7. THE LABYRINTH
231
data are available. Poggendorf (1952) measured the absolute values of
the threshold sound pressure in dynes per square centimeter in Ameiurus
nebulosus for a range of frequencies and found a steep rise of thresholds
above 1600 Hz. At the optimum frequency of 800 Hz, the absolute threshold is as low as that for the optimum frequency of 3200 Hz in man. At
low frequencies Ameiurus is considerably more, and at high frequencies
considerably less, sensitive than man. In cyprinids, too (Stetter, 1929; von
Boutteville, 1935), the relative sensitivity to sounds in the middle frequency range was found to be of the same order of magnitude as in man.
It is eminently clear that fish in which the labyrinth is associated with
some kind of air space are very significantly more sensitive to sound than
others (Enger, 1968). They also respond to frequencies far above 1000
Hz whereas many of the others are sensitive to low frequencies only. A
specific physical link between air bladder and labyrinth such as the chain
of Weberian ossicles in the cyprinids, characinids, and silurids (Fig. 10)
appears to contribute to the superiority in sound reception of these fish
over other ostariophysan forms (Table I).
Poggendorf (1952) found that in the catfish the operative removal
of one of the Weberian ossicles, the so-called malleus, reduced the sensitivity by 30-40 dB and the destruction of the air bladder of the catfish
results in a loss of sensitivity by 13 dB at 330-750 Hz and 30 dB at 1500
Hz ( Kleerekoper and Roggenkamp, 1959).
The highest sensitivity for sound lies generally well below 1000 Hz
in nonostariophysan fish, often below 500 Hz or between 600 and 800 Hz.
It is at present doubtful whether extrusions of the air bladder toward
the labyrinth, as found in the Sparidae and Clupeidae, for instance, always confer higher sensitivity and upward extension of the audible frequency range (Dijkgraaf, 1952; Tavolga and Wodinsky, 1963, 1965;
Enger, 1968). The best auditory performance is recorded for those nonostariophysan fish in which the labyrinth is associated with closely adjacent air-filled cavities such as the Mormyridae and the Anabantidae
( TabIe I).
Apart from the study of unconditioned and conditioned behavioral
responses, audiograms can be obtained by recording the impulse responses
in the eighth nerve or the parts of the brain associated with it. This
method is of crucial importance in the investigation of the localization of
acoustic responses (vide infra), but it has yielded useful information on
sensitivity and frequency limits. Thus Enger (1968), recording from
auditory neurons in the medulla oblongata of the herring, Clupea
harengus, found a threshold of probably less than -20 dB ref. 1 pbar for
frequencies up to 1200 HZ with a steep rise in threshold above this frequency and a probable upper limit of responsiveness at 4000 Hz.
231
data are available. Poggendorf (1952) measured the absolute values of
the threshold sound pressure in dynes per square centimeter in Ameiurus
nebulosus for a range of frequencies and found a steep rise of thresholds
above 1600 Hz. At the optimum frequency of 800 Hz, the absolute threshold is as low as that for the optimum frequency of 3200 Hz in man. At
low frequencies Ameiurus is considerably more, and at high frequencies
considerably less, sensitive than man. In cyprinids, too (Stetter, 1929; von
Boutteville, 1935), the relative sensitivity to sounds in the middle frequency range was found to be of the same order of magnitude as in man.
It is eminently clear that fish in which the labyrinth is associated with
some kind of air space are very significantly more sensitive to sound than
others (Enger, 1968). They also respond to frequencies far above 1000
Hz whereas many of the others are sensitive to low frequencies only. A
specific physical link between air bladder and labyrinth such as the chain
of Weberian ossicles in the cyprinids, characinids, and silurids (Fig. 10)
appears to contribute to the superiority in sound reception of these fish
over other ostariophysan forms (Table I).
Poggendorf (1952) found that in the catfish the operative removal
of one of the Weberian ossicles, the so-called malleus, reduced the sensitivity by 30-40 dB and the destruction of the air bladder of the catfish
results in a loss of sensitivity by 13 dB at 330-750 Hz and 30 dB at 1500
Hz ( Kleerekoper and Roggenkamp, 1959).
The highest sensitivity for sound lies generally well below 1000 Hz
in nonostariophysan fish, often below 500 Hz or between 600 and 800 Hz.
It is at present doubtful whether extrusions of the air bladder toward
the labyrinth, as found in the Sparidae and Clupeidae, for instance, always confer higher sensitivity and upward extension of the audible frequency range (Dijkgraaf, 1952; Tavolga and Wodinsky, 1963, 1965;
Enger, 1968). The best auditory performance is recorded for those nonostariophysan fish in which the labyrinth is associated with closely adjacent air-filled cavities such as the Mormyridae and the Anabantidae
( TabIe I).
Apart from the study of unconditioned and conditioned behavioral
responses, audiograms can be obtained by recording the impulse responses
in the eighth nerve or the parts of the brain associated with it. This
method is of crucial importance in the investigation of the localization of
acoustic responses (vide infra), but it has yielded useful information on
sensitivity and frequency limits. Thus Enger (1968), recording from
auditory neurons in the medulla oblongata of the herring, Clupea
harengus, found a threshold of probably less than -20 dB ref. 1 pbar for
frequencies up to 1200 HZ with a steep rise in threshold above this frequency and a probable upper limit of responsiveness at 4000 Hz.