192 Visual Perception of Objects
proceed from global, coarse-grained analysis to local, fine-
grained analysis.
Further investigation suggested a more complex story,
however. Kinchla and Wolfe (1979) found that the speed of
naming local versus global forms depended on their retinal
sizes. Identifying global letters was faster than local ones
when the global stimuli were smaller than about 8–10° of
visual angle, but identifying local letters was faster than
global ones when the stimuli were larger than this. Other ex-
periments suggest that global and local levels of information
are being processed simultaneously rather than sequentially.
For example, when subjects were monitoring for a target letter
at either the global or the local levels, their responses were
faster when a target letter was present at both global and
local levels than when there was a target letter present at ei-
ther level alone (Miller, 1981). The findings on global versus
local precedence may therefore be best understood as the re-
sult of parallel processing in different size channels, with some
channels being processed slightly faster than others, rather
than as reflecting a fixed global-to-local order of processing.
Further experiments by Robertson and her colleagues
studying patients with brain damage have shown that global
and local information is processed differently in the two cere-
bral hemispheres. Several lines of evidence show that there is
an advantage for global processing in the right temporal-
parietal lobe, whereas there is an advantage for local process-
ing in the left temporal-parietal lobe (Robertson, Lamb, &
Knight, 1988). For example, Figure 7.16 shows how patients
with lesions in the left versus right temporal-parietal re-
gion copied the hierarchical stimulus shown on the left in part
A (Delis, Robertson, & Efron, 1986). The patient with right
hemisphere damage, who suffers deficits in global process-
ing, is able to reproduce the small letters making up the
global letter, but is unable to reproduce their global structure.
The patient with left hemisphere damage, who suffers deficits
in local processing, is able to reproduce the global letter, but
not the small letters that comprise it.
Further psychological evidence that global properties are
primary in human perception comes from experiments in
which discrimination of parts is found to be superior when they
are embedded within meaningful or well-structured wholes.
Not only is performance better than in comparable control
conditions in which the same parts must be discriminated
within meaningless or ill-structured contexts, but it is also su-
perior compared to discriminating the same parts in isolation.
This evidence comes from several different phenomena, such
as the word superiority effect (Reicher, 1969), the object supe-
riority effect (Weisstein & Harris, 1974), the configural orien-
tation effect (Palmer, 1980; Palmer & Bucher, 1981), and the
configural superiority effect (Pomerantz, Sager, & Stover,
1977). Although space limitations do not permit discussion of
these interesting experiments, their results generally indicate
that perceptual performance on various simple local discrimi-
nation tasks does not occur in the local-to-global order.
Exactly how these contextual effects should be interpreted
is open to debate, however. One possibility is that neural pro-
cessing proceeds from local parts to global wholes, but feed-
back from the holistic level to the earlier part levels then
facilitates processing of local elements, if they are part of
coherent patterns at the global level. This is the mechanism
proposed in the influentialinteractive activation modelof
letter and word processing (McClelland & Rumelhart, 1981;
Rumelhart & McClelland, 1982). Another possibility is that
although neural processing proceeds from local parts to
global wholes, people may gain conscious access to the re-
sults in the opposite order, from global wholes to local parts
(Marcel, 1983). Regardless of what mechanism is ultimately
found to be responsible, the results of many psychological ex-
periments rule out the possibility that the perception of local
structure necessarily precedes that of global structure. The
truth, as usual, is much more interesting and complex.Frames of ReferenceAnother set of perceptual phenomena that support the prior-
ity of global, large-scale structure in perceptual organization
is the existence of what are called reference frameeffects (see
Rock, 1990, for a review). A frame of reference in visual per-
ception is a set of assumed reference standards with respect
to which the properties of perceptual objects are encoded.
Visual reference frames are often considered to be analogousStimulus Right Damage Left DamageFigure 7.16 Drawings of hierarchical stimuli from patients with lesions
in the right hemisphere (central column) and patients with lesions in the
left hemisphere (right column). Source: From Delis, Robertson, and Efron,
1986.