Behavior: Basic Psychology of the User - Foundations for Designing User-Centered Systems - page 114

Finally, you need to think carefully about your users. People are different: some
are driven mostly by extrinsic rewards (particularly money), whereas others may
do things for intrinsic rewards, such as the enjoyment or satisfaction they get from
doing them.
4.8 Summary
This chapter has provided a more detailed theory of what information users get
from their primary perceptual systems. Nearly all users interact through vision and
sound, and a deeper understanding of how users get information from these senses
provides numerous suggestions for how to improve systems.
Many designers start out with a theory that the eye is like a camera—and so it is
in some ways, having a lens and a surface on which the image is registered (the
retina). However, as with many metaphors and analogies, the use of the camera
metaphor is problematic, and is often called 'naive realism'. It is an inadequate
theory of perception.
There are some critical differences between cameras and photography and the
eye and visual perception. These differences mean that there is not a simple one-to-
one correspondence between the context of a scene and what we perceive. The
most important point is that light sensitivity varies across the whole of the retina. It
is best in the center of the retina, the fovea, and worst at the edges. The eye thus
has to move (saccade) over the visual scene all the time to see the details. Users
have to actively do this, and if they do not know where to look or do not know how
to interpret an object, they will not see what the designer intends.
If you want to view the eye as a camera, you have to view the eye as a very odd
camera. It has a more variable speed film (or sensor) to support wide changes in
light than you can buy. It has a poor focusing system (it has to be on the retina to
be well developed), and poor quality film over much of the remaining negative
(rods). The user has to move the camera to see details. If you view it this way, you
probably have a reasonable model of the eye in mind, but a very odd camera.
Hearing is more straightforward. The differences between how the ear works
and folk psychology are less drastic. The ear is a little bit more sensitive than most
might believe, and can distinguish a wide variety of sounds, but without attention
or training some sounds will not be distinguished.
In the future you will see (a) improved displays and (b) more attention given to
the integration of types of perception and action. In the first area, of improved
displays, you will see continued improvement in the quality of displays. Sound
appears to stop improving around 44 kHz sample rates; above that, increasing the
quality of the sound is not very noticeable—CDs do not sound a lot different from
MP3 files, or so many consumers believe. A similar effect will be found as displays
get better, in that the eye can still see more than a display can show. When a
display provides the details that the fovea can see across its whole surface, or when