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C D Geisler

Publications and source records attributed to C D Geisler.

At least 55 records · Page 3Linked to original sources
PubMed1982

Responses of primary auditory fibers to brief tone bursts.

Responses of primary auditory fibers to short triangularly modulated bursts of tone were obtained in the anesthetized cat. Based on discharge rate alone, the characteristics of the "response areas" obtained with these tone bursts were found to depend on the best frequency of the fiber. For a fiber with low best frequency (below 1 kHz), tones of greater than 10-ms duration had to be presented in order for the frequency resolution of the neuron to be as good as it was for long tones. For fibers with high best frequencies (above 10 kHz), tones of 2 or even 1 ms caused responses that were nearly as frequency selective as those obtained with long tones. A linear minimum-phase model based on the steady-state frequency selectivity of the fibers has been developed and shows generally comparable responses, but with some interesting exceptions. Synchronization of discharges to the waveform of the low-frequency tone bursts was measured and also shown to be generally compatible with the minimum-phase model. Trapezoidally modulated tone bursts were also used.

Acoustic Stimulation↗
PubMed1982

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 EPSP's, 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.

Action Potentials↗
PubMed1981

A model for discharge patterns of primary auditory-nerve fibers.

A model for the synapse between an inner hair cell and afferent fiber is presented. The hair cell is assumed to release 25-100 quantized neurotransmitter packets per sec. Each packet causes an exponentially shaped unitary excitatory postsynaptic potential (EPSP). Any particular afferent fiber is assumed to have a discharge threshold either above or below that of the unitary EPSP. Using any reasonable distribution of threshold values, the model produces a bimodal distribution of spontaneous discharge patterns. The group producing high spontaneous rates (greater than 20/sec) all have discharge thresholds below the unitary EPSP level, while the low-spontaneous group (rates less than 20/sec) all have discharge thresholds above that level. Other physiologically realistic results are obtained from the two groups.

Animals↗
PubMed1981

Auditory-nerve fiber responses to frequency-modulated tones.

Discharge patterns of cat auditory-nerve fibers were obtained in response to frequency-modulated (FM) tones. The rate and direction of frequency change and the sound-pressure level of the sweep tones were systematically varied, and aspects of the discharge patterns were compared to aspects of the discharge patterns elicited by pure tones. Increases in SPL broaden the frequency range over which the fiber responds, as is the case with pure-tone stimuli. Increases in the rate of frequency change have little effect on frequency selectivity for the rates tested. In general, the pure-tone response area is a good predictor of the response area to FM. Although approximately equal numbers of spikes are elicited by ascending and descending sweeps, the discharge patterns differ slightly; for each direction of frequency change, the FM response area is shifted in the direction of the earliest-occurring frequencies. Most of this shift can be accounted for by neural adaptation. This asymmetry is small, relative to those observed in the central nervous system.

Acoustic Stimulation↗
PubMed1980

Responses of primary auditory fibers to combined noise and tonal stimuli.

Responses to tonal stimuli, with and without added noise of different bandwidths, were obtained from anesthetized cat auditory-nerve fibers using glass micropipettes. When low-pass noise with a cut-off frequency at least one octave below best (or characteristic) frequency was used, every fiber tested at high enough intensities showed a suppression of the tonal response. This suppression did not cause a general reduction of neural responsiveness to all sounds, but rather took the general form of a frequency-specific reduction in the effective intensity of the tonal stimuli. The suppression mechanism(s) involved thus adjust the sensitivity of these fibers to cover higher intensity ranges in the presence of noise. The frequency of the most severely affected tones was always at or near best frequency, in confirmation of previous work (Abbas, P.J. and Sachs, M.B. (1976): J. Acoust. Soc. Am. 59, 112-122; Kiang, N.Y.-S. and Moxon, E.C. (1974): J. Acoust. Soc. Am. 55, 620-630). The suppresson is a direct but highly nonlinear function of the intensity and bandwidth of the noise. The effects on tonal response of wide-band noise were more variable, sometimes causing suppression similar to that induced by the low-pass noise and sometimes causing only 'strong-signal capture' effects. A model of noise-induced suppression has been developed whereby each sound produces both an excitatory effect, sharply tuned at best frequency, and a suppressive effect, which also has its lowest threshold at best frequency but is more broadly tuned.

Acoustic Stimulation↗
PubMed1980

Voltage-dependent elements are involved in the generation of the cochlear microphonic and the sound-induced resistance changes measured in scala media of the guinea pig.

The injection of d.c. current into scale media alters both the cochlear microphonic (CM) and the acoustically synchronized changing resistance (CR) measured in scala media. Positive current increases the CM and decreases the CR. The effect on the CM is greatest at high sound pressure level (SPL), whereas the effect on CR is greatest at low SPL. Negative current has a similar but opposite effect on both the CM and the CR. The results suggest that a voltage-dependent nonlinear element exists in cochlear hair cells.

Acoustic Stimulation↗
PubMed1980

Stimulation of efferents alters the cochlear microphonic and the sound-induced resistance changes measured in scale media of the guinea pig.

Electrical stimulation of the crossed olivo-cochlear bundle (COCB) increases both the cochlear microphonic and the acoustically synchronized changing resistance (CR) and it causes a decrease in the electrical impedance of scala media of the guinea pig. The similarity between the change in CR due to COCB stimulation and the change in CR due to negative d.c. polarization (Mountain, D.C., Hubbard, A.E. and Geisler, C.D. (1980): Hearing Res. 3, 215-229) suggests that the CR is dependent on the hair cell membrane potential measured with respect to scale tympani.

Acoustic Stimulation↗
PubMed1980

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.

Animals↗
PubMed1980

Sound-induced resistance changes in the inner ear.

A new technique for measuring sound-induced resistance changes (CR) in scala media in response to pure-tone stimuli by injecting alternating current into guinea-pig cochleas was reported recently [C.D. Geisler et al., J. Acoust. Soc. Am. 61, 1557-1566 (1977)]. Detailed measurements with this technique indicate that while the CR behaves approximately as does the cochlear microphonic (CM) there can be very significant differences between the two variables under certain experimental conditions. Computer analysis of simultaneously recorded CR voltage components and CM indicates that the CR harmonics, in both amplitude and phase, behaved differently with sound intensity and with asphyxia than did the CM harmonies (A.E. Hubbard et al., J. Acoust. Soc. Am 66, 431-445 (1979)]. Direct current injection and stimulation of the crossed olivocochlear bundle (COCB) indicate further differences between CM and CR (D.C. Mountain, Ph.D. thesis, University of Wisconsin-Madison, 1978). Positive dc caused a relative augmentation of CM that grew with sound intensity, and a relative reduction in CR magnitude that decreased with intensity. Negative dc caused effects of similar magnitude but opposite sign. COCB stimulation caused enhancement of both CM and CR. Present models cannot account quantitatively for these results.

Acoustic Stimulation↗
PubMed1979

Further studies on the Schroeder-Hall hair-cell model.

The Schroeder-Hall hair-cell model [M.R. Shroeder and J.L. Hall, "Model for mechanical to neural transduction in the auditory receptor," J. Acoust. Soc. Am. 55, 1055-1060 (1974] was further explored using additional stimulus waveforms and analysis techniques. The model is shown to have other interesting properties such as the ability to generate realistic two-tone interactions. Amended to limit the growth of transmitter release, the model also produces realistic adaptation and incremental response data. Other amendments improved high-intensity period histogram waveshapes. No one amendment, however, allowed the model to produce both realistic adaptation curves as well as period histogram waveforms that faithfully mimicked physiological data.

Hair Cells, Auditory↗
PubMed1979

The spectral content of the cochlear microphonic measured in scala media of the guinea pig cochlea.

Cochlear microphonic (CM) in response to low-frequency tonal stimuli, measured as a function of sound-pressure level (SPL) in scala media of the guinea pig cochlea, was averaged and Fourier analyzed. The slope of the amplitude of the Nth CM harmonic versus sound intensity in log-log coordinates was approximately N (1 less than or equal to N less than or equal to 5) in the first three cochlear turns, but notable variations on such a slope rule were found to apply to CM in turn I. CM harmonic phases plotted versus SPL were found to group into two distinctive categories expressly delimited by whether the order of the harmonic was even or odd. Some difference between CM recorded between scala media and scala tympani and recorded between scala media and the animal's neck could be attributed to neural contamination. We also found CM in its saturation region to have a hysteretic relation to the input sound pressure. At high sound levels, large, physiologically produced acoustic harmonics existed at the animal's eardrum. Our data support an asymmetrical, saturating, single-valued nonlinearity as a model for CM generation at low sound levels. At higher sound levels a different, more complex, hysteretic nonlinearity seems mandatory.

Acoustic Stimulation↗
PubMed1979

Comparison of the spectra of the cochlear microphonic and of the sound-elicited electrical impedance changes measured in scala media of the guinea pig.

The harmonic structure of the cochlear microphonic (CM) and that of a sound-elicited signal which we have considered as an (apparent) changing resistance (CR) were simultaneously determined in scala media of the first turn of the guinea pig cochlea. We analyzed our data in the context of the Davis variable resistance hair-cell model (1965), which predicts CM and CR to be proportional to each other. But, plotted as functions of the sound-pressure level, CM and CR were found to have qualitatively similar but quantitatively disproportionate spectra. The preparations with the highest endolymphatic potential showed the least correspondence between the spectra of the two measured quantities. The phase angles of the fundamental components in CM and CR were equal within approximately 10 degrees, but the phase of the even harmonics of the two independent measures commonly differed by approximately 180 degrees at lower SPLs. Although most data were collected using 160-Hz tonal stimulation, tones with frequencies up to 1280 Hz produced qualitatively similar results. The CM and the CR both varied slightly with the level of the alternating current used to probe the CR. Considered on a quantitative basis, consistent with the accuracy of our measurements, any model which reduces to a fixed source, a fixed resistance, and a single linear, time-varying resistance cannot mimic the most significant, commonly found aspects of our CM and CR data. An alternate model incorporating a nonlinear, time-invariant resistance is able to account for some of the data. The output of the model is correctly considered a (time) changing resistance, or apparent changing resistance; but the model demonstrates that similar experimental results are not necessarily evidence for a time-varying resistor as originally proposed by Davis.

Acoustic Stimulation↗
PubMed1978

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 tone's 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 neuron's 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.

Acoustic Stimulation↗
PubMed1978

Auditory nerve fiber response to wide-band noise and tone combinations.

1. Responses of single auditory nerve fibers to combinations of noise and tone were obtained. The results were found to depend on the relative effectiveness of each stimulus when presented alone. 2. When the response rate to one stimulus presented alone was considerably greater than the response rate to the other stimulus presented alone, the more effective stimulus dominated the responses when the two stimuli were combined. The more effective stimulus captured the response of the neuron. Thus, intense noise was found to mask responses to weaker tones, and intense tones were found to mask responses to weaker noise. This masking of the weaker stimulus is thought to enhance the signal-to-noise ratio of the most prominent response component. 3. When the two stimuli had similar effectiveness, complex interactions occurred. When the tone was near best (characteristic) frequency, partial summation effects occured. The tone partially suppressed the responses to the noise if other frequencies were used. Tones above best frequency caused particularly powerful suppression. 4. The bandwidth of the noise was varied somewhat. While bandwidth affected the effectiveness of the noise, it did not affect the types of interactions observed. 5. For a neuron which was essentially silent in the absence of acoustic stimuli, adding a weak level of noise lowered the threshold of responsiveness to the tone.

Animals↗