3. Impulse Sound Sources
125
diagonal membrane (Mead 1975), the air sacs (Lilly 1962), the blowhole ligament (Evans and Maderson 1973; Heyning 1989), and the monkey lips and
the spermaceti organ (Norris and Harvey 1972), as well as the nasal plugs
with their peculiar nodes (Evans and Prescott 1962).
Nasal phonation proponents had failed to demonstrate or propose a
single common and specific anatomic site upon which to focus their investigative attention. Consequently, laryngeal phonation proponents continued
to press their case (Pilleri et al. 1976; Pilleri et al. 1980a, b; Pilleri et al. 1983;
Pilleri et al.1983; Pilleri 1990) even though their experimental evidence was
weakened by a multitude of confounding factors. In 1983, Purves and Pilleri
published a book that expounded upon the laryngeal phonation hypothesis and, as recently as 1988, Reidenberg and Laitman proposed a scenario
for phonation based on morphological studies of odontocete larynges. All
these studies were largely inconclusive and without experimental support.
On the other hand, support for the nasal phonation hypothesis was, by
this time, nearly overwhelming. A survey of past work will reveal a group
of papers that collectively establish and demonstrate that impulse sounds
are generated in the odontocete forehead by the nasal apparatus. This "top
ten" list stands out because it encompasses a variety of techniques, yet
points to the same conclusion. The inexhaustive list includes: acoustic and
behavioral observations during echolocation (Norris et al. 1961); cineradiography during sound generation (Norris et al.1971); acoustic triangulation
on echolocation signals (Diercks et al. 1971); comparison of extreme
anatomic example (Norris and Harvey 1972); detailed comparison of nasal
anatomy by dissection (Mead 1975); electromyography and pressure events
during sound generation in a single species (Ridgway et al. 1980); ultrasound imaging (Mackay and Liaw 1981); multispecies comparison of electromyography and pressure events during sound generation (Amundin and
Andersen 1983); effects of helium-oxygen substitution on sound generation
(Amundin 1991b); comparison of odontocete anatomic geometry from
remote imaging (Cranford 1992a); and direct observations of the sound
generation process (Cranford et al. 1997).
In fact, it is likely that all of the internally produced impulsive sounds
(clicks, pulse bursts, and bangs) are produced in the nasal apparatus by
similar means. It is also likely that whistles are produced somewhere in the
upper nasal passages, because pressure rises in the nares before they are
generated. Generally, their modulated low-frequency characteristics and
harmonic structure point to a primarily airborne phenomenon coupled to
tissue, perhaps by resonance. The implication is not that all internally generated odontocete sounds are, without question, produced nasally, because
on rare occasions a strange sort of sound may be produced with a partially
open airway, possibly using the larynx (Ridgway et al. 1980; Cranford, personal observation). However these are not commonly produced sounds and
their phonic character seems to be unlike that of echolocation sounds.
The intractable problem of identifying the exact nasal source of sonar
sounds in odontocetes lay dormant until the latter part of the 1980s.
125
diagonal membrane (Mead 1975), the air sacs (Lilly 1962), the blowhole ligament (Evans and Maderson 1973; Heyning 1989), and the monkey lips and
the spermaceti organ (Norris and Harvey 1972), as well as the nasal plugs
with their peculiar nodes (Evans and Prescott 1962).
Nasal phonation proponents had failed to demonstrate or propose a
single common and specific anatomic site upon which to focus their investigative attention. Consequently, laryngeal phonation proponents continued
to press their case (Pilleri et al. 1976; Pilleri et al. 1980a, b; Pilleri et al. 1983;
Pilleri et al.1983; Pilleri 1990) even though their experimental evidence was
weakened by a multitude of confounding factors. In 1983, Purves and Pilleri
published a book that expounded upon the laryngeal phonation hypothesis and, as recently as 1988, Reidenberg and Laitman proposed a scenario
for phonation based on morphological studies of odontocete larynges. All
these studies were largely inconclusive and without experimental support.
On the other hand, support for the nasal phonation hypothesis was, by
this time, nearly overwhelming. A survey of past work will reveal a group
of papers that collectively establish and demonstrate that impulse sounds
are generated in the odontocete forehead by the nasal apparatus. This "top
ten" list stands out because it encompasses a variety of techniques, yet
points to the same conclusion. The inexhaustive list includes: acoustic and
behavioral observations during echolocation (Norris et al. 1961); cineradiography during sound generation (Norris et al.1971); acoustic triangulation
on echolocation signals (Diercks et al. 1971); comparison of extreme
anatomic example (Norris and Harvey 1972); detailed comparison of nasal
anatomy by dissection (Mead 1975); electromyography and pressure events
during sound generation in a single species (Ridgway et al. 1980); ultrasound imaging (Mackay and Liaw 1981); multispecies comparison of electromyography and pressure events during sound generation (Amundin and
Andersen 1983); effects of helium-oxygen substitution on sound generation
(Amundin 1991b); comparison of odontocete anatomic geometry from
remote imaging (Cranford 1992a); and direct observations of the sound
generation process (Cranford et al. 1997).
In fact, it is likely that all of the internally produced impulsive sounds
(clicks, pulse bursts, and bangs) are produced in the nasal apparatus by
similar means. It is also likely that whistles are produced somewhere in the
upper nasal passages, because pressure rises in the nares before they are
generated. Generally, their modulated low-frequency characteristics and
harmonic structure point to a primarily airborne phenomenon coupled to
tissue, perhaps by resonance. The implication is not that all internally generated odontocete sounds are, without question, produced nasally, because
on rare occasions a strange sort of sound may be produced with a partially
open airway, possibly using the larynx (Ridgway et al. 1980; Cranford, personal observation). However these are not commonly produced sounds and
their phonic character seems to be unlike that of echolocation sounds.
The intractable problem of identifying the exact nasal source of sonar
sounds in odontocetes lay dormant until the latter part of the 1980s.