Search PubMed⌕ Search

Biomedical subjects

B C Moore

Publications and source records attributed to B C Moore.

At least 199 records · Page 11Linked to original sources
PubMed1984

Auditory filter asymmetry in the hearing impaired.

Thresholds for 2-kHz sinusoidal signals were determined in the presence of a notched-noise masker, for six normal-hearing listeners and 12 listeners with cochlear hearing losses. Following Patterson and Nimmo Smith [J. Acoust. Soc. Am. 67, 229-245 (1980)], conditions were used where the notch was placed both symmetrically and asymmetrically about the signal frequency. The auditory filter shape for both the low- and high-frequency side of the filter was calculated using the rounded-exponential form of the filter. In six hearing-impaired listeners, the auditory filter shape showed a shallow low-frequency skirt indicating pronounced susceptibility to the upward spread of masking. In two hearing-impaired listeners, the filter shape showed a shallow high-frequency skirt, indicating pronounced susceptibility to the downward spread of masking. Two other listeners with mild threshold losses had steeper and more symmetric filters than normal, suggesting either a small conductive loss or an attenuation factor of sensorineural origin not associated with a degradation of frequency resolution. In the remaining two listeners, the auditory filter had too little selectivity for its shape to be reliably determined.

Adult↗
PubMed1984

Intensity discrimination: a severe departure from Weber's law.

These experiments were designed to assess the importance of different types of information which might be used in detecting intensity changes for pure tones. Thresholds for detecting an intensity change, expressed as 10 log (delta I/I), were measured over a wide range of frequencies and levels under conditions where one or more sources of information was either present or was removed. Spread of excitation was restricted by using bandstop noise centered at the signal frequency. Information conveyed by dynamic responses to signal onsets and offsets was eliminated by masking onsets and offsets with bursts of bandpass noise. Phase-locking information was eliminated by using high-frequency signals (above 5 kHz). Dynamic responses to signal onsets and offsets appear to play little role in intensity discrimination. Phase locking does appear to be important since Weber's law or a near-miss to it was observed at low frequencies, whereas at high frequencies performance deteriorated at moderate sound levels, and improved again at high levels. A preliminary experiment, using 225-ms stimuli revealed only a small midlevel deterioration at high frequencies. However, when 30-ms stimuli were used a large deterioration was observed, performance being worse when bandstop noise was presented with the tone. Hence at short durations and high frequencies spread of excitation seems to be important: When it is restricted by bandstop noise values of 10 log (delta I/I) observed at moderate levels it can be as large as 14 dB. The results of the experiments are consistent with a bimodal distribution of thresholds in primary auditory neurons; at intermediate levels neither population will operate effectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMed1984

Dynamic range and asymmetry of the auditory filter.

This experiment was designed to measure the shape and asymmetry of the auditory filter over a wider dynamic range than has been measured previously. Thresholds were measured for 2-kHz sinusoidal signals in the presence of two 800-Hz-wide noise bands, one above and one below the signal frequency. The spectrum level of the noise was 45 dB (re: 20 muPa), and the noise bands were placed both symmetrically and asymmetrically about the signal frequency. The deviation of the signal frequency from the nearer edge of each noise band varied from 0 to 0.8 times the signal frequency. Each ear of six subjects was tested, and the subjects' ages ranged from 22 to 74 years. The auditory filters derived from the data were somewhat asymmetric, with steeper slopes on the high-frequency side; the degree of asymmetry varied across subjects. The asymmetry could be characterized as a uniform stretching of the (linear) frequency scale on one side of the filter. The dynamic range of the auditory filter exceeded 60 dB in the younger listeners, but the dynamic range and sharpness of the filter tended to decrease with increasing age.

Adult↗
PubMed1983

Speech signal presentation to the totally deaf.

We have developed a system for single-channel electrical stimulation of the totally deaf. The patient wears a removeable electrode assembly which stimulates the cochlear promontory and can be inserted and removed like the earmould of a hearing aid. This approach minimises the risk of mechanical or electro-chemical damage to structures within the cochlea. Charge-balanced stimulation is used to present those speech pattern elements that are matched to the patients' lipreading needs and their new sensory abilities. Objective tests show improvements both in patients' perceptive and productive abilities.

Cochlear Implants↗
PubMed1983

Masking patterns for synthetic vowels in simultaneous and forward masking.

Two synthetic vowels /i/ and /ae/ with a fundamental frequency of 100 Hz served as maskers for brief (5 or 15 ms) sinusoidal signals. Threshold was measured as a function of signal frequency, for signals presented immediately following the masker (forward masking, FM) or just before the cessation of the masker (simultaneous masking, SM). Three different overall masker levels were used: 50, 70, and 90 dB SPL. In order to compare the data from simultaneous and forward masking, and to compensate for the nonlinear characteristics of forward masking, each signal threshold was expressed as the level of a flat-spectrum noise which would give the same masking. The internal representation of the formant structure of the vowels, as inferred from the transformed masking patterns, was enhanced in FM and "blurred" in SM in comparison to the physical spectra, suggesting that suppression plays a role in enhancing spectral contrasts. The first two or three formants were usually visible in the masking patterns and the representation of the formant structure was impaired only slightly at high masker levels. For high levels, filtering out the relatively intense low-frequency components enhanced the representation of the higher formants in FM but not in SM, indicating a broadly tuned remote suppression from lower formants towards higher ones. The relative phase of the components in the masker had no effect on thresholds in forward masking, indicating that the detailed temporal structure of the masker waveform is not important.

Auditory Threshold↗
PubMed1983

Pitch of components of complex tones.

Subjects made pitch matches to individual components in complex tones consisting of either the 4th to 7th or the 1st to 7th harmonics of a 200-Hz fundamental. All components were at equal levels (either 31-, 51-, or 71-dB SPL per component) and the matching pure tone was equal in level to the component being matched. Attention was drawn to the component to be matched either by giving the matching tone an initial frequency close to that of the component (standard condition) or by suppressing and then introducing the component (emergent condition). The pitch matches did not differ significantly for the two conditions, and did not change with overall level. For two subjects, matches to components in the context of the complexes were very close to matches obtained for the components presented in isolation. For a third subject, matches in context were shifted slightly upwards for the lowest component, and downwards for the highest component. A control condition showed that subjects were able accurately to match a small shift in frequency of one component in a four-tone complex. An adaptive forced-choice method described by Jesteadt [Percept. Psychophys. 28, 85-88 (1980)] was also used to estimate the pitches of the components. A very slight bias was apparent in the results, but the pitches of components in context were again found to be very close to those of components in isolation.

Humans↗
PubMed1983

Growth of forward masking for sinusoidal and noise maskers as a function of signal delay; implications for suppression in noise.

The first two experiments were designed to determine whether mutual suppression in broadband noise increases in strength with increasing overall level. In experiment I masking functions (signal threshold versus masker level) were measured in forward masking as a function of the delay time of a 10-ms signal, both for a broadband noise masker (low-pass filtered at 8 kHz) and for sinusoidal maskers at 1, 2 and 4 kHz. In the latter case the signal frequency equaled the masker frequency. For short signal delays the masking functions were steeper for the sinusoidal masker than for the noise masker. At longer delays the slopes for both masker types decreased and the slopes for the two masker types became more nearly equal. In experiment II we investigated the effect of gating a low-level noise cue with the sinusoidal masker. At the longer signal delays the masking functions had equal slopes for the broadband noise masker and the sinusoidal masker with cue. At short signal delays the masking functions for sinusoidal maskers may be "artificially" steepened, since the subject lacks an effective cue to distinguish the signal from the masker. The equal slopes at longer delays indicate that mutual suppression of the components within a broadband noise does not increase in strength with increasing overall level. In experiment III we attempted to estimate the magnitude of mutual suppression in a broadband noise by comparing masking functions for a broadband noise and for a noise whose bandwidth was 20% of the center frequency. The suppression was estimated to be about 2 dB at 4 kHz and 8 dB at 2 kHz. A simple mathematical expression, suggested by Jesteadt et al. [J. Acoust. Soc. Am. 71, 950-962 (1982)], was found to give an accurate description of the amount of masking produced by the broadband masker as a function of masker level and signal delay.

Auditory Threshold↗
PubMed1983

Forward masking patterns for harmonic complex tones.

Complex tones containing the first ten harmonics at equal amplitude, and with fundamental frequencies of 100, 200, or 400 Hz, served as maskers for brief sinusoidal signals (10-, 20-, or 40-ms duration) presented immediately following the maskers. Threshold was measured as a function of signal frequency, using an adaptive, two-alternative forced-choice procedure. The starting phase of the signal relative to the masker had no significant effect on threshold. The masking patterns showed clear peaks corresponding to the first 3 or 4 harmonics, but no peaks were visible for higher harmonics. It is concluded that the "ripple" in the internal spectra of the maskers amounts to 3 dB or less for harmonics above the fifth.

Adaptation, Physiological↗
PubMed1983

Gap detection as a function of frequency, bandwidth, and level.

The threshold for detection of a temporal gap in a noiseband was measured. A notched noise masker was used to restrict listening to a limited spectral region. Threshold was measured as a function of center frequency, bandwidth, and level. For a signal bandwidth of one-half the center frequency, the gap threshold decreased from 22.5 ms for a center frequency of 0.2 kHz to 3.2 ms at 8.0 kHz: a wideband condition provided an estimate of 2.3 ms, a value in agreement with previously published estimates. Bandwidth manipulation showed that the variation with frequency was not due to changes in absolute bandwidth alone. The effect of changes in level was determined at three frequencies, 0.4, 1.0, and 6.5 kHz, using a signal bandwidth of half the center frequency. At all frequencies gap threshold decreased as the signal spectrum level was raised from 10 to 25 dB, but a further increase to 40 dB showed no additional improvement. At frequencies up to about 1.0 kHz, the variation of gap threshold with frequency matches well the reciprocal of the bandwidth of the auditory filter, as determined from masking experiments using a notched-noise masker. This suggests that the temporal response of the auditory filter may limit gap detection at low frequencies.

Auditory Perception↗
PubMed1983

Suggested formulae for calculating auditory-filter bandwidths and excitation patterns.

Recent estimates of auditory-filter shape are used to derive a simple formula relating the equivalent rectangular bandwidth (ERB) of the auditory filter to center frequency. The value of the auditory-filter bandwidth continues to decrease as center frequency decreases below 500 Hz. A formula is also given relating ERB-rate to frequency. Finally, a method is described for calculating excitation patterns from filter shapes.

Acoustics↗
PubMed1983

A comparison of behind-the-ear high-fidelity linear hearing aids and two-channel compression aids, in the laboratory and in everyday life.

Eight patients suffering from sensorineural hearing losses with recruitment took part in a trial comparing their own hearing aids (or no aid if they did not normally wear one) with 'high-fidelity' linear aids and with aids incorporating two-channel syllabic compression. All aids were worn behind the ear. Speech intelligibility was measured both in quiet and in noise, and the patients were given questionnaires enquiring about the effectiveness of the aids in everyday situations. Both the intelligibility tests and the questionnaires indicated that the linear aids were substantially better than own/no aid, and the compressor aids were substantially better than the linear aids, allowing good speech discrimination over a wide range of sound levels. Six out of the eight patients derived significant benefit from being fitted with two aids rather than one. The use of directional microphones in the linear and compressor aids allowed a significant improvement for speech intelligibility in noise when the speech and noise were spatially separated.

Adult↗
PubMed1983

Tactile perception.

Explore the source record for details and available documents.

Communication Devices for People with Disabilities↗
PubMed1982

Contralateral and ipsilateral cueing in forward masking.

Threshold was measured for a 20-ms, 1-kHz sinusoidal signal following a narrow-band noise masker centered at 1 kHz with an overall level of 70 dB SPL. The effect of temporal uncertainty was investigated by providing a broadband, low-level noise cue, gated synchronously either with the masker intervals or the signal intervals. The cue could be either in the same ear as the signal-plus-masker, or in the opposite ear. In every case the cue produced a reduction in signal threshold, the largest reduction (about 20 dB) occurring when the cue was gated with the masker. The results indicate that in specific conditions, when the signal is similar in quality to the masker (having a similar center frequency and bandwidth), forward masking can involve a high degree os temporal uncertainty. Effects resembling "suppression" can be produced by providing a temporal cue. Adding a 1.2-kHz sinusoid at 90 dB SPL to the masker produced a 10-dB larger reduction in threshold than the noise cue. This greater effect is probably attributable to suppression of the masker by the sinusoid.

Acoustic Stimulation↗
PubMed1982

Auditory filter shapes in forward masking as a function of level.

Thresholds were measured for 1-kHz, 5-ms sinusoidal signals following noise maskers with a spectral notch of variable width centered at 1 kHz. In one set of conditions threshold was measured as a function of notch width for three fixed noise levels: 30, 40, and 50 dB SPL/Hz. In order to compensate for the decay of masking, each signal threshold was transformed to the level of a flat-spectrum noise which would give the same masking effect. In a second set of conditions the noise level required for threshold was measured as a function of notch width for three fixed signal levels, separated by 5 dB. The auditory filters derived from the data were essentially the same for the two sets of conditions, and did not vary significantly with masker or signal level. The filters had a mean 3-dB bandwidth of 90 Hz.

Auditory Threshold↗
PubMed1982

Off-frequency listening and masker uncertainty.

This experiment was designed to determine if masker uncertainty can reduce the effects of off-frequency listening on psychophysical tuning curves (PTCs). PTCs were determined in simultaneous masking with a 1-kHZ signal at 12 dV SPL, using an adaptive two-alternative forced-choice procedure. In a given run the center frequency on the narrow-band noise masker was either fixed, or varied randomly between up to eight values distributed equally above and below the signal frequency. In a control condition off-frequency listening was restricted using a "notched" broadband noise added to fixed-frequency masker. The notch was 200 HZ wide, centered at the signal frequency, and the spectrum level in the passband was - 8 dB SPL/Hz. The "restricted listening" PTCs were considerably broader than the "traditional" PTCs, but uncertainty about masker frequency had little effect. It appears that prior knowledge of masker frequency is not necessary for off-frequency listening to be effective.

Auditory Threshold↗
PubMed1982

Interpreting the role of suppression in psychophysical tuning curves.

We describe two models which make different assumptions about the factors determining threshold for psychophysical tuning curves (PTCs) determined in simultaneous masking. The models make different predictions about the amount of activity evoked by off-frequency maskers in the frequency region of the signal. The predictions were tested by using a forward-masking technique to estimate the amount of this activity. The data support a model which assumes that threshold in simultaneous masking corresponds to a "swamping" of the signal activity by that of the masker, rather than a suppression of the low-level signal to its absolute threshold. To explain the fact that PTCs in forward masking are sharper than those in simultaneous masking, the model requires that suppression acts to sharpen the excitation pattern of the masker. This sharpening is not seen in simultaneous masking, since suppression in a given frequency region affects both signal and masker.

Auditory Threshold↗