Chapter 2 Principles of Stereoscopic Depth Perception and ...

2. Principles of Stereoscopic Depth Perception and Reproduction
Stelmach 1998). Temporal effects in stereoscopic vision will be discussed
in more detail in Chapter 3.
The single most common cause of stereoblindness is strabismus, the misalignment
of the two eyes. If this condition is surgically corrected at an
early age, stereoscopic vision may develop normally. Stereopsis also fails
to develop when children have good vision in only one eye, due to monocular
nearsightedness or a cataract. Obviously, stereoblind individuals can
still perceive depth, but are restricted to information sources other than
binocular disparity.
It is well-known that visual abilities deteriorate with age. The major age
differences in visual functioning are the result of two types of changes in
the structure of the eye. The first type of change is related to the transmissiveness
and accommodative power of the lens that begins to manifest
itself between the ages of 35 and 45. This affects binocular depth perception,
sensitivity to glare, and colour sensitivity. The second type of change
occurs in the retina and the nervous system, and usually starts to occur
between 55 and 65 years of age. This affects the size of the visual field,
sensitivity to low light levels, and sensitivity to flicker (Hayslip Jr. &
Panek 1989). A recent study by Norman, Dawson & Butler (2000) demonstrated
that older adults were less sensitive than younger adults to perceiving
stereoscopic depth, in particular when image disparity was higher.
Overall however, older adults performed to 75% of their expected depth
intervals, demonstrating that their stereoscopic abilities have largely been
preserved during the process of aging.
2.2.4 Cue combination in depth perception
Traditionally, monocular and binocular depth cues that are important
in achieving a representation of distance, depth and spatial structure
have been studied in isolation. This research was carried out under
the assumption that depth is processed in separate modules that correspond
to different sources of three-dimensional information. However,
it is also interesting to find out how these modules, if independent,
might be integrated to provide a coherent 3-D percept (Johnston, Cumming
& Parker 1993, Landy, Maloney, Johnston & Young 1995, Landy &
Brenner 2001). The relative efficiency and robustness of our perception
of the natural visual world suggests that we integrate multiple sources of
information into a single percept. Further interest in cue integration has
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