3. Impulse Sound Sources
141
acoustic features will be affected by the interactions of several factors.
Ideally, we should understand the degree of inflation and position of nearby
air spaces, the proximity of connective tissue structures, and the shape of
fatty acoustic pathways (as determined by genetics or muscle tension),
the timing of actuation for multiple sound sources, and the kinesiology of
swimming during echolocation. The rich morphological diversity and
the intricate interactive effects of these various factors greatly increase the
difficulty in understanding odontocete sonar beam formation. Computer
modeling has some potential for unscrambling this conglomeration of
factors through its capacity to allow change in selected variables while
holding others constant and simulating the resulting effects (Flint et al.
1997; Aroyan et aI., Chapter 10).
6. Future Directions
The scientific method can yield answers to focused questions; although
hard-won answers inevitably generate more questions. Such is the case with
any field of scientific endeavor. No doubt, many readers who have come
this far in the chapter have already spawned questions of their own. In these
last few paragraphs, the intent is to cast a few questions that I am curious
to explore. At the same time, this list is not exhaustive and there are many
more interesting questions on this subject than could be enumerated here.
6.1 The Sound Generation Mechanism
6.1.1 What's Shaking, Quaking, or Quivering?
The foremost void in our knowledge of this subject is that we still do not
know exactly which structure(s) are responsible for the ultrasonic peaks in
sonar click spectra. At this point, it has been demonstrated that the clicks
are generated as an air stream passes over the phonic lips and sets them
into vibration. It is also certain that this activity must set the juxtaposed
tissue complex into motion and that the consistent, repeatable nature of
the pulse waveforms suggests that the form and function of the oscillators
are also consistent, even if their timing and emphasis may be mixed to
varying degrees.
At the same time that there is consistency in dolphin sonar signals, over
years in some cases, there is also intriguing evidence that the animals maintain some adaptability and control over the signal characteristics (Au et al.
1985; Moore and Pawloski 1990). The experiments conducted by Moore and
Pawloski demonstrated that it is possible to use standard training techniques to bring the frequency and amplitude characteristics of T. truncatus
echolocation signals under stimulus control. Their results point to new
questions that can be posed regarding the degree of control over the signal.
Foremost among them concerns the degree of control over frequency
141
acoustic features will be affected by the interactions of several factors.
Ideally, we should understand the degree of inflation and position of nearby
air spaces, the proximity of connective tissue structures, and the shape of
fatty acoustic pathways (as determined by genetics or muscle tension),
the timing of actuation for multiple sound sources, and the kinesiology of
swimming during echolocation. The rich morphological diversity and
the intricate interactive effects of these various factors greatly increase the
difficulty in understanding odontocete sonar beam formation. Computer
modeling has some potential for unscrambling this conglomeration of
factors through its capacity to allow change in selected variables while
holding others constant and simulating the resulting effects (Flint et al.
1997; Aroyan et aI., Chapter 10).
6. Future Directions
The scientific method can yield answers to focused questions; although
hard-won answers inevitably generate more questions. Such is the case with
any field of scientific endeavor. No doubt, many readers who have come
this far in the chapter have already spawned questions of their own. In these
last few paragraphs, the intent is to cast a few questions that I am curious
to explore. At the same time, this list is not exhaustive and there are many
more interesting questions on this subject than could be enumerated here.
6.1 The Sound Generation Mechanism
6.1.1 What's Shaking, Quaking, or Quivering?
The foremost void in our knowledge of this subject is that we still do not
know exactly which structure(s) are responsible for the ultrasonic peaks in
sonar click spectra. At this point, it has been demonstrated that the clicks
are generated as an air stream passes over the phonic lips and sets them
into vibration. It is also certain that this activity must set the juxtaposed
tissue complex into motion and that the consistent, repeatable nature of
the pulse waveforms suggests that the form and function of the oscillators
are also consistent, even if their timing and emphasis may be mixed to
varying degrees.
At the same time that there is consistency in dolphin sonar signals, over
years in some cases, there is also intriguing evidence that the animals maintain some adaptability and control over the signal characteristics (Au et al.
1985; Moore and Pawloski 1990). The experiments conducted by Moore and
Pawloski demonstrated that it is possible to use standard training techniques to bring the frequency and amplitude characteristics of T. truncatus
echolocation signals under stimulus control. Their results point to new
questions that can be posed regarding the degree of control over the signal.
Foremost among them concerns the degree of control over frequency