Responses Of Cochlear Nerve Fibers Research Articles

Cochlear nerve fiber responses to amplitude-modulated stimuli: variations with spontaneous rate and other response characteristics

1. Single-fiber responses to sinusoidally amplitude-modulated (AM) tones were recorded from the cochlear nerves of anesthetized guinea pigs. Stimuli were presented at the fiber's characteristic frequency (CF) and covered the intensity range between the fiber's minimum rate threshold and 90-100 dB SPL in 5- or 6-dB steps. The amount of modulation in each fiber's response and the average rate of the responses were quantified. The observed response modulation was compared with the modulation to be expected on the assumption that the instantaneous discharge rates varied with intensity in the same way that the average rates did (i.e., as predicted from each fiber's average-rate vs. level function). 2. The difference between the observed and expected response modulation varied widely across fibers. In most fibers' the responses to a limited range of stimulus intensities (typically between 20 and 30 dB above the fiber's rate threshold) were modulated far more than expected on the basis of their average rates, with responses to stimuli either above or below this range differing progressively less from expectation. Little or no response modulation was observed above approximately 70 dB SPL in these fibers. Other fibers exhibited response modulation that exceeded the expected modulation by smaller amounts, but maintained this modulation to much higher sound pressure levels. 3. The discrepancy between the observed and expected responses to AM stimuli also varied with the frequency of modulation (fm) within individual fibers. The discrepancies were least pronounced at low fms (e.g., 10 Hz) but became progressively larger as fm was increased to between 50 and 320 Hz (subject to the inter-fiber variations described in 2, above). 4. The AM response characteristics varied systematically with the fiber's spontaneous rate and other response characteristics (e.g., rate threshold, CF rate vs. level function type, and rapid adaptation characteristics). In particular, the most sensitive, high spontaneous rate fibers had responses that adapted rapidly after the onset of a stimulus, and showed the greatest enhancement of AM-related information at low-to-moderate stimulus intensities. However, these fibers appeared incapable of encoding AM-related information at high intensities, since their response rates "saturated" and their AM response enhancements diminished around 30 dB above threshold. In contrast, the less sensitive (i.e., higher threshold), lower spontaneous rate fibers showed less evidence of rapid adaptation near the onsets of their response, and lesser enhancements of the modulated responses predicted from their average-rate versus level functions.(ABSTRACT TRUNCATED AT 400 WORDS)

Cochlear processes reflected in responses of the cochlear nerve.

The effects of sound frequency, intensity, and duration on responses of cochlear-nerve fibers and inner hair cells (IHCs) are reviewed and compared. The frequency selectivity observed in the nerve is already present in the IHC receptor potential but synaptic transmission appears to influence some other properties of the nerve response. First, the average rate-intensity function of a nerve fiber spans a smaller operating range than the IHC input-output characteristic. However, nerve fibers with different sensitivities can innervate the same IHC and respond over different regions of its characteristic. Second, adaptation is present in the nerve-fiber response but not observed in the IHC. It appears to result from a decrease in synaptic transmission and produces temporal contrast and a decrease in operating range. Interactions among the various effects have important influences on the spatiotemporal pattern of cochlear-nerve responses to complex stimuli.

A model for signal transmission in an ear having hair cells with free-standing stereocilia. I. Empirical basis for model structure

No adequate theory for the signal-transmission properties of the peripheral auditory system exists for any vertebrate ear. Because the mammalian ear seems to pose conceptual and technical problems that complicate the development of an adequate theory, it is worthwhile to investigate simpler ears. The ear of the alligator lizard is simpler than mammalian ears in several respects: the motion of the basilar membrane is approximately independent of longitudinal position and is approximately linearly related to the sound pressure at the tympanic membrane; in a large region of the cochlea the hair cells have free-standing stereocilia that are not in contact with a tectorial membrane; the receptor potential of these hair cells is related to the sound pressure at the tympanic membrane in a relatively simple manner; the cochlear-nerve fiber responses from this region do not exhibit two-tone rate suppression. Also, the relative accessibility of this ear has enabled measurement of several response variables: tympanic-membrane volume velocity, extracolumella velocity, basilar-membrane velocity, hair-cell stereociliary displacement, hair-cell receptor potentials, and cochlearnerve-fiber discharges. A model is developed to represent these results in terms of underlying anatomical structures and physiological mechanisms. The model consists of four cascaded signal-processing stages: 1. (1) a macromechanical stage that relates the sound pressure at the tympanic membrane to the velocity of the basilar membrane by an acoustico-mechanical network model of the middle and inner ear and which acts as a bandpass, linear, time-invariant filter; 2. (2) a micromechanical stage that relates the velocity of the basilar membrane to the angular displacement of the hair-cell stereocilia by a hydrodynamic system that acts as a tonotopically-organized, bandpass, linear, time-invariant filter; 3. (3) a mechanoelectric transduction stage that relates the angular displacement of the stereocilia to a change in membrane resistance through a set of angular-displacement-controlled membrane ionic channels and which behaves as a memoryless nonlinear function; 4. (4) an electric stage that relates the change in resistance to the receptor potential by an electric network model of a hair cell that behaves approximately as a lowpass filter. This model predicts most — but not all — of the measured signal-transmission properties of this ear.

Author index

No adequate theory for the signal-transmission properties of the peripheral auditory system exists for any vertebrate ear. Because the mammalian ear seems to pose conceptual and technical problems that complicate the development of an adequate theory, it is worthwhile to investigate simpler ears. The ear of the alligator lizard is simpler than mammalian ears in several respects: the motion of the basilar membrane is approximately independent of longitudinal position and is approximately linearly related to the sound pressure at the tympanic membrane; in a large region of the cochlea the hair cells have free-standing stereocilia that are not in contact with a tectorial membrane; the receptor potential of these hair cells is related to the sound pressure at the tympanic membrane in a relatively simple manner; the cochlear-nerve fiber responses from this region do not exhibit two-tone rate suppression. Also, the relative accessibility of this ear has enabled measurement of several response variables: tympanic-membrane volume velocity, extracolumella velocity, basilar-membrane velocity, hair-cell stereociliary displacement, hair-cell receptor potentials, and cochlearnerve-fiber discharges. A model is developed to represent these results in terms of underlying anatomical structures and physiological mechanisms. The model consists of four cascaded signal-processing stages: 1.(1) a macromechanical stage that relates the sound pressure at the tympanic membrane to the velocity of the basilar membrane by an acoustico-mechanical network model of the middle and inner ear and which acts as a bandpass, linear, time-invariant filter;2.(2) a micromechanical stage that relates the velocity of the basilar membrane to the angular displacement of the hair-cell stereocilia by a hydrodynamic system that acts as a tonotopically-organized, bandpass, linear, time-invariant filter;3.(3) a mechanoelectric transduction stage that relates the angular displacement of the stereocilia to a change in membrane resistance through a set of angular-displacement-controlled membrane ionic channels and which behaves as a memoryless nonlinear function;4.(4) an electric stage that relates the change in resistance to the receptor potential by an electric network model of a hair cell that behaves approximately as a lowpass filter. This model predicts most — but not all — of the measured signal-transmission properties of this ear.

Cochlear microphonic evidence for mechanical propagation of distortion products (ƒ 2 − ƒ 1) and (2ƒ 1 − ƒ 2)

The present cochlear microphonic (CM) study was undertaken to help resolve a conflict in the literature regarding cochlear nonlinear properties. The CM studies of Dallos and his coworkers have concluded that “(up to 70–80 dB SPL [re 20 μPa]), all orders of distortion components … do not seem to be accompanied by traveling waves of their own” (Dallos P. (1973): The Auditory Periphery: Biophysics and Physiology. Academic Press, New York). However, studies of spatial distributions of cochlear nerve fiber responses, acoustic distortion products in the ear canal, and related modeling studies of Kim et al. (Kim D.O. and Molnar C.E. (1975): in: The Nervous System. Vol. 3: Human Communication and Its Disorders. Editor: D.B. Tower, Raven Press, New York; Kim D.O., Molnar C.E. and Matthews J.W. (1980): J. Acoust. Soc. Am. 67, 1704–1721) have led to conclusions to the contrary. In the present study, CM data were obtained from the second and third turns of the chinchilla cochlea using fluid-filled glass micropipettes in scala media and nichrome wire electrodes in scala vestibuli and scala tympani. We sought responses containing predominant distortion products (ƒ 2 − ƒ 1) and (2ƒ 1 − ƒ 2) by fixing a distortion frequency (ƒ d ) near the characteristic frequency (CF) of the recording site and varying the stimulus frequencies ƒ 1 and ƒ 2 and SPLs (with L 1 = L 2). By subsequently varying the distortion frequency around the CF, e.g., fixing ƒ 1 well above the CF and varying ƒ 2, we measured the tuning characteristics of the distortion products (ƒ 2 − ƒ 1) and (2ƒ 1 − ƒ 2). Tuning characteristics of single-tone responses were measured by applying single-tone stimuli of various frequencies with a constant SPL at the eardrum. We have observed, with SPLs as low as 25 dB, that these distortion products in CM display tuning similar to the single-tone response which is consistent with the above neural results. From these tuning similarities, we conclude that our CM data reflect the presence of mechanically propagated distortion products at low SPLs, in agreement with the above studies by Kim et al. Validity of our results is supported by the sensitivity and sharp tuning of our CM data and, in the case of the scala media recordings, by the presence of a normal d.c. endolymphatic potential. Plausible explanations for the opposing conclusions of previous studies of Dallos et al. and the present study are discussed.

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

Effects of hair cell lesions on responses of cochlear nerve fibers. II. Single- and two-tone intensity functions in relation to tuning curves.

Effects of hair cell lesions on responses of cochlear nerve fibers. II. Single- and two-tone intensity functions in relation to tuning curves.

Average‐rate, fundamental and harmonic‐distortion components of responses of cochlear nerve fibers to single‐frequency tone bursts: Comparison with an exponential model

The effects of stimulus envelope on the response characteristics of cochlear nerve fibers can be studied with a class of stimuli of the form p(t) = ex(t) sin (ωt). In this study, the modulating function eg(t) was chosen to produce a train of tone bursts of specified duty cycle and rise/fall times. The technique of Fourier analysis of period histograms described by Kim et al. (preceding abstract) has been extended to handle variations in response components R0,R1, and θ1 as a function of time both within and between each tone burst in a train of bursts. Using tone bursts of 320 ms duration and 20 ms rise/fall times with a duty cycle of 21% we have observed that, during the course of a tone burst: (1) both R0 and R1 rapidly reach a peak value and then decline over the following 50–100 ms to quasi‐steady—state values; (2) the time courses of R0 and R1 during a tone burst are almost identical in shape, i.e., the ratio, R1/R0, reaches its maximum value rapidly and remains constant throughout the duration of a tone burst despite noticeable fluctuations in R1 and R0; (3) the fundamental phase θ1, is constant throughout the total duration of a tone burst; (4) R1R0 saturates at lower sound pressure levels (SPL) than either R0 or R1; (5) the shapes of R0 and R1 vs SPL curves change substantially and progressively for successive periods during the onset portion of the response; and (6) in some cases, the R0 and R1 versus SPL curves for individual periods during the first 12–20 ms following tone burst onset show pronounced nonmonotonic behavior with maxima occurring at as low as 50 dB re 20 μN/m2.

Single-tone and two-tone responses of cochlear-nerve fibers: changes after kanamycin and noise treatments

Responses to single tones and two-tone inhibition (TTI) above CF were determined in untreated Mongolian gerbils and after kanamycin or impulse-noise treatment. Kanamycin produced maximum hair-cell damage in the basal cochlear turn, the noise, in the mid-cochlear region and sometimes in the base. Fibers associated with 100% loss of outer hair cells (OHC) in the basal turn showed elevated CF thresholds, reduced slopes of tuning curves, no TTI, steep rate-intensity curves above CF, and excitation during basilar-membrane displacement towards scala vestibuli. In the presence of 50–95% OHC loss restricted to 2–4 mm of the midcochlear region, corresponding fibers exhibited less homogeneous characteristics. CF thresholds corresponding to the basal boundary of the lesion were nearly normal and increased toward and beyond the apical boundary. The tuning curves tended to be somewhat broadened and TTI, though reduced, was still present in fibers with elevated CF thresholds. Fiber excitation usually occurred during basilar-membrane displacement towards scala vestibuli. Some fibers from both treated groups showed increased sensitivity below CF despite elevated CF thresholds. Tuning curves associated with no TTI had high-frequency slopes between 70–200 dB/oct.

Erratum: ’’Cochlear nerve fiber responses: Distribution along the cochlear partition’’

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Cochlear nerve fiber responses: distribution along the cochlear partition.

Fourier analysis of discharge patterns in response to sinusoidal acoustic stimulation provides a consistent and repeatable measure of response phase and amplitude. The distribution of the fundamental components of response for large populations of fibers as a function of their characteristic frequency provides a link between the spatiotemporal characteristics of basilar membrane vibration and single fiber response. Subject Classification: 65.42, 65.40.

Combination Tone 2f1—f2 in Responses of Single Cochlear Nerve Fibers: Evidence against Essential Non-Linearity

Fourier analyses have been conducted upon period histograms of responses of single cochlear nerve fibers to a pair of phase-locked, equal-amplitude tones whose frequencies f1 and f2 in relation to the characteristic frequency (CF) of the nerve fiber under study are given by the ratio CF:f1:f2 = i:j:k, where i, j, and k are positive integers satisfying i<j<k and i = 2j−k (typically i = 10, j = 11, and k = 12). For moderate-to-high stimulus levels, the relative level of the 2f1−f2 component with respect to the primary components changes only slightly, which is consistent with the previous report by Goldstein and Kiang [Proc. IEEE 56, 981 (1968)]. Confirming the prediction of a nonlinear basilar-membrane model which showed the above high-level property of the distortion component 2f1−f2 as well as a smooth transition into effectively linear response characteristics for sufficiently low input levels [Kim et al., J. Acoust. Soc. Am. 53, 324 (1973)], we have observed that the 2f1−f2 component in cochlear nerve responses decreases with decreasing stimulus levels faster than the primary components for low stimulus, levels. The low-level characteristic of the 2f1−f3 component leads to a theoretically important conclusion that the 2f1−f2 combination tone in responses of a cochlear nerve fiber is not a result of an essential nonlinearity, and supports the linear characterization [Littlefield et al., J. Acoust. Soc. Am. 54 (1973) (in press)] of single cochlear nerve fiber responses for the most sensitive region of the response area corresponding to low stimulus levels.

Prediction of Click Responses of Cochlear Nerve Fibers from Responses to Sinusoidal Stimuli

A method for deriving tuning curves of single cochlear nerve fibers based upon a phase-locking response criterion [Littlefield el al., J. Acoust. Soc. Am. 51, 93 (1972)] yields gain and phase information as a function of the frequency of the stimulating tone. For a range of low-level and low-frequency stimuli, the response of cochlear nerve fibers has been shown to be consistent with a number of criteria for linearity [Littlefield el al., J. Acoust. Soc. Am. 54 (1973) (in press)]. If system linearity is assumed, measurements of gain and phase at discrete frequencies n/T, where n is a positive integer, can be used to predict the Fourier series of the response to any periodic stimulus of period T. By this method, we have calculated theoretical responses of low CF cochlear nerve fibers to periodic click trains, using gain and phase measurements taken within the range of stimulus conditions that have been found to produce responses consistent with a linear system hypothesis. Examples of gain and phase curves and click responses calculated from them will be presented and compared with directly obtained click responses. These comparisons may assist in evaluating linear and nonlinear properties of neural excitation. [This research was supported by PHS research grants from the National Institutes of Health.]

Comparison of Cochlear Nerve Fiber Responses to Cochlear Microphonics

The Fourier analysis of period histograms of spike discharges of single cochlear nerve fibers in response to continuous, single sinusoidal stimuli reveals properties that are remarkably similar to those of the cochlear microphonic (CM) as measured in individual turns of the cochlea. We compare phase shift, as a function of stimulus frequency, for the fundamental component of response of single fibers (as obtained by us) to that for the CM from different turns of the cochlea (from the literature). Curves from both sets of data can be closely approximated by two straight lines. The changes in slopes, and the positions of the break points of the straight line segments behave similarily with changes in characteristic frequency (CF) of the fibers (0.37–5.4 kHz) and changes in the frequency of maximum sensitivity of the CM. For both sets of data, intercepts of extrapolations of the straight lines depart from the origin; for one, as CF increases; for the other, as turn number decreases. Relative amplitudes of the fundamental and second and third harmonics versus stimulus level and versus stimulus frequency also behave in a manner similar to the corresponding CM measurements. These data, resulting from single sinusoidal stimuli, suggest that CM is closely associated with the mechanisms affecting the structure of the spike discharge trains sent to the brain. [This investigation was supported by PHS research grants from the National Institutes of Health.]

Time-domain measurements of cochlear nonlinearities using combination click stimuli.

The interleaving peak structure of poststimulus time (PST) histograms of low-frequency cochlear-nerve-fiber responses to acoustic clicks of both polarities implies that a cochlear neuron is excited by a damped oscillatory waveform, referred to here as a click excitation function (CEF) that is half wave rectified. For a stimulus consisting of two closely spaced clicks, the amplitude and delay of the second click relative to the first click can be adjusted so that one-half cycle of the CEF due to the first click nulls or cancels a particular half-cycle of the other CEF. A null produced in this manner can be detected from the PST histograms of responses of a particular fiber to both polarities of the click-pair stimulus. This nulling technique has been used to study the responses of cochlear nerve fibers to combination click stimuli. Details of these measurements are given, and the interpretation of the results leads to the consideration of two apparently different nonlinear phenomena. These results and the techniques used to obtain them provide a means by which certain constraints on the mechanisms of the peripheral auditory system can be evaluated.

A Cochlear Temporal Nonlinearity Determined from Spike Discharge Patterns for Combination Click Stimuli

The nulling technique described in the preceding abstract has been used to study the responses of cochlear nerve fibers with low characteristic frequency (CF) to combination click stimuli. For a given fiber the intensities of two clicks separated by some multiple of half the period of the fiber's CF can be adjusted to null a particular peak in the corresponding PST histogram. If the two clicks are assumed to produce identical, linearly superposing click excitation functions (CEF's), the relative amplitudes of adjacent peaks of the CEF can be obtained from nulls in the PST histograms obtained with a click separation of half the period of the CF of the fiber. The relative amplitudes of peaks separated by k half-periods can be obtained indirectly from these measurements or by direct measurement using the nulling technique with click separations of k half-periods. The results obtained by these two methods do not agree and hence are inconsistent with the assumption of linear superposition of CEF's. In all cases, the nulls obtained at longer click separations require smaller intensities of the second click (from a few decibels to more than 25 dB) than would be expected for linear superposition of the CEF's. Furthermore, for a given fiber, the deviation from linearity increases with increased second click delay (delays range from 0.3 to 4 msec). Thus it seems appropriate to term this effect a temporal nonlinearity. These measurements point out a fundamental defect in existing models of the peripheral auditory system, none of which, to the best of our knowledge, include the effect of such a temporal nonlinearity. [This investigation was supported by PHS research grants from the National Institutes of Health.]

A Test for Cochlear Linearity from Cochlear Nerve Spike Discharges in Response to Combination Click Stimuli

The interleaving peak structure of poststimulus time (PST) histograms of low-frequency cochlear nerve fiber responses to acoustic clicks of both polarities implies that a cochlear neuron is excited by a damped oscillatory waveform that is half-wave rectified. The oscillatory waveform is presumably related to the impulse response of the basilar membrane and is referred to here as a click excitation function (CEF). For a stimulus consisting of two closely spaced clicks the amplitude and delay of the second click relative to the first click can be adjusted so that one-half cycle of the CEF due to the first click nulls or cancels a particular half-cycle of the other CEF. A null produced in this manner can be detected from the PST histograms of responses of a particular fiber to both polarities of the click pair stimulus. This nulling technique has been used on many cochlear nerve fibers, with characteristic frequencies from 250 to 1700 Hz, to measure the amplitudes of half-cycles of one CEF relative to those of the other to within ±1 dB. If linear superposition of the CEF's due to individual clicks occurs, the null measurements from the PST histograms must satisfy certain self-consistency relations. Thus, this nulling technique provides a means of testing the linear superposition of CEF's that is usually assumed in models of the peripheral auditory system. [This investigation was supported by PHS research grants from the National Institutes of Health.]