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Introduction. 
The title, fixed by Comm. VII, seems well chosen, but 
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LO if one tries to work it out, an overwhelming number of 
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Lit LIL facts and figures, of laws and illusions, of characte- 
LL. |— L-  ristics and mechanisms, of acuities and activities, 
Lt — — — 
se spreads over the floor - yes, because a table is by far 
too small. At this stage, one wonders how it will ever 
be possible to split the cards into a physiological and 
a psychological group, aren't they too intimately related and cooperating? 
And is there not a third group, or a fourth? Moreover - can we restrict 
such a treatise to photo-interpretational aspects only - do photogramme- 
rists have different eyes or brains? » e 
I think we cannot divide visual perception into Comm. VII and Comm, I 
or V, therefore, both professions may find interest in this paper. 
One remark on the word "Aspects': The purpose of this 
>> 
‘a m I 30 minutes talk should not be to list experimental facts 
of and findings, for information of this kind the pocket- 
« [ay book press supplies the market with a dozen books and 
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reprints a year. Therefore, after long hesitation, the 
@ Ww choice felt on a presentation in the form of an overall 
scheme. It is a personal view, a subjective matrix, but 
it allows to oversee the various basic and secundary 
aspects of visual perception - and, more to the point, of photo interpre- 
tation. It also makes it possible to opponents to fight this somewhat 
provocating approach, because a printed scheme can easier be attacked than e e 
a non-published line of thought. Eventually, a next victim for an invited 
paper may present, over four years, a more acceptable review. 
[ The line of thinking passes through the following stations: 
2e Basic physiological aspects — objective and measurable properties 
3e Important psychological aspects — subjective and variable properties 
4. Mixed aspects - responses to complex visual tasks 
5, Adaptation and training — changes during lifetime 
6. Technical and Human Aspects of Photo-Interpretation 
T. Some practical consequences for photo-interpretation ]