196 Visual Perception of Objects
Figure 7.18 Different perspective views of a horse (see text). Source:
From Palmer, Rosch, and Chase, 1981.
perspective views. Closer study indicates that this is not true.
Palmer, Rosch, and Chase (1981) systematically investigated
and documented perspective effects in object identification.
They began by having participants view many pictures of the
same object (such as the horse series in Figure 7.18) and
make subjective ratings of how much each one looked like
the objects they depicted using a scale from 1 (very like) to 7
(very unlike). Participants made the average ratings indicated
below the pictures. Other individuals were then asked to
name the entry-level categories of these pictures, as quickly
as possible, using five perspectives (from the best to the
worst) based on the ratings. Pictures rated as the best (or
canonical) perspective were named fastest, and naming
latencies gradually increased as the goodness of the views de-
clined, with the worst ones being named much more slowly
than the best ones.
It seems possible that such perspective effects could be
explained by familiarity: Perhaps canonical views are simply
the most frequently seen views. More recent studies have ex-
amined perspective effects using identification of novel ob-
jects to control for frequency effects. For example, Edelman
and Bülthoff (1992) found canonical view effects in recogni-
tion time for novel bent paper-clip objects that were initially
presented to subjects in a sequence of static views that pro-
duced apparent rotation of the object in depth (Figure 7.19).
Because each single view was presented exactly once in this
motion sequence, familiarity effects should be eliminated.
Even so, recognition performance varied significantly over
viewpoints, consistent with the perspective effects reported
by Palmer et al. (1981).
Further studies have shown that familiarity does matter,
however. When only a small subset of views was displayed in
the initial training sequence, later recognition performance
was best for the views seen during the training sequence and
decreased with angular distance from these training views
(Bülthoff & Edelman, 1992; Edelman & Bülthoff, 1992).
These results suggest that subjects may be storing specific
two-dimensional views of the objects and matching novel
views to them via processes that deteriorate with increasing
disparity between the novel and stored views.
Further experiments demonstrated that when multiple
views of the same objects were used in the training session,
recognition performance improved, but the improvement de-
pended on the relation of the test views to the training views
(Bülthoff & Edelman, 1992). In particular, if the novel test
views were related to the training views by rotation about the
sameaxis through which the training views were related to
each other, recognition was significantly better than for novel
views that were rotations about an orthogonalaxis. This sug-
gests that people may be interpolating between and extrapo-
lating beyond specific two-dimensional views in recognizing
three-dimensional objects. This possibility will be important
in this chapter’s section entitled “Theories of Object Identifi-
cation,” in which view-based theories of object categoriza-
tion are described (e.g., Poggio & Edelman, 1990; Ullman,
1996; Ullman & Basri, 1991).
A different method of study, known as thepriming para-
digm,has produced interesting but contradictory results
about perspective views. The basic idea behind this experi-
mental design is that categorizing a particular picture of an
object will be faster and more accurate if the same picture is
presented a second time, because the processes that accom-Figure 7.19 Stimuli used in an experiment on object recognition from dif-
ferent viewpoints. Source: From Bülthoff and Edelman, 1992.