Frequency and intensity discrimination in human infants and adults

Frequency and intensity DLs were measured in 26 human infants (ages 7-9 months) and six young adults using a repeating standard "yes-no" operant headturning technique and an adaptive staircase (tracking) psychophysical procedure. Subjects were visually reinforced for responding to frequency increments, frequency decrements, intensity increments, or intensity decrements in an ongoing train of 1.0-kHz tone bursts, and stimulus control was monitored using randomly interleaved probe and catch trials. Infants were easily conditioned to respond to both increments and decrements in frequency, and DLs ranged from 11-29 Hz, while adult DLs ranged from 3-5 Hz. Infants also easily discriminated intensity increments, and DLs ranged from 3-12 dB, while adult DLs ranged from 1-2 dB. No infants successfully discriminated intensity decrements, although adults experienced no difficulty with this task and produced DLs similar to those for increments. The apparent inability of infants to discriminate intensity decrements suggests that the infant CNS may not be well adapted to monitor rate decreases in populations of peripheral auditory neurons.     

Sound intensity processing by the goldfish

Capacities of the goldfish for intensity discrimination were studied using classical respiratory conditioning and a staircase psychophysical procedure. Physiological studies on single saccular (auditory) nerve fibers under similar stimulus conditions helped characterize the dimensions of neural activity used in intensity discrimination. Incremental intensity difference limens (IDLs in dB) for 160-ms increments in continuous noise, 500-ms noise bursts, and 500-ms, 800-Hz tone bursts are 2 to 3 dB, are independent of overall level, and vary with signal duration according to a power function with a slope averaging - 0.33. Noise decrements are relatively poorly detected and the silent gap detection threshold is about 35 ms. The IDLs for increments and decrements in an 800-Hz continuous tone are about 0.13 dB, are independent of duration, and are level dependent. Unlike mammalian auditory nerve fibers, some goldfish saccular fibers show variation in recovery time to tonal increments and decrements, and adaptation to a zero rate. Unit responses to tone increments and decrements show rate effects generally in accord with previous observations on intracellular epsp's in goldfish saccular fibers. Neurophysiological correlates of psychophysical intensity discrimination data suggest the following: (1) noise gap detection may be based on spike rate increments which follow gap offset; (2) detection of increments and decrements in continuous tones may be determined by steep low-pass filtering in peripheral neural channels which enhance the effects of spectral "splatter" toward the lower frequencies; (3) IDLs for pulsed signals of different duration can be predicted from the slopes of rate-intensity functions and spike rate variability in individual auditory nerve fibers; and (4) at different sound pressure levels, different populations of peripheral fibers provide the information used in intensity discrimination.     

Detection of time- and bandlimited increments and decrements in a random-level noise.

The purpose of this study was to compare detection of increments and decrements occurring over limited regions of time and frequency within a 500-ms broadband (0-6000 Hz) noise. Three listeners tracked detection thresholds adaptively in a two-interval, two-alternative forced-choice task. Thresholds were measured for both increments and decrements in level [delta L = 10 log10(1 + delta N0/N0) dB, where N0 is the spectral power density of the noise] as a function of signal duration (T = 30-500 ms) for a range of signal bandwidths (W = 62-6000 Hz) that were logarithmically centered around 2500 Hz. Listeners were forced to rely on temporal- and spectral-profile cues for detection due to randomization of overall presentation level from interval to interval, which rendered overall energy an inconsistent cue. Increments were detectable for all combinations of W and T, whereas decrements were not consistently detectable for W < 500 Hz. Narrow-band decrements were not detectable due to spread of excitation from the spectral edges of the noise into the decrements. Increment and decrement thresholds were similar for W > or = 1000 Hz. Temporal- and spectral-integration effects were observed for both increments and decrements. The exceptions were for random-level conditions in which the signal matched the bandwidth or duration of the standard. A multicue decision process is described qualitatively to explain how the combination of temporal- and spectral-profile cues can produce temporal- and spectral-integration effects in the absence of overall-energy cues.     

Frequency and intensity discrimination in humans and monkeys

Frequency and intensity DLs were compared in humans and monkeys using a repeating standard "yes-no" procedure in which subjects reported frequency increments, frequency decrements, intensity increments, or intensity decrements in an ongoing train of 1.0-kHz tone bursts. There was only one experimental condition (intensity increments) in which monkey DLs (1.5-2.0 dB) overlapped those of humans (1.0-1.8 dB). For discrimination of both increments and decrements in frequency, monkey DLs (16-33 Hz) were approximately seven times larger than those of humans (2.4-4.8 Hz), and for discrimination of intensity decrements, monkey DLs (4.4-7.0 dB) were very unstable and larger than those of humans (1.0-1.8 dB). For intensity increment discrimination, humans and monkeys also exhibited similar DLs as SL was varied. However, for frequency increment discrimination, best DLs for humans occurred at a high (50 dB) SL, whereas best DLs for monkeys occurred at a moderate (30 dB) SL. Results are discussed in terms of various neural mechanisms that might be differentially engaged by humans and monkeys in performing these tasks; for example, different amounts of temporal versus rate coding in frequency discrimination, and different mechanisms for monitoring rate decreases in intensity discrimination. The implications of these data for using monkeys as models of human speech sound discrimination are also discussed.     

Two phase effects in roughness perception.

The respective influences of spectral and temporal aspects of sound in roughness perception are examined by way of phase manipulations. In a first experiment, the phase of the central component of three-component signals is shown to modify perceived roughness, for a given amplitude spectrum, regardless of whether it modifies the waveform envelope. A second experiment shows that the shape of the waveform envelope, for a given amplitude spectrum and a given modulation depth, also influences perceived roughness. We interpret both of these results by considering the envelope of an internal representation that is deduced from the physical signal by taking into account peripheral auditory processing. The results indicate that the modulation depth of such an internal representation is not the only determinant of roughness, but that an effect of temporal asymmetry is also to be taken into account.     

The detection of increments and decrements is not facilitated by abrupt onsets or offsets

Two experiments measured thresholds for the detection of increments and decrements in the intensity of a quasi-continuous broadband-noise (experiment 1) or increments in a 477-Hz pure-tone pedestal (experiment 2). A variety of onset and offset ramps for the intensity change were tested, from instantaneous onsets or offsets to ramps lasting several tens of milliseconds. For increments and decrements with equal duration, the characteristics of the ramps had little effect on performance. Abrupt rise times, which are associated with strong transient responses in auditory neurons, did not facilitate detection in comparison to much slower rise times. The temporal window model of temporal resolution provided a good account of the data when the decision statistic was the maximum magnitude of the change in the output of the window produced by the increment or decrement, but provided a poor account of the data when the decision statistic was the maximum rate of change in the output of the window over time. Overall the results suggest that, in the absence of cues in the audio-frequency domain, rapid changes in envelope contribute little to near-threshold increment or decrement detection.     

Acoustic distortion products in humans: systematic changes in amplitudes as a function of f2/f1 ratio

The effects of primary-tone separation on the amplitude of distortion-product emissions (DPEs) at the 2f1-f2 frequency were systematically examined in ten ears of five subjects. All individuals had normal hearing and middle-ear function based upon standard clinical measures. Acoustic-distortion products were elicited at 1, 2.5, and 4 kHz by equilevel primaries at 65, 75, and 85 dB SPL, while f2/f1 ratios were varied in 0.02 increments from 1.01-1.41 (4 kHz), 1.01-1.59 (2.5 kHz), or 1.01-1.79 (1 kHz). A principal outcome reflected in the detailed structure of both average and individual ratio functions was a nonmonotonic change in DPE amplitude as the ratio of f2/f1 increased. Despite the presence of amplitude nonmonotonicities, there was clearly a region of f1 and f2 separation that generated a maximum DPE. The effects of primary-tone separation on DPE amplitudes were systematically related to DPE frequency and primary-tone level. For all three levels of stimulation, the f2/f1 ratio was inversely related to DPE frequency. Thus larger ratios reflecting a greater separation of f1 and f2 were more effective in generating DPEs at 1 kHz rather than at 4 kHz. The optimal ratio for 2.5 kHz fell at an intermediate value. Conversely, acoustic distortion-product amplitude as a function of primary-tone level was directly related to the frequency separation of the primary tones. Regardless of the frequency region of the primary tones, smaller f2/f1 ratios were superior in generating DPEs in response to 65-dB stimuli, whereas larger ratios elicited bigger DPEs with primaries at 75 and 85 dB SPL. Within any specific stimulus-parameter combination, individual variability in DPE amplitude was noted. When all stimulus conditions describing the variations in frequency and level were considered, an f2/f1 ratio of 1.22 was most effective in maximizing DPE amplitude.     

Hybrid measurement of auditory steady-state responses and distortion product otoacoustic emissions using an amplitude-modulated primary tone

A maximum auditory steady-state response (ASSR) amplitude is yielded when the ASSR is elicited by an amplitude-modulated tone (f(c)) with a fixed modulation frequency (f(m) = 40 Hz), whereas the maximum distortion product otoacoustic emission (DPOAE) level is yielded when the DPOAE is elicited using a fixed frequency ratio of the primary tones (f2/f1 = 1.2). When eliciting the DPOAE and ASSR by the same tone pair, optimal stimulation is present for either DPOAE or ASSR and thus adequate simultaneous DPOAE/ASSR measurement is not possible across test frequency f2 or f(c), respectively. The purpose of the present study was to determine whether the ASSR and DPOAE can be measured simultaneously without notable restrictions using a DPOAE stimulus setting in which one primary tone is amplitude modulated. A DPOAE of frequency 2f1-f2 and ASSR of modulation frequency 41 Hz were measured in ten normal hearing subjects at a test frequency between 0.5 and 8 kHz (f2 = f(c)). The decrease in the DPOAE level and the loss in ASSR amplitude during hybrid mode stimulation amounted, on average, to only 2.60 dB [standard deviation (SD) = 1.38 dB] and 1.83 dB (SD = 2.38 dB), respectively. These findings suggest simultaneous DPOAE and ASSR measurements to be feasible across all test frequencies when using a DPOAE stimulus setting where the primary tone f2 is amplitude modulated.     

The effect of amplitude envelope on the pitch of sine wave tones

Psychophysical experiments show that the pitch of a short sine wave tone depends upon the amplitude envelope of the tone. Subjects find that the pitch of an exponentially decaying tone (1dB/ms) is higher than the pitch of a (20-ms) rectangularly gated tone of equal frequency. The percentage difference in frequency required to produce equal pitches with the two envelopes depends upon frequency fo: 2.6% at fo = 412 Hz, 1.4% at fo = 825 Hz, 1% at fo = 1650 Hz, and 0.7% at fo = 3300 Hz. The pitch change is insensitive to the relative intensities of the two tones. The spectra of tones with the two different envelopes suggest no obvious explanation for the pitch change. However, the weighted time-varying spectra for tones with two different envelopes evolve differently with time. Alternatively the pitch change can be derived from a modified version of the auditory phase theory of Huggins.     

Effects of frequency and duration on psychometric functions for detection of increments and decrements in sinusoids in noise

Psychometric functions for detecting increments or decrements in level of sinusoidal pedestals were measured for increment and decrement durations of 5, 10, 20, 50, 100, and 200 ms and for frequencies of 250, 1000, and 4000 Hz. The sinusoids were presented in background noise intended to mask spectral splatter. A three-interval, three-alternative procedure was used. The results indicated that, for increments, the detectability index d' was approximately proportional to delta I/I. For decrements, d' was approximately proportional to delta L. The slopes of the psychometric functions increased (indicating better performance) with increasing frequency for both increments and decrements. For increments, the slopes increased with increasing increment duration up to 200 ms at 250 and 1000 Hz, but at 4000 Hz they increased only up to 50 ms. For decrements, the slopes increased for durations up to 50 ms, and then remained roughly constant, for all frequencies. For a center frequency of 250 Hz, the slopes of the psychometric functions for increment detection increased with duration more rapidly than predicted by a "multiple-looks" hypothesis, i.e., more rapidly than the square root of duration, for durations up to 50 ms. For center frequencies of 1000 and 4000 Hz, the slopes increased less rapidly than predicted by a multiple-looks hypothesis, for durations greater than about 20 ms. The slopes of the psychometric functions for decrement detection increased with decrement duration at a rate slightly greater than the square root of duration, for durations up to 50 ms, at all three frequencies. For greater durations, the increase in slope was less than proportional to the square root of duration. The results were analyzed using a model incorporating a simulated auditory filter, a compressive nonlinearity, a sliding temporal integrator, and a decision device based on a template mechanism. The model took into account the effects of both the external noise and an assumed internal noise. The model was able to account for the major features of the data for both increment and decrement detection.     

基于样本熵的听觉神经锁相机理的实验分析

锁相是指系统的响应与周期性刺激的特定相位同步的物理现象. 听觉神经的锁相对揭示人的听觉认知基本的神经机理及改善听觉感知有重要意义. 然而, 现有研究主要集中于心理物理方法和幅度谱分析, 不能有效区分包络响应和时域细节结构响应, 不能直观反映神经锁相. 本文主要利用拔靴法和离散傅里叶变换, 提出了基于样本熵的时域细节结构频率跟随响应(temporal-fine-structure-related frequency following response, FFR_T)的神经锁相值(phase locking value, PLV)计算方法, 用于分析神经物理实验数据. 两个脑电实验结果表明: FFR_T的PLV样本熵显著大于包络相关频率跟随响应(envelope-related frequency following response, FFR_E)的PLV, 且二者正交独立, 新方法能有效地分别反映听觉系统对包络和时间细节结构的锁相机理; 基频处的响应主要来源于FFR_E的锁相; 基频处, 不可分辨谐波成分包络的锁相能力优于对可分辨谐波; 基频缺失时, 畸变产物是不同的听觉神经通路的FFR_E的混合; 谐波处, FFR_E 集中于低频, FFR_T则集中于中、高频; 听觉神经元锁相能力与声源的频率可分辨性相关. FFR_T的PLV方法克服了现有FFR分析的局限性, 可用于深入研究听觉神经机理.     

The effect of broadband noise on the human brainstem auditory evoked response. II. Frequency specificity

A series of experiments evaluated the effects of broadband noise (ipsilateral) on wave V of the brainstem auditory evoked response (BAER) elicited by tone bursts or clicks in the presence of high-pass masking noise. Experiment 1 used 1000- and 4000-Hz, 60-dB nHL tone bursts in the presence of broadband noise. With increasing noise level, wave V latency shift was greater for the 1000-Hz tone bursts, while amplitude decrements were similar for both tone-burst frequencies. Experiment 2 varied high-pass masker cutoff frequency and the level of subtotal masking in the presence of 50-dB nHL clicks. The effects of subtotal masking on wave V (increase in latency and decrease in amplitude) increased with increasing derived-band frequency. Experiment 3 covaried high-pass masker cutoff frequency and subtotal masking level for 1000- and 4000-Hz tone-burst stimuli. The effect of subtotal masking on wave V latency was reduced for both tone-burst frequencies when the response-generating region of the cochlear partition was limited by high-pass maskers. The results of these three experiments suggest that most of the wave V latency shift associated with increasing levels of broadband noise is mediated by a place mechanism when the stimulus is a moderate intensity (60 dB nHL), low-frequency (1000 Hz) tone burst. However, the interpretation of the latency shifts produced by broadband noise for 4000-Hz tone-burst stimuli is made more complex by multiple technical factors discussed herein.     

Detection of modulation in spectral envelopes and linear-rippled noises by budgerigars (Melopsittacus undulatus)

Budgerigars were trained to discriminate complex sounds with two different types of spectral profiles from flat-spectrum, wideband noise. In one case, complex sounds with a sinusoidal ripple in (log) amplitude across (log) frequency bandwidth were generated by combining 201 logarithmically spaced tones covering the frequency region from 500 Hz to 10 kHz. A second type of rippled stimulus was generated by delaying broadband noise and adding it to the original noise in an iterative fashion. In each case, thresholds for modulation depth (i.e., peak-to-valley in dB) were measured at several different ripple frequencies (i.e., cycles/octave for logarithmic profiles) or different repetition pitches (i.e., delay for ripple noises). Budgerigars were similar to humans in detecting ripple at low spatial frequencies, but were considerably more sensitive than humans in detecting ripples in log ripple spectra at high spatial frequencies. Budgerigars were also similar to humans in detecting linear ripple in broadband noise over a wide range of repetition pitches. Taken together, these data show that the avian auditory system is at least as good, if not better, than the human auditory system at detecting spectral ripples in noise despite gross anatomical differences in both the peripheral and central auditory nervous systems.     

Discrimination of modulation depth of sinusoidal amplitude modulation (SAM) noise

The detection of sinusoidal amplitude modulation (SAM) provides a lower bound on the degree to which temporal information in the envelope of complex waveforms is encoded by the auditory system. The extent to which changes in the amount of modulation are discriminable provides additional information on the ability of the auditory system to utilize envelope fluctuations. Results from an experiment on the discrimination of modulation depth of broadband noise are presented. Discrimination thresholds, expressed as differences in modulation power, increase monotonically with the modulation depth of the standard, but do not obey Weber's law. The effects of carrier level and of modulation frequency are consistent with those observed in modulation detection: Changes in carrier level have little effect on modulation discrimination; changes in modulation frequency also have little effect except for standards near the modulation detection threshold. The discrimination of modulation depth is consistent with the leaky-integrator model of modulation detection for standards below--10 dB (20 log ms); for standards greater than--10 dB, the leaky integrator predicts better performance than that observed behaviorally.     

A masking level difference due to harmonicity

The role of harmonicity in masking was studied by comparing the effect of harmonic and inharmonic maskers on the masked thresholds of noise probes using a three-alternative, forced-choice method. Harmonic maskers were created by selecting sets of partials from a harmonic series with an 88-Hz fundamental and 45 consecutive partials. Inharmonic maskers differed in that the partial frequencies were perturbed to nearby values that were not integer multiples of the fundamental frequency. Average simultaneous-masked thresholds were as much as 10 dB lower with the harmonic masker than with the inharmonic masker, and this difference was unaffected by masker level. It was reduced or eliminated when the harmonic partials were separated by more than 176 Hz, suggesting that the effect is related to the extent to which the harmonics are resolved by auditory filters. The threshold difference was not observed in a forward-masking experiment. Finally, an across-channel mechanism was implicated when the threshold difference was found between a harmonic masker flanked by harmonic bands and a harmonic masker flanked by inharmonic bands. A model developed to explain the observed difference recognizes that an auditory filter output envelope is modulated when the filter passes two or more sinusoids, and that the modulation rate depends on the differences among the input frequencies. For a harmonic masker, the frequency differences of adjacent partials are identical, and all auditory filters have the same dominant modulation rate. For an inharmonic masker, however, the frequency differences are not constant and the envelope modulation rate varies across filters. The model proposes that a lower variability facilitates detection of a probe-induced change in the variability, thus accounting for the masked threshold difference. The model was supported by significantly improved predictions of observed thresholds when the predictor variables included envelope modulation rate variance measured using simulated auditory filters.     

Some effects of auditory grouping factors on modulation detection interference (MDI).

The ability to detect the existence of amplitude modulation at a target frequency is reduced when amplitude modulation exists at a flanking frequency. This effect has been termed modulation detection interference (MDI) [Yost and Sheft, J. Acoust. Soc. Am. 85, 848-857 (1989)]. One explanation for MDI holds that the masking and target frequencies are grouped together by the auditory system such that it is difficult to analyze the modulation at each frequency separately. The present study investigated conditions where the asynchrony of temporal gating of the target and flanking frequencies was manipulated in order to make the frequencies more or less likely to be grouped together by the auditory system and perceived as originating from a single putative source. A second experimental manipulation attempted to perceptually segregate the masking and target frequencies on the basis of harmonicity or spectral proximity. The results of the experiments indicated that manipulations that were intended to enhance the segregation of the masking and target frequencies reduced the magnitude of MDI effects. This generally supported an interpretation that MDI is related in some way to auditory grouping. A final experiment was performed in which the subject had to detect the presence of amplitude modulation, but also had to identify which of two frequency components carried the modulation. Subjects were often poor in discriminating which of two frequencies was amplitude modulated, even when the modulation itself was clearly audible. It was concluded that part of the MDI effect might be due to the poor ability of the auditory system to associate modulation with the carrier of the modulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Spectral sharpness and vowel dissimilarity

The effect of sharpening or smoothing the spectral envelopes of synthetic vowel-like sounds on the dissimilarities perceived among these sounds was investigated by means of triadic comparisons. When a spectral envelope (dB on a log-frequency scale) is considered the sum of a series of sinusoidal spectral modulations (or ripples) of different densities (the ripple spectrum), spectral sharpening or smoothing can be described as an amplification or attenuation of a part of the original ripple spectrum. For a set of nine sounds comprising different degrees of spectral sharpening of a single vowel, the perceived dissimilarities were found to be dominated by a specific part of the ripple spectrum, i.e., by spectral modulations with a density of about 2 ripples/oct. The possible role of lateral suppression in relation to this dominant region is discussed. For a set of 18 sounds comprising six vowels, each in three different versions (sharpened, normal, or smoothed), the dissimilarities were found to be determined mainly by the global shape of the spectral envelopes, i.e., by spectral modulations up to about 1.5-2 ripples/oct. Details of the spectral envelope (including the region of 2 ripples/oct where lateral suppression is effective) appear to be of minor influence on vowel dissimilarities.     

Effects of degradation of intensity, time, or frequency content on speech intelligibility for normal-hearing and hearing-impaired listeners

Many hearing-impaired listeners suffer from distorted auditory processing capabilities. This study examines which aspects of auditory coding (i.e., intensity, time, or frequency) are distorted and how this affects speech perception. The distortion-sensitivity model is used: The effect of distorted auditory coding of a speech signal is simulated by an artificial distortion, and the sensitivity of speech intelligibility to this artificial distortion is compared for normal-hearing and hearing-impaired listeners. Stimuli (speech plus noise) are wavelet coded using a complex sinusoidal carrier with a Gaussian envelope (1/4 octave bandwidth). Intensity information is distorted by multiplying the modulus of each wavelet coefficient by a random factor. Temporal and spectral information are distorted by randomly shifting the wavelet positions along the temporal or spectral axis, respectively. Measured were (1) detection thresholds for each type of distortion, and (2) speech-reception thresholds for various degrees of distortion. For spectral distortion, hearing-impaired listeners showed increased detection thresholds and were also less sensitive to the distortion with respect to speech perception. For intensity and temporal distortion, this was not observed. Results indicate that a distorted coding of spectral information may be an important factor underlying reduced speech intelligibility for the hearing impaired.     

Central, auditory mechanisms of perceptual compensation for spectral-envelope distortion.

The spectral envelope is a major determinant of the perceptual identity of many classes of sound including speech. When sounds are transmitted from the source to the listener, the spectral envelope is invariably and diversely distorted, by factors such as room reverberation. Perceptual compensation for spectral-envelope distortion was investigated here. Carrier sounds were distorted by spectral envelope difference filters whose frequency response is the spectral envelope of one vowel minus the spectral envelope of another. The filter /I/ minus /e/ and its inverse were used. Subjects identified a test sound that followed the carrier. The test sound was drawn from an /Itch/ to /etch/ continuum. Perceptual compensation produces a phoneme boundary difference between /I/ minus /e/ and its inverse. Carriers were the phrase "the next word is" spoken by the same (male) speaker as the test sounds, signal-correlated noise derived from this phrase, the same phrase spoken by a female speaker, male and female versions played backwards, and a repeated end-point vowel. The carrier and test were presented to the same ear, to different ears, and from different apparent directions (by varying interaural time delay). The results show that compensation is unlike peripheral phenomena, such as adaptation, and unlike phonetic perceptual phenomena. The evidence favors a central, auditory mechanism.     

Psychophysical evidence against the autocorrelation theory of auditory temporal processing.

Nowadays, it is widely believed that the temporal structure of the auditory nerve fibers' response to sound stimuli plays an important role in auditory perception. An influential hypothesis is that information is extracted from this temporal structure by neural operations akin to an autocorrelation algorithm. The goal of the present work was to test this hypothesis. The stimuli consisted of sequences of unipolar clicks that were high-pass filtered and mixed with low-pass noise so as to exclude spectral cues. In experiment 1, "interfering" clicks were inserted in an otherwise periodic (isochronous) click sequence. Each click belonging to the periodic sequence was followed, after a random portion of the period, by one interfering click. This disrupted the detection of temporal regularity, even when the interfering clicks were 5 dB less intense than the periodic clicks. Experiments 2-4 used click sequences that showed a single peak in their autocorrelation functions. For some sequences, this peak originated from "first-order" temporal regularities, that is from the temporal relations between consecutive clicks. For other sequences, the peak originated instead from "second-order" regularities, relative to nonconsecutive clicks. The detection of second-order regularities appeared to be much more difficult than the detection of comparable first-order regularities. Overall, these results do not tally with the current autocorrelation models of temporal processing. They suggest that the extraction of temporal information from a group of closely spaced spectral components makes no use of time intervals between nonconsecutive peaks of the amplitude envelope.