180
WILLIAM N. TAVOLGA
physines: Umbra (Westerfield, 1921), Anguilla (Diesselhorst, 1938),
Macropodus ( Schneider, 1941), and the lemon shark, Negaprion (D. R.
Nelson, 1967a). In addition to possessing lower absolute thresholds, the
Ostariophysi also appear to have better discriminatory capacities, and the
possibility appears that the Weberian apparatus may play a role in frequency analysis.
The mechanism of frequency discrimination in fish was investigated
by Enger (1963) by means of neurophysiological techniques. In the
sculpin, Cottus, he demonstrated the presence of four types of neural
units, some of which displayed a following response to the acoustic
stimulus. He concluded that frequency discrimination in fishes takes place
in part by the following response, and in part by a separation into low
and high frequency sensitive units. This volley theory would not, however,
explain the fine degree of discrimination demonstrated above (Jacobs
and Tavolga, 1968). Furthermore, Enger used extremely high sound
levels up to 50 dB pb, and van Bergeijk (1967a) pointed out that such
intensities at close range would stimulate inertial receptors as well as
acoustic receptors and produce, in effect, a vertigo.
The inadequacies of a volley theory to explain human auditory discrimination led to the classic work of von B6k6sy (1960), where he demonstrated the applicability of a place theory. The place theory, however,
rests on the morphological basis of a cochlea with a basilar membrane
that is differentially responsive to different frequencies. Fish do not have
a cochlea, or anything apparently analogous to a basilar membrane. The
question of the mechanism of frequency analysis by the fish ear remains
an intriguing problem.
Much of the support for the place theory in human hearing is derived
from psychophysical data on the effects of masking noise and the presence
of a critical band (Fletcher and Munson, 1937; J. E. Hawkins and
Stevens, 1950; Scharf, 1961,1966). Some evidence has been presented that
a critical band for masking may exist in fish (Tavolga, 1967b), and van
Bergeijk (1967a,b) pointed out that a basilar membrane as such is not
essential for a place theory to apply. Any structure with some acoustic
asymmetry would respond differentially to traveling waves of different
frequencies. Even a bongo drum can generate sounds over a range of
at least an octave, and van Bergeijk (1967b) presented a most plausible
explanation for frequency analysis in the fish‘s ear. This “bongo drum
hypothesis” depends upon the fact that the saccular otolith and its underlying macula behaves as a bounded membrane with sufficient acoustic
asymmetry to resonate differentially at different frequencies.
The problem of whether a fish can detect the direction of a sound
source has been given little attention until recently. Kleerekoper and
WILLIAM N. TAVOLGA
physines: Umbra (Westerfield, 1921), Anguilla (Diesselhorst, 1938),
Macropodus ( Schneider, 1941), and the lemon shark, Negaprion (D. R.
Nelson, 1967a). In addition to possessing lower absolute thresholds, the
Ostariophysi also appear to have better discriminatory capacities, and the
possibility appears that the Weberian apparatus may play a role in frequency analysis.
The mechanism of frequency discrimination in fish was investigated
by Enger (1963) by means of neurophysiological techniques. In the
sculpin, Cottus, he demonstrated the presence of four types of neural
units, some of which displayed a following response to the acoustic
stimulus. He concluded that frequency discrimination in fishes takes place
in part by the following response, and in part by a separation into low
and high frequency sensitive units. This volley theory would not, however,
explain the fine degree of discrimination demonstrated above (Jacobs
and Tavolga, 1968). Furthermore, Enger used extremely high sound
levels up to 50 dB pb, and van Bergeijk (1967a) pointed out that such
intensities at close range would stimulate inertial receptors as well as
acoustic receptors and produce, in effect, a vertigo.
The inadequacies of a volley theory to explain human auditory discrimination led to the classic work of von B6k6sy (1960), where he demonstrated the applicability of a place theory. The place theory, however,
rests on the morphological basis of a cochlea with a basilar membrane
that is differentially responsive to different frequencies. Fish do not have
a cochlea, or anything apparently analogous to a basilar membrane. The
question of the mechanism of frequency analysis by the fish ear remains
an intriguing problem.
Much of the support for the place theory in human hearing is derived
from psychophysical data on the effects of masking noise and the presence
of a critical band (Fletcher and Munson, 1937; J. E. Hawkins and
Stevens, 1950; Scharf, 1961,1966). Some evidence has been presented that
a critical band for masking may exist in fish (Tavolga, 1967b), and van
Bergeijk (1967a,b) pointed out that a basilar membrane as such is not
essential for a place theory to apply. Any structure with some acoustic
asymmetry would respond differentially to traveling waves of different
frequencies. Even a bongo drum can generate sounds over a range of
at least an octave, and van Bergeijk (1967b) presented a most plausible
explanation for frequency analysis in the fish‘s ear. This “bongo drum
hypothesis” depends upon the fact that the saccular otolith and its underlying macula behaves as a bounded membrane with sufficient acoustic
asymmetry to resonate differentially at different frequencies.
The problem of whether a fish can detect the direction of a sound
source has been given little attention until recently. Kleerekoper and