Handbook of Psychology, Volume 4: Experimental Psychology

198 Visual Perception of Objects

complement (Figure 7.20; B), or a different object from
the same category (Figure 7.20; C). The results showed that
the line-complement drawings produced just as much prim-
ing (170 ms) as the identical drawings (168 ms), and much
more than the same-name drawings (93 ms). Biederman and
Cooper (1991) argued that the stronger priming in the first
two conditions was due to the fact that the same parts were
perceived both in the identical and the line-complement
drawings.
To be sure that this pattern was not due merely to the fact
that the same object was depicted in the same pose in both of
these conditions, they performed a second experiment, in
which half of the parts were deleted in the initial priming
block (Figures 7.21; A–C). Then, in the test block, they found
that priming by the part-complement drawings was much
less (108 ms) than was priming by the identical drawings
(190 ms). In fact, part-complement priming was no different
from that in the same-name control condition (110 ms). Thus,
the important feature for obtaining significantly more prim-
ing than for mere response repetition is that the same parts
must be visible in the priming and test blocks. This result
supports the inference that object identification is mediated
by part perception.

Contextual Effects

All of the phenomena of object identification considered thus
far concern the nature of the target object itself: how typical
it is of its category, the perspective from which it is viewed,

and its size, position, orientation, and visible parts. But identi-

fication can also be influenced by contextual factors:the spa-

tial array of objects that surround the target object. One well-

known contextual effect can be demonstrated by the phrase

, which everyone initially perceives as THE CAT.

This seems entirely unproblematic—until one realizes that

the central letters of both words are actually identical and am-

biguous, midway between an Hand an A. It is therefore pos-

sible that the letter strings could be perceived as TAE CHT,

TAE CAT, orTHE CHT,but this almost never happens.

There have been several well-controlled experiments doc-

umenting that appropriate context facilitates identification,

whereas inappropriate context hinders it. In one such study,

Palmer (1975a) presented subjects with line drawings of

common objects to be identified following brief presentations

of contextual scenes (Figure 7.22). The relation between the

Second

Presentation

First

Presentation

Priming

Condition

Priming

Effect

A. Identity 168 msec.

B. Line

Complement

C. Different

Exemplar

170 msec.

93 msec.

787 msec.

710 msec.

712 msec.

880 msec.

Figure 7.20 A line-complement priming experiment (see text). Source:
From Palmer, 1999.

Second

Presentation

First

Presentation

Priming

Condition

Priming

Effect

A. Identity 192 msec.

B. Part

Complement

C. Different

Exemplar

108 msec.

110 msec.

760 msec.

762 msec.

678 msec.

870 msec.

Figure 7.21 A part-complement priming experiment (see text). Source:

From Palmer, 1999.

Figure 7.22 Stimuli from an experiment on contextual effects on object

identification (see text). Source: From Palmer, 1975a.