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C D Geisler

Publications and source records attributed to C D Geisler.

At least 37 records · Page 2Linked to original sources
PubMed1990

Estimation of eardrum acoustic pressure and of ear canal length from remote points in the canal.

Sound pressure distributions in the human ear canal, whether unoccluded or occluded with ear molds, were studied using a probe tube technique. On average, for frequencies below 6 kHz, the measuring probe tube had to be placed within 8 mm of the vertical plane containing the top of the eardrum (TOD), determined optically, in order to obtain sound pressure magnitudes within 6 dB of "eardrum pressure." To obtain that accuracy in all of the eight subjects studied, the probe had to be within 6 mm of the TOD. Since probe location relative to the drum has to be known, a purely acoustic method was developed which can be conveniently used to localize the probe-tip position, utilizing the standing wave property of the sound pressure in the ear canal. The acoustically estimated "drum location" generally lay between the optically determined vertical planes containing the TOD and the umbo. On average, the "drum location" fell 1 mm medial to the TOD. Of the 32 estimates made acoustically in various occluded and unoccluded conditions in 14 subjects, 30 estimates lay within a +/- 2-mm range of this average.

Acoustic Stimulation↗
PubMed1989

Responses of "high-spontaneous" auditory-nerve fibers to consonant-vowel syllables in noise.

Responses of "high-spontaneous" single auditory-nerve fibers in anesthetized cat to nine different spoken stop and nasal consonant-vowel syllables presented in four different levels of speech-shaped noise are reported. The temporal information contained in the responses was analyzed using "composite" spectrograms and pseudo-3D spatial-frequency plots. Spectral characteristics of both consonant and vowel segments of the CV syllables were strongly encoded at S/N ratios of 30 and 20 dB. At S/N = 10 dB, formant information during the vowel segments was all that was reliably detectable in most cases. Even at S/N = 0 dB, most vowel formants were detectable, but only with relatively long analysis windows (40 ms). The increases (and decreases) in discharge rate during various phases of the responses were also determined. The rate responses to the "release" and to the voicing of the stop-consonant syllables were quite robust, being detectable at least half of the time, even at the highest noise level. Comparisons with psychoacoustic studies using similar stimuli are made.

Animals↗
PubMed1989

The responses of models of "high-spontaneous" auditory-nerve fibers in a damaged cochlea to speech syllables in noise.

The responses of four high-spontaneous fibers from a damaged cat cochlea responding to naturally uttered consonant-vowel (CV) syllables [m], [p], and [t], each with [a], [i], and [u] in four different levels of noise were simulated using a two-stage computer model. At the lowest noise level [+30 dB signal-to-noise (S/N) ratio], the responses of the models of the three fibers from a heavily damaged portion of the cochlea [characteristic frequencies (CFs) from 1.6 to 2.14 kHz] showed quite different response patterns from those of fibers in normal cochleas: There was little response to the noise alone, the consonant portions of the syllables evoked small-amplitude wide-bandwidth complexes, and the vowel-segment response synchrony was often masked by low-frequency components, especially the first formant. At the next level of noise (S/N = 20 dB), spectral information regarding the murmur segments of the [m] syllables was essentially lost. At the highest noise levels used (S/N = +10 and 0 dB), the noise was almost totally disruptive of coding of the spectral peaks of the consonant portions of the stop CVs. Possible implications of the results with regard to the understanding of speech by hearing-impaired listeners are discussed.

Acoustic Stimulation↗
PubMed1987

Responses of auditory-nerve fibers to nasal consonant-vowel syllables.

Responses of single auditory-nerve fibers in anesthetized cat to spoken nasal consonant-vowel syllables were recorded. Analyses in the form of spectrograms and of three-dimensional spatial-time and spatial-frequency plots were made. Among other features, formant transitions are clearly represented in the fibers' response synchronization properties. During vocalic segments, especially those in /mu/and/ma/, at a stimulus level near 75 dB SPL, a strong dominance in the responses by frequencies near the second formant (F2) is found for most fibers whose characteristic frequencies (CFs) are at or above F2. In contrast, at more moderate levels, the same fibers may show response synchrony to frequencies closer to their own CFs. There are significant differences in the response properties of high and low/medium-spontaneous-rate fibers.

Animals↗
PubMed1987

Responses of auditory-nerve fibers to multiple-tone complexes.

To relate level-dependent properties of auditory-nerve-fiber responses to nasal consonant-vowels to the basic frequency selective and suppressive properties of the fibers, multitone complexes, with the amplitude of a single (probe) component incremented, were used as stimuli. Quantitative relations were obtained between the systematic increase of fiber synchrony to the probe tone and the decrease of synchrony to CF, as the amplitude of the probe tone was increased. When such relations are interpreted as a measure of fiber frequency selectivity based on a relative synchrony criterion, a breadth of frequency tuning is obtained, at a 70-dB SPL multitone sound-pressure level, which is generally broader than that of the fiber's threshold tuning curve. Quantitative comparisons with the same fiber's responses to the nasal speech sounds indicate that the fiber's speech responses share some common features with its probe-tone responses.

Animals↗
PubMed1987

A composite auditory model for processing speech sounds.

A composite inner-ear model, containing the middle ear, basilar membrane (BM), hair cells, and hair-cell/nerve-fiber synapses, is presented. The model incorporates either a linear-BM stage or a nonlinear one. The model with the nonlinear BM generally shows a high degree of success in reproducing the qualitative aspects of experimentally recorded cat auditory-nerve-fiber responses to speech. In modeling fiber population responses to speech and speech in noise, it was found that the BM nonlinearity allows bands of fibers in the model to synchronize strongly to a common spectral peak in the stimulus. A cross-channel correlation algorithm has been devised to further process the model's population outputs. With output from the nonlinear-BM model, the cross-channel correlation values are appreciably reduced only at those channels whose CFs coincide with the formant frequencies. This observation also holds, to a large extent, for noisy speech.

Basilar Membrane↗
PubMed1986

A model of the effect of outer hair cell motility on cochlear vibrations.

A model of cochlear function is presented in which deformation forces within outer hair cells are assumed to occur in synchronized response to generator potentials. Assuming a 90 degree phase lag between the generator potentials and the deformation forces, it is shown that the forces act to reduce cochlear-partition damping and thus increase frequency selectivity. A number of other experimentally observed phenomena, such as the effects of efferent-fiber stimulation and electrical polarization, can also be accounted for with this model.

Basilar Membrane↗
PubMed1986

A temporal analysis of auditory-nerve fiber responses to spoken stop consonant-vowel syllables.

Auditory-nerve fiber spike trains were recorded in response to spoken English stop consonant-vowel syllables, both voiced (/b,d,g/) and unvoiced (/p,t,k/), in the initial position of syllables with the vowels /i,a,u/. Temporal properties of the neural responses and stimulus spectra are displayed in a spectrographic format. The responses were categorized in terms of the fibers' characteristic frequencies (CF) and spontaneous rates (SR). High-CF, high-SR fibers generally synchronize to formants throughout the syllables. High-CF, low/medium-SR fibers may also synchronize to formants; however, during the voicing, there may be sufficient low-frequency energy present to suppress a fiber's synchronized response to a formant near its CF. Low-CF fibers, from both SR groups, synchronize to energy associated with voicing. Several proposed acoustic correlates to perceptual features of stop consonant-vowel syllables, including the initial spectrum, formant transitions, and voice-onset time, are represented in the temporal properties of auditory-nerve fiber responses. Nonlinear suppression affects the temporal features of the responses, particularly those of low/medium-spontaneous-rate fibers.

Acoustic Stimulation↗
PubMed1986

Frequency selectivity of single cochlear-nerve fibers based on the temporal response pattern to two-tone signals.

The physiological basis of auditory frequency selectivity was investigated by recording the temporal response patterns of single cochlear-nerve fibers in the cat. The characteristic frequency and sharpness of tuning was determined for low-frequency cochlear-nerve fibers with two-tone signals whose frequency components were of equal amplitude and starting phase. The measures were compared with those obtained with sinusoidal signals. The two-tone characteristic frequency (2TCF) is defined as the arithmetic-center frequency at which the fiber is synchronized to both signal frequencies in equal measure. The 2TCF closely corresponds to the characteristic frequency as determined by the frequency threshold curve. Moreover, the 2TCF changes relatively little (2%-12%) over a 60-dB intensity range. The 2TCF generally shifts upward with increasing intensity for cochlear-nerve fibers tuned to frequencies below 1 kHz and shifts downward as a function of intensity for units with characteristic frequencies (CF's) above 1 kHz. The shifts in the 2TCF are considerably smaller than those observed with sinusoidal signals. Filter functions were derived from the synchronization pattern to the two-tone signal by varying the frequency of one of the components over the fiber's response area while maintaining the other component at the 2TCF. The frequency selectivity of the two-tone filter function was determined by dividing the vector strength to the variable frequency signal by the vector strength to the CF tone. The filter function was measured 10 dB down from the peak (2T Q 10 dB) and compared with the Q 10 dB of the frequency threshold curve. The correlation between the two measures of frequency selectivity was 0.72. The 2T Q 10 dB does change as a function of intensity. The magnitude and direction of the change is dependent on the sharpness of tuning at low and moderate sound-pressure levels (SPL's). The selectivity of the more sharply tuned fibers (2T Q 10 dB greater than 3) diminishes at intensities above 60 dB SPL. However, the broadening of selectivity is relatively small in comparison to discharge rate-based measures of selectivity. The selectivity of the more broadly tuned units remains unchanged or improves slightly at similar intensity levels. The present data indicate that the frequency selectivity and tuning of low-frequency cochlear-nerve fibers are relatively stable over a 60-dB range of SPL's when measured in terms of their temporal discharge properties.

Animals↗
PubMed1986

A two-stage nonlinear cochlear model possesses automatic gain control.

A model of the cochlea is explored using as stimuli two simultaneously presented sinusoids of equal amplitude. The model consists of two stages: a linear bandpass filter, followed by a reservoir-type representation of the hair-cell/nerve-fiber complex. Fast Fourier transforms of the model's output were computed. While the amplitudes of the individual response components were strongly nonlinear functions of intensity, the ratio of the magnitudes of the response components at the frequencies of the two stimulating sinusoids was found to be nearly equal, over a wide intensity range, to the ratio of the amplitudes which those stimulating sinusoids possessed at the output of the filter. Thus the reservoir stage exerts "automatic gain control".

Adaptation, Physiological↗
PubMed1985

Thresholds for primary auditory fibers using statistically defined criteria.

The discharge behavior of auditory-nerve fibers near "threshold" was investigated in anesthetized cats using low-intensity sinusoidal stimuli presented at the respective characteristic frequencies. Particular attention was paid to fibers with "low" and "medium" rates. Estimates of threshold derived from statistically significant increases in discharge rate indicate that the average threshold values for low-spontaneous fibers are only slightly higher (ca. 5 dB) than the averages for the corresponding high-spontaneous fibers, with the medium-spontaneous fibers having intermediate averages. The difference between these average values is considerably less than the more than 20-dB difference obtained using threshold criteria based on an absolute increment in discharge rate [e.g., M. C. Liberman, J. Acoust. Soc. Am. 63, 442-455 (1978)]. The main reason for the difference between the results of the two techniques is the fact that the slopes of the rate-intensity functions for the high-spontaneous fibers are considerably steeper near "threshold" than those for fibers of the other two classes. The results are taken as supportive of a recent model of primary-fiber discharge [C. D. Geisler, Brain Res. 212, 198-201 (1981)].

Animals↗
PubMed1985

Changes in the phase of excitor-tone responses in cat auditory-nerve fibers by suppressor tones and fatigue.

The responses of single auditory-nerve fibers in anesthetized cats to two-tone stimuli were studied. One of the two tones, F1, was near, above, or below characteristic frequency (CF). The second tone, F2, was located above CF. With sufficient care, F2 was made purely suppressive, eliciting no synchrony responses by itself. The vector phases of the associated period histogram calculated for F1 were carefully studied. For 78% of the fibers under study, a statistically significant increase in phase lag was consistently observed when a suppression of rate discharge occurred. The phase-intensity curve did not approximate a horizontally shifted version of the unsuppressed curve, as is seen for the related rate- and synchrony-intensity curves; rather, the amount of phase shift at any one stimulus condition tended to be monotonically related to the amount of rate suppression generated (vertical shift). Using two different measures, a significant correlation was found between the added phase lag and the discharge-rate reduction caused by F2. The amount of phase lag, along with the corresponding rate reduction, increases with the increasing intensity of F2 within the suppression area, and decreases as F2 moves away from it. These phase-lag effects were found to be uncorrelated with a fiber's CF, with its spontaneous rate, with its threshold, or with its Q value. By contrast, a reduction of discharge rate due to adaptation was not accompanied by any significant phase shift. Fatigue of the fiber due to lengthy sound exposure was found to have strong effects on the shift of response phase to single-tone stimuli.

Acoustic Stimulation↗
PubMed1984

Wiener kernel analysis of responses from anteroventral cochlear nucleus neurons.

Responses to pseudo-random Gaussian white noise, tones and clics were recorded from neurons in the anteroventral cochlear nucleus (AVCN) of barbiturate anesthetized cats. The responses to white noise were used to calculate estimates of the zero-, first- and second-order Wiener kernels for these neurons. The Wiener kernels did contain useful information on the fundamental, DC and second harmonic components of the responses of AVCN neurons to tones, clicks and noise. However, they generally did not provide predictions of the difference tone distortion products found in the peripheral auditory system. Overall, the addition of the second kernel improved a prediction based on the zero- and first-order kernels, but not by very much. If the estimates of the Wiener kernels were not very good, then a second-order prediction could be worse than a first-order one. To produce good estimates of the Wiener kernels, many repetitions of very long Gaussian white noise stimuli are necessary. Therefore the technique does not permit rapid data collection. Further, exposure to long duration high intensity noise can result in acoustic trauma. This damage effects the mechanism that generates the difference tone distortion products, and it can also affect the tuning of the auditory neurons. Thus Wiener's nonlinear system identification theory has only limited usefulness in the analysis of the peripheral auditory system.

Acoustic Stimulation↗
PubMed1984

Comparison of the responses of auditory nerve fibers to consonant-vowel syllables with predictions from linear models.

The responses of cat auditory-nerve fibers to synthesized consonant-vowel syllables were compared with predictions from linear models based on individual fibers' threshold tuning curves. Comparisons with the linear predictions provided information about the specific effects of peripheral nonlinearities on the representation of speech sounds. Spectral peaks, such as the formants of vowels, were more prominently represented in synchronized discharge patterns than in the linear predictions. Suppression of responses to other spectral peaks and to stimulus components between spectral peaks accounted for the differences. While profiles of fibers' synchronized responses were usually dominated by a single formant, predicted linear responses often included broad responses having two or more formants as well as components near the fibers' characteristic frequencies. In contrast, when no stimulus peak fell within a fiber's response area, the agreement between the neural response and the linear prediction was quite good. The results suggest that one role for peripheral nonlinearities in the auditory system may be to enhance the neural representation of spectral features such as formants.

Animals↗
PubMed1983

Responses of auditory-nerve fibers to consonant-vowel syllables.

The discharge patterns elicited by a set of synthesized consonant-vowel (CV) syllables were studied in the auditory nerve of the cat. The syllables, heard as /ba/, /da/, or /ga/, included a 25-, 50-, or 75-ms formant transition followed by a segment of steady-state vowel. The data were analyzed in terms of average discharge rate and in terms of the synchrony of discharges with respect to various spectral components of the stimuli. The results differ slightly from those of previous reports of the responses to vowels [Sachs and Young, J. Acoust. Soc. Am. 66, 470-479 (1979); Young and Sachs, J. Acoust. Soc. Am. 66, 1381-1403 (1979)], in that average discharge rates appear to provide more information about the spectra of formant transitions than they do about the spectra of steady-state vowels. This difference reflects changes in the spectrum of the syllable produced by movements of the formants. The synchrony of discharges, however, may provide more detailed information about the spectra of CVs than does average discharge rate. Each fiber's response at a particular peristimulus time may be characterized by the "dominant response component," the largest peak in the Fourier transform of the period histogram. The trajectories of the first three formants can be inferred from changes in the "dominant components" in a sample of fibers.

Animals↗
PubMed1983

Comparison of click responses of primary auditory fibers with minimum-phase predictions.

Minimum-phase impulse responses were constructed from the frequency threshold-response curves of primary auditory fibers in the anesthetized cat. These impulse responses had many of the same characteristics as the experimental click responses. The two types of responses had similar inter-peak intervals as well as similar (+/- 1.5 ms) latencies to the principal mode and similar (+/- 1.0 ms) intervals from response onset to the principal mode.

Animals↗