Nevertheless, also interpretation maps have to be percieved. The growing gap 
between remote sensing "specialists" and "users" demands a new attention for 
the visual interpretation problematic too. 
VISUAL PERCEPTION IN RELATION TO IMAGE INTERPRETATION 
1. Factors influencing the visual perception. 
Modern cognitive psychology considers the processing of the 
data we percieve as a dynamic process of structurization, involving at least 
three stages : (1) sensation, (2) perception, (3) cognition or concept-formation 
Factors influencing the perception may be grouped in three 
classes : a) physiological factors ; b) psychological factors (for example 
experience and semantic background of the observer ; attention of the observer : 
both active and passive ; expectations of the observer) ; c) properties of the 
object observed, especially shape, size, contrast, colour and texture. 
All information percieved is decoded and used immediately again in the follo- 
wing decoding. "Convergence of evidence" is the main tool to reduce misinterpre- 
tations of our complex visual sensations. The entire process happens almost 
immediate and unconciously. 
Our visual perception is perhaps the most intensively used of 
our senses. While looking at two-dimensional images, two abilities can be 
trained naturally : reading which involves a more or less systematic eye- 
scanning, and television-watching which demands fast image differentiation and 
image completion. It is important to notice that the training of text-reading 
has been overemphazed. We do not read letter by letter, but entities of words, 
sentences and even parts of the text. Because these entities change a lot in 
size and information, the eyes really jump from one entity to the other with 
a rather irregular movement . In fact we percieve holistic entities or 
"Gestalts". 
2. Gestalt-laws. 
Gestalt theory has been studied mainly in human and social 
sciences and had an important influence upon the development of the holism 
and behaviorism. In natural sciences only restricted applications are found, 
expecially in the landscape or physiognomic approach in landclassification 
(J.MABBUTT 1968) and in landscape ecology (S.TJALLINGII & A.DE VEER, 1982). 
Some brief discussion of the main background and principles of Gestalt-theory 
may be useful. 
Gestalt theory considers the primary perception as being more 
original and complete than all analyses and deduction which can be made of. 
Consequently, the "whole" or Gestalt has to be considered as being more than 
the sum of its composing parts. In other words, each part recieves its meaning 
only through the surrounding ones. the first impression when percieving a 
Gestalt is always confusion and a high degree of complexity. In fact, we recie- 
ve an overload of information and the natural reaction of our mind is?Àttempt 
to divide the Gestalt into smaller units which are less complex and thus easier 
to handle and to recognize. This stage is referred to as gradual differentiation 
which according information theory, could also be called "decoding". 
The gradual differentiation is conditioned by many factors and 
determines what information will be selected. This process continues until 
the Gestalt becomes "familiar" and identifiable. In termsof information theory 
this could be described as a halting in the decoding because a sufficient level 
of redundancy has been reached. The learning process will be achieved and the 
understanding of the Gestalt will be reached, after a restructurization of the 
differentiated parts into a meaningful system. m 
898 
Als 
One 
la: 
nec 
by 
whe 
anc 
ma 
anc 
pai 
cas 
det 
by 
frc 
ex 
squ 
con 
Thi 
ana 
bac 
exa 
exp 
eas 
of 
our 
tra 
tex 
Obs 
ste 
ima 
vis 
per 
com 
Whe 
ly