66
JERALD J. BERNSTEIN
olds, but the average value was the same as for the burst activity unit
(21 dB) . Units with irregular spontaneous activity were invariably not
responsive to the 100 Hz tone.
There were two responses of units to pure tone stimulation, the
adaptive (habituating) and the nonadaptive. Adaptive units responded
initially with an increased rate of discharge which was highest during
the initial phase of stimulation and then gradually decreased or habituated. This initial high discharge rate was of the same frequency as the
stimulus tone, or a multiple thereof. Adaptation occurred in two steps,
a fast adaptation within 200 msec and a slow one within 1 min. This
adaptive response was found in all units except those with spontaneous
burst activity. The nonadaptive response was found in units with spontaneous burst activity only. The spontaneous rcsponse was disrupted by
the perception of sound waves, and the unit started to follow the
response with little or no adaptation. Units usually gave the same response to each of two successive stimulations which were separated in
time by at least 2 sec. However, stimuli of long duration resulted in a
definite reduction in response to the second stimulus. The spoiitancous
activity of the unit always showed a poststimulatory depression (Enger,
1963).
A relationship was found between sound intensity and the response
of the units. After a slight initial increase in discharge rate, increased
sound pressure resulted in a single spike which followed until further
increase of sound pressure resulted in a train of impulses. At frequencies
up to 150 Hz the units followed the tone used for stimulation. At 300 Hz
or above, neither of the two stimuli elicited more than a few spikes at
following rate. There was also a relationship between the sound frequency and the response of the units. As frequency increased the three
different types of units were clearly distinguishable ( Enger, 1963).
It would appear from these data that ostariophysid fishes have pitch
discrimination based upon a synchronization between sound frequency
and neuronal discharge frequency. The ability to discriminate low and
medium tone frequencies by synchronization of ncrve impulses with
some frequency is called the “volley theory.” This theory seeks to
explain pitch discrimination as an interplay between scveral neurons,
each one following with a diffcrent phase relation to the sound waves
(Enger, 1963). The discharge rate would depend upon both frequcncy
and intensity and a number of neurons should, togcthcr, impose,on thc
central nervous system a complete following response. This has been
found to be true in Engcr’s studies (1963). However, frequency discrimination based on the following mechanism does not appear to be
extremely elaborate in the fish. There may bc other mechanisms in-
JERALD J. BERNSTEIN
olds, but the average value was the same as for the burst activity unit
(21 dB) . Units with irregular spontaneous activity were invariably not
responsive to the 100 Hz tone.
There were two responses of units to pure tone stimulation, the
adaptive (habituating) and the nonadaptive. Adaptive units responded
initially with an increased rate of discharge which was highest during
the initial phase of stimulation and then gradually decreased or habituated. This initial high discharge rate was of the same frequency as the
stimulus tone, or a multiple thereof. Adaptation occurred in two steps,
a fast adaptation within 200 msec and a slow one within 1 min. This
adaptive response was found in all units except those with spontaneous
burst activity. The nonadaptive response was found in units with spontaneous burst activity only. The spontaneous rcsponse was disrupted by
the perception of sound waves, and the unit started to follow the
response with little or no adaptation. Units usually gave the same response to each of two successive stimulations which were separated in
time by at least 2 sec. However, stimuli of long duration resulted in a
definite reduction in response to the second stimulus. The spoiitancous
activity of the unit always showed a poststimulatory depression (Enger,
1963).
A relationship was found between sound intensity and the response
of the units. After a slight initial increase in discharge rate, increased
sound pressure resulted in a single spike which followed until further
increase of sound pressure resulted in a train of impulses. At frequencies
up to 150 Hz the units followed the tone used for stimulation. At 300 Hz
or above, neither of the two stimuli elicited more than a few spikes at
following rate. There was also a relationship between the sound frequency and the response of the units. As frequency increased the three
different types of units were clearly distinguishable ( Enger, 1963).
It would appear from these data that ostariophysid fishes have pitch
discrimination based upon a synchronization between sound frequency
and neuronal discharge frequency. The ability to discriminate low and
medium tone frequencies by synchronization of ncrve impulses with
some frequency is called the “volley theory.” This theory seeks to
explain pitch discrimination as an interplay between scveral neurons,
each one following with a diffcrent phase relation to the sound waves
(Enger, 1963). The discharge rate would depend upon both frequcncy
and intensity and a number of neurons should, togcthcr, impose,on thc
central nervous system a complete following response. This has been
found to be true in Engcr’s studies (1963). However, frequency discrimination based on the following mechanism does not appear to be
extremely elaborate in the fish. There may bc other mechanisms in-