Biomedical subjects

B C Moore

Publications and source records attributed to B C Moore.

At least 145 records · Page 8Linked to original sources

PubMed1990

Temporal window shape as a function of frequency and level.

In an earlier article [Moore et al., J. Acoust. Soc. Am. 83, 1102-1116 (1988)], preliminary work on the temporal-window model of temporal resolution in the auditory system was described. The temporal window is conceived of as a temporal integrator that slides in time and that is implemented as an intensity-weighting function. The shape of the temporal window was estimated by measuring the threshold for a brief sinusoidal signal presented in a temporal gap between two bursts of noise as a function of the duration of the gap and the position of the signal within the gap. In this paper, a much more thorough examination of the effects of level and frequency on the shape of the window is presented, using the same basic technique. Temporal window shapes were measured at four different frequencies (300, 900, 2700, and 8100 Hz) and at three different masker levels covering a 20-dB range at each frequency. The shape of the temporal window was well described by modeling each side as the sum of two rounded-exponential (roex) functions. The equivalent rectangular duration (ERD) of the window decreased from about 13 to 9 ms as the center frequency increased from 300 to 900 Hz, but decreased only slightly, to 7 ms, as the center frequency increased to 8100. The greater ERD at 300 Hz does not seem to be explicable in terms of "ringing" in the auditory filter. The ERD decreased somewhat with increasing level, for example, having a value of about 10 ms at 2700 Hz with a 20-dB masker spectrum level and about 7 ms with a 40-dB masker spectrum level.

Adult↗

PubMed1990

Across-channel masking and comodulation masking release.

These experiments on across-channel masking (ACM) and comodulation masking release (CMR) were designed to extend the work of Grose and Hall [J. Acoust. Soc. Am. 85, 1276-1284 (1989)] on CMR. They investigated the effect of the temporal position of a brief 700-Hz signal relative to the modulation cycle of a 700-Hz masker 100% sinusoidally amplitude modulated (SAM) at a 10-Hz rate, which was either presented alone (reference masker) or formed part of a masker consisting of the 3rd to 11th harmonics of a 100-Hz fundamental. In the harmonic maskers, each harmonic was either SAM with the same 10-Hz modulator phase (comodulated masker) or with a shift in modulator phase of 90 degrees for each successive harmonic (phase-incoherent masker). When the signal was presented at the dips of the envelope of the 700-Hz component, the comodulated masker gave lower thresholds than the reference masker, while the phase-incoherent masker gave higher thresholds, i.e., a CMR was observed. No CMR was found when the signal was presented at the peaks of the envelope. In experiment 1, we replicated the experiment of Grose and Hall, but with an additional condition in which the 600- and 800-Hz components were removed from the masker, in order to investigate the role of within-channel masking effects. The results were similar to those of Grose and Hall. In experiment 2, the signal was added at the peaks of the envelope of the 700-Hz component, but in antiphase to the carrier of that component and at a level chosen to transform the peaks into dips. No CMR was found. Rather, performance was worse for both the comodulated and phase-incoherent maskers than for the reference masker. This was true even when the flanking components in the maskers were all remote in frequency from 700 Hz. In experiment 3, the masker components were all 50% SAM and the signal was added in antiphase at a dip of the envelope of the 700-Hz component, thus making the dip deeper. Performance was worse for the phase-incoherent than for the reference masker and was worse still for the comodulated masker. The results of all three experiments indicate strong ACM effects. CMR was found only when the signal was placed in the dips of the masker envelope and when it produced an increase in level relative to that in adjacent bands.

Adult↗

PubMed1990

Comodulation masking release as a function of bandwidth and time delay between on-frequency and flanking-band maskers.

The threshold for a signal masked by a narrow band of noise centered at the signal frequency (the on-frequency band) may be reduced by adding to the masker a second band of noise (the flanking band) whose envelope is correlated with that of the first band, an effect called comodulation masking release (CMR). This paper examines CMR as a function of masker bandwidth and time delay between the envelopes of the on-frequency and flanking bands. The 1.0-kHz sinusoidal signal had a duration of 400 ms. The on-frequency band was presented alone (reference condition) or with the flanking band. The flanking-band envelope was either correlated or uncorrelated with that of the on-frequency band. Flanking-band center frequencies ranged from 0.25-2.0 kHz. The flanking band was presented either in the same ear as the on-frequency band (monaural condition) or in the opposite ear (dichotic condition). The noise bands had bandwidths of 6.25, 25, or 100 Hz. In the correlated conditions, the flanking-band envelope was delayed with respect to that of the on-frequency band by 0, 5, 10, or 20 ms. For the 100-Hz bandwidth, CMRs were small (typically less than 1 dB) in both monaural and dichotic conditions at all delay times. For the 25-Hz bandwidth, CMRs were about 3.5 dB for the 0-ms delay, and decreased to about 1.5 dB for the 20-ms delay. For the 6.25-Hz bandwidth, CMRs averaged about 5 dB and were almost independent of delay time. The results suggest that the absolute delay time is not the critical variable determining CMR. The magnitude of CMR appears to depend on the correlation between the envelopes of the on-frequency and flanking bands. However, the results do not support a model of CMR that assumes that signal threshold corresponds to a constant change in across-band envelope correlation when the correlation is transformed to Fisher's z.

Attention↗

PubMed1990

Auditory filter shapes at low center frequencies.

Auditory-filter shapes were estimated in normally hearing subjects for signal frequencies (fs) of 100, 200, 400, and 800 Hz using the notched-noise method [R. D. Patterson and I. Nimmo-Smith, J. Acoust. Soc. Am. 67, 229-245 (1980)]. Two noise bands, each 0.4fs wide, were used; they were placed both symmetrically and asymmetrically about the signal frequency to allow the measurement of filter shape and asymmetry. Two overall noise levels were used: 77 and 87 dB SPL. In deriving the shapes of the auditory filters, account was taken of the nonflat frequency response of the Sennheiser HD424 earphone, and also of the frequency-dependent attenuation produced by the middle ear. The auditory filters were asymmetric; the upper skirt was steeper than the lower skirt. The asymmetry tended to be greater at the higher noise level. The equivalent rectangular bandwidths (ERBs) of the filters at the lower noise level had average values of 36, 47, 87, and 147 Hz for values of fs of 100, 200, 400, and 800 Hz, respectively. The standard deviations of the ERBs across subjects were typically about 10% of the ERB values. The signal-to-masker ratio at the output of the auditory filter required to achieve threshold increased markedly with decreasing fs.

Adult↗

PubMed1990

Auditory filter shapes at 8 and 10 kHz.

Auditory filter shapes were derived from notched-noise masking data at center frequencies of 8 kHz (for three spectrum levels, N0 = 20, 35, and 50 dB) and 10 kHz (N0 = 50 dB). In order to minimize variability due to earphone placement, insert earphones (Etymotic Research ER2) were used and individual earmolds were made for each subject. These earphones were designed to give a flat frequency response at the eardrum for frequencies up to 14 kHz. The filter shapes were derived under the assumption that a frequency-dependent attenuation was applied to all stimuli before reaching the filter; this attenuation function was estimated from the variation of absolute threshold with frequency for the three youngest normally hearing subjects in our experiments. At 8 kHz, the mean equivalent rectangular bandwidths (ERBs) of the filters derived from the individual data for three subjects were 677, 637, and 1011 Hz for N0 = 20, 35, and 50 dB, respectively. The filters at N0 = 50 dB were roughly symmetrical, while, at the lower spectrum levels, the low-frequency skirt was steeper than the high-frequency skirt. The mean ERB at 10 kHz was 957 Hz. At this frequency, the filters for two subjects were steeper on the high-frequency side than the low-frequency side, while the third subject showed a slight asymmetry in the opposite direction.

Adult↗

PubMed1990

The influence of extraneous sounds on the perceptual estimation of first-formant frequency in vowels.

The contribution of extraneous sounds to the perceptual estimation of the first-formant (F1) frequency of voiced vowels was investigated using a continuum of vowels perceived as changing from/I/to/epsilon/as F1 was increased. Any phonetic effects of adding extraneous sounds were measured as a change in the position of the phoneme boundary on the continuum. Experiments 1-5 demonstrated that a pair of extraneous tones, mistuned from harmonic values of the fundamental frequency of the vowel, could influence perceived vowel quality when added in the F1 region. Perceived F1 frequency was lowered when the tones were added on the lower skirt of F1, and raised when they were added on the upper skirt. Experiments 6 and 7 demonstrated that adding a narrow-band noise in the F1 region could produce a similar pattern of boundary shifts, despite the differences in temporal properties and timbre between a noise band and a voiced vowel. The data are interpreted using the concept of the harmonic sieve [Duifhuis et al., J. Acoust. Soc. Am. 71, 1568-1580 (1982)]. The results imply a partial failure of the harmonic sieve to exclude extraneous sounds from the perceptual estimation of F1 frequency. Implications for the nature of the hypothetical harmonic sieve are discussed.

Adult↗

PubMed1990

Some factors affecting the magnitude of comodulation masking release.

This paper examines some of the factors that can affect the magnitude of comodulation masking release (CMR). In experiment I, psychometric functions were measured for the detection of a 1-kHz sinusoidal signal in a "multiplied" narrow-band noise centered at 1 kHz (reference condition) and the same noise with two comodulated flanking bands added. The functions were slightly steeper for the comodulated than for the reference masker. Thus CMRs measured at a high percent correct point were slightly (0.4 dB) larger than CMRs measured at a low percent correct point. Large individual differences were found for the reference masker but not for the comodulated masker. Experiment II compared CMRs obtained with narrow-band Gaussian noise and multiplied noise, using a single flanking band. For a flanking band remote from the signal frequency, the CMRs were smaller and more variable for the multiplied noise than for the Gaussian noise. This variability arose mainly from individual differences in the reference condition. Experiment III compared growth-of-masking functions for a signal centered in Gaussian noise and multiplied noise. Thresholds were lower for the multiplied than for the Gaussian noise, and the differences were greatest at high noise levels. The results are consistent with the idea that, for multiplied noise, some subjects can detect a change in the distribution of the envelope of the stimulus, when the signal is added to the masker. Such subjects have low thresholds in the reference condition, and give small CMRs. Other subjects are relatively insensitive to this cue. They have higher thresholds in the reference condition, and give larger CMRs. For Gaussian noise, thresholds for the reference condition are relatively stable across subjects and CMRs tend to be substantial, even for flanking-band frequencies remote from the signal frequency.

Adult↗

PubMed1990

Residual frequency selectivity in the profoundly hearing-impaired listener.

The extent to which auditory frequency analysis is retained in profoundly hearing-impaired listeners has major implications for hearing aid design. We have measured simplified psychoacoustic tuning curves in nine such listeners, using sinusoidal probes at 125 and 250 Hz, and 80-Hz wide narrow-band noise maskers. Two listeners showed PTCs at 125 and 250 Hz whose shapes were independent of probe frequency and parallel to their absolute thresholds, indicating the complete absence of frequency selectivity. Seven listeners showed evidence of frequency selectivity at 125 or 250 Hz or at both frequencies; at 250 Hz, frequency selectivity was evident in the six listeners whose 250-Hz hearing level was 95 dB or less, but not in the listeners with 250 Hz hearing levels above 95 dB. Where conventional 'v'-shaped PTCs were observed, estimated 3-dB auditory filter bandwidths were two to three times larger than those typically found in normal listeners. Notched-noise masking results at 250 Hz from the least hearing-impaired listener gave an estimated 3-dB bandwidth in reasonable agreement with that from the same listener's PTC data. Listeners who retain some frequency selectivity are able to make some use of first formant information in vowel identification, and preliminary results from one patient showed the ability to distinguish a variety of noise spectra. Both of these abilities could be of potential importance as a basis for the recoding of speech spectral patterning through stimulation matched to the listener's residual frequency selectivity.

Auditory Threshold↗

PubMed1990

Co-modulation masking release: spectro-temporal pattern analysis in hearing.

The peripheral auditory system is often modelled as containing an array of bandpass filters (called the auditory filters), each tuned to a different centre frequency. When a subject tries to detect a sinusoidal signal in noise, it has traditionally been assumed that performance is based on the output of the single auditory filter which gives the highest signal-to-masker ratio. However, recent experiments demonstrate the ability to compare the outputs of different auditory filters to enhance signal detection. This enhancement takes place especially when the envelope of the masker fluctuates over time, and when the fluctuations are coherent or correlated across different frequency bands. This phenomenon is called comodulation masking release (CMR) and it demonstrates the ability of the auditory system to perform a highly flexible spectro-temporal pattern analysis. CMR appears to be reduced or absent in persons with cochlear hearing loss, and this may partly account for the difficulties experienced by these persons in understanding speech in noisy backgrounds.

Auditory Pathways↗

PubMed1990

How much do we gain by gain control in hearing aids?

This paper considers three rationales for the use of automatic gain control (AGC) in hearing aids, and particularly multi-channel AGC. One rationale is to restore loudness relations among the acoustical elements of speech to what they would be for a normal ear. At present, there seems to be little evidence to support the idea that such loudness relations are critical for speech intelligibility. A second rationale is to reduce the effects of narrowband interfering sounds. This may be applicable in some restricted situations, but not in many others. The third rationale, the one considered here to be most important, is to ensure that all of the important elements in speech are comfortably audible. This can be achieved using two forms of AGC: slow-acting AGC operating on the whole speech signal, to compensate for variations in overall sound level from one situation to another; and fast-acting (syllabic) compression acting independently in a number of bands, to compensate for differences in level of acoustical elements within speech. To reduce spectral and temporal distortions introduced by the syllabic compression, the number of bands should be small (probably two or three) and the amount of compression should be the minimum required to ensure that all of the important elements in speech are audible. It is concluded that gain control can be useful for increasing user comfort and for ensuring the audibility of speech sounds. It is not likely to restore impaired hearing to normal for most patients, but may usefully be employed in conjunction with other forms of signal processing.

Equipment Design↗

PubMed1990

Spectral enhancement to improve the intelligibility of speech in noise for hearing-impaired listeners.

At speech-to-noise ratios between -3 and 6 dB, many hearing-impaired listeners have difficulty in understanding speech, but spectrograms reveal that the formant peaks of voiced speech and some of the spectral peaks associated with unvoiced speech stand out against the background noise. Our speech-enhancement process is based on the assumption that increasing spectral contrast will result in improved intelligibility. The enhancement involves calculating an auditory excitation pattern from the magnitude spectrum of overlapping short segments of the speech signal. This pattern is convolved with a difference-of-Gaussians function whose bandwidth varies with frequency in the same way as the auditory filter bandwidth. Magnitude values from this enhanced pattern are combined with the unchanged phase spectrum from the original signal to produce the enhanced speech. The processing was used to enhance Boothroyd and Bench-Kowal-Bamford Audiometric lists which had been digitally combined with speech-shaped noise at speech-to-noise ratios between -3 and 6 dB. The subjects had moderate to severe sensorineural hearing losses. The processing produced small but significant improvements in intelligibility for the hearing-impaired listeners tested. Possibilities for improving the processing are discussed.

Hearing Loss, Sensorineural↗

PubMed1990

Psychoacoustic aspects of speech pattern coding for the deaf.

The SiVo aid, which provides a sinusoidal signal indicating voice fundamental frequency and voicing information, was compared as an aid to lipreading to a conventional hearing aid having extended low-frequency output. Speech perceptual measures of consonant confusions in lipreading and the identification of a simple intonation contrast were collected from a group of 8 profoundly deaf adults. Audiometric and psychoacoustic measures were also collected. In the intonation task, 6 of the 7 patients tested performed better with the SiVo aid and the seventh scored perfectly with both aids. Four patients (out of 8) preferred to use the SiVo aid rather than the conventional aid, and 2 of these showed a significant advantage with the SiVo aid in the aided lipreading of consonants. The remaining 4 patients preferred the conventional aid, although none of these patients showed a significant advantage with the conventional aid in the lipreading of consonants. The 4 patients who preferred the SiVo aid over the conventional aid had very profound hearing loss and minimal dynamic range at 500 Hz and above, and those receiving the greatest benefit showed no measurable frequency selectivity. In the 2 patients who preferred the SiVo aid, yet showed no significant advantage for the SiVo aid in consonant lipreading, consonant confusions were also measured for aided lipreading, using a prototype aid providing both voice fundamental frequency and voiceless excitation patterns. Both patients showed additional and significant benefit from inclusion of the voiceless pattern element.

Audiometry, Pure-Tone↗

PubMed1989

Performance of some of the better cochlear-implant patients.

The main purpose of this study was to provide an independent corroboration of open-set word recognition in some of the better cochlear-implant patients. These included the Chorimac, Nucleus (one group from the U.S.A. and one group from Hannover, Germany), Symbion, Duren/Cologne and 3M/Vienna implants. Three experiments are reported: (1) word recognition in word lists and in sentences; (2) environmental sound perception, and (3) gap detection. On word recognition, the scores of 6 Chorimac patients averaged 2.5% words and 0.7% words in sentences correct in the French tests. In the German tests, the scores averaged 17% words and 10% words in sentences for 10 Duren/Cologne patients, 15% words and 16% words in sentences for 9 3M/Vienna patients, and 10% words and 16% words in sentences (3% to 26%) for 10 Nucleus/Hannover patients. In the English tests, the scores averaged 11% words and 29.6% words in sentences for 10 Nucleus-U.S.A. patients, and 13.7% words and 35.7% words in sentences for the 9 Symbion patients. The ability to recognize recorded environmental sounds was measured with a closed set of 18 sounds. Performance averaged 23% correct for Chorimac patients, 41% correct for 3M/Vienna patients, 44% correct for Nucleus/Hannover patients, 21% correct for Duren/Cologne patients, 58% correct for Nucleus/U.S.A. patients, and 83% correct for Symbion patients. A multidimensional scaling analysis suggested that patients were, in part, utilizing information about the envelope and about the periodic/aperiodic nature of some of the sounds. Gap detection thresholds with a one-octave wide noise centered at 500 Hz varied widely among patients. Typically, patients with gap thresholds less than 40 ms showed a wide range of performance on speech perception tasks, whereas patients with gap-detection thresholds greater than 40 ms showed poor word recognition skills.

Adolescent↗

PubMed1989

Detection of temporal gaps in sinusoids by normally hearing and hearing-impaired subjects.

A two-alternative forced-choice task was used to measure psychometric functions for the detection of temporal gaps in a 1-kHz, 400-ms sinusoidal signal. The signal always started and finished at a positive-going zero crossing, and the gap duration was varied from 0.5 to 6.0 ms in 0.5-ms steps. The signal level was 80 dB SPL, and a spectrally shaped noise was used to mask splatter associated with the abrupt onset and offset of the signal. Two subjects with normal hearing, two subjects with unilateral cochlear hearing loss, and two subjects with bilateral cochlear hearing loss were tested. The impaired ears had confirmed reductions in frequency selectivity at 1 kHz. For the normal ears, the psychometric functions were nonmonotonic, showing minima for gap durations corresponding to integer multiples of the signal period (n ms, where n is a positive integer) and maxima for durations corresponding to (n - 0.5) ms. For the impaired ears, the psychometric functions showed only small (nonsignificant) nonmonotonicities. Performance overall was slightly worse for the impaired than for the normal ears. The main features of the results could be accounted for using a model consisting of a bandpass filter (the auditory filter), a square-law device, and a sliding temporal integrator. Consistent with the data, the model demonstrates that, although a broader auditory filter has a faster transient response, this does not necessarily lead to improved performance in a gap detection task. The model also indicates that gap thresholds do not provide a direct measure of temporal resolution, since they depend at least partly on intensity resolution.

Aged↗

PubMed1989

Detection and discrimination of spectral peaks and notches at 1 and 8 kHz.

The ability of subjects to detect and discriminate spectral peaks and notches in noise stimuli was determined for center frequencies fc of 1 and 8 kHz. The signals were delivered using an insert earphone designed to produce a flat frequency response at the eardrum for frequencies up to 14 kHz. In experiment I, subjects were required to distinguish a broadband reference noise with a flat spectrum from a noise with either a peak or a notch at fc. The threshold peak height or notch depth was determined as a function of bandwidth of the peak or notch (0.125, 0.25, or 0.5 times fc). Thresholds increased with decreasing bandwidth, particularly for the notches. In experiment II, subjects were required to detect an increase in the height of a spectral peak or a decrease in the depth of a notch as a function of bandwidth. Performance was worse for notches than for peaks, particularly at narrow bandwidths. For both experiments I and II, randomizing (roving) the overall level of the stimuli had little effect at 1 kHz, but tended to impair performance at 8 kHz, particularly for notches. Experiments III-VI measured thresholds for detecting changes in center frequency of sinusoids, bands of noise, and spectral peaks or notches in a broadband background. Thresholds were lowest for the sinusoids and highest for the peaks and notches. The width of the bands, peaks, or notches had only a small effect on thresholds. For the notches at 8 kHz, thresholds for detecting glides in center frequency were lower than thresholds for detecting a difference in center frequency between two steady sounds. Randomizing the overall level of the stimuli made frequency discrimination of the sinusoids worse, but had little or no effect for the noise stimuli. In all six experiments, performance was generally worse at 8 kHz than at 1 kHz. The results are discussed in terms of their implications for the detectability of spectral cues introduced by the pinnae.

Adult↗

PubMed1989

Comodulation masking release for various monaural and binaural combinations of the signal, on-frequency, and flanking bands.

The threshold for a signal masked by a narrow band of noise centered at the signal frequency (the on-frequency band) may be reduced by adding to the masker a second band of noise (the flanking band) whose envelope is correlated with that of the first band. This effect is called comodulation masking release (CMR). These experiments examine two questions. (1) How does the CMR vary with the number and ear of presentation of the flanking band(s)? (2) Is it possible to obtain a CMR when a binaural masking level difference (BMLD) is already present, and vice versa? Thresholds were measured for a 400-ms signal in a continuous 25-Hz-wide noise centered at signal frequencies (fs) of 250, 1000, and 4000 Hz. This masker was presented either alone or with one or more continuous flanking bands whose envelopes were either correlated or uncorrelated with that of the on-frequency band; their frequencies ranged from 0.5fs to 1.5fs. CMRs were measured for six conditions in which the signal, the on-frequency band, and the flanking band(s) were presented in various monaural and binaural combinations. When a single flanking band was used, the CMR was typically around 2-3 dB. The CMR increased to 5-6 dB if an additional flanking band was added. The effect of the additional band was similar whether it was in the same ear as the original band or in the opposite ear. At the lowest signal frequency, a large CMR was observed in addition to a BMLD and vice versa. At the highest signal frequency, the extra release from masking was small. The results are interpreted in terms of the cues producing the CMR and the BMLD.

Acoustic Stimulation↗

PubMed1989

Comodulation masking release (CMR) as a function of masker bandwidth, modulator bandwidth, and signal duration.

These experiments examine how comodulation masking release (CMR) varies with masker bandwidth, modulator bandwidth, and signal duration. In experiment 1, thresholds were measured for a 400-ms, 2000-Hz signal masked by continuous noise varying in bandwidth from 50-3200 Hz in 1-oct steps. In one condition, using random noise maskers, thresholds increased with increasing bandwidth up to 400 Hz and then remained approximately constant. In another set of conditions, the masker was multiplied (amplitude modulated) by a low-pass noise (bandwidth varied from 12.5-400 Hz in 1-oct steps). This produced correlated envelope fluctuations across frequency. Thresholds were generally lower than for random noise maskers with the same bandwidth. For maskers less than one critical band wide, the release from masking was largest (about 5 dB) for maskers with low rates of modulation (12.5-Hz-wide low-pass modulator). It is argued that this release from masking is not a "true" CMR but results from a within-channel cue. For broadband maskers (greater than 400 Hz), the release from masking increased with increasing masker bandwidth and decreasing modulator bandwidth, reaching an asymptote of 12 dB for a masker bandwidth of 800 Hz and a modulator bandwidth of 50 Hz. Most of this release from masking can be attributed to a CMR. In experiment 2, the modulator bandwidth was fixed at 12.5 Hz and the signal duration was varied. For masker bandwidths greater than 400 Hz, the CMR decreased from 12 to 5 dB as the signal duration was decreased from 400 to 25 ms.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗

PubMed1989

Difference limens for phase in normal and hearing-impaired subjects.

These experiments measure the ability to detect a change in the relative phase of a single component in a harmonic complex tone. Complex tones containing the first 20 harmonics of 50, 100, or 200 Hz, all at equal amplitude, were used. All of the harmonics except one started in cosine phase. The remaining harmonic started in cosine phase, but was shifted in phase half-way through either the first or the second of the two stimuli comprising a trial. The subject had to identify the stimulus containing the phase-shifted component. For normally hearing subjects tested at a level of 70 dB SPL per component, thresholds for detecting the phase shift [i.e., phase difference limens (DLs)] were smallest (2 degrees-4 degrees) for harmonics above the eighth and for the lowest fundamental frequency (F0). Changes in phase were not detectable for harmonic numbers below three or four at the lowest F0 and below 5-13 at the highest F0. The DLs increased slightly for the highest harmonics in the complexes. The DLs increased markedly with decreasing level, except for the highest harmonic, where only a small effect of level was found. Subjects reported that the phase-shifted harmonic appeared to "pop out" and was heard with a pure-tone quality. A pitch-matching experiment demonstrated that the pitch of this tone corresponded to the frequency of the phase-shifted component. For the highest harmonic, the phase shift was associated with a downward shift of the edge pitch heard in the reference (all cosine phase) stimulus. When the phases of the components in the reference stimulus were randomized, phase DLs were much higher (and often impossible to measure), the pop-out phenomenon was not observed, and no edge pitch was heard. Subjects with unilateral cochlear hearing impairment generally showed poorer phase sensitivity in their impaired than in their normal ears, when the two ears were compared at equal sound-pressure levels. However, at comparable sensation levels, the impaired ears sometimes showed lower phase DLs. The results are explained by considering the waveforms that would occur at the outputs of the auditory filters in response to these stimuli.

Aged↗