Md. Hauser et al., ORIENTING ASYMMETRIES IN RHESUS-MONKEYS - THE EFFECT OF TIME-DOMAIN CHANGES ON ACOUSTIC PERCEPTION, Animal behaviour, 56, 1998, pp. 41-47
Humans exhibit left-hemisphere dominance for processing spoken languag
e, a species-specific acoustic signal characterized by a suite of spec
tre-temporal parameters. Some nonhuman primates (genus Macaca) also ex
hibit left-hemisphere dominance for processing their species-specific
vocalizations, as evidenced by right-ear biases in orienting and react
ion-time studies, and more damaging effects from left- than right-hemi
sphere lesions. Little, however, is known about the acoustic features
underlying such biases, We conducted field playback experiments on adu
lt rhesus monkeys, Macaca mulatta, to determine whether asymmetries in
perception (measured as an orienting bias) are sensitive to changes i
n the temporal characteristics of their calls. If the observed right-e
ar bias for perceiving conspecific calls (Hauser & Andersson 1994, Pro
ceedings of the National Academy of Sciences, U.S.A., 91, 3946-3948) d
epends upon particular acoustic parameters, then experimental manipula
tions beyond the species-typical range of signal variation will cause
a change in perceptual asymmetry, either reversing the pattern (i.e. r
ight to left ear) or wiping it out (i.e. no asymmetry). We presented m
anipulated and unmanipulated exemplars of three pulsatile call types w
ithin the rhesus repertoire: an affiliative signal 'grunt', an alarm s
ignal 'shrill bark', and a mating signal 'copulation scream'. Signal m
anipulations involved either (1) a reduction of the interpulse interva
l to zero or the population minimum or (2) an expansion of the interpu
lse interval to the population maximum, or two times the maximum. For
the grunt and shrill bark, manipulations of interpulse interval outsid
e the range of natural variation either eliminated the orienting bias
or caused a shift from right- to left-ear bias. For the copulation scr
eam, however, a right-ear bias was observed in response to all stimuli
, manipulated and unmanipulated. Results show that for some call types
within the repertoire, temporal properties such as interpulse interva
l provide significant information to listeners about whether the signa
l is from a conspecific or not. We interpret the orienting bias as evi
dence that hemispheric asymmetries underly this perceptual effect. (C)
1998 the Association for lire Study of Animal Behaviour.