called cocktail party effect (Cherry and Taylor 1954) and more generally in
terms of auditory stream segregation (Bregman 1990). Despite its obvious
importance, only a relatively few studies have addressed this phenomenon
in nonhumans (Fay 1998; MacDougall-Shackleton et al. 1998b). Only a
single study has examined stream segregation using natural stimuli (Hulse
et al. 1997). It may be that the acoustic parameters governing stream segregation of acoustic communication signals vary dramatically from those
involved in the segregation of pure tone sequences. In any case, the basic
ability is likely to be widespread, and initial data suggest that such processing occurs at or before the level of the primary auditory cortex
(Fishman et al. 2001). Recent reviews cover both stream segregation and
the closely related topic of auditory spatial localization in nonhuman
animals (Feng and Ratnam 2000; Klump 2000), and we do not address them
further. Most research using conspecific communication signals assumes
that the test subject has successfully extracted the target signal by presenting stimuli in isolation. This also assumes independence of segregation and
subsequent classification behaviors.
Once an auditory object is formed, a second general class of behavior
emerges as these objects or events are organized into behaviorally relevant
classes. For example, females might rely on male vocalizations to help
choose a mate and therefore are likely, under appropriate conditions,
to distinguish between heterospecific and conspecific male vocalizations.
The presence of such distinctions, or class boundaries, implies discrimination among multiple auditory objects along with an associative link between
the resulting internal representation and some behavioral response.
At the behavioral level, these processes are collectively referred to as
recognition.
According to this definition, recognition can take many forms, depending on the specific boundaries between classes of vocalizations. Often these
acoustic boundaries correspond to other behaviorally relevant distinctions
(e.g., species, sex, kin, and individual). That is, they are not arbitrary but
rather reflect the ecology of the particular animal under consideration.
Although not all forms of recognition behavior are likely to be mediated
by the same neural mechanisms, there are likely to be shared features across
species, particularly when relevant classification requires discrimination
among subsets of conspecific vocalizations. Recognition based on intraspecific acoustic variation is widespread (Boughman and Moss, Chapter 4),
and several of the most recent examples from different taxa are given
below.
3.2. Intraspecific Recognition Behavior
One common distinction within species is in the degree of relatedness
between individuals. Vocal recognition often follows these lines. For
example, king penguin chicks, Aptenodytes patagonicus, and emperor
7. Neuroethology of Vocal Communication
355
terms of auditory stream segregation (Bregman 1990). Despite its obvious
importance, only a relatively few studies have addressed this phenomenon
in nonhumans (Fay 1998; MacDougall-Shackleton et al. 1998b). Only a
single study has examined stream segregation using natural stimuli (Hulse
et al. 1997). It may be that the acoustic parameters governing stream segregation of acoustic communication signals vary dramatically from those
involved in the segregation of pure tone sequences. In any case, the basic
ability is likely to be widespread, and initial data suggest that such processing occurs at or before the level of the primary auditory cortex
(Fishman et al. 2001). Recent reviews cover both stream segregation and
the closely related topic of auditory spatial localization in nonhuman
animals (Feng and Ratnam 2000; Klump 2000), and we do not address them
further. Most research using conspecific communication signals assumes
that the test subject has successfully extracted the target signal by presenting stimuli in isolation. This also assumes independence of segregation and
subsequent classification behaviors.
Once an auditory object is formed, a second general class of behavior
emerges as these objects or events are organized into behaviorally relevant
classes. For example, females might rely on male vocalizations to help
choose a mate and therefore are likely, under appropriate conditions,
to distinguish between heterospecific and conspecific male vocalizations.
The presence of such distinctions, or class boundaries, implies discrimination among multiple auditory objects along with an associative link between
the resulting internal representation and some behavioral response.
At the behavioral level, these processes are collectively referred to as
recognition.
According to this definition, recognition can take many forms, depending on the specific boundaries between classes of vocalizations. Often these
acoustic boundaries correspond to other behaviorally relevant distinctions
(e.g., species, sex, kin, and individual). That is, they are not arbitrary but
rather reflect the ecology of the particular animal under consideration.
Although not all forms of recognition behavior are likely to be mediated
by the same neural mechanisms, there are likely to be shared features across
species, particularly when relevant classification requires discrimination
among subsets of conspecific vocalizations. Recognition based on intraspecific acoustic variation is widespread (Boughman and Moss, Chapter 4),
and several of the most recent examples from different taxa are given
below.
3.2. Intraspecific Recognition Behavior
One common distinction within species is in the degree of relatedness
between individuals. Vocal recognition often follows these lines. For
example, king penguin chicks, Aptenodytes patagonicus, and emperor
7. Neuroethology of Vocal Communication
355