7. THE LABYRINTH
235
Hz) were recorded from nerve twigs from the anterior part of the sacculus macula, from the unloaded part of the utriculus macula (lacinia
utriculi), and from the macula neglecta situated in the roof of the sacculus cavity. No such vibration responses were found in the lagena which
proved to contain gravity receptors only. A cranial window, the fenestra
of Scarpa, is anatomically related to the vicinity of the sacculus and the
macula neglecta, and it is quite possible that the vibration sensitivity of
part of the utriculus macula may not be utilized by the animal.
It must not be overlooked that the participation of the lateral line
in the elicitation of responses to sound is to be seriously considered in
cases where the sound source is situated near enough to give rise to
water displacement in the vicinity of the fish. The lateral line and its
function is discussed elsewhere (Chapter 8 by Flock). However, it
must be stated here that in a number of the experiments especially with
elasmobranchs near-field effects could not be excluded. In the lower
frequency range to which elasmobranchs are chiefly sensitive such
near-field effects extend for a considerable distance from the source. At
100 Hz, for instance, or a wavelength of 15 meters the far- and near-field
effects are equal at a distance of 2.4 meters from the source (Enger,
1968). It is therefore imperative, especially in the study of directional
responses, to make clear the conditions of stimulation obtaining the
experiments.
Accepting the effect of a basic vibration sensitivity of the otolith
organs in fishes, the great differences in the acuity of hearing and the
power of pitch discrimination found to exist between the Ostariophysi
and the rest may well result entirely from the elaboration of resonators
and sound conductors associated with the labyrinth. The remarkable fact
of a highly developed power of pitch discrimination in the absence of a
morphologically obvious frequency analyzer still remains one of the
problems of fish physiology. It is probable, however, that this may be
based upon a synchronization between the stimulus frequency and the
frequency of the impulse discharge. The fact that pitch discrimination
is absent above 800 Hz would be compatible with this assumption on
neurological grounds ( Lowenstein and Roberts, 1951).
That there may after all be differential frequency sensitivity within
the area of a given otolith organ has been claimed by Enger (1963). In
an analysis of the responses of single “auditory” neurons in the brain of
the sculpin, Cottus scorpius, Enger found four types of neurons classified
by their resting activity which responded differently to sound. Type I
had a regular resting activity but did not respond to sound, but Enger
believes these to be static units. Type I1 units had no resting discharge
and responded to sounds below 200 Hz. Type I11 units had an irregular
235
Hz) were recorded from nerve twigs from the anterior part of the sacculus macula, from the unloaded part of the utriculus macula (lacinia
utriculi), and from the macula neglecta situated in the roof of the sacculus cavity. No such vibration responses were found in the lagena which
proved to contain gravity receptors only. A cranial window, the fenestra
of Scarpa, is anatomically related to the vicinity of the sacculus and the
macula neglecta, and it is quite possible that the vibration sensitivity of
part of the utriculus macula may not be utilized by the animal.
It must not be overlooked that the participation of the lateral line
in the elicitation of responses to sound is to be seriously considered in
cases where the sound source is situated near enough to give rise to
water displacement in the vicinity of the fish. The lateral line and its
function is discussed elsewhere (Chapter 8 by Flock). However, it
must be stated here that in a number of the experiments especially with
elasmobranchs near-field effects could not be excluded. In the lower
frequency range to which elasmobranchs are chiefly sensitive such
near-field effects extend for a considerable distance from the source. At
100 Hz, for instance, or a wavelength of 15 meters the far- and near-field
effects are equal at a distance of 2.4 meters from the source (Enger,
1968). It is therefore imperative, especially in the study of directional
responses, to make clear the conditions of stimulation obtaining the
experiments.
Accepting the effect of a basic vibration sensitivity of the otolith
organs in fishes, the great differences in the acuity of hearing and the
power of pitch discrimination found to exist between the Ostariophysi
and the rest may well result entirely from the elaboration of resonators
and sound conductors associated with the labyrinth. The remarkable fact
of a highly developed power of pitch discrimination in the absence of a
morphologically obvious frequency analyzer still remains one of the
problems of fish physiology. It is probable, however, that this may be
based upon a synchronization between the stimulus frequency and the
frequency of the impulse discharge. The fact that pitch discrimination
is absent above 800 Hz would be compatible with this assumption on
neurological grounds ( Lowenstein and Roberts, 1951).
That there may after all be differential frequency sensitivity within
the area of a given otolith organ has been claimed by Enger (1963). In
an analysis of the responses of single “auditory” neurons in the brain of
the sculpin, Cottus scorpius, Enger found four types of neurons classified
by their resting activity which responded differently to sound. Type I
had a regular resting activity but did not respond to sound, but Enger
believes these to be static units. Type I1 units had no resting discharge
and responded to sounds below 200 Hz. Type I11 units had an irregular