5. Acoustics and Social Behavior
251
We do not know if dolphin vocalizations are discrete, graded, or a mixture
of types. When graded acoustic repertoires exists, they may still be treated
as perceptually discrete because the resulting behavior itself can be a
distinct decision such as to flee, fight, or terminate an interaction. Changes
in pitch across a sequence of calls encodes the termination of a bout by its
relationship of signals, in this case frequency over time (Hauser and Fowler
1991). A variety of acoustic parameters can be modulated to encode information (Table 5.4) including signal duration (Ehret 1992) and frequency
modulation (May et al. 1989). Sophisticated and detailed analysis has
also been applied to visual and facial features of human behavior (Ekman
1982).
Other potential detection cues in the production of social signals
includes: (1) The directionality of sounds, which has come into question
based on the directionality of echolocation clicks and the debate over continuum and mechanisms (Murray 1997). Allowing a conspecific to locate
you in space would have distinct advantages in the wild. In many animal
communication systems the sender of information changes source levels for
different recipients and distances (Smith 1977). (2) The tactile issues of
sound reception remain unresolved regarding the role of the trigeminal
nerve and synesthetic qualities of perception. (3) The role of silence and
listening as a cue and a mode of operation. For a discussion of the
evolutionary pressures and issues of the development of communication
systems see Evans and Norris (1988) and Hauser (1996).
TABLE 5.4. Examples of acoustic and visual modulation of information
Frequency
Acoustic Downsweeps, upsweeps May, Moody, and
Stebbins 1989
Signal duration
Acoustic Ultrasonic clicks by
Ehret 1992
packets of time
Frequency
Visual
Distance between eyes
Ekman 1982
Spacing
Changes of features
Relative position
Symmetry of features
Mice
Humans
Species
Type of Modulation Modality
Examples
Reference
Macaques
Potential parameters to be modulated in a dolphin communication system.
Type of Modulation
Modality
Examples
Frequency
Amplitude/intensity
Duration/spacing
Acoustics
Visual
Tactile
Acoustic
Visual/tactile
Acoustic/visual
Tactile
Numbers of types of vocalizations per unit time
Numbers of visual signals per unit time
Rate of rubs bouts, etc.
Source levels, changes in
Rates of activity per unit time
Absolute or relative time durations of signals
or intersignal intervals.
251
We do not know if dolphin vocalizations are discrete, graded, or a mixture
of types. When graded acoustic repertoires exists, they may still be treated
as perceptually discrete because the resulting behavior itself can be a
distinct decision such as to flee, fight, or terminate an interaction. Changes
in pitch across a sequence of calls encodes the termination of a bout by its
relationship of signals, in this case frequency over time (Hauser and Fowler
1991). A variety of acoustic parameters can be modulated to encode information (Table 5.4) including signal duration (Ehret 1992) and frequency
modulation (May et al. 1989). Sophisticated and detailed analysis has
also been applied to visual and facial features of human behavior (Ekman
1982).
Other potential detection cues in the production of social signals
includes: (1) The directionality of sounds, which has come into question
based on the directionality of echolocation clicks and the debate over continuum and mechanisms (Murray 1997). Allowing a conspecific to locate
you in space would have distinct advantages in the wild. In many animal
communication systems the sender of information changes source levels for
different recipients and distances (Smith 1977). (2) The tactile issues of
sound reception remain unresolved regarding the role of the trigeminal
nerve and synesthetic qualities of perception. (3) The role of silence and
listening as a cue and a mode of operation. For a discussion of the
evolutionary pressures and issues of the development of communication
systems see Evans and Norris (1988) and Hauser (1996).
TABLE 5.4. Examples of acoustic and visual modulation of information
Frequency
Acoustic Downsweeps, upsweeps May, Moody, and
Stebbins 1989
Signal duration
Acoustic Ultrasonic clicks by
Ehret 1992
packets of time
Frequency
Visual
Distance between eyes
Ekman 1982
Spacing
Changes of features
Relative position
Symmetry of features
Mice
Humans
Species
Type of Modulation Modality
Examples
Reference
Macaques
Potential parameters to be modulated in a dolphin communication system.
Type of Modulation
Modality
Examples
Frequency
Amplitude/intensity
Duration/spacing
Acoustics
Visual
Tactile
Acoustic
Visual/tactile
Acoustic/visual
Tactile
Numbers of types of vocalizations per unit time
Numbers of visual signals per unit time
Rate of rubs bouts, etc.
Source levels, changes in
Rates of activity per unit time
Absolute or relative time durations of signals
or intersignal intervals.