expected manner. Correctly presented image pairs can give 
a pseudo impression as to the height of some detail, e.g. water, which 
is expected to be lower than the surrounding land, but in the Dutch 
polders often it is higher, An inexperienced interpretor sometimes 
sees the water level in the canals below the polder level. On the 
other hand, many observers will not see houses pointing into the 2 
ground, instead of towards the sky, if the prints are presented in the e a 
wrong position (left-right reversed). This "squared" pseudo Stereoscopy 
happens frequently with familiar objects. 
The third category is purely of psychological nature: people see a 
meaning in vague objects and configurations, which was not intended by 
the designers, or simply is not there. This continuous search for a 
meaning can do harm to perception as well as be of profit to the memory, 
The man in the moon gives children a false impression; clouds and 
castles or cows are merely interesting; the Italian "leg", and Thailand 
as a part of a tiger's head may even facilitate recall of memorized 
data. Since old times, animated stellar constellations allow man to 
see order in the myriads of stars. 
As a general principle, Vernon quotes Bartlett, who stated already 
in 1932 that all our perceptions are continually characterized by 
"an effort after meaning" (Vernon, 1962, p. 239).