Biomedical subjects

B C Moore

Publications and source records attributed to B C Moore.

At least 181 records · Page 10Linked to original sources

PubMed1986

Auditory filter shapes in subjects with unilateral and bilateral cochlear impairments.

The shape of the auditory filter was estimated at three center frequencies, 0.5, 1.0, and 2.0 kHz, for five subjects with unilateral cochlear impairments. Additional measurements were made at 1.0 kHz using one subject with a unilateral impairment and six subjects with bilateral impairments. Subjects were chosen who had thresholds in the impaired ears which were relatively flat as a function of frequency and ranged from 15 to 70 dB HL. The filter shapes were estimated by measuring thresholds for sinusoidal signals (frequency f) in the presence of two bands of noise, 0.4 f wide, one above and one below f. The spectrum level of the noise was 50 dB (re: 20 mu Pa) and the noise bands were placed both symmetrically and asymmetrically about the signal frequency. The deviation of the nearer edge of each noise band from f varied from 0.0 to 0.8 f. For the normal ears, the filters were markedly asymmetric for center frequencies of 1.0 and 2.0 kHz, the high-frequency branch being steeper. At 0.5 kHz, the filters were more symmetric. For the impaired ears, the filter shapes varied considerably from one subject to another. For most subjects, the lower branch of the filter was much less steep than normal. The upper branch was often less steep than normal, but a few subjects showed a near normal upper branch. For the subjects with unilateral impairments, the equivalent rectangular bandwidth of the filter was always greater for the impaired ear than for the normal ear at each center frequency. For three subjects at 0.5 kHz and one subject at 1.0 kHz, the filter had too little selectivity for its shape to be determined.

Adolescent↗

PubMed1986

Detection of tones in noise and the "severe departure" from Weber's law.

Thresholds were measured for the detection of 20-ms sinusoids, with frequencies 500, 4000, or 6500 Hz, presented in bursts of bandpass noise of the same duration and centered around the signal frequency. A range of noise levels from 35 to 80 dB SPL was used. Noise at different center frequencies was equated in terms of the total noise power in an assumed auditory filter centered on the signal frequency. Thresholds were expressed as the signal levels, relative to these noise levels, necessary for subjects to achieve 71% correct. For 500-Hz signals, thresholds were about 5 dB regardless of noise level. For 6500-Hz signals, thresholds reached a maximum of 14 dB at intermediate noise levels of 55-65 dB SPL. For 4000-Hz signals, a maximum threshold of 10 dB was observed for noise levels of 45-55 dB SPL. When the bandpass noises were presented continuously, however, thresholds for 6500-Hz, 20-ms signals remained low (about 1 dB) and constant across level. These results are similar to those obtained for the intensity discrimination of brief tones in bandstop noise [R. P. Carlyon and B. C. J. Moore, J. Acoust. Soc. Am. 76, 1369-1376 (1984); R. P. Carlyon and B. C. J. Moore, J. Acoust. Soc. Am. 79, 453-460 (1986)].

Auditory Threshold↗

PubMed1986

Continuous versus gated pedestals and the "severe departure" from Weber's law.

Thresholds were compared for the detection of 20-ms sinusoidal signals presented with either continuous or gated sinusoidal pedestals of the same frequency (500 or 6500 Hz). Pedestal levels ranged from 35-80 dB SPL. For 500-Hz signals, thresholds were lower in the continuous-pedestal condition than in the gated-pedestal condition, for all pedestal levels above 35 dB SPL. When the pedestal level was 35 dB, thresholds were higher in the continuous-pedestal condition than in the gated-pedestal condition. This was also true at all pedestal levels when bandstop noise centered around the pedestal frequency was added to the pedestal. For 6500-Hz signals, a deterioration in performance at intermediate levels, similar to that reported by Carlyon and Moore [J. Acoust. Soc. Am. 76, 1369-1376 (1984)], was found in the gated-pedestal condition. No such deterioration occurred in the continuous-pedestal condition. However, masking signal onsets and offsets by bursts of bandpass noise produced a midlevel deterioration in the continuous-pedestal condition. This was true when bandstop noise was absent, and when it was gated on and off in each observation interval. When continuous bandstop noise was present, no midlevel deterioration was observed, even when onsets and offsets were masked. The results suggest that in the continuous-pedestal condition subjects may normally maintain performance across level at 6500 Hz by attending to a transient response to signal onsets. Presenting bursts of bandpass noise disrupts the detection of such a response. The absence of a midlevel deterioration when continuous bandstop noise was present may be related to the adaptation to the sinusoidal pedestal that was caused by the bandstop noise.

Auditory Threshold↗

PubMed1986

Thresholds for hearing mistuned partials as separate tones in harmonic complexes.

When a low harmonic in a harmonic complex tone is mistuned from its harmonic value by a sufficient amount it is heard as a separate tone, standing out from the complex as a whole. This experiment estimated the degree of mistuning required for this phenomenon to occur, for complex tones with 10 or 12 equal-amplitude components (60 dB SPL per component). On each trial the subject was presented with a complex tone which either had all its partials at harmonic frequencies or had one partial mistuned from its harmonic frequency. The subject had to indicate whether he heard a single complex tone with one pitch or a complex tone plus a pure tone which did not "belong" to the complex. An adaptive procedure was used to track the degree of mistuning required to achieve a d' value of 1. Threshold was determined for each ot the first six harmonics of each complex tone. In one set of conditions stimulus duration was held constant at 410 ms, and the fundamental frequency was either 100, 200, or 400 Hz. For most conditions the thresholds fell between 1% and 3% of the harmonic frequency, depending on the subject. However, thresholds tended to be greater for the first two harmonics of the 100-Hz fundamental and, for some subjects, thresholds increased for the fifth and sixth harmonics. In a second set of conditions fundamental frequency was held constant at 200 Hz, and the duration was either 50, 110, 410, or 1610 ms. Thresholds increased by a factor of 3-5 as duration was decreased from 1610 ms to 50 ms. The results are discussed in terms of a hypothetical harmonic sieve and mechanisms for the formation of perceptual streams.

Auditory Threshold↗

PubMed1986

Comparisons of frequency selectivity in simultaneous and forward masking for subjects with unilateral cochlear impairments.

Two experiments are described in which frequency selectivity was estimated, in simultaneous and forward masking, for each ear of subjects with moderate (25-60 dB HL) unilateral cochlear hearing losses. In both experiments, the signal level was fixed for a given ear and type of masking (simultaneous or forward), and the masker level was varied to determine threshold, using an adaptive, two-alternative forced-choice procedure. In experiment I, the masker was a noise with a spectral notch centered at the signal frequency (either 1.0 or 1.5 kHz); threshold was determined as a function of notch width. Signal levels were chosen so that the noise level required at threshold for a notch width of zero was similar for the normal and impaired ear of each subject in both simultaneous and forward masking. The function relating threshold to notch width had a steeper slope for the normal ear than for the impaired ear of each subject. For the normal ears, these functions were steeper in forward masking than in simultaneous masking. This difference was interpreted as resulting from suppression. For the impaired ears, significant differences in the same direction were observed for three of the five subjects, but the differences were smaller. In experiment II, psychophysical tuning curves (PTCs) were determined in the presence of a fixed notched noise centered at the signal frequency (1.0 kHz). For the normal ears, the PTCs were sharper in forward masking than in simultaneous masking. For the impaired ears, the PTCs were similar in simultaneous and forward masking, but those in forward masking tended to be sharper at masker frequencies far removed from the signal frequency. Overall, the results suggest that suppression is reduced, but not completely absent in cases of moderate cochlear hearing loss.

Aged↗

PubMed1986

Temporal effects in masking and their influence on psychophysical tuning curves.

Psychophysical tuning curves (PTCs) were obtained in simultaneous and forward masking for a 20-ms, 1000-Hz signal presented at 10 dB SL. The signal was presented at the beginning of, at the temporal center of, at the end of, or immediately following a 400-ms masker. The first experiment was done in quiet; the second experiment was done in the presence of two bands of noise on either side of 1000 Hz. The results were similar in quiet and in noise. In simultaneous masking, the PTCs were broadest for the signal at masker onset, and generally sharpest for the signal at temporal center; the differences were largest on the high-frequency side. In most cases, there was virtually no difference in Q10 between the forward-masking PTC and the simultaneous-masking PTC with the signal temporally centered, although the high-frequency slope was always steeper in forward masking. These results indicate that, at least for brief signals, frequency selectivity measured with simultaneous-masking PTCs and the degree of sharpening revealed in forward-masking PTCs depend upon the temporal position of the signal within the simultaneous masker.

Adult↗

PubMed1986

Parallels between frequency selectivity measured psychophysically and in cochlear mechanics.

One of the most important features of the auditory system is its action as a frequency analyser. The frequency analysis appears to have its basis in the mechanical patterns of vibration on the basilar membrane (BM). Its properties can be measured psychophysically using masking experiments and the results explained using the concept of the auditory filter (critical bandwidth). A method of measuring the auditory filter shape at a particular centre frequency is described. This method is based upon the power-spectrum model of masking which assumes: 1) when detecting a signal in a masker the observer uses the single filter giving the highest signal-to-masker ratio; 2) threshold corresponds to a fixed signal-to-masker ratio at the output of that filter. The variation of the auditory filter bandwidth with centre frequency is described and related to measurements of the frequency-position map on the BM in man. The equivalent rectangular bandwidth (ERB) of the auditory filter corresponds approximately to a constant distance of 0.9 mm on the BM. Changes in the auditory filter shape with level are described and are shown to correspond, at least qualitatively, to input-output functions measured on the BM and in single neurones of the auditory nerve. Finally, a method is described for deriving the excitation pattern of a sound from its power spectrum, using the results of auditory-filter measurements. The excitation pattern derived in this way probably corresponds to the distribution of excitation along the BM.

Animals↗

PubMed1986

A comparison of two-channel and single-channel compression hearing aids.

Eight subjects with bilateral sensorineural hearing losses took part in a trial comparing listening unaided with listening binaurally through two types of hearing aid, aid A and aid B. Both aids incorporated slow-acting automatic gain control (AGC) operating on the whole speech signal. However, aid A also incorporated two-channel syllabic compression. The two aids were chosen to be as similar as possible in other respects, and both were worn behind the ear. Subjects were tested in a counter-balanced order, and had at least 2 weeks of everyday experience with each aid before testing took place. Performance was evaluated in three ways: by measuring speech intelligibility in quiet for sentences at three peak sound levels, 55, 70 and 85 dB SPL; by measuring the level of speech required for 50% intelligibility (called the SRT) of sentences in two levels of speech-shaped noise, 60 and 75 dB SPL; and by administering questionnaires about experience with the aids in everyday life. Both aid A and aid B improved the intelligibility of speech in quiet relative to unaided listening, particularly at the lowest sound level. However, aid A gave lower (i.e., superior) SRTs in speech-shaped noise than aid B or unaided listening. The questionnaires also indicated that aid A gave better performance in noisy situations. The results strongly suggest that two-channel syllabic compression, combined with slow-acting AGC operating on the whole speech signal, can give superior results to slow-acting AGC alone, particularly in noisy situations.

Adolescent↗

PubMed1985

The danger of using narrow-band noise maskers to measure "suppression".

These experiments investigated whether perceptual cueing plays a role in the "unmasking" effects which have been observed in forward masking for narrow-band noise maskers and brief signals. The forward masking produced by a 100-Hz-wide noise masker at a level of 60 dB SPL was measured for a 1-kHz sinusoidal signal with a raised-cosine envelope and a duration of 10 ms at the 6-dB-down points, both for the masker alone, and with various components added to the masker (and gated synchronously with the masker). Unmasking was found to occur even for components which were extremely unlikely to produce a significant suppression of the masker: these included a 75-dB SPL 4-kHz sinusoid, a 50-dB SPL 1.4-kHz sinusoid, a noise low-pass filtered at 4 kHz with a spectrum level of 0 dB, and a noise low-pass filtered at 4 kHz with a spectrum level of 20 dB presented in the opposite ear to the masker-plus-signal. It is concluded that perceptual cueing can play a significant role in producing unmasking for brief signals following narrow-band noise maskers, and that it is unwise to interpret the unmasking solely in terms of suppression.

Acoustic Stimulation↗

PubMed1985

Detection of temporal gaps in bandlimited noise: effects of variations in bandwidth and signal-to-masker ratio.

Thresholds were measured for the detection of a temporal gap in a bandlimited noise signal presented in a continuous wideband masker, using an adaptive forced-choice procedure. In experiment I the ratio of signal spectrum level to masker spectrum level (the SMR) was fixed at 10 dB and gap thresholds were measured as a function of signal bandwidth at three center frequencies: 0.4, 1.0, and 6.5 kHz. Performance improved with increasing bandwidth and increasing center frequency. For a subset of conditions, gap threshold was also measured as bandwidth was varied keeping the upper cutoff frequency of the signal constant. In this case the variation of gap threshold with bandwidth was more gradual, suggesting that subjects detect the gap using primarily the highest frequency region available in the signal. At low center frequencies, however, subjects may have a limited ability to combine information in different frequency regions. In experiment II gap thresholds were measured as a function of SMR for several signal bandwidths at each of three center frequencies: 0.5, 1.0, and 6.5 kHz. Gap thresholds improved with increasing SMR, but the improvement was minimal for SMRs greater than 12-15 dB. The results are used to evaluate the relative importance of factors influencing gap threshold.

Auditory Perception↗

PubMed1985

Thresholds for the detection of inharmonicity in complex tones.

Thresholds were measured for the detection of inharmonicity in complex tones. Subjects were required to distinguish a complex tone whose partials were all at exact harmonic frequencies from a similar complex tone with one of the partials slightly mistuned. The mistuning which allowed 71% correct identification in a two-alternative forced-choice task was estimated for each partial in turn. In experiment I the fundamental frequency was either 100, 200, or 400 Hz, and the complex tones contained the first 12 harmonics at equal levels of 60 dB SPL per component. The stimulus duration was 410 ms. For each fundamental the thresholds were roughly constant when expressed in Hz, having a mean value of about 4 Hz (range 2.4-7.3 Hz). In experiment II the fundamental frequency was fixed at 200 Hz, and thresholds for inharmonicity were measured for stimulus durations of 50, 110, 410, and 1610 ms. For harmonics above the fifth the thresholds increased from less than 1 Hz to about 40 Hz as duration was decreased from 1610-50 ms. For the lower harmonics (up to the fourth) threshold changed much less with duration, and for the three shorter durations thresholds for each duration were roughly a constant proportion of the harmonic frequency. The results suggest that inharmonicity is detected in different ways for high and low harmonics. For low harmonics the inharmonic partial appears to "stand out" from the complex tone as a whole. For high harmonics the mistuning is detected as a kind of "beat" or "roughness," presumably reflecting a sensitivity to the changing relative phase of the mistuned harmonic relative to the other harmonics.(ABSTRACT TRUNCATED AT 250 WORDS)

Auditory Threshold↗

PubMed1985

Effects of flanking noise bands on the rate of growth of loudness of tones in normal and recruiting ears.

Five subjects with unilateral cochlear hearing impairments and three normally hearing subjects made loudness matches between tones presented alternately to two ears, as a function of the intensity of the tone in the impaired ear (or the left ear of the normal subjects). The impaired ears showed recruitment; the rate of growth of loudness with increasing intensity was more rapid in the impaired ear than the normal ear. Presenting the tone in the impaired ear with two noise bands on either side of the tone frequency, at a fixed signal-to-noise ratio, did not abolish the recruitment. This suggests that recruitment is not caused by an abnormally rapid spread of excitation in the peripheral auditory system. At low signal-to-noise ratios, a continuous background noise reduced the loudness of the tone more than a noise gated with the tone, suggesting that the continuous noise induces adaptation to the tone. The noise had a greater effect on the loudness of the tone in normal ears than in impaired ears. It is possible that the loudness reduction of the tone in noise is mediated by suppression; suppression is weak or absent in impaired ears, and so the loudness reduction is smaller.

Aged↗

PubMed1985

Additivity of simultaneous masking, revisited.

Lutfi [J. Acoust. Soc. Am. 73, 262-267 (1983)] compared simultaneous masking functions (signal threshold versus masker level) for individual sinusoidal and narrow-band noise maskers, and for those maskers presented in pairs. Lutfi found that the pairs of maskers produced 10-17 dB "excess" masking over that predicted from the linear sum of their individual masking and explained the results in terms of a model in which the effects of the maskers are summed after undergoing independent compressive transformations. This paper describes experiments similar to those of Lutfi, and presents evidence suggesting that Lutfi's results may have been influenced by two factors: (1) combination-product detection, and (2) the use of different detection cues for single maskers and for pairs of maskers. Experiment I showed that when the stimulus conditions were chosen so as to minimize the likelihood of combination-product detection, "excess" masking was only 3-5 dB. Experiment II supported the idea that for a single narrow-band noise masker, subjects make use of the relatively slow envelope fluctuations to enhance performance. When two independent narrow-band noise maskers are added, the effectiveness of this cue is reduced, and between 3 and 9 dB of "excess" masking occurs. When the two noises are derived from the same source, and have correlated envelope fluctuations, no "excess" masking occurs. The results indicate that Lufti's compressive-nonlinearity model clearly fails in some situations.

Auditory Threshold↗

PubMed1985

Improvements in speech intelligibility in quiet and in noise produced by two-channel compression hearing aids.

Eight subjects suffering from bilateral sensorineural hearing losses with recruitment were fitted binaurally with two-channel compression hearing aids, worn behind the ear. After they had worn the aids for some time, measures of speech intelligibility were compared for two conditions: listening unaided, and listening aided. the dynamic range for speech, defined as the difference in level between the speech reception threshold in quiet and the highest comfortable level for speech, was substantially increased in the aided condition for seven of the eight subjects (the exception was a subject with almost normal low-frequency hearing). Speech reception thresholds were also measured in two levels of background noise ('babble'), 60 and 75 dB SPL. Seven of the eight subjects showed a reduced speech reception threshold (i.e. an improvement) in the aided condition for at least one of the two noise levels, although the size of the improvement differed considerably from one subject to another. The subjects were also given a battery of psycho-acoustical tests in an attempt to better characterise their hearing loss, and to gain more insight into individual differences. Results of measurements of frequency selectivity, frequency discrimination, temporal acuity and temporal masking are described and related to the measures of speech intelligibility.

Aged↗

PubMed1985

Frequency selectivity and temporal resolution in normal and hearing-impaired listeners.

Methods of measuring the frequency selectivity of the auditory system using masking techniques are outlined and described in terms of the concept of the auditory filter. The relationship between the auditory filter shape and excitation patterns is described. Evidence is reviewed showing that frequency selectivity is usually reduced in people with cochlear hearing losses. Methods of measuring the temporal resolution of the auditory system are also reviewed, and results are compared for normally hearing and hearing-impaired subjects. Temporal resolution is impaired in most but not all cases of sensorineural hearing loss. It is concluded that the loss of frequency and temporal resolution accompanying cochlear hearing loss is a major cause of the difficulties encountered by the hearing impaired in understanding speech in noisy situations.

Auditory Threshold↗

PubMed1984

Comparison of auditory filter shapes derived with three different maskers.

Auditory filter shapes were derived for three different masker types, by measuring threshold for a 1-kHz sinusoidal signal masked by: (a) a noise with a spectral notch of variable width; (b) two tones with variable frequency separation; and (c) a noise with a sinusoidally rippled spectrum with variable ripple density. In each case the masker spectrum was symmetric about the signal frequency, the signal level was fixed, and the masker level was varied to determine threshold using an adaptive, two-alternative, forced-choice procedure. Both simultaneous and forward masking were used. The auditory filter shapes derived from the data were broader in simultaneous masking than in forward masking for all three masker types. In simultaneous masking the derived filters were similar for the three masker types, although there was a tendency for the filters derived from the rippled-noise data to be broader than those for the other maskers. In forward masking the auditory filters derived from the data for three masker types differed considerably in bandwidth and the slope of the filter skirts, and in that a portion of the rippled-noise filter was negative valued. The results are consistent with the idea that suppression has the effect of enhancing frequency selectivity, and that this effect is revealed in forward but not in simultaneous masking. However, the degree and nature of the enhancement differs for different masker types.

Auditory Perception↗

PubMed1984

Frequency and intensity difference limens for harmonics within complex tones.

A two-interval, two-alternative forced choice task was used to estimate frequency difference limens (DLs) for individual harmonics within complex tones, and DLs for the periodicity (i.e., number of periods per s) of the whole complexes. For complex tones with equal-amplitude harmonics, the DLs for the lowest harmonics were small (less than one percent). The DLs increased rather abruptly around the fifth to seventh harmonic. The highest harmonic in each complex was also well discriminated, and the discriminability of a single high harmonic was markedly improved by increasing its level relative to the other components. The DL for a complex tone was generally smaller than the frequency DL of its most discriminable component. The DL for a complex was found to be predictable from the DLs of the harmonics comprising the complex, using a formula derived by Goldstein [J. Acoust. Soc. Am. 54, 1496-1516 (1973)] from his optimum processor theory for the formation of the pitch of complex tones. The DL for a complex is sometimes primarily determined by high harmonics, such as the highest harmonic, or a harmonic whose level exceeds that of adjacent harmonics. We also measured intensity DLs for individual harmonics within complex tones. The intensity DLs were smallest for low harmonic numbers, and for the highest harmonic in a complex. An excitation-pattern model was used to determine whether the frequency DLs of harmonics within complex tones could be explained in terms of place mechanisms, i.e., in terms of changes in the amount of excitation at appropriate frequency places. We conclude that place mechanisms are not adequate, and that information about the frequencies of individual harmonics is probably carried in the time patterning of neural impulses.

Auditory Perception↗

PubMed1984

Refining the measurement of psychophysical tuning curves.

Four experiments were performed in an attempt to refine the measurement of psychophysical tuning curves (PTCs). PTCs were determined using sinusoidal signals and narrow-band noise maskers, in both simultaneous and forward masking. In experiment I a fixed low-level notched noise was gated with the masker in order to restrict off-frequency listening and to eliminate "confusions" between the signal and masker in forward masking. In contrast to previous work, this procedure produced PTCs with similar round tips in both simultaneous and forward masking. The PTCs differed mainly in that the high-frequency skirts were steeper in forward masking. Experiment II compared PTCs with and without an additional notched-noise masker, for a number of signal levels. The notched noise had the effect of broadening the tips of the PTCs, this effect being greater in forward masking than in simultaneous masking. With increasing signal level the high-frequency skirt of the PTC became slightly steeper, and the low-frequency skirt slightly shallower. Experiment III studied the effect of signal duration on PTCs determined in simultaneous masking. Duration had little effect when off-frequency listening was restricted with a fixed notched-noise masker, but had a substantial effect in the absence of such a masker. Experiment IV studied the effect of signal delay in forward masking. When off-frequency listening was restricted and the signal levels adjusted to produce similar masker levels at threshold for each delay, the shape of the PTC was not affected by delay. It is concluded that, when PTCs are determined in the presence of notched noise, suppression is probably responsible for most of the differences between simultaneous and forward masking. Previous work may have overestimated the influence of suppression, because it did not control off-frequency listening and/or provide appropriate detection cues in forward masking.

Adult↗