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554 22. Visual Perception
can at best provide a summary of key points, and it is important to avoid over
generalizing from what is presented here. More in-depth treatments of visual per-
ception can be found in Wandell (1995) and Palmer (1999); Gregory (1997) and
Yantis (2000) provide additional useful information. A good computer vision ref-
erence such as Forsyth and Ponce (2002) is also helpful. It is important to note
that despite over 150 years of intensive research, our knowledge of many aspects
of vision is still very limited and imperfect.
22.1 Vision Science
Vision is generally agreed to be the most powerful of the senses in humans.
Vision produces more useful information about the world than does hearing,
Light:
• travels far
• travels fast
• travels in straight lines
• interacts with stuff
• bounces off things
• is produced in nature
• has lots of energy
—Steven Shafer
Figure 22.1. The nature of
light makes vision a power-
ful sense.
touch, smell, or taste. This is a direct consequence of the physics of light (Fig-
ure 22.1). Illumination is pervasive, especially during the day but also at night
due to moonlight, starlight, and artificial sources. Surfaces reflect a substantial
portion of incident illumination and do so in ways that are idiosyncratic to par-
ticular materials and that are dependent on the shape of the surface. The fact
that light (mostly) travels in straight lines through the air allows vision to acquire
information from distant locations.
The study of vision has a long and rich history. Much of what we know
about the eye traces back to the work of philosophers and physicists in the 1600s.
Starting in the mid-1800s, there was an explosion of work by perceptual psy-
chologists exploring the phenomenology of vision and proposing models of how
vision might work. The mid-1900s saw the start of modern neuroscience, which
investigates both the fine-scale workings of individual neurons and the large-scale
architectural organization of the brain and nervous system. A substantial portion
of neuroscience research has focused on vision. More recently, computer science
has contributed to the understanding of visual perception by providing tools for
precisely describing hypothesized models of visual computations and by allow-
ing empirical examination of computer vision programs. The term vision science
was coined to refer to the multidisciplinary study of visual perception involving
perceptual psychology, neuroscience, and computational analysis.
Vision science views the purpose of vision as producing information about
objects, locations, and events in the world from imaged patterns of light reach-
ing the viewer. Psychologists use the term distal stimulus to refer to the physical
world under observation and proximal stimulus to refer to the retinal image.
1
Us-
1
In computer vision, the term scene is often used to refer to the external world, while the term
image is used to refer to the projection of the scene onto a sensing plane.