Biomedical subjects

Brian C J Moore

Publications and source records attributed to Brian C J Moore.

At least 19 recordsLinked to original sources

PubMed2005

The relationship between stream segregation and frequency discrimination in normally hearing and hearing-impaired subjects.

We examined the relationship between the fission boundary (FB) at which a sequence of pure tones alternating between two frequencies cannot be heard as two separate streams and the frequency difference limen (FDL), using normally hearing subjects and subjects with cochlear hearing loss. The stimuli used in the two tasks were as similar as possible in duration and inter-tone interval. The frequency range examined was 250-8000 Hz for the normally hearing subjects and 250-2000 Hz for the hearing-impaired subjects. For normally hearing subjects, the FBs were almost invariant with frequency when expressed as ERB(N) values; the mean FB was about 0.4 ERB(N). The FDLs, also expressed as ERB(N) values, increased for frequencies above 2000 Hz. The ratio FB/FDL was roughly constant at 7-9 in the frequency region 250-2000 Hz, but decreased for higher frequencies, reaching about 1 at 8000 Hz. For the hearing-impaired subjects, FB/FDL ratios varied over a large range (1-40), and were not systematically related to the amount of hearing loss. These results suggest that the FB is not determined solely by the discriminability of successive tones.

Acoustic Stimulation↗

PubMed2005

Factors affecting psychophysical tuning curves for hearing-impaired subjects with high-frequency dead regions.

A dead region (DR) is a region of the cochlea where there are no functioning inner hair cells and/or neurons. DRs can be detected using the threshold-equalizing-noise (TEN) test, but psychophysical tuning curves (PTCs) are sometimes used to give a more precise estimate of the edge frequency of a DR; a shifted tip of the PTC indicates a DR. We show here that the shapes of PTCs for hearing-impaired subjects can be influenced by the detection of beats and simple difference tones (SDTs). As a result, PTCs can have tips at f(s), even when f(s) falls in a DR. PTCs were measured for subjects with mild to moderate low-frequency and severe high-frequency hearing loss using sinusoidal and narrowband noise maskers (80-, 160-, 320-Hz wide): (1) in quiet; (2) in the presence of additional lowpass filtered noise (LF noise) designed to mask SDTs; (3) in the presence of a pair of low-frequency tones designed to interfere with the detection of beats (MDI tones). In condition (1), the PTCs were often W-shaped, with a sharp tip at f(s). This occurred less for the wider noise bandwidths. For subjects with good low-frequency hearing, the LF noise often reduced or eliminated the tip at f(s), suggesting that this tip was partly caused by detection of SDTs. For the sinusoidal and 80-Hz wide noise maskers, the addition of the MDI tones reduced the masker level required for threshold for masker frequencies adjacent to f(s), for nearly all subjects, suggesting a strong influence of beat detection. To minimize the influence of beats, we recommend using noise maskers with a bandwidth of 160 or (preferably) 320 Hz. In cases of near-normal hearing at low frequencies, we recommend using an additional LF noise to mask SDTs.

Acoustic Stimulation↗

PubMed2005

Dead regions and noisiness of pure tones.

Some hearing-impaired subjects report pure tones as sounding highly distorted and noise-like. We assessed whether such reports indicate that the tone frequency falls inside a dead region (DR). Nine hearing-impaired and four normally hearing subjects rated pure tones on a scale from 1 to 7, where 1 indicates clear tone and 7 indicates noise. A white noise was presented as a reference for a sound that should be rated as 7. Stimuli covered the whole audible range of frequencies and levels. The noisiness ratings were, on average, higher for hearing-impaired subjects than for normally hearing subjects. For the former, the ratings were not markedly different for tones with frequencies just outside or inside a DR. However, ratings always exceeded 3 for tones falling more than 1.5 octaves inside a DR. The results indicate that judgement of a tone as sounding noise-like does not reliably indicate that the tone frequency falls in a DR. Both normally hearing and hearing-impaired subjects rated 0.125 kHz and 12 kHz tones as somewhat noise-like, independently of the existence of a DR.

Adult↗

PubMed2005

Comparison of two adaptive procedures for fitting a multi-channel compression hearing aid.

We compared two adaptive procedures for fitting a multi-channel compression hearing aid. "Camadapt" uses judgements of the loudness of speech stimuli and the tonal quality of music stimuli. "Eartuner" uses judgements of the loudness and clarity of speech stimuli with differing spectral characteristics. Sixteen new users of hearing aids were fitted unilaterally, using each procedure. The fittings were assigned to Programs 1 and 2 in the aid, in a counter-balanced order. Subjects kept a diary of their experiences with each program in everyday life. Following 2-4 weeks of experience, they filled in the APHAB and other questionnaires and were re-fitted using both procedures. Camadapt generally led to higher low-level gains and lower high-level gains than Eartuner. Gains recommended by the procedures did not change following experience. Eight subjects preferred the Camadapt fitting and eight preferred the Eartuner fitting. Most subjects gave high overall satisfaction ratings for both procedures. Test-retest reliability was better for Eartuner than for Camadapt. Preference for the Camadapt fitting was associated with slightly better speech communication with Camadapt, while preference for the Eartuner fitting was associated with fewer problems with aversion for that procedure.

Acoustic Stimulation↗

PubMed2005

Development of a fast method for determining psychophysical tuning curves.

Psychophysical tuning curves (PTCs) can be used to assess the frequency selectivity of the auditory system and to detect and delimit "dead regions" in the cochlea. However, the traditional method for determining PTCs takes too long for use in clinical practice. We evaluated a fast method for determining PTCs, using a band of noise that sweeps in centre frequency and a Békésy method to adjust the masker level required for threshold. The shapes of the PTCs were similar for the fast and traditional methods, for both normally hearing and hearing-impaired subjects. Rates of change of masker level of 2 dB/s or less gave the most reliable results. A relatively wide bandwidth (20 percent of the signal frequency or 320 Hz, whichever is the smaller) was needed to minimise the influence of beat detection. When the signal frequency fell within a dead region, the fast method gave PTCs with shifted tips.

Acoustic Stimulation↗

PubMed2005

Reassessment of cochlear dead regions in hearing-impaired teenagers with severe-to-profound hearing loss.

The aim of this study was to reassess cochlear dead regions after an interval of twelve months, using the Threshold Equalising Noise (TEN) test. Thirty-four ears of 24 teenagers (mean age of 14 years) with longstanding severe-to-profound sensorineural hearing impairment were tested. Testing was repeated after an interval of 12 months using the same experimental set-up. A total of eight (23.5%) out of 34 ears changed category on retest: this decreased to two (7.1%) out of 27 ears when the inconclusive category was removed from the analysis. In both of these ears (of the same participant) the criteria were met at a single frequency, and the masked threshold was only 10 dB above the TEN level per ERBN. When all of the data were examined on a frequency-by-frequency basis, the instances that changed category ranged from 15 to 51%. The range decreased to between 4 and 34% when the inconclusive category was removed from the analysis.

Adolescent↗

PubMed2005

Effects of three amplification strategies on speech perception by children with severe and profound hearing loss.

OBJECTIVE: Traditionally in the United Kingdom, children with severe and profound hearing loss have been fitted with linear, analog hearing aids. Fast-acting, wide-dynamic-range compression (WDRC) has been shown to give better discrimination of speech than linear amplification for moderately hearing-impaired young adults. For severe and profound hearing losses, higher compression ratios are needed. The resultant distortion of the temporal envelope and reduced modulation depth may offset improvements in audibility offered by WDRC. In this study, speech recognition and discrimination were assessed for severely and profoundly hearing-impaired children, using three different amplification strategies, including WDRC. DESIGN: Fifteen children (ages 7 to 15 yr) with severe and profound hearing loss were fitted bilaterally with high-power, multichannel compression hearing aids, incorporating one of three different amplification strategies: linear with peak clipping, linear with compression limiting, or WDRC. Output responses were matched to Desired Sensation Level (DSL i/o) targets. The children wore hearing aids programmed with each of the amplification strategies in turn, for at least 1 wk, in a counterbalanced order across children. After using a particular amplification strategy for at least 1 wk, speech perception tests were carried out. RESULTS: Speech scores on closed-set testing for the profound group showed significant benefit for WDRC over the other two algorithms. None of the other results showed a statistically significant effect of algorithm on speech performance. CONCLUSIONS: WDRC amplification sometimes led to better performance than linear amplification with peak clipping or output limiting, and it never led to poorer performance. Therefore, it appears to be safe to use well-designed WDRC for hearing-impaired children with severe or profound hearing loss.

Adolescent↗

PubMed2005

Tolerable hearing-aid delays: IV. effects on subjective disturbance during speech production by hearing-impaired subjects.

OBJECTIVE: We assessed the effects of time delay in a hearing aid on subjective disturbance and reading rates while the user of the aid was speaking, using hearing-impaired subjects and real-time processing. The time delay was constant across frequency. DESIGN: A digital signal processor was programmed as a four-channel, fast-acting, wide-dynamic-range compression hearing aid. One of four delays could be selected on the aid to produce a total delay of 13, 21, 30, or 40 msec between microphone and receiver. Twenty-five subjects, mostly with near-symmetric hearing impairment of cochlear origin, were fitted bilaterally with behind-the-ear aids connected to the processor. The aids were programmed with insertion gains prescribed by the CAMEQ loudness equalization procedure for each subject and ear. Subjects were asked to read aloud from scripts: speech production rates were measured and subjective ratings of the disturbance of the delay were obtained. Subjects required some training to recognize the effects of the delay to rate it consistently. RESULTS: Subjective disturbance increased progressively with increasing delay and was a nonmonotonic function of low-frequency hearing loss. Subjects with mild or severe low-frequency hearing loss were generally less disturbed by the delay than those with moderate loss. Disturbance ratings tended to decrease over successive tests. Word production rates were not significantly affected by delay over the range of delays tested. CONCLUSIONS: The results follow a pattern similar to those presented in , obtained using a simulation of hearing loss and normally hearing subjects, except for the nonmonotonic variation of disturbance with low-frequency hearing loss. We hypothesize that disturbance is maximal when the levels in the ear canal of the low-frequency components are similar for the unaided and aided sounds. A rating of 3, which is probably just acceptable, was obtained for delays ranging from 14 to 30 msec, depending on the hearing loss. Some acclimatization to the subjective disturbance occurred over a time scale of about 1 hour.

Attitude↗

PubMed2005

Effect of frequency-modulation coherence for inharmonic stimuli: frequency-modulation phase discrimination and identification of artificial double vowels.

The ability to compare patterns of frequency modulation (FM) in separate frequency regions was explored. In experiment 1, listeners had to distinguish whether the FM applied to two nonharmonically related sinusoidal carriers was in phase or out of phase. The FM rate was the same for each carrier. The starting phase of the modulation was randomized for each stimulus in a three alternative, forced-choice (3AFC) trial. Subjects were sensitive to relative FM phase for modulation rates of 2 and 4 Hz, but not for higher rates. In experiment 2, vowel identification was compared for artificial single and double vowels. The vowels were constructed from complex tones with components spaced at 2-ERB(N) (equivalent rectangular bandwidth) intervals, by increasing the levels of three components by 15 dB, to create three "formants." In the double vowels, the components of the two vowels were interleaved, to give 1-ERB(N) spacing. The three "formant" components were frequency modulated at 2, 4, or 8 Hz, with either the same or different rates for the two vowels. The identification of double vowels was not improved by a difference in FM rate across vowels, suggesting that differences in FM rate do not support perceptual segregation of inharmonic stimuli.

Acoustic Stimulation↗

PubMed2005

Modulation masking produced by second-order modulators.

Recent studies suggest that an auditory nonlinearity converts second-order sinusoidal amplitude modulation (SAM) (i.e., modulation of SAM depth) into a first-order SAM component, which contributes to the perception of second-order SAM. However, conversion may also occur in other ways such as cochlear filtering. The present experiments explored the source of the first-order SAM component by investigating the ability to detect a 5-Hz, first-order SAM probe in the presence of a second-order SAM masker beating at the probe frequency. Detection performance was measured as a function of masker-carrier modulation frequency, phase relationship between the probe and masker modulator, and probe modulation depth. In experiment 1, the carrier was a 5-kHz sinusoid presented either alone or within a notched-noise masker in order to restrict off-frequency listening. In experiment 2, the carrier was a white noise. The data obtained in both carrier conditions are consistent with the existence of a modulation distortion component. However, the phase yielding poorest detection performance varied across experimental conditions between 0 degrees and 180 degrees, confirming that, in addition to nonlinear mechanisms, cochlear filtering and off-frequency listening play a role in second-order SAM perception. The estimated magnitude of the modulation distortion component ranges from 5%-12%.

Adolescent↗

PubMed2005

Pitch discrimination interference: the role of pitch pulse asynchrony.

Gockel, Carlyon, and Plack [J. Acoust. Soc. Am. 116, 1092-1104 (2004)] showed that discrimination of the fundamental frequency (F0) of a target tone containing only unresolved harmonics was impaired when an interfering complex tone with fixed F0 was added to the target, but filtered into a lower frequency region. This pitch discrimination interference (PDI) was greater when the interferer contained resolved harmonics than when it contained only unresolved harmonics. Here, it is examined whether this occurred because, when the interferer contained unresolved harmonics, "pitch pulse asynchrony (PPA)" between the target and interferer provided a cue that enhanced performance; this was possible in the earlier experiment because both target and interferer had components added in sine phase. In experiment 1, it was shown that subjects were moderately sensitive to the direction of PPA across frequency regions. In experiments 2 and 3, PPA cues were eliminated by adding the components of the target only, or of both target and interferer, in random phase. For both experiments, an interferer containing resolved harmonics produced more PDI than an interferer containing unresolved harmonics. These results show that PDI is smaller for an interferer with unresolved harmonics even when cues related to PPA are eliminated.

Acoustic Stimulation↗

PubMed2005

Dead regions and pitch perception.

The perception of pitch for pure tones with frequencies falling inside low- or high-frequency dead regions (DRs) was examined. Subjects adjusted a variable-frequency tone to match the pitch of a fixed tone. Matches within one ear were often erratic for tones falling in a DR, indicating unclear pitch percepts. Matches across ears of subjects with asymmetric hearing loss, and octave matches within ears, indicated that tones falling within a DR were perceived with an unclear pitch and/or a pitch different from "normal" whenever the tones fell more than 0.5 octave within a low- or high-frequency DR. One unilaterally impaired subject, with only a small surviving region between 3 and 4 kHz, matched a fixed 0.5-kHz tone in his impaired ear with, on average, a 3.75-kHz tone in his better ear. When asked to match the 0.5-kHz tone with an amplitude-modulated tone, he adjusted the carrier and modulation frequencies to about 3.8 and 0.5 kHz, respectively, suggesting that some temporal information was still available. Overall, the results indicate that the pitch of low-frequency tones is not conveyed solely by a temporal code. Possibly, there needs to be a correspondence between place and temporal information for a normal pitch to be perceived.

Acoustic Stimulation↗

PubMed2004

Effects of masker component phase on the forward masking produced by complex tones in normally hearing and hearing-impaired subjects.

For normally hearing subjects, harmonic complex tones that give "peaky" waveforms on the basilar membrane (Schroeder-positive phase, sine phase or cosine phase) lead to less forward masking than complex tones that give less peaky waveforms (Schroeder-negative phase or random phase), but have the same power spectrum. This difference has been attributed mainly to the combined effects of peripheral compression and suppression, both of which depend on the operation of the active mechanism in the cochlea. If this explanation is correct, the phase effect should be reduced or absent for subjects with moderate cochlear hearing loss. We measured growth-of-masking functions for forward maskers containing the first 40 harmonics of a 100-Hz fundamental, with components added either in cosine phase or random phase, using both normally hearing subjects and subjects with moderate cochlear hearing loss. The signal frequency was 1 or 2 kHz. For the normally hearing subjects, the mean slopes of the growth-of-masking functions at 1 and 2 kHz, respectively, were 0.53 and 0.44 for the random-phase masker and 0.31 and 0.26 for the cosine-phase masker. For high masker levels, the former produced considerably more masking than the latter. The phase effect was smaller for the hearing-impaired than for the normally hearing subjects, which is consistent with the idea that it is partly caused by peripheral compression and suppression. However, three of the five hearing-impaired subjects showed a significant effect of masker phase for at least one signal frequency. In one case, this occurred when the hearing loss at the signal frequency was 65 dB. The slopes of the growth-of-masking functions were consistently less than one for the hearing-impaired subjects. Further testing suggested that the efferent system was not involved in producing the phase effect.

Acoustic Stimulation↗

PubMed2004

Auditory streaming based on temporal structure in hearing-impaired listeners.

The influence of temporal cues on sequential stream segregation was investigated using five elderly hearing-impaired listeners. In experiment 1, an alternating pattern of A and B tones was used. Each tone was a harmonic complex with a 100-Hz fundamental, with one of three passbands (1250-2500, 1768-3636, or 2500-5000 Hz) and one of three component-phase relationships (cosine, alternating, or random). The complexes had an overall level of 96 dB SPL. The detection of a change in relative timing of the A and B tones was measured in a two-interval-forced-choice paradigm. The sequence in one interval remained isochronous while the sequence in the other started isochronously but became increasingly irregular with the addition of a cumulative delay between the A and B tones. Component phase relationship and passband difference both had significant effects on the minimum detectable delay, indicating that temporal structure produced obligatory stream segregation. In experiment 2, subjects continuously reported whether tones presented in a 30-s ABA-ABA- sequence were perceived as segregated or integrated. Differences in component phase between A and B significantly increased perceived segregation, but passband did not. In conclusion, stream segregation due to differences in temporal structure is robust in elderly subjects with cochlear hearing loss and comparable to that found previously in young normally hearing subjects.

Acoustic Stimulation↗

PubMed2004

Factors affecting psychophysical tuning curves for normally hearing subjects.

These experiments were conducted to clarify the influence of beats and combination products on psychophysical tuning curves (PTCs) for normally hearing subjects. PTCs for 1- and 4-kHz sinusoidal signals were determined using as maskers a sinusoidal tone and 80-, 160-, and 320-Hz wide bands of noise. PTCs obtained using the sinusoidal masker showed distinct irregularities, particularly for masker frequencies close to the signal frequency. The PTCs determined for the noise maskers were more regular. The broader the masker, the more regular were the shapes of the PTCs. To reduce the detectability of beats produced by the interaction of the signal and masker, a pair of low-frequency tones, called "Modulation detection interference (MDI) tones", was used to introduce beats at the same rate. The MDI tones reduced the threshold level of the sinusoidal masker by up to 20 dB for frequencies within 300 Hz of the signal frequency; a similar but smaller effect was found when an 80-Hz wide masker was used. Adding a lowpass filtered (LF) noise to the sinusoidal or narrowband noise masker did not affect the low-frequency sides of the PTCs, suggesting no influence of combination products. The LF noise did affect the high-frequency sides of the PTCs, but this can be attributed to it reducing off-frequency listening. To achieve a PTC whose shape around the tip is minimally affected by beats, we propose using a noise masker with a bandwidth approximately equal to the bandwidth of the auditory filter for which the PTC is measured.

Acoustic Stimulation↗

PubMed2004

A revised model of loudness perception applied to cochlear hearing loss.

We previously described a model for loudness perception for people with cochlear hearing loss. However, that model is incompatible with our most recent and most satisfactory model of loudness for normal hearing. Here, we describe a loudness model that is applicable to both normal and impaired hearing. In contrast to our earlier model for impaired hearing, the new model correctly predicts: (1) that a sound at absolute threshold has a small but finite loudness; (2) that, for levels very close to the absolute threshold, the rate of growth of loudness is similar for normal ears and ears with cochlear hearing loss; (3) the relation between monaural and binaural threshold and loudness; (4) recent measures of equal-loudness contours. Like the earlier model, the new model can account for the loudness recruitment and reduced loudness summation that are typically associated with cochlear hearing loss.

Cochlea↗

PubMed2004

Auditory processing efficiency and temporal resolution in children and adults.

Children have higher auditory backward masking (BM) thresholds than adults. One explanation for this is poor temporal resolution, resulting in difficulty separating brief or rapidly presented sounds. This implies that the auditory temporal window is broader in children than in adults. Alternatively, elevated BM thresholds in children may indicate poor processing efficiency. In this case, children would need a higher signal-to-masker ratio than adults to detect the presence of a signal. This would result in poor performance on a number of psychoacoustic tasks but would be particularly marked in BM due to the compressive nonlinearity of the basilar membrane. The objective of the present study was to examine the competing hypotheses of "temporal resolution" and "efficiency" by measuring BM as a function of signal-to-masker interval in children and adults. The children had significantly higher thresholds than the adults at each of the intervals. Subsequent modeling and analyses showed that the data for both children and adults were best fitted using the same, fixed temporal window. Therefore, the differences in BM threshold between adults and children were not due to differences in temporal resolution but to reduced detection efficiency in the children.

Acoustic Stimulation↗

PubMed2004

Comparison of three procedures for initial fitting of compression hearing aids. II. Experienced users, fitted unilaterally.

This paper is the second in a series comparing three procedures for the initial fitting of multichannel compression hearing aids. The first paper reported the results for a group of 10 experienced hearing aid users fitted bilaterally. This paper reports the results for a different group of 10 experienced hearing aid users fitted unilaterally. The three procedures were: (1) CAMEQ, which aims to amplify speech so as to give equal loudness per critical band over the frequency range 500-5000 Hz, and to give similar overall loudness to normal over a wide range of speech levels; (2) CAMREST, which aims to amplify speech so as to restore normal specific loudness patterns, over a wide range of speech levels; and (3) DSL [i/o], which aims to map the dynamic range of normal-hearing people into the reduced dynamic range of hearing-impaired people, with full restoration of audibility. Each subject was fitted with one Danalogic 163D digital hearing aid, using each of the three fitting procedures in turn; the order was counter-balanced across subjects. Prescribed insertion gains for 55 and 80 dB SPL input levels were verified using real-ear measurements. Immediately after fitting with a given procedure, and 1 week after fitting. the gains were adjusted, when required, by the minimum amount necessary to achieve acceptable fittings. On average, the adjustments were smallest for the CAMREST procedure, slightly larger for the CAMEQ procedure, and largest of all for DSL [i/o]. For the DSL [i/o] the gain changes were mostly negative, especially for high frequencies and the higher input level. After these gain adjustments, users wore the aids for at least 3 weeks before speech reception thresholds (SRTs) for sentences in quiet and in steady and fluctuating background noise were measured. The APHAB questionnaire was also administered. The hearing aids were then refitted with the next procedure. SRTs and APHAB scores did not differ significantly between the three procedures. We conclude that the CAMEQ and CAMREST procedures provide a more appropriate initial fitting than DSL [i/o] for unilaterally experienced hearing aid wearers. Comparison with our earlier study based on bilateral fittings suggests that the preferred gains are similar for unilateral and bilateral fittings.

Acoustic Stimulation↗