5. Acoustics and Social Behavior
233
all be critical information for a receiver. Some species of Cetacea use click
trains for both navigation and social purposes (Dawson 1991; Richardson
et al. 1995). Many dolphins species emit high-frequency click trains during
echolocation and orientation tasks, but the existence and use of these components in social contexts are unexplored.
2.1 Categorical Issues of Perception
Basic psychoacoustics (Nachtigall et aI., Chapter 8), physiology (Ridgway,
Chapter 6), and electrophysiological aspects of auditory processing
(Dolphin, Chapter 7) are described. There has been little experimental
work on categorical perception by dolphins to conspecific sounds or to the
critical features and parameters of artificially created sounds. Recent
anatomical (Cranford et al. 1996, and Chapter 3; Ketten, Chapter 2), structural (McGowan and Reiss 1995; Murray 1997), and behavioral (Norris et
al. 1994; Herzing 1996) evidence suggests that both our analysis techniques
and previous human categorical tendencies may not best describe delphinid
vocalizations.
The lack of consistent and perceptually accurate categories of delphinid
vocalizations may represent methodological difficulties inherent both in
the human ear and analysis equipment (Watkins 1967). Our ability to
discriminate individual clicks and high-repetition-rate pulsed sounds is
limited, and burst-pulsed sounds have, in the past, been given a variety of
names based on aural characteristics. Recent techniques in analyzing
graded signals (Murray 1997) may indicate more quantitative and comparable methods.
In addition to analyzing the psychoacoustics of dolphins, we need to
explore their "social acoustics," or use of conspecific vocalizations and
sounds. A bias toward the analysis of low-frequency, frequency-modulated
whistles has limited our understanding of the full repertoire and complexity of delphinid signal repertoires. Looking at the functional use of communication signals in the wild may be productive in assessing potential
categories used and heard by delphinids. How do dolphins perceive the
social vocalizations of their conspecifics? It has been demonstrated that dolphins discriminate pitch, duration, frequency, frequency modulation, amplitude modulation, contour, intersound interval, sequencing patterns, and
octave adjustments (Ralston and Herman 1989). However, the decoding of
these potentially salient features within delphinid social vocalizations is
unexplored.
Natural categories of vocalizations in behavioral contexts yield potential
information about boundaries for dolphin conspecific sound use. Preferred
range of frequency, duration, intensity, signals relations, and intersignal
space should be analyzed while including the behavioral context and age
classes of individuals utilizing such signals. Developmental aspects of signal
use (i.e., generalized versus refined acoustic features) are apparent in vervet
233
all be critical information for a receiver. Some species of Cetacea use click
trains for both navigation and social purposes (Dawson 1991; Richardson
et al. 1995). Many dolphins species emit high-frequency click trains during
echolocation and orientation tasks, but the existence and use of these components in social contexts are unexplored.
2.1 Categorical Issues of Perception
Basic psychoacoustics (Nachtigall et aI., Chapter 8), physiology (Ridgway,
Chapter 6), and electrophysiological aspects of auditory processing
(Dolphin, Chapter 7) are described. There has been little experimental
work on categorical perception by dolphins to conspecific sounds or to the
critical features and parameters of artificially created sounds. Recent
anatomical (Cranford et al. 1996, and Chapter 3; Ketten, Chapter 2), structural (McGowan and Reiss 1995; Murray 1997), and behavioral (Norris et
al. 1994; Herzing 1996) evidence suggests that both our analysis techniques
and previous human categorical tendencies may not best describe delphinid
vocalizations.
The lack of consistent and perceptually accurate categories of delphinid
vocalizations may represent methodological difficulties inherent both in
the human ear and analysis equipment (Watkins 1967). Our ability to
discriminate individual clicks and high-repetition-rate pulsed sounds is
limited, and burst-pulsed sounds have, in the past, been given a variety of
names based on aural characteristics. Recent techniques in analyzing
graded signals (Murray 1997) may indicate more quantitative and comparable methods.
In addition to analyzing the psychoacoustics of dolphins, we need to
explore their "social acoustics," or use of conspecific vocalizations and
sounds. A bias toward the analysis of low-frequency, frequency-modulated
whistles has limited our understanding of the full repertoire and complexity of delphinid signal repertoires. Looking at the functional use of communication signals in the wild may be productive in assessing potential
categories used and heard by delphinids. How do dolphins perceive the
social vocalizations of their conspecifics? It has been demonstrated that dolphins discriminate pitch, duration, frequency, frequency modulation, amplitude modulation, contour, intersound interval, sequencing patterns, and
octave adjustments (Ralston and Herman 1989). However, the decoding of
these potentially salient features within delphinid social vocalizations is
unexplored.
Natural categories of vocalizations in behavioral contexts yield potential
information about boundaries for dolphin conspecific sound use. Preferred
range of frequency, duration, intensity, signals relations, and intersignal
space should be analyzed while including the behavioral context and age
classes of individuals utilizing such signals. Developmental aspects of signal
use (i.e., generalized versus refined acoustic features) are apparent in vervet