Handbook of Psychology, Volume 4: Experimental Psychology

CHAPTER 7

Visual Perception of Objects

STEPHEN E. PALMER

179

PERCEPTUAL ORGANIZATION 179
Perceptual Grouping 180
Region Segmentation 184
Figure-Ground Organization 185
Parsing 187
Visual Interpolation 187
Parts and Wholes 191
Frames of Reference 192
OBJECT IDENTIFICATION 194
Typicality and Basic-Level Categories 195
Perspective Effects 195

Orientation Effects 197

Part Structural Effects 197

Contextual Effects 198

Visual Agnosia 199

THEORIES OF OBJECT IDENTIFICATION 200

Representing Objects and Categories 200

Comparison and Decision Processes 203

Part-Based Theories 203

View-Specific Theories 205

REFERENCES 207

Visual perception begins when light entering the eye acti-
vates millions of retinal receptors. The initial sensory state of
the organism at a given moment can therefore be completely
described by the neural activity of each receptor. Perhaps
the most astonishing thing about this description of sensory
information, aside from its sheer complexity, is how enor-
mously it differs from the nature of the visual experiences
that arise from it. Instead of millions of independent points of
color, we perceive a visual world structured into complex,
meaningful objects and events, consisting of people, houses,
trees, and cars. This transformation from receptor activity to
highly structured perceptions of meaningful objects, rela-
tions, and events is the subject matter of this chapter. It is
divided into two related subtopics: how people organize
visual input into perceptual objects and how people identify
these objects as instances of known, meaningful categories
such as people, houses, trees, and cars.
This chapter describes perceptual organization and object
identification in the visual modality only. This is not because
either organization or identification is absent in other sensory
modes—quite the contrary. But the specific stimulus infor-
mation and processing mechanisms are different enough
across modalities that it makes more sense to discuss them
separately. Some of the issues covered in this chapter for
vision are therefore also discussed in the chapter by Yost for
audition, in the chapter by Fowler for speech perception, and

in the chapter by Klatzky and Lederman for touch (all in this

volume). Indeed, the present chapter concentrates mainly

on organization and identification in static scenes because

dynamic issues are considered in the chapter by Proffitt and

Caudek in this volume for visual perception of depth and

events.

PERCEPTUAL ORGANIZATION

The term perceptual organizationrefers somewhat ambigu-

ously both to the structure of experiences based on sensory

activity and to the underlying processes that produce that per-

ceived structure. The importance and difficulty of achieving

useful organization in the visual modality can perhaps be

most easily appreciated by considering the output of the reti-

nal mosaic simply as a numerical array, in which each num-

ber represents the neural response of a single receptor. The

main organizational problem faced by the visual nervous sys-

tem is to determine object structure:what parts of this array

go together, so to speak, in the sense of corresponding to the

same objects, parts, or groups of objects in the environment.

This way of stating the problem implies that much of percep-

tual organization can be understood as the process by which

apart-whole hierarchyis constructed for an image (Palmer,

in press-b). There is more to perceptual organization than