51 8
GOUTEUX, THINUS-BLANC, AND VAUCLAIR
is their small size. As a matter of fact, when we tested the effects
on performance of cue size (Experiments 6 and 7), we observed
that monkeys were able to correctly reorient only with large or
intermediate-sized cues (entire wall of Experiments 2 and 3; Ex-
periment 7) but not with the small-size cues used in Experiment 6
(and also in Experiments 3 and 4 but at different locations). Data
of Experiments 5 and 8 support this view. Indeed, monkeys were
confronted to the same experimental environment, except for the
size of the corner cues. In Experiment 4 (small comer cues),
subjects failed to correctly locate the rewarded box, but with larger
cues, they perfectly succeeded in the task.
Taken together, these results strongly suggest that the use of
nongeometric information to reorient is tightly related to physical
intrinsic characteristics (e.g., the size) and to the stable status of the
informative elements. According to our data (Experiments 6, 7,
and 8), even when the presence of a cue is obvious for the
monkeys, they are unable to use it to reorient unless its size is large
enough. It should be mentioned that children also seem to use
nongeometric cues only when these cues appear as stable land-
marks and are also of a sufficiently large size. (Even if the truck
toy used in Hermer & Spelke's experiment was not considered as
immobile, we can also suggest that its size could have played an
important role for being treated as a landmark.)
In short, the data of the present experiments bring some ques-
tions to the notion of a geometric module for spatial processing.
Some studies have shown that a conspicuous local cue (a colored
wall, for instance) is neglected by toddlers or by human adults who
perform a dual-task (Hermer-Vasquez et al., 1999). Those data fit
the properties of such a module well. However, in other experi-
ments salient physical features of the local cues appear likely to
induce a further processing (Acredolo, 1990). In the latter case, an
explanation in terms of modular processing is inadequate, because
modules are defined with properties such as encapsulation or
impenetrability. We propose that the salience of local information
may lead subjects to take it into account, but only in a second
phase, that is, after a modular but sometimes insufficient process-
ing. The fact that geometric features are never neglected suggests
that their processing is automatic and systematic. In contrast, using
local information to disambiguate the situation would depend on
the properties of the local cues themselves and perhaps also on
other interacting factors such as motivation, age of the subjects,
and so forth.
Also, concerning our experimental situation, an alternative ex-
planation to the modularity hypothesis could be formulated. We
suggest that instead of automatically processing the geometric
information of the environment, the rhesus monkeys could use a
more basic procedure to reorient. This procedure may be based on
some perceptual mechanisms that could encode different types of
spatial information, according to their respective salience in the
environment. In effect, when no landmarks were available in the
experimental room (e.g., Experiment 1), monkeys relied on the
most salient and perceptible spatial information available, namely
the shape of the room. This geometric information was also the
only information to be used even when small-size cues were
available in the room (Experiments 4, 5, and 6), suggesting that
when the salience or weight of perceptible information is not
sufficient, monkeys ignore it. This prediction is confirmed by
results of Experiments 2, 3, 7, and 8. In these experiments, the
relative weight of nongeometric information compared with the
weight of geometric information provided by the shape of the
room is sufficient to allow the monkeys to rely simultaneously on
these two types of spatial information, leading the reorientation
mechanisms to be more efficient. In sum, we suggest that, in
addition to referring to a modular processing, our results could also
be explained in terms of perceptual attractiveness.
Despite the fact that nonhuman primates are able to combine
geometric and nongeometric spatial information without language,
this finding does not allow us to conclude that humans do not solve
the disorientation problem by encoding the available information
linguistically. In fact, data from human adults and children (see
Hermer-Vasquez et al., 1999) suggest that language is necessary to
human beings for combining these two different aspects of core
knowledge. This specific human mechanism, which is based on
language, may have emerged across evolution and could account
for the better flexibility of the human being with respect to other
mammals. However, this hypothesized mechanism and its func-
tioning required further investigations. It is precisely the compar-
ative approach with nonhuman primates that could help us to better
understand this human peculiarity.
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