Geography Reference
In-Depth Information
Stereoscopic vision
Owing to specific focus depending on where we look, we are able to closely observe objects
from both eyes directly with their neural response signals occurring at the same neighbouring
regions of the brain. This gives us fine-grained and very useful stereoscopic vision for very
specific points in space.
In an immersive projected system, to maintain a similar quality of visual image, it is
often necessary to have multiple projectors that are stereoscopically enabled. To create the
illusion each eye needs to see a slightly different view of the world and the visual system
fuses these images into one three-dimensional stereo view (Slater, Steed and Chrysanthou,
2002). The difference in the two images is called binocular disparity. In stereoscopy special
glasses are often used to fuse the images - fooling the mind's vision into believing it is
seeing three dimensions. Most stereoscopic systems, excluding holographic images, have
the disadvantage of requiring the user to focus on the screen plane, thus causing slight
discomfort if the stimulus is uncomfortable or mis-aligned.
Perfect matching of colours and intensities between displays is very difficult even with
professional colour-matching solutions. As we have shown, in the human visual system
if the same colour presented on two displays is fractionally different, this may be very
noticeable (see illusion in Figure 11.3). Large visualization systems virtually always use
multiple projectors, and this can cause an immediate issue regarding quality with regard
to matching colours and intensity values. A common solution has been to go for an edge
blended system. Blending using interpolation can be handled by extra hardware, built into
the projects or occasionally via software. This can both solve the edge issues and match
colour and brightness values. Using multiple projectors has the advantages of increasing
resolution and providing stereoscopic cues (one projector per eye), as well as providing a
method to increase brightness.
These examples show how we can see things that are not there, see things differently from
the periphery as opposed to the central focus regions of our vision and indicate the way we
fail to consider absolute variations in values, as well as creating the illusion of stereoscopic
effects.
The significance of illusion has also been considered by art. This is because the science of art
has already considered many of these illusions, and discussed some of them in great detail -
many a long time before the neurological investigation of the vision system (Gombrich,
2002; Gregory and Gombrich, 1998). For example, the movement in optical art has been
presenting work for many years, most notably within the 1950s to the 1970s. Three of the
main terms used by the Op-Art movement have direct neurological explanations (Parola,
1996; images in Figures 11.7-11.9 have been adapted from illustrations within this text).
Assimilation
Assimilation is our tendency to minimize stimuli and create uniformity. It is a simplifying
process, sometimes termed grouping with respect to proximity or similarity. Figure 11.7
illustrates how it is difficult to differentiate the lines into groups so, although they are
thinner on the left, the whole looks very similar as a single group.
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