C. Daniel Geisler

Transient response of the basilar membrane measured in squirrel monkeys using the Mössbauer effect.

Measurements of the transient response of the basilar membrane were conducted using the Mossbauer effect on 33 squirrel monkeys using an experimental preparation identical to that of Rhode (1971). The stimuli were acoustic clicks 150 μsec in duration repeated 100 000–400 000 times. The amplitude of the click was varied and the responses of the malleus and of the basilar membrane at a point in the basal turn were measured. The basilar membrane’s click response is oscillatory, with a period near that of the characteristic frequency. The first few response peaks behave almost linearly with stimulus intensity, while the later peaks exhibit a pronounced nonlinearity. This behavior is shown to be consistent with the nonlinearity reported using steady‐state measurement methods (Rhode, 1971). The transient response observed in some of the preparations was very lightly damped; however, a wide range in the damping of the responses was found in the different animals. A progressive increase in the rate of decay of th...

Two‐tone suppression in auditory nerve of the cat: Rate‐intensity and temporal analyses

Responses to two-tone stimuli were recorded from auditory-nerve fibers in anesthetized cats. One tone, the suppressor, was set at a frequency above characteristic frequency and was fixed in intensity. A second tone was set at an excitatory frequency and was varied in intensity. The suppressor tone, when set at a sufficient level, always reduced the response to the excitatory tone by an amount equivalent to a fixed number of decibels, regardless of the excitatory tones intensity. Estimates of suppression magnitude were derived from shifts in rate-intensity function obtained when the suppressor tone was present relative to the functions obtained for the excitatory tone alone. When suppressor-tone intensity was increased, suppression magnitude likewise increased. When the two tones were increasingly separated in frequency, either by varying the excitor or by varying the suppressor, suppression magnitude decreased monotonically. Suppression behaved in the same manner regardless of whether suppresor tone was excitatory or nonexcitatory. When frequency separation was small enough and when both tones were above the neurons characteristic frequency, responses synchronized to low-order combination tones could be elicited. These responses usually possessed different rate-intensity characteristics and resulted in estimates of suppression magnitude which were spuriously low. When frequency separation is normalized with regard to position of traveling wave maxima within the cochlear duct, the magnitude of two-tone suppression for a given suppressor-tone intensity is seen to be frequency independent.

Model of the Displacement between Opposing Points on the Tectorial Membrane and Reticular Lamina

A quantitative model of the relative motion between the tectorial membrane and reticular lamina of the mammalian cochlea is presented. The model is proposed for the stapes side of the region of maximum deflection during sinusoidal excitation. Based on familiar concepts, the model assumes that basilar membrane deflection causes a sliding motion between the tectorial membrane and the reticular lamina. Equations for the motion between opposing points on these two structures are derived in terms of various cochlear dimensions and of the basilar‐membrane displacement. Average values of these dimensions, obtained from eight cat ears, were used to achieve numerical answers.

Peripheral Origin of Auditory Responses Recorded from the Eighth Nerve of the Bullfrog

Single‐unit recordings have been obtained from the posterior branch of the bullfrogs eighth nerve at points peripheral to the ganglion. These units can be fitted into the three classes (viz., simple, complex, and non‐auditory) that were established by Frishkopf and Goldstein in a previous study [J. Acoust. Soc. Am. 35, 1219–1228 (1963)]. The sequence in which units of different classes were encountered on any one electrode pass supports the hypothesis that the complex units originate in the amphibian papilla and the simple units originate in the basilar papilla.

A hybrid-computer model of the cochlear partition.

A hybrid‐computer simulation of the Peterson‐Bogert model of the cochlea is reported. The present simulation is shown to be a good representation of the original model except near 10 kHz. The output of the model at one point has many similarities to recent experimental data. In particular, the low‐frequency slope of the amplitude function is +6 dB/oct and the high‐frequency slope is steeply negative. The phase function shows a break from linearity near the resonance frequency and approaches +90° at low frequencies. Quantitative discrepancies between model and experimental data exist, but they could be appreciably reduced by changes in parameter values. Incorporating nonlinear membrane damping in the simulation produces nonlinear effects similar to those observed in the cochlea. With increasing intensity, the displacement peak becomes relatively reduced and occurs at a somewhat lower frequency.

The phases of basilar‐membrane vibrations

Experimental phase data from the Mossbauer‐effect measurements of basilar‐membrane vibration are given. The phase lag increased with intensity for frequencies less than best frequency, but was a decreasing function of intensity above best frequency. A series of linear minimum‐phase representations of the basilar membrane’s motion were also calculated; they show similar trends.

Model of crossed olivocochlear bundle effects

A modification of the familiar variable‐resistance electrical circuit is presented as a model of the crossed olivocochlear bundles effects mediated by efferent synapses on the outer hair cells. The models field potentials and neural discharges are compared with experimental findings.

Multiple reservoir model of neurotransmitter release by a cochlear inner hair cell

A probabilistic model is described for transmitter release from hair cells, auditory neuron EPSPs, and discharge patterns. The present model assumes that several reservoirs of neurotransmitter exist, having individual probability-of-release functions centered at successively higher intensities. The model accurately mimics the adaptation of successive EPSP amplitudes of the afferent neuron of the goldfish sacculus and, for mammalian auditory-nerve fibers, the adaptation of neural discharge rate, the saturation of onset and steady-state neural rate versus intensity, and the change in neural rate in response to incremental stimuli. The model also produces realistic interval and period histograms. The data shown support the hypothesis that multiple populations of neurotransmitter are involved in the afferent hair-cell synapses.

Hypothesis on the function of the crossed olivocochlear bundle

It is suggested that a function of the crossed olivocochlear bundle is to shift to a higher level the range of intensities to which auditory‐nerve neurons are rate sensitive. Some available behavioral data seems consistent with this hypothesis.

Auditory‐nerve fiber encoding of two‐tone approximations to steady‐state vowels

Responses to two harmonically related tones, approximating the lowest formants of nine American English vowels, were recorded from single auditory-nerve fibers. Data were compiled as period histograms for tones presented singly and in combination using the fundamental frequency of the two-tone complex as the time base. The amplitudes of the primary frequency components present in a histogram were estimated by least-squares fitting a half-wave rectified sum of the stimulating sinusoids plus a constant. Nonlinear interactions resulted for most two-tone stimuli: one tone dominated the response. When one tone was equal to best frequency, that tone always controlled discharge timing, usually suppressing the response to the second tone. Complicated interactions took place when the stimulating frequencies bracketed best frequency. The tone nearest best frequency was most effective near threshold, while higher stimulus levels usually favored the low-frequency tone. Nevertheless, the suppression mechanisms appear to provide an effective spatial separation in the cochlea for the response components to each vowel approximation. Fourier analysis of the period histograms yielded qualitatively similar results.