Changes In Frequency Selectivity Research Articles

Word Recognition and Frequency Selectivity in Cochlear Implant Simulation: Effect of Channel Interaction.

In cochlear implants (CI), spread of neural excitation may produce channel interaction. Channel interaction disturbs the spectral resolution and, among other factors, seems to impair speech recognition, especially in noise. In this study, two tests were performed with 20 adult normal-hearing (NH) subjects under different vocoded simulations. First, there was a measurement of word recognition in noise while varying the number of selected channels (4, 8, 12 or 16 maxima out of 20) and the degree of simulated channel interaction (“Low”, “Medium” and “High”). Then, there was an evaluation of spectral resolution function of the degree of simulated channel interaction, reflected by the sharpness (Q10dB) of psychophysical tuning curves (PTCs). The results showed a significant effect of the simulated channel interaction on word recognition but did not find an effect of the number of selected channels. The intelligibility decreased significantly for the highest degree of channel interaction. Similarly, the highest simulated channel interaction impaired significantly the Q10dB. Additionally, a strong intra-individual correlation between frequency selectivity and word recognition in noise was observed. Lastly, the individual changes in frequency selectivity were positively correlated with the changes in word recognition when the degree of interaction went from “Low” to “High”. To conclude, the degradation seen for the highest degree of channel interaction suggests a threshold effect on frequency selectivity and word recognition. The correlation between frequency selectivity and intelligibility in noise supports the hypothesis that PTCs Q10dB can account for word recognition in certain conditions. Moreover, the individual variations of performances observed among subjects suggest that channel interaction does not have the same effect on each individual. Finally, these results highlight the importance of taking into account subjects’ individuality and to evaluate channel interaction through the speech processor.

Changes in audiometric threshold and frequency selectivity correlate with cochlear histopathology in macaque monkeys with permanent noise-induced hearing loss

Exposure to loud noise causes damage to the inner ear, including but not limited to outer and inner hair cells (OHCs and IHCs) and IHC ribbon synapses. This cochlear damage impairs auditory processing and increases audiometric thresholds (noise-induced hearing loss, NIHL). However, the exact relationship between the perceptual consequences of NIHL and its underlying cochlear pathology are poorly understood. This study used a nonhuman primate model of NIHL to relate changes in frequency selectivity and audiometric thresholds to indices of cochlear histopathology. Three macaques (one Macaca mulatta and two Macaca radiata) were trained to detect tones in quiet and in noises that were spectrally notched around the tone frequency. Audiograms were derived from tone thresholds in quiet; perceptual auditory filters were derived from tone thresholds in notched-noise maskers using the rounded-exponential fit. Data were obtained before and after a four-hour exposure to a 50-Hz noise centered at 2 kHz at 141 or 146 dB SPL. Noise exposure caused permanent audiometric threshold shifts and broadening of auditory filters at and above 2 kHz, with greater changes observed for the 146-dB-exposed monkeys. The normalized bandwidth of the perceptual auditory filters was strongly correlated with audiometric threshold at each tone frequency. While changes in audiometric threshold and perceptual auditory filter widths were primarily determined by the extent of OHC survival, additional variability was explained by including interactions among OHC, IHC, and ribbon synapse survival. This is the first study to provide within-subject comparisons of auditory filter bandwidths in an animal model of NIHL and correlate these NIHL-related perceptual changes with cochlear histopathology. These results expand the foundations for ongoing investigations of the neural correlates of NIHL-related perceptual changes.

Unusual mechanical processing of sounds at the apex of the Guinea pig cochlea

One of the tenets of mammalian auditory physiology is that the frequency selectivity at the cochlear base decreases as a function of stimulus level. Changes in frequency selectivity have been shown to be accompanied by changes in response phases as a function of stimulus level. The existence of such nonlinear properties has been revealed by the analysis of either direct or indirect recordings of mechanical vibrations of the cochlea. Direct measurements of cochlear mechanical vibrations, however, have been carried out with success primarily in cochlear regions that are tuned to frequencies >7 kHz, but not in regions sensitive to lower frequencies. In this paper we continue to analyze recently published data from measurements of sound-induced vibrations at four locations near the apex of the intact guinea pig cochlea, in a region encompassing approximately 25% of its total length. Analysis of the responses at all locations reveal level-dependent phase properties that are rather different from those usually reported at the base of the cochlea of laboratory animals such as the chinchilla. Cochlear group delays, for example, increase or remain constant with increasing stimulus. Similarly, frequency selectivity at all the regions increases as a function of stimulus level.

A simulation of neural coding and auditory frequency analysis

Our understanding of the neural mechanisms underlying the very fine auditory frequency discrimination exhibited by listeners remains far from complete. To investigate this question we developed a functional model of the cochlear process in sufficient detail to allow the simulation of the principal characteristics of the cochlea's response to multi-tone and noise stimuli over a wide range of input levels. The model simulates level-dependent changes in frequency selectivity, combination-tone distortion, tone-on-tone suppression and masking, adaptation, and critical-band masking. The model is structured as 3000 channels, each consisting of a basilar membrane bandpass filter and inner-hair cell assembly. Input to each channel is the stapes displacement signal, and the output consists of ten independent stochastic point processes that are transmitted to the CNS on auditory-nerve fibers (ANFs). Our main purpose is to address these questions: (1) What narrowband spectrum information is available in the cochlea output? (2) How is this information encoded on the ANFs? (3) How might it be decoded in the CNS? An analysis of ensemble coding of the cochlear output showed that the precision (signal-to-noise ratio) of the information decoded by the CNS frequency analysis is directly related to the bandwidth of the basilar membrane filters.

Auditory Models of Suprathreshold Distortion and Speech Intelligibility in Persons with Impaired Hearing

Hearing-impaired (HI) individuals with similar ages and audiograms often demonstrate substantial differences in speech-reception performance in noise. Traditional models of speech intelligibility focus primarily on average performance for a given audiogram, failing to account for differences between listeners with similar audiograms. Improved prediction accuracy might be achieved by simulating differences in the distortion that speech may undergo when processed through an impaired ear. Although some attempts to model particular suprathreshold distortions can explain general speech-reception deficits not accounted for by audibility limitations, little has been done to model suprathreshold distortion and predict speech-reception performance for individual HI listeners. Auditory-processing models incorporating individualized measures of auditory distortion, along with audiometric thresholds, could provide a more complete understanding of speech-reception deficits by HI individuals. A computational model capable of predicting individual differences in speech-recognition performance would be a valuable tool in the development and evaluation of hearing-aid signal-processing algorithms for enhancing speech intelligibility. This study investigated whether biologically inspired models simulating peripheral auditory processing for individual HI listeners produce more accurate predictions of speech-recognition performance than audiogram-based models. Psychophysical data on spectral and temporal acuity were incorporated into individualized auditory-processing models consisting of three stages: a peripheral stage, customized to reflect individual audiograms and spectral and temporal acuity; a cortical stage, which extracts spectral and temporal modulations relevant to speech; and an evaluation stage, which predicts speech-recognition performance by comparing the modulation content of clean and noisy speech. To investigate the impact of different aspects of peripheral processing on speech predictions, individualized details (absolute thresholds, frequency selectivity, spectrotemporal modulation [STM] sensitivity, compression) were incorporated progressively, culminating in a model simulating level-dependent spectral resolution and dynamic-range compression. Psychophysical and speech-reception data from 11 HI and six normal-hearing listeners were used to develop the models. Eleven individualized HI models were constructed and validated against psychophysical measures of threshold, frequency resolution, compression, and STM sensitivity. Speech-intelligibility predictions were compared with measured performance in stationary speech-shaped noise at signal-to-noise ratios (SNRs) of -6, -3, 0, and 3 dB. Prediction accuracy for the individualized HI models was compared to the traditional audibility-based Speech Intelligibility Index (SII). Models incorporating individualized measures of STM sensitivity yielded significantly more accurate within-SNR predictions than the SII. Additional individualized characteristics (frequency selectivity, compression) improved the predictions only marginally. A nonlinear model including individualized level-dependent cochlear-filter bandwidths, dynamic-range compression, and STM sensitivity predicted performance more accurately than the SII but was no more accurate than a simpler linear model. Predictions of speech-recognition performance simultaneously across SNRs and individuals were also significantly better for some of the auditory-processing models than for the SII. A computational model simulating individualized suprathreshold auditory-processing abilities produced more accurate speech-intelligibility predictions than the audibility-based SII. Most of this advantage was realized by a linear model incorporating audiometric and STM-sensitivity information. Although more consistent with known physiological aspects of auditory processing, modeling level-dependent changes in frequency selectivity and gain did not result in more accurate predictions of speech-reception performance.

Experience-Dependent Adult Cortical Plasticity Requires Cognitive Association between Sensation and Reward

We tested the involvement of cognition in adult experience-dependent neuroplasticity using primate cortical implants. In a prior study, learning an operant sensory discrimination increased cortical excitability and target selectivity. Here, the prior task was separated into three behavioral phases. First, naive animals were exposed to stimulus-reward pairings from the prior study. These yoked animals did not have to discriminate to be rewarded and did not learn the discrimination. The plasticity observed in the prior study did not occur. Second, the animals were classically conditioned to discriminate the same stimuli in a simplified format. Learning was accompanied by increased sensory response strength and an increased range of sensory inputs eliciting responses. The third study recreated the original operant discrimination, and selectivity for task targets increased. These studies demonstrate that cognitive association between sensory stimuli and reinforcers accompanies adult experience-dependent cortical plasticity and suggest that selectivity in representation and action are linked.

State-Dependent Sensory Gating in Olfactory Cortex

Sensory systems show behavioral state-dependent gating of information flow that largely depends on the thalamus. Here we examined whether the state-dependent gating occurs in the central olfactory pathway that lacks a thalamic relay. In urethane-anesthetized rats, neocortical EEG showed a periodical alternation between two states: a slow-wave state (SWS) characterized by large and slow waves and a fast-wave state (FWS) characterized by faster waves. Single-unit recordings from olfactory cortex neurons showed robust spike responses to adequate odorants during FWS, whereas they showed only weak responses during SWS. The state-dependent change in odorant-evoked responses was observed in a majority of olfactory cortex neurons, but in only a small percentage of olfactory bulb neurons. These findings demonstrate a powerful state-dependent gating of odor information in the olfactory cortex that works in synchrony with the gating of other sensory systems. They suggest a state-dependent switchover of signal processing modes in the olfactory cortex.

Auditory thalamus neurons during sleep: changes in frequency selectivity, threshold, and receptive field size.

The present study describes how the frequency receptive fields (RF) of auditory thalamus neurons are modified when the state of vigilance of an unanesthetized animal naturally fluctuates among wakefulness (W), slow-wave sleep (SWS), and paradoxical sleep (PS). Systematic quantification of several RF parameters-including strength of the evoked responses, response latency, acoustic threshold, shape of rate-level function, frequency selectivity, and RF size-was performed while undrugged, restrained guinea pigs presented spontaneous alternances of W, SWS, and PS. Data are from 102 cells recorded during W and SWS and from 53 cells recorded during W, SWS, and PS. During SWS, thalamic cells behaved as an homogeneous population: as compared with W, most of them (97/102 cells) exhibited decreased evoked spike rates. The frequency selectivity was enhanced and the RF size was reduced. In contrast during PS, two populations of cells were identified: one (32/53 cells) showed the same pattern of changes as during SWS, whereas the other (21/53 cells) expressed values of evoked spike rates and RF properties that did not significantly differ from those in W. These two populations were equally distributed in the different anatomical divisions of the auditory thalamus. Last, during both SWS and PS, the responses latency was longer and the acoustic threshold was higher than in W but the proportion of monotonic versus nonmonotonic rate-level functions was unchanged. During both SWS and PS, no relationship was found between the changes in burst percentage and the changes of the RF properties. These results point out the dual aspect of sensory processing during sleep. On the one hand, they show that the auditory messages sent by thalamic cells to cortical neurons are reduced both in terms of firing rate at a given frequency and in terms of frequency range. On the other hand, the fact that the frequency selectivity and the rate-level function are preserved suggests that the messages sent to cortical cells are not deprived of informative content, and that the analysis of complex acoustic sounds should remain possible. This can explain why, although attenuated, reactivity to biologically relevant stimuli is possible during sleep.

Notched-noise measures of frequency resolution in children: What acoustic cues are available at children’s threshold levels?

It has been suggested that young children’s masked detection thresholds are obtained at signal-to-noise ratios for which the signals produce changes in multiple features of the masker [Allen et al., J. Acoust. Soc. Am. (in press)]. In this study 500-, 2000-, and 4000-Hz tonal signals were added to flat- and notched-spectrum noise maskers at signal-to-noise ratios corresponding to children’s threshold levels measured in a previous study of frequency resolution [Allen et al., J. Speech Hear. Res. 32, 317–324 (1989)]. The magnitudes of level, frequency, and periodicity cues were determined, assuming several degrees of frequency selective filtering. Results suggested that for all signal plus masker combinations, independent of frequency and masker spectrum, children’s thresholds had been obtained at signal-to-noise ratios for which little or no frequency selectivity would have been required to produce potentially discriminable level differences [Jensen and Neff, Psychol. Sci. 4, 1-4-107] of approximately 6 dB, which were often accompanied by average frequency and/or periodicity differences. Age-related changes in frequency selectivity therefore may not be required to explain children’s higher masked detection thresholds as they are obtained at signal-to-noise ratios where multiple cues are present. [Work supported by NSERC.]

Binaural inhibition is important in shaping the free-field frequency selectivity of single neurons in the inferior colliculus.

1. We have shown previously that under free-field stimulation in the frontal field, frequency selectivity of the majority of inferior colliculus (IC) neurons became sharper when the loudspeaker was shifted to ipsilateral azimuths. These results indicated that binaural inhibition may be responsible for the direction-dependent sharpening of frequency selectivity. To test the above hypothesis directly, we investigated the frequency selectivity of IC neurons under several conditions: monaural stimulation using a semiclosed acoustical stimulation system, binaural stimulation dichotically also using a semiclosed system, free-field stimulation from different azimuths, and free-field stimulation when the ipsilateral ear was occluded monaurally (coated with a thick layer of petroleum jelly, which effectively attenuated acoustic input to this ear). 2. The binaural interaction pattern of 98 IC neurons of northern leopard frogs (Rana pipiens pipiens) were evaluated; of these neurons, there were 34 EE and 64 EO neurons. The majority of IC neurons (92 of 98) showed some degree of binaural inhibition (i.e., showing diminished response when the ipsilateral and contralateral ears were stimulated simultaneously) whether they were designated as EE or EO; these IC neurons thus were classified as EE-I or EO-I. Neurons were classified as exhibiting strong inhibition if the ILD function showed a pronounced response decrement, i.e., a decrease of > or = 50% of the response to monaural stimulation of the contralateral ear. Those neurons that showed smaller response decrements (decrease was > or = 25% but < 50%) were designated as showing weak inhibition. Most of these EE-I and EO-I neurons (n = 68) showed strong binaural inhibition. 3. In agreement with results from our earlier studies, frequency threshold curves (FTCs) of IC neurons were altered by sound azimuth. Independent of binaural interaction pattern, most IC neurons (59 of 98) showed a narrowing of the FTC as sound direction was changed from contralateral 90 deg (c90 degrees) to ipsilateral 90 deg (i90 degrees). IC neurons that exhibited the largest direction-dependent changes in frequency selectivity were typically those that displayed stronger binaural inhibition. Occlusion of the ipsilateral ear, which reduced the strength of binaural inhibition by this ear, abolished direction-dependent frequency selectivity. 4. FTCs of IC neurons that exhibited little to moderate direction-dependent effects on frequency selectivity were associated typically with neurons that displayed weak binaural inhibition. Associated with this weak binaural inhibition, central neural responses under monaural occlusion also displayed only small effects; the FTCs were only slightly broader than those derived in the intact condition, and as before, the experimental manipulation resulted in abolishment of direction-dependent frequency selectivity. 5. In contrast to most IC neurons, which showed direction-dependent narrowing of the FTC, about one-third (34 of 98) of IC neurons studied showed a broadening of the FTC when sound direction was shifted to ipsilateral azimuths. Interestingly, for 90% of these 34 neurons, monaural occlusion resulted in narrowing of the bandwidth at each azimuth instead of broadening of the FTC bandwidth. We have evidence to suggest that this direction-dependent broadening is actually a consequence of a truncation or loss of the tip of the FTC derived at c90 degrees, which results from strong binaural inhibition. 6. To compare the frequency threshold tuning in response to monaural stimulation of each ear with free-field FTCs, we measured FTCs for each of the 34 EE neurons to independent contralateral and ipsilateral stimulation. FTCs derived from ipsilateral monaural stimulation were significantly narrower than those resulting from contralateral monaural stimulation, independent of a neuron's direction-dependent changes in frequency selectivity.

Auditory filter shapes in normal-hearing, noise-masked normal, and elderly listenersa)

To dissociate the effects of age and hearing impairment on changes in frequency selectivity, auditory filter shapes were measured at 2 kHz in four groups of subjects: (1) normal-hearing young subjects; (2) normal-hearing elderly subjects; (3) elderly hearing-impaired listeners; and (4) young normal-hearing listeners with simulated hearing losses. Filter shapes were derived using a modified version of the notched-noise procedure [Glasberg and Moore, Hear, Res. 47, 103-138 (1990)]. Equivalent rectangular bandwidths (ERBs) of auditory filters were not significantly different in young and elderly subjects with normal 2-kHz hearing. Furthermore, filter widths for young subjects with 20- and 40-dB simulated hearing losses overlapped with those obtained from elderly subjects with corresponding degrees of actual hearing loss. One measure that did show significant differences between actual and simulated hearing losses was the degree of filter asymmetry; auditory filters in hearing-impaired listeners were more asymmetrical than those obtained from noise-masked normal-hearing subjects. The dynamic range of auditory filters, however, was comparable for hearing-impaired and noise-masked listeners. Lastly, post-filter detection efficiency was also similar for young and elderly subjects with equivalent hearing levels. These findings suggest that the reduced frequency selectivity often reported for older listeners can be attributed, primarily, to hearing loss rather than increased age. Implications of the results for speech perception in the elderly and models of hearing impairment are discussed.

Directional dependence of auditory sensitivity and frequency selectivity in the leopard frog

Direction-dependent changes in frequency selectivity were documented in three populations of neurons in the auditory periphery of the leopard frog: low-, mid-, and high-frequency sensitive fibers. These changes were most pronounced in the mid-frequency (720-1199 Hz) sensitive fibers which exhibited positive shifts in characteristic frequencies (CFs) and concomitant narrowed bandwidths from posterior speaker presentations. Maximum sensitivities were observed for ipsilateral speaker presentations in these fibers. Low-frequency (63-500 Hz) sensitive fibers exhibited mean threshold shifts at their CFs of up to -7 dB with posterior speaker presentations. Low- and high-frequency sensitive fibers whose CFs closely correspond to the peaks of spectral energy of the species' mating call were the most sensitive (exhibited lowest thresholds) but showed little directional-dependent frequency selectivity. Directional-dependent variation in frequency selectivity and sensitivity in low- and mid-frequency sensitive fibers was attributed to pressure and phase differences impinging on the inner surface of the eardrum.

Auditory filter shapes in normal-hearing, noise-masked, and elderly subjects.

Previous studies of frequency selectivity have suggested a strong positive correlation between age and the width of auditory filters [Patterson etal., J. Acoust. Soc. Am. 72, 1788–1803 (1982)]. However, given that absolute thresholds are generally higher in older listeners, it is unclear whether the broader filter shapes are a consequence of aging perse or are associated with changes in absolute sensitivity. To dissociate the effects of hearing loss and increased age on changes in frequency selectivity, this study measured auditory filter shapes at 2 kHz in (1) normal-hearing young subjects; (2) elderly (over age 65) subjects with normal 2-kHz thresholds; (3) young subjects with 2-kHz thresholds elevated either 20 or 40 dB by a narrow-band masker; and (4) elderly subjects with varying degrees of hearing loss at 2 kHz. Rounded exponential filter shapes were derived from the data using the method described by Patterson [J. Acoust. Soc. Am. 59, 640–654 (1976)]. Equivalent rectangular bandwidths (ERBs) of auditory filters were not significantly different in young and elderly subjects with normal 2-kHz hearing. Furthermore, filter widths for young subjects with 20- and 40-dB simulated hearing losses overlapped with those obtained from elderly subjects with corresponding degrees of actual hearing loss. These results suggest that the reduced frequency selectivity reported for older listeners can be attributed, primarily, to hearing loss rather than increased age. [Work supported by NIH.]

Frequency Selectivity for Hearing-Impaired and Broadband-noise-masked Normal Listeners

When evaluating frequency selectivity, it is difficult to determine if the deviation from normal performance observed for hearing-impaired listeners reflects abnormal cochlear function or normal, level-dependent changes in frequency selectivity. This experiment was designed to investigate the dependence of frequency-selectivity measures on threshold and signal level. Auditory-filter characteristics, critical ratios, forward-masked psychophysical tuning curves, and narrowband-noise masking patterns were obtained from normal-hearing listeners in quite and in the presence of broadband noise at five levels. These findings were then compared to previously obtained frequency-selectivity measurements for subjects with mild-to-moderate sensorineural hearing loss whose absolute thresholds are comparable to the normal-hearing listeners' masked thresholds. The results suggest that frequency selectivity deterioriates as threshold increases for all subjects. However, the poor frequency selectivity exhibited by hearing-impaired listeners may not be explained entirely by the effects of threshold and signal level. Nevertheless, because frequency selectivity is poorer in the normal auditory system at higher stimulus levels, the deviation from normal performance observed for hearing-impaired listeners may not be as large as previously suggested.

Frequency selectivity in noise‐exposed chinchillas

Evoked‐potential tuning curves (TCs) were recorded from chronic electrodes in the inferior colliculus of 102 chinchillas before and after acoustic overstimulation in order to relate the effects of changes in frequency selectivity to the condition of the cochlea. Pre‐ and post‐exposure measures of auditory threshold and masked thresholds (simultaneous tone‐on‐tone paradigm) were obtained at 0.5, 1, 2, 4, 8, and 11.2 kHz. The three TC variables Q 10 dB, and the low‐ and high‐frequency slopes were compared in two different groups of chinchillas: (1) animals (N = 54) with cochleas that showed distinctly normal and lesioned regions, and (2) animals (N = 48) that had near‐normal thresholds, but either had lesions that were not manifested in the threshold measures or had nearly normal sensory cell populations. In the first group, the TCs measured from normal regions of the cochlea, in general, showed no statistically (t test) significant decreases in the group averaged low‐ or high‐frequency slope, i.e., upward or downward spread of masking, for lesions located either apical or basal of the CF, respectively. In the second group, no significant differences in the TC variables were found in lesioned and nonlesioned cochleas with little or no PTS. These results show that (1) the quality of tuning is not necessarily altered in normal regions of the noise damaged cochlea, and (2) the TC cannot be considered as a reliable measure of sensory cell damage when the amount of PTS is small. [Research supported by NIOSH and USAARL.]

The relation among hearing loss, sensory cell loss and tuning characteristics in the chinchilla

Evoked-potential tuning curves were obtained on over 150 chinchillas before and after acoustic overstimulation in order to relate the effects of changes in frequency selectivity to sensory cell loss over a wide range of hearing loss. Pre- and post-exposure measures of auditory thresholds and masked thresholds (simultaneous tone-on-tone paradigm) were obtained in each animal at 0.5, 1.0, 2.0, 4.0, 8.0 and 11.2 kHz, using the auditory evoked potential recorded from the inferior colliculus. Three tuning curve variables ( Q 10 dB , low-frequency slope and high-frequency slope) were compared to the amount of noise-induced permanent threshold shift and to the percent sensory cell loss produced by a variety of noise exposures. Based upon large sample averages, frequencies showing permanent threshold shifts in excess of 10 dB also showed statistically significant differences between pre- and post-exposure measures of all three tuning curve variables. Shifts of less than 10 dB were not accompanied by statistically significant changes in the tuning curve variables. The percentage of outer hair cell loss, and percentage change in tuning curve characteristics showed systematic and parallel increases as threshold shifts increased at all probe tone frequencies except 8.0 and 11.2 kHz. In general, the results were consistent in showing that there is a systematic change in the variables which define the quality of tuning as hearing loss progressively increases and that these changes are clearly related to outer hair cell losses.

Changes in frequency selectivity in the chinchilla following a noise induced permanent threshold shift

Evoked‐potential tuning curves (TC) were obtained on 106 chinchillas before and after acoustic overstimulation in order to assess the effects of the magnitude of hearing loss on frequency selectivity. Pre‐ and postexposure measures of auditory thresholds and masked thresholds (simultaneous tone‐on‐tone paradigm) were obtained in each animal at 0.5, 1, 2, 4, 8, and 11.2 kHz, using the evoked auditory response recorded from the inferior colliculus. Three TC variables (Q‐10 dB, tail‐tip difference, and the high‐frequency slope) and sensory cell losses were compared to the amount of noise‐induced permanent threshold shift (PTS) produced by a variety of noise exposures. Based upon large sample averages, frequencies showing PTS⩾20 dB also showed statistically significant differences between pre‐ and postexposure measures of all three TC variables. For 10 < PTS < 20 dB only the tail‐tip difference showed a statistically significant change, while for PTS ⩽ 10 dB there were no measurable changes in the TC variables. The percentage of outer hair cell loss showed an orderly and systematic increase as PTS increased and as TC variables changed across the entire range of test frequencies. The inner hair cells were essentially unaffected. These results show that there is a systematic change in the TC variables that define the quality of tuning as hearing loss progressively increases and that these changes are clearly related to outer hair cell losses. [Research supported by NIOSH and DOD.]

Medial geniculate body of the cat: responses to tonal stimuli of neurons in medial division.

Medial geniculate body of the cat: responses to tonal stimuli of neurons in medial division.L M AitkinL M AitkinPublished Online:01 Mar 1973https://doi.org/10.1152/jn.1973.36.2.275MoreSectionsPDF (2 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformationCited BySpecies Differences in the Organization of the Ventral Cochlear Nucleus6 January 2018 | The Anatomical Record, Vol. 301, No. 5Modulation of thalamic auditory neurons by the primary auditory cortexJie Tang, Weiguo Yang, and Nobuo Suga1 August 2012 | Journal of Neurophysiology, Vol. 108, No. 3Tone-Specific and Nonspecific Plasticity of the Auditory Cortex Elicited by Pseudoconditioning: Role of Acetylcholine Receptors and the Somatosensory CortexWeiqing Ji, and Nobuo Suga1 September 2008 | Journal of Neurophysiology, Vol. 100, No. 3Multiparametric corticofugal modulation and plasticity in the auditory system1 October 2003 | Nature Reviews Neuroscience, Vol. 4, No. 10Auditory Processing in the Primate Brain15 April 2003Spectrotemporal Organization of Excitatory and Inhibitory Receptive Fields of Cat Posterior Auditory Field NeuronsWilliam C. 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Wenstrup1 November 1999 | Journal of Neurophysiology, Vol. 82, No. 5Changes of single unit activity in the cat's auditory thalamus and cortex associated to different anesthetic conditionsNeuroscience Research, Vol. 19, No. 3Response properties of single units in areas of rat auditory thalamus that project to the amygdalaExperimental Brain Research, Vol. 98, No. 2Response properties of single units in areas of rat auditory thalamus that project to the amygdalaExperimental Brain Research, Vol. 98, No. 2Binaural response patterns in subdivisions of the medial geniculate bodyBrain Research, Vol. 640, No. 1-2Binaural stimulation reveals functional differences between midline and temporal components of the middle latency in guinea pigsElectroencephalography and Clinical Neurophysiology/Evoked Potentials Section, Vol. 84, No. 4Frequency selectivity is related to temporal processing in parallel thalamocortical auditory pathwaysBrain Research, Vol. 583, No. 1-2The descending auditory pathway and acousticomotor systems: connections with the inferior colliculusBrain Research Reviews, Vol. 15, No. 3Functional organization of the medial division of the medial geniculate body of the cat: Tonotopic organization, spatial distribution of response properties and cortical connectionsHearing Research, Vol. 39, No. 1-2Involvement of cortical and thalamic auditory regions in retention of differential bradycardiac conditioning to acoustic conditioned stimuli in rabbitsBrain Research, Vol. 412, No. 2Physiological plasticity in auditory cortex: Rapid induction by learningProgress in Neurobiology, Vol. 29, No. 1Ibotenic acid lesions in the medial geniculate region prevent the acquisition of differential Pavlovian conditioning of bradycardia to acoustic stimuli in rabbitsBrain Research, Vol. 382, No. 1The role of the medial geniculate region in differential Pavlovian conditioning of bradycardia in rabbitsBrain Research, Vol. 374, No. 1Functional organization of the medial geniculate body's subdivisions of the awake squirrel monkeyBrain Research, Vol. 360, No. 1-2Afferent fibers to the anterior suprasylvian gyrus from the medial geniculate body of catNeuroscience Letters, Vol. 51, No. 1The human medial geniculate bodyHearing Research, Vol. 15, No. 3Neuron types in the central nucleus of the inferior colliculus that project to the medial geniculate bodyNeuroscience, Vol. 11, No. 2Measurement of frequency selectivity of single neurons in the central auditory pathwayHearing Research, Vol. 11, No. 3Evidence of sub-collicular auditory projections to the medial geniculate nucleus in the cat: An autoradiographic and horseradish peroxidase studyBrain Research, Vol. 259, No. 1Properties of single neurons in the anterior auditory field (AAF) of cat cerebral cortexBrain Research, Vol. 248, No. 2Auditory cortex in the marsupial possum Trichosurus vulpeculaHearing Research, Vol. 7, No. 1Neural processing of vocalizations and artificial stimulin the medial geniculate body of squirrel monkeyHearing Research, Vol. 3, No. 2Phase-locked responses to low frequency tones in the medial geniculate bodyHearing Research, Vol. 1, No. 3Effects of ethanol, caffeine, and placebo on the auditory evoked responseElectroencephalography and Clinical Neurophysiology, Vol. 44, No. 5Processing of sensory informationProgress in Neurobiology, Vol. 9, No. 1-2Subdivisions of the medial geniculate body in the tree shrew (Tupaia glis)Brain Research, Vol. 86, No. 2Representation of the cochlea within the inferior colliculus of the catBrain Research, Vol. 77, No. 3 More from this issue > Volume 36Issue 2March 1973Pages 275-83 https://doi.org/10.1152/jn.1973.36.2.275PubMed4574714History Published online 1 March 1973 Published in print 1 March 1973 Metrics

Discharge patterns of single geniculate neurons during the rapid eye movements of sleep.

Discharge patterns of single geniculate neurons during the rapid eye movements of sleep.