assess whether the subject had habituated to the playback situation in
general or to the particular call type.For example,if an individual fails
to respond on the test trial,it could be for one of two reasons:it has per-
ceptually clustered the habituation and test stimuli into one category
(i.e.,they are the same) or it has habituated to all sounds coming from
this test area.Response to the posttest suggests that the first explanation
is correct:habituation and test stimuli are processed as a single,percep-
tually meaningful category.
Figure 6.4 shows results from within- and between-referent sessions.
For within-referent sessions (left panel),subjects showed a stronger
response to the harmonic arch than to the warble on the first trial.Due
to the experimental design,however,all subjects entered the test phase
after failing to respond on two consecutive trials.In the test trial,sub-
jects failed to respond even though they consistently responded in the
posttest trial.This suggests that warbles and harmonic arches are clus-
tered into one category,even though they are acoustically different.
Turning to between-referent sessions,subjects consistently responded in
the test trial,but response magnitude was contingent on the stimuli pre-
sented during the habituation series.Specifically,when subjects were
habituated to grunts,they showed a strong and highly significant
response to either the warble or harmonic arch.In contrast,when they
were habituated to the warble or harmonic arch,their response to the
grunt was weak.Putting it in anthropomorphic terms,grunts are to pota-
toes as warbles and harmonic arches are to caviar and salmon eggs.If
you have been eating potatoes for a while,a switch to caviar represents
a welcome change.In contrast,if you share my gustatory biases,a switch
from caviar to potatoes is far less exciting.Similarly,it appears rhesus
are far more interested in a switch from chow to coconut than to the
reverse.What remains a puzzle is why they have what appear to be three
acoustically distinctive calls for the same food category.Are they like
synonyms:food,chow,grub,eats? Or,are they emotional turns? When
the caviar first arrives,you might shout,“Caviar”with gusto.Once you
have had a few spoonfuls,you might say “caviar”in a more moderate
fashion.It is still caviar,however.
These results,together with those obtained from other species,suggest
one conservative interpretation and one radical one.We have sufficient
data to argue that in certain animals the acoustic morphology of the
repertoire consists of some featural components that map onto the
caller’s affective state and other components that map onto objects and
events in the external environment.Although we are in a somewhat
primitive state with respect to identifying the precise emotion or refer-
ent,we are equipped with a set of powerful tools for investigating the
problem more deeply.The more radical idea is this:although animal86 Marc D.Hauser