Game Development Reference
In terms of quality, this law means the following in the case of vision: For a light
of low intensity perceived by the eye, a small variation in the intensity can be detected,
whereas for a light of high intensity perceived by the eye, the variation needs to be
of high intensity for it to be detected by the eye. In addition, a stimulus must last
for a minimum duration for it to be perceived. On the other hand, if a stimulation is
maintained constant, generally the sensation will disappear or will be reduced (adap-
tation phenomenon), except in the case of pain and certain nerve fibres. Besides, when
we discuss the resolution of interfaces, we will see the importance of the density of
receptors and its local variation in the sensory organs. The accuracy of human senses is
equally important to be understood to prepare suitable sensory interfaces. In general,
the absolute accuracy of senses is low in comparison with the relative accuracy since
humans have a high capacity of comparing two stimuli, for example:
It is difficult to define a colour of a single object, but it is easier to notice a slight
difference between two colours observed simultaneously;
Absolute perception of depth is difficult to estimate compared to the detection of
a slight difference in depth between two neighbouring objects;
It is difficult to quantify the absolute temperature of air or water coming in contact
with our skin. However, we easily detect a slight difference in temperature between
two fluids that are observed simultaneously.
The maximum frequency Fm of variation of a sensory stimulus perceptible by humans
is an important characteristic to be understood. Whenever it is technically possible,
the sensory interfaces should have a frequency band of 0Hz to Fm. For example, it
is recommended to display the images at the rate of more than 25 (30) images per
second 1 , which allows an animated virtual world to be viewed in a continuous flow.
Designing a good-quality visual interface is more difficult than it appears because the
human vision is a complex sense which is often undervalued. It is so natural that we
forget its complexity and its informative power. It is important to remember that the
study of this sense, like the other senses, can only be understood completely on the
basis of a study of its physical, physiological and cognitive functions.
The functioning of the visual system does not end at a static analysis of images
that are projected on the retina; it dynamically constructs a visual world. When light
falls on the retina, it is converted first into chemical and then into electric signals; the
special processes then work in parallel and break down the information. The images
formed on the two retinas are broken down according to the criteria of depth, shape,
colour and movement. However, before the extraction of shapes or depth, lower-level
information is processed and used: frequency channels 2
that work in parallel are in
1 Though there are screens that show images at this frequency, the problem of having a computer
that can calculate them and transfer them to the screen at this frequency still remains.
2 For frequencies in the spatial domain of images, see further on.