Auditory Nerve Fiber Tuning Research Articles

Estimation of Cochlear Frequency Selectivity Using a Convolution Model of Forward-Masked Compound Action Potentials.

Frequency selectivity is a fundamental property of the peripheral auditory system; however, the invasiveness of auditory nerve (AN) experiments limits its study in the human ear. Compound action potentials (CAPs) associated with forward masking have been suggested as an alternative to assess cochlear frequency selectivity. Previous methods relied on an empirical comparison of AN and CAP tuning curves in animal models, arguably not taking full advantage of the information contained in forward-masked CAP waveforms. To improve the estimation of cochlear frequency selectivity based on the CAP, we introduce a convolution model to fit forward-masked CAP waveforms. The model generates masking patterns that, when convolved with a unitary response, can predict the masking of the CAP waveform induced by Gaussian noise maskers. Model parameters, including those characterizing frequency selectivity, are fine-tuned by minimizing waveform prediction errors across numerous masking conditions, yielding robust estimates. The method was applied to click-evoked CAPs at the round window of anesthetized chinchillas using notched-noise maskers with various notch widths and attenuations. The estimated quality factor Q10 as a function of center frequency is shown to closely match the average quality factor obtained from AN fiber tuning curves, without the need for an empirical correction factor. This study establishes a moderately invasive method for estimating cochlear frequency selectivity with potential applicability to other animal species or humans. Beyond the estimation of frequency selectivity, the proposed model proved to be remarkably accurate in fitting forward-masked CAP responses and could be extended to study more complex aspects of cochlear signal processing (e.g., compressive nonlinearities).

Temporal Coding of Single Auditory Nerve Fibers Is Not Degraded in Aging Gerbils.

People suffering from age-related hearing loss typically present with deficits in temporal processing tasks. Temporal processing deficits have also been shown in single-unit studies at the level of the auditory brainstem, midbrain, and cortex of aged animals. In this study, we explored whether temporal coding is already affected at the level of the input to the central auditory system. Single-unit auditory nerve fiber recordings were obtained from 41 Mongolian gerbils of either sex, divided between young, middle-aged, and old gerbils. Temporal coding quality was evaluated as vector strength in response to tones at best frequency, and by constructing shuffled and cross-stimulus autocorrelograms, and reverse correlations, from responses to 1 s noise bursts at 10-30 dB sensation level (dB above threshold). At comparable sensation levels, all measures showed that temporal coding was not altered in auditory nerve fibers of aging gerbils. Furthermore, both temporal fine structure and envelope coding remained unaffected. However, spontaneous rates were decreased in aging gerbils. Importantly, despite elevated pure tone thresholds, the frequency tuning of auditory nerve fibers was not affected. These results suggest that age-related temporal coding deficits arise more centrally, possibly due to a loss of auditory nerve fibers (or their peripheral synapses) but not due to qualitative changes in the responses of remaining auditory nerve fibers. The reduced spontaneous rate and elevated thresholds, but normal frequency tuning, of aged auditory nerve fibers can be explained by the well known reduction of endocochlear potential due to strial dysfunction in aged gerbils.SIGNIFICANCE STATEMENT As our society ages, age-related hearing deficits become ever more prevalent. Apart from decreased hearing sensitivity, elderly people often suffer from a reduced ability to communicate in daily settings, which is thought to be caused by known age-related deficits in auditory temporal processing. The current study demonstrated, using several different stimuli and analysis techniques, that these putative temporal processing deficits are not apparent in responses of single-unit auditory nerve fibers of quiet-aged gerbils. This suggests that age-related temporal processing deficits may develop more central to the auditory nerve, possibly due to a reduced population of active auditory nerve fibers, which will be of importance for the development of treatments for age-related hearing disorders.

Neuronal frequency selectivity in the inferior colliculus and cochlear nucleus of the awake behaving macaque monkey

Frequency selectivity relates to the ability to process complex signals and can be measured through auditory filters. Behavioral filters show broader tuning compared to cochlear and auditory nerve fiber tuning. To test whether filters evolve across the auditory pathway or if they are established in the periphery, we estimated neural filters in the cochlear nucleus (CN) and inferior colliculus (IC) and compared with simultaneously measured behavioral filters in macaques. Three macaques were trained to detect tones (signal = unit characteristic frequency (CF)) in spectrally notched maskers of varying width while single unit responses were recorded in the CN and IC. Filter shapes and bandwidths were estimated from the masked thresholds using the rounded exponential fit. Behavioral and neural filters increased in bandwidth with increasing CF. Behavioral and neural bandwidths were significantly correlated and not significantly different from each other for the CN and IC. Neural filter bandwidths were variable across units and structures, possibly reflecting heterogeneity of neuronal encoding strategies. These findings support a model in which behavioral frequency selectivity is established early in the auditory pathway. These data form the baseline for ongoing studies of macaques with noise-induced hearing loss and future studies of emerging hearing loss therapeutics.

Unexceptional sharpness of frequency tuning in the human cochlea

The responses to sound of auditory-nerve fibers are well known in many animals but are topics of conjecture for humans. Some investigators have claimed that the auditory-nerve fibers of humans are more sharply tuned than are those of various experimental animals. Here we invalidate such claims. First, we show that forward-masking psychophysical tuning curves, which were used as the principal support for those claims, greatly overestimate the sharpness of cochlear tuning in experimental animals and, hence, also probably in humans. Second, we calibrate compound action potential tuning curves against the tuning of auditory-nerve fibers in experimental animals and use compound action potential tuning curves recorded in humans to show that the sharpness of tuning in human cochleae is not exceptional and that it is actually similar to tuning in all mammals and birds for which comparisons are possible. Third, we note that the similarity of frequency of tuning across species with widely diverse cochlear lengths and auditory bandwidths implies that for any given stimulus frequency the "cochlear amplifier" is confined to a highly localized region of the cochlea.

Two modes of motion of the alligator lizard cochlea: Measurements and model predictions

Measurements of motion of an in vitro preparation of the alligator lizard basilar papilla in response to sound demonstrate elliptical trajectories. These trajectories are consistent with the presence of both a translational and rotational mode of motion. The translational mode is independent of frequency, and the rotational mode has a displacement peak near 5 kHz. These measurements can be explained by a simple mechanical system in which the basilar papilla is supported asymmetrically on the basilar membrane. In a quantitative model, the translational admittance is compliant while the rotational admittance is second order. Best-fit model parameters are consistent with estimates based on anatomy and predict that fluid flow across hair bundles is a primary source of viscous damping. The model predicts that the rotational mode contributes to the high-frequency slopes of auditory nerve fiber tuning curves, providing a physical explanation for a low-pass filter required in models of this cochlea. The combination of modes makes the sensitivity of hair bundles more uniform with radial position than that which would result from pure rotation. A mechanical analogy with the organ of Corti suggests that these two modes of motion may also be present in the mammalian cochlea.

Efficient coding of natural sounds.

The auditory system encodes sound by decomposing the amplitude signal arriving at the ear into multiple frequency bands whose center frequencies and bandwidths are approximately exponential functions of the distance from the stapes. This organization is thought to result from the adaptation of cochlear mechanisms to the animal's auditory environment. Here we report that several basic auditory nerve fiber tuning properties can be accounted for by adapting a population of filter shapes to encode natural sounds efficiently. The form of the code depends on sound class, resembling a Fourier transformation when optimized for animal vocalizations and a wavelet transformation when optimized for non-biological environmental sounds. Only for the combined set does the optimal code follow scaling characteristics of physiological data. These results suggest that auditory nerve fibers encode a broad set of natural sounds in a manner consistent with information theoretic principles.

Frequency tuning of basilar membrane and auditory nerve fibers in the same cochleae.

Responses to tones of a basilar membrane site and of auditory nerve fibers innervating neighboring inner hair cells were recorded in the same cochleae in chinchillas. At near-threshold stimulus levels, the frequency tuning of auditory nerve fibers closely paralleled that of basilar membrane displacement modified by high-pass filtering, indicating that only relatively minor signal transformations intervene between mechanical vibration and auditory nerve excitation. This finding establishes that cochlear frequency selectivity in chinchillas (and probably in mammals in general) is fully expressed in the vibrations of the basilar membrane and renders unnecessary additional ("second") filters, such as those present in the hair cells of the cochleae of reptiles.

Nonlinear feedback models for the tuning of auditory nerve fibers.

The tuning of auditory nerve (AN) fibers is generally characterized by an increase in bandwidth and, for mid- to high-frequency fibers, a downward shift in the center frequency as sound level increases. Changes in bandwidth are accompanied by changes in the phase properties of the fibers; thus the timing of neural discharges also changes as a function of sound level. This study focuses on the magnitude and phase properties of models designed to reproduce the nonlinear properties of AN fibers that were studied electrophysiologically. The forward path of each model consisted of a linear second-order resonance, and each feedback path contained a saturating nonlinearity. In model 1, the feedback path was a simple memoryless, saturating nonlinearity. In model 2, a low-pass filter was added after the feedback nonlinearity. The ability of each model to simulate aspects of the nonlinear tuning of AN fibers is discussed. Model 2 was able to simulate a wider range of nonlinear behavior for different AN fibers and thus has promise for use in simulations of populations of fibers tuned to different frequencies.

Shapes of cat auditory nerve fiber tuning curves

Tuning curves of auditory nerve fibers in normal-hearing cats were fitted by a computational model comprising four processes. One process accounts for sensitivity in tuning curve tails and consists of an approximation to bandpass filtering by extracochlear structures. The second and third processes describe passive and active components of basilar membrane (BM) mechanics, respectively. The former consists of a lowpass filter function, which provides baseline threshold sensitivity and filtering above characteristic frequency (CF), and the latter consists of a Gaussian that accounts for sharp tuning and high sensitivity around CF. A fourth process, modeled as a high-pass filter, was needed in many fits to account for breaks and plateaus in threshold sensitivity at frequencies above CF. The latter three processes operated on cochlear spatial coordinates rather than stimulus frequency. The four-process description closely accounted for shapes of most tuning curves. Tuning curve tails possessed minima at 40–80 dB SPL, and minima increased with fiber CF. High-frequency cutoffs of tail filters tended to increase with CF, but low-frequency cutoffs were generally constant across CF. Functions describing tails varied from ear to ear but behaved in a similar manner for fibers from a single ear. Passive components of BM resonances possessed baselines with sensitivities that decreased with CF and cutoff slopes that increased with CF. The magnitude of the active component increased smoothly with CF over an 80 + dB range, and its spatial extent was essentially constant at 1.5 mm or 6% of cochlear length regardless of gain magnitude, fiber CF, or threshold sensitivity. Tuning curves from fibers with high and medium spontaneous rates (SRs) and similar CFs had nearly identical shapes, with the sole difference being essentially constant differences in sensitivity across the entire excitatory frequency range. Tuning curve shapes from fibers with low SRs were more variable. These could either resemble those obtained from similarly-tuned fibers with higher SRs, or they could exhibit lower tip-to-tail ratios and reduced active component magnitudes. The latter were typically associated with low maximum discharge rates.

Frequency selectivity in the auditory periphery: Similarities between damaged and developing ears

Single fiber tuning curves (stimulus frequency versus neural threshold curves) were obtained from 198 auditory nerve fibers in 24 kittens between birth and the 16th postnatal day and from 74 auditory nerve fibers in adult cats. Three developmental stages during which adult-like frequency-resolving capacity was acquired were identified. During the early stage of postnatal development, all auditory nerve fibers were essentially untuned and responded to a narrow range of low to middle frequency tone bursts presented at intensities exceeding 110 dB sound pressure level (SPL) re 20 μPa. In the intermediate stage, which occurred during the second postnatal week, auditory nerve fibers tuned to low- and mid-range frequencies acquired adult-like frequency-resolving capacity. Fibers tuned to high frequencies, which were recorded later in development than those tuned to lower frequencies, were as sharply tuned as their adult counterparts, but exhibited a low contrast between thresholds at characteristic frequency (tip) and lower (tail) frequencies (ie, low tip-to-tail ratios). Adult-like tuning curves were observed during the third stage, primarily as a consequence of the acquisition of adult-like tip-to-tail ratios. Our understanding of the cochlear mechanism(s) by which frequency selectivity is produced in adult animals has recently been enhanced by a combined anatomy and physiology investigation conducted by Liberman and Dodds, 1 in which clear anatomic foci of cochlear damage were identified in cats with functionally characterized hearing loss. Similarly, descriptions of anatomic differentiation in the feline auditory end-organ 2 correlate with functional measures of peripheral auditory system development. In this report, anatomic and physiologic similarities between developing and damaged ears are considered in an attempt to better characterize the process whereby normal frequency selectivities and thresholds are developed. Our findings support the notion that anatomic changes in the cochlea during development, primarily the development of adult-like anatomic relations between the tectorial membrane and sensory cells, underlie the acquisition of adult-like auditory nerve fiber tuning.

Spontaneous rates, thresholds and tuning of auditory-nerve fibers in the gerbil: Comparisons to cat data

Characteristics of 245 auditory nerve fibers in eleven Mongolian gerbils are described in terms of spontaneous rates, thresholds, and tuning curves. The animals were reared in a low-noise environment and had similar hearing thresholds across frequency. Tuning curves were obtained with an algorithm developed to characterize the tuning of auditory fibers in cat, thereby allowing direct comparisons to published data from cat. The results demonstrate that basic similarities exist between gerbil and cat data, although some minor differences are also apparent. Tuning curve bandwidths, as measured 10 and 40 dB above the thresholds at the characteristic frequency (CF), follow trends found in cat data. Like cat, auditory nerve fibers in the gerbil have a range of spontaneous rates. In individual gerbils, fibers associated with low spontaneous rates have higher thresholds than do fibers of similar CF with high rates. Five of the eleven gerbils showed profiles of spontaneous rate across frequency reminiscent of those obtained from quiet-raised young cats. The profiles of the remaining gerbils tended to be compressed to a smaller range of spontaneous rates for characteristic frequencies above about five kHz, much like older cats with unknown noise histories. The cause of the spontaneous compression is not obvious. The correspondence between cat and gerbil with regard to spontaneous rate and CF threshold implies the presence of fundamental mechanisms that are common to mammalian auditory systems.

Automatic gain control in the bat's sonar receiver and the neuroethology of echolocation

The sensitivity of the echolocating bat, Eptesicus fuscus, to sonar echoes at different time delays after sonar emissions was measured in a two-choice echo detection experiment. Since echo delay is perceptually equivalent to target range, the experiment effectively measured sensitivity to targets at different ranges. The bat's threshold for detecting sonar echoes at a short delay of only 1.0 msec after emissions (corresponding to a range of 17 cm) was 36 dB SPL (peak to peak), but the threshold decreased to 8 dB SPL at a longer delay of 6.4 msec (a range of 1.1 m). Prior research has shown that, at even longer delays (corresponding to ranges of 3 to 5 m), the bat's threshold is in the region of 0 dB SPL. Contractions of the bat's middle ear muscles synchronized with the production of echolocation sounds cause a transient loss in hearing sensitivity which appears to account for the observed echo detection threshold shifts. The bat's echo detection thresholds increase by approximately 11 dB for each reduction in target range by a factor of 2 over the span from 17 cm to 1.1 m. As range shortens, the amplitude of echoes from small targets also increases, by 12 dB for each 2-fold reduction in range. Thus, when approaching a target, the bat compensates for changes in echo strength as target range shortens by changing its hearing threshold. Since this compensation appears to occur in the middle ear, the bat regulates echoes reaching the cochlea to a stable amplitude during its approach to a target such as a flying insect. In addition to this automatic gain control linked to target range, the bat aims its head to track a target's position during approach, thus stabilizing echo amplitude even if the target's direction changes. We hypothesize that the bat's directional emissions, directional hearing, middle ear muscle contractions, and head aim response collectively create a three-dimensional spatial tracking filter which the bat locks onto targets to stabilize echo amplitudes during interception of prey. We further hypothesize that this regulation, which cancels echo amplitude changes caused by the target's changing spatial position, leaves the bat free to observe echo amplitude changes caused by the target's own actions, such as insect wing beats. Elimination of spatially dependent echo amplitude changes removes the cause of potentially troublesome changes in neural response latency and keeps stimulation from echoes in the "tip" region of auditory nerve fiber tuning curves.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of continuous noise backgrounds on rate response of auditory nerve fibers in cat.

This study describes the effects of broadband background noise on the average discharge rate to best-frequency (BF) tones of auditory nerve fibers in the cat. The effects of exposure to long-term continuous noise are compared to the effects of noise gated on and off simultaneously with test tones. Addition of background noise causes a shift of the dynamic portion of tone-evoked rate versus level functions to higher tone intensities. The shift occurs at a mean rate of 0.61 dB of shift for each 1-dB increment in noise level. The rate of shift is independent of best frequency and spontaneous discharge rate. The noise level at which the shift begins is frequency dependent and is consistent with the frequency-dependent bandwidths of auditory nerve fiber tuning curves. The adjustment of the dynamic range shows many similarities to two-tone suppression. Therefore, it is most likely that it is caused by suppression of the response to the BF test tone by energy present in the noise at surrounding frequencies. At high noise levels, the ability of auditory nerve fibers to respond to test tones is limited by the rate response to the noise. As noise level increases, the discharge rate it evokes approaches a fiber's saturation rate and ultimately eliminates the fiber's ability to respond to test tones. Low spontaneous rate fibers, which have been shown to have higher thresholds and wider dynamic range (17,29), are significantly more resistant to saturation by high noise levels. Exposure to broadband noise prior to onset of test tones produces an overall decrement in response rate. This phenomenon is similar to the effects of short-term adaptation (32) and seems to develop independently of the shift of dynamic range. At high noise levels, previous exposure to the noise produces a small dynamic range shift. This effect is similar to that produced by suppression but is smaller. The effect is occluded in continuous noise backgrounds by the adjustment of sensitivity produced by suppression.

Cilium length: influence on neural tonotopic organization.

Previous studies have suggested that variations in the length of the hair cell cilia contribute to auditory nerve fiber tuning and tonotopic organization. In the granite spiny lizard, cilium length and the tonotopic organization of nerve fibers are correlated: fiber characteristic frequency increases as cilium length decreases. This results in an increasing fiber characteristic frequency in both the apical and basal direction. a pattern not previously seen in any vertebrate.

Eighth-nerve action-potential tuning curves in cats before and after inducement of an acute noise trauma.

Potentials and limitations of eighth-nerve action-potential tuning curves (APTC) in providing us with a measure of frequency selectivity are studied in cats. APTCs are measured, using a forward-masking technique. They are essentially wider than auditory-nerve fiber tuning curves. Width of APTCs is dependent upon test-tone sound pressure level (SPL) and masking criterion. This can be explained by assuming that APs are formed by discharges of fiber with different CFs. Acoustic traumata are induced halfway into the experiments in order to measure APTCs before and during the trauma in the same animal. This broad-band noise exposure resulted in a long-lasting temporary threshold shift which remained fairly steady during the experiment. In the traumatized ear APTCs are wider than in the normal ear. This widening, also observed in auditory-nerve fibers, is not simply an SPL effect.

Effects of hair cell lesions on responses of cochlear nerve fibers. I. Lesions, tuning curves, two-tone inhibition, and responses to trapezoidal-wave patterns.

Effects of hair cell lesions on responses of cochlear nerve fibers. I. Lesions, tuning curves, two-tone inhibition, and responses to trapezoidal-wave patterns.R A Schmiedt, J J Zwislocki, and R P HamernikR A Schmiedt, J J Zwislocki, and R P HamernikPublished Online:01 May 1980https://doi.org/10.1152/jn.1980.43.5.1367MoreSectionsPDF (3 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformationCited ByLessons from Rodent Models for Genetic and Age-Related Hearing Loss29 August 2018Aging Effects on Behavioural Estimates of Suppression with Short Suppressors15 April 2016A Theoretical Analysis of Normal- and Impaired-Hearing Intensity DiscriminationIEEE Transactions on Speech and Audio Processing, Vol. 12, No. 3Response Growth With Sound Level in Auditory-Nerve Fibers After Noise-Induced Hearing LossMichael G. Heinz, and Eric D. Young1 February 2004 | Journal of Neurophysiology, Vol. 91, No. 2An auditory-periphery model of the effects of acoustic trauma on auditory nerve responsesThe Journal of the Acoustical Society of America, Vol. 113, No. 1Cisplatin-Induced Hyperactivity in the Dorsal Cochlear Nucleus and Its Relation to Outer Hair Cell Loss: Relevance to TinnitusJames A. Kaltenbach, John D. Rachel, T. Alecia Mathog, Jinsheng Zhang, Pamela R. Falzarano, and Matthew Lewandowski1 August 2002 | Journal of Neurophysiology, Vol. 88, No. 2Shapes of cat auditory nerve fiber tuning curvesHearing Research, Vol. 81, No. 1-2Cochlear basal and apical differences reflected in the effects of cooling on responses of single auditory nerve fibersHearing Research, Vol. 80, No. 2Responses of peripheral auditory neurons to two-tone stimuli during development: I. Correlation with frequency selectivityHearing Research, Vol. 77, No. 1-2Two-tone suppression and distortion production on the basilar membrane in the hook region of cat and guinea pig cochleaeHearing Research, Vol. 66, No. 1Physiological and histological changes associated with the reduction in threshold shift during interrupted noise exposureHearing Research, Vol. 62, No. 2Electrical stimulation of the auditory nerve in deaf kittens: Effects on cochlear nucleus morphologyHearing Research, Vol. 56, No. 1-2Auditory nerve of the normal and jaundiced rat. II. Frequency selectivity and two-tone rate suppressionHearing Research, Vol. 54, No. 1Enhanced evoked response amplitudes in the inferior colliculus of the chinchilla following acoustic traumaHearing Research, Vol. 50, No. 1-2Tuning and suppression in auditory nerve fibers of aged gerbils raised in quiet or noiseHearing Research, Vol. 45, No. 3Spontaneous rates, thresholds and tuning of auditory-nerve fibers in the gerbil: Comparisons to cat dataHearing Research, Vol. 42, No. 1Eighth nerve fiber firing features in normal-hearing rabbitsHearing Research, Vol. 36, No. 2-3Evoked response ‘forward masking’ patterns in chinchillas with temporary hearing lossHearing Research, Vol. 27, No. 3Ventral cochlear nucleus neural discharge characteristics in the absence of outer hair cellsBrain Research, Vol. 342, No. 2A comparison of brainstem, whole-nerve AP and single-fiber tuning curves in the gerbil: Normative dataHearing Research, Vol. 17, No. 3Single-neuron labeling and chronic cochlear pathology. III. Stereocilia damage and alterations of threshold tuning curvesHearing Research, Vol. 16, No. 1Furosemide selectively reduces one component in rate-level functions from auditory-nerve fibersHearing Research, Vol. 15, No. 1Neurophysiologic Assessment of Endolymphatic Hydrops28 June 2016 | Annals of Otology, Rhinology & Laryngology, Vol. 93, No. 3Correlates of tone-on-tone masked thresholds in the chinchilla auditory nerveHearing Research, Vol. 13, No. 3Some electrical circuit properties of the organ of Corti. I. Analysis without reactive elementsHearing Research, Vol. 12, No. 1Spontaneous and impulsively evoked otoacoustic emission: indicators of cochlear pathology?Hearing Research, Vol. 10, No. 3Response patterns of auditory nerve fibers during temporary threshold shiftHearing Research, Vol. 10, No. 1AP unmasking and AP tuning in normal and pathological human earsHearing Research, Vol. 8, No. 2Boundaries of two-tone rate suppression of cochlear-nerve activityHearing Research, Vol. 7, No. 3Intracellular and extracellular responses in the organ of Corti of the gerbilHearing Research, Vol. 7, No. 2Modulation of responses of spiral ganglion cells in the guinea pig cochlea by low frequency soundHearing Research, Vol. 7, No. 2 More from this issue > Volume 43Issue 5May 1980Pages 1367-89 https://doi.org/10.1152/jn.1980.43.5.1367PubMed7373368History Published online 1 May 1980 Published in print 1 May 1980 Metrics

Physiological masking functions in normal and acoustically traumatized cats

In cats that have undergone acoustic traumatization, it has been observed that several characteristics in the shape of single auditory nerve fiber tuning curves correspond to histological changes in the hair cells of the cochlea [N. Y. S. Kiang, M. C. Liberman, and R. A. Levine, Ann. Otol. Rhinol. Laryngol. 85, 752–768 (1976)]. Dallos and Cheatham (J. Acoust. Soc. Am. 59, 591–597 (1976)] using the whole‐nerve action potential as a response have demonstrated masking curves in normal animals similar in shape to single‐fiber tuning curves. We have measured whole‐nerve action potential tuning curves (AP tuning curve) in both normal and acoustically traumatized cats to investigate the sensitivity of such a measure in reflecting changes in single‐fiber tuning curves. A tonal masker in a forward‐masking paradigm was used to elicit the measured responses. AP tuning curves were generated at several signal frequencies in order to measure the physiological changes at different places along the cochlea. A preliminary review of the data indicate that the AP tuning curves in acoustically traumatized animals can show a broadening of the tip region relative to normals.

Some effects of stimulus intensity on response of auditory nerve fibers in the squirrel monkey.

Some effects of stimulus intensity on response of auditory nerve fibers in the squirrel monkey.