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PubMed2004

Clear speech perception in acoustic and electric hearing.

When instructed to speak clearly for people with hearing loss, a talker can effectively enhance the intelligibility of his/her speech by producing "clear" speech. We analyzed global acoustic properties of clear and conversational speech from two talkers and measured their speech intelligibility over a wide range of signal-to-noise ratios in acoustic and electric hearing. Consistent with previous studies, we found that clear speech had a slower overall rate, higher temporal amplitude modulations, and also produced higher intelligibility than conversational speech. To delineate the role of temporal amplitude modulations in clear speech, we extracted the temporal envelope from a number of frequency bands and replaced speech fine-structure with noise fine-structure to simulate cochlear implants. Although both simulated and actual cochlear-implant listeners required higher signal-to-noise ratios to achieve normal performance, a 3-4 dB difference in speech reception threshold was preserved between clear and conversational speech for all experimental conditions. These results suggest that while temporal fine structure is important for speech recognition in noise in general, the temporal envelope carries acoustic cues that contribute to the clear speech intelligibility advantage.

Adult↗

PubMed1984

Identification and discrimination of rise time: is it categorical or noncategorical?

Previous studies have reported that rise time of sawtooth waveforms may be discriminated in either a categorical-like manner under some experimental conditions or according to Weber's law under other conditions. In the present experiments, rise time discrimination was examined with two experimental procedures: the traditional labeling and ABX tasks used in speech perception studies and an adaptive tracking procedure used in psychophysical studies. Rise time varied from 0 to 80 ms in 10-ms intervals for sawtooth signals of 1-s duration. Discrimination functions for subjects who simply discriminated the signals on any basis whatsoever as well as functions for subjects who practiced labeling the endpoint stimuli as " pluck " and "bow" before ABX discrimination were not categorical in the ABX task. In the adaptive tracking procedure, the Weber fraction obtained from the jnds of rise time was found to be a constant above 20-ms rise time. The results from the two discrimination paradigms were then compared by predicting a jnd for rise time from the ABX discrimination data by reference to the underlying psychometric function. Using this method of analysis, discrimination results from previous studies were shown to be quite similar to the discrimination results observed in this study. Taken together the results demonstrate clearly that rise time discrimination of sawtooth signals follows predictions derived from Weber's law.

Adult↗

PubMed1992

Problems associated with mechanical heart valve sounds.

A cross-sectional study of 50 randomly selected patients 12-36 months following mechanical heart valve replacement with Bjork-Shiley tilting disc valves was undertaken to investigate the factors which affect perception of, and reaction to, sounds generated by mechanical heart valves implanted in patients. Numerous problems were generated by the valves, including annoyance (68%), sleep disturbance (52% in patients; and 46% in patients' partners), interference with concentration (36%) and social embarrassment (28%). These findings are not affected by the measured level of sound or any variation in the number or anatomical position of the valve(s), though age and sex do seem to matter, more problems being reported by younger patients and those of the female sex. Aspects of the patient's personality did not seem to alter the difficulties experienced, though a high level of psychological morbidity was identified in the group as a whole. Most patients experience problems due directly to the noise generated by their valve and should be adequately warned of this before operation. This should also be taken into consideration in designing and evaluating new valve prostheses.

Adaptation, Psychological↗

PubMed1983

Intensity perception. XII. Effect of presentation probability on absolute identification.

Identification experiments using 13 tone-pulse stimuli (1000 Hz, 500 ms) spaced by equal decibel increments from 42 to 90 dB SPL were conducted under three conditions: all intensities equally likely (denoted Q), the middle intensity presented on roughly 1/3 of the trials (M), and each of the extreme intensities presented on roughly 1/5 of the trials (E). Experiments were performed both with and without feedback, and results were analyzed in terms of sensitivity and bias. Similar results were obtained with and without feedback: listeners generally shifted biases in the M and E conditions relative to the Q condition to increase percent-correct scores, but there were only minor changes in sensitivity from condition to condition. However, sensitivities were generally higher and biases more optimal when feedback was available. The results on sensitivity are consistent with those associated with payoff variation [Lippmann et al., J. Acoust. Soc. Am. 59, 129-134 (1976)], but are inconsistent with those reported for presentation probability variation in tone frequency identification [Cuddy et al., J. Exp. Psychol. 100, 218-220 (1973)]. In an auxilliary experiment concerned with tone frequency identification, results consistent with those obtained for intensity, but inconsistent with those reported by Cuddy et al., were obtained.

Feedback↗

PubMed1984

Intensity perception. XIII. Perceptual anchor model of context-coding.

In our preliminary theory of intensity resolution [e.g., see N. I. Durlach and L. D. Braida, J. Acoust. Soc. Am. 46, 372-383 (1969)], two modes of memory operation are postulated: the trace mode and the context-coding mode. In this paper, we present a revised model of the context-coding mode which describes explicitly a process by which sensations are coded relative to the context and which predicts a resolution edge effect [L. D. Braida and N. I. Durlach, J. Acoust. Soc. Am. 51, 483-502 (1972); J. E. Berliner, L. D. Braida, and N. I. Durlach, J. Acoust. Soc. Am. 61, 1256-1267 (1977)]. The sensation arising from a given stimulus presentation is coded by determining its distance from internal references or perceptual anchors. The noise in this process, combined with the sensation noise, constitutes the limitation on resolution in the model. In the revised model the probability density functions of the decision variable are not precisely Gaussian (and cannot be expressed analytically in closed form). This paper outlines the predictions of the model for one-interval paradigms and for fixed-level two-interval paradigms and derives estimates of the values of model parameters.

Discrimination Learning↗

PubMed1993

[Perception of traffic noise emission in Basel City canton in comparison to actually measured noise levels].

The objective of this study was to assess to what extent the subjective annoyance is influenced by the actually measured or calculated street traffic noise and by sociodemographic factors. In the study on air pollution and health in Basle a representative sample of 1033 families with children up to five years were asked how they perceived street traffic noise. The extent of annoyance was assessed with a scale from 0 (no annoyance) to 10 (unbearably annoyed). The actual noise levels were taken from the official noise-register. Nearly 30% of the families were exposed to > 65 dB(A) in daytime. Immigrant families as well as participants with low education more frequently lived in streets with higher noise levels than Swiss families or participants with higher education. 16.4% considered themselves heavily annoyed by traffic noise (scale 8-10). The proportion of heavily annoyed participants was positively correlated with the actual noise levels, the slope was steepest at a noise level between 60-65 dB(A). By means of a multiple regression it could be shown that, adjusting for education level and city district, the actual noise level was the best predictor of subjective annoyance.

Adolescent↗

PubMed1992

Auditory intensity perception: successive versus simultaneous, across-channel discriminations.

This study measures the ability of observers to compare the intensities of two stimuli occupying different frequency regions. It includes three experiments, each experiment having two conditions. In one condition, the two stimuli to be compared were presented simultaneously within each interval; this condition has been called profile analysis. In the other condition, the two stimuli were presented successively within each interval. Because the overall level of the stimuli was randomized between intervals, the observers were encouraged to compare the intensities of the two stimuli within each observation interval rather than between intervals. The stimuli were two simple tones in experiment 1 and two tonal complexes in both experiments 2 and 3. The stimuli used in experiments 2 and 3 differed in frequency. The results show that simultaneous comparisons are superior to successive comparisons. For simple tones, the difference in threshold is about 8 dB; for complexes with 10 to 11 components, the difference in threshold is about 15 dB. These differences can be explained by assuming that internal noises in different channels were partially correlated when stimuli in those channels were presented simultaneously and were independent when the stimuli were presented successively. Cancellation of the correlated noise is therefore possible with simultaneous comparisons, making such discrimination better than that achievable with successive comparisons.

Acoustic Stimulation↗

PubMed1988

Central and peripheral representation of whispered and voiced speech.

Whispered speech is very different acoustically from normally voiced speech, yet listeners appear to have little trouble perceiving whispered speech. Two selective adaptation experiments explored the basis for the common perception of whispered and voiced speech, using two synthetic /ba/-/wa/ continua (one voiced, and one whispered). In the first experiment the endpoints of each series were used as adaptors, along with several nonspeech adaptors. Speech adaptors produced reliable labeling shifts of syllables matching in periodicity (i.e., whispered-whispered or voiced-voiced); somewhat smaller effects were found with mismatched periodicity. A periodic nonspeech tone with short rise time (the "pluck") produced adaptation effects like those for /ba/. These shifts occurred for whispered test syllables as well as voiced ones, indicating a common abstract level of representation for voiced and whispered stimuli. Experiment 2 replicated and extended Experiment 1, using same-ear and cross-ear adaptation conditions. There was perfect cross-ear transfer of the nonspeech adaptation effect, again implicating an abstract level of representation. The results support the existence of two levels of processing for complex acoustic signals. The commonality of whispered and voiced speech arises at the second, abstract level. Both this level, and the earlier, more directly acoustic level, are susceptible to adaptation effects.

Attention↗

PubMed2006

Perception of amplitude modulation by hearing-impaired listeners: the audibility of component modulation and detection of phase change in three-component modulators.

Two experiments were conducted to assess whether hearing-impaired listeners have a reduced ability to process suprathreshold complex patterns of modulation applied to a 4-kHz sinusoidal carrier. Experiment 1 examined the ability to "hear out" the modulation frequency of the central component of a three-component modulator, using the method described by Sek and Moore [J. Acoust. Soc. Am. 113, 2801-2811 (2003)]. Scores were around 70-80% correct when the components in the three-component modulator were widely spaced and when the frequencies of the target and comparison different sufficiently, but decreased when the components in the modulator were closely spaced. Experiment 2 examined the ability to hear a change in the relative phase of the components in a three-component modulator with harmonically spaced components. The frequency of the central component, f, was either 50 or 100 Hz. Scores were about 70% correct when the component spacing was < or = 0.5fc, but decreased markedly for greater spacings. Performance was only slightly impaired by randomizing the overall modulation depth from one stimulus to the next. For both experiments, performance was only slightly worse than for normally hearing listeners, indicating that cochlear hearing loss does not markedly affect the ability to process suprathreshold complex patterns of modulation.

Acoustic Stimulation↗

PubMed1995

Pitch matching of amplitude-modulated current pulse trains by cochlear implantees: the effect of modulation depth.

An experiment was conducted with four cochlear implantees, which investigated the pitch evoked by amplitude-modulating current pulse trains delivered to a single cochlear location. These stimuli produce a pitch percept which may be similar to that of acoustic stimuli such as modulated noise for modulation frequencies in the range 80-300 Hz, approximately. The experiments investigated the effect of modulation depth on the way pitch was matched to that of unmodulated pulse trains. The method of constant stimuli was used, in which the variable parameter was the rate of the unmodulated stimulus. The modulated stimuli comprised pulses having one of two possible current values, with the higher value occurring once in every modulation period. The results showed that the matched rate fell exponentially from a value close to the carrier rate towards a value equal to the modulation frequency as the modulation depth increased. The results were compared to the predictions of a simple model in which the matched rate corresponded to a weighted average of carrier and modulation frequencies, with the weightings proportional to the number of neurons firing at each of these frequencies. The results agreed with the predictions of the model reasonably well, except in cases where the carrier rate was 700 Hz or higher, and for one subject at the highest intensity level.

Adult↗

PubMed1991

The perception of back vowels: centre of gravity hypothesis.

According to the formant centre of gravity (FCOG) hypothesis, two vowel formants in close proximity are merged during perceptual analysis, and their contribution to vowel quality depends on the centre of gravity of the formant cluster. Findings consistent with this hypothesis are that two formants can be replaced by a single formant of intermediate centre frequency, provided their separation is less than 3-3.5 Bark; and that changes in their relative amplitudes produce systematic shifts in vowel quality. In Experiment 1, listeners adjusted the frequencies of F1 and F2 in a synthesized 6-formant vowel (with the F1-F2 separation fixed at 250 Hz, i.e. less than 3 Bark) to find the best phonetic match to a reference vowel with modified formant amplitudes. Contrary to FCOG predictions, F2 attenuation did not produce lower frequency matches. Raising the amplitude of F2 led to predicted upward shifts in formant frequencies of the matched vowel, but with increased variability of matches for some stimuli. In Experiment 2, listeners identified synthesized vowels with a range of separations of F1 and F2. Formant amplitude manipulations had no effect on listeners' judgements when the fundamental frequency was low (125 Hz). Small shifts in vowel quality appeared for stimuli with a high fundamental (250 Hz), but the shifts were significantly larger for F1-F2 separations greater than 3.5 Bark. These effects of formant amplitude are qualitatively different from those observed with single-formant vowels and are generally incompatible with a formant-averaging mechanism.

Attention↗

PubMed2003

Extending the domain of center frequencies for the compressive gammachirp auditory filter.

The gammatone filter was imported from auditory physiology to provide a time-domain version of the roex auditory filter and enable the development of a realistic auditory filterbank for models of auditory perception [Patterson et al., J. Acoust. Soc. Am. 98, 1890-1894 (1995)]. The gammachirp auditory filter was developed to extend the domain of the gammatone auditory filter and simulate the changes in filter shape that occur with changes in stimulus level. Initially, the gammachirp filter was limited to center frequencies in the 2.0-kHz region where there were sufficient "notched-noise" masking data to define its parameters accurately. Recently, however, the range of the masking data has been extended in two massive studies. This paper reports how a compressive version of the gammachirp auditory filter was fitted to these new data sets to define the filter parameters over the extended frequency range. The results show that the shape of the filter can be specified for the entire domain of the data using just six constants (center frequencies from 0.25 to 6.0 kHz and levels from 30 to 80 dB SPL). The compressive, gammachirp auditory filter also has the advantage of being consistent with physiological studies of cochlear filtering insofar as the compression of the filter is mainly limited to the passband and the form of the chirp in the impulse response is largely independent of level.

Attention↗

PubMed2002

Binaural weighting of pinna cues in human sound localization.

Human sound localization relies on binaural difference cues for sound-source azimuth and pinna-related spectral shape cues for sound elevation. Although the interaural timing and level difference cues are weighted to produce a percept of sound azimuth, much less is known about binaural mechanisms underlying elevation perception. This problem is particularly interesting for the frontal hemifield, where binaural inputs are of comparable strength. In this paper, localization experiments are described in which hearing for each ear was either normal, or spectrally disrupted by a mold fitted to the external ear. Head-fixed saccadic eye movements were used as a rapid and accurate indicator of perceived sound direction in azimuth and elevation. In the control condition (both ears free) azimuth and elevation components of saccadic responses were well described by a linear regression line for the entire measured range. For unilateral mold conditions, the azimuth response components did not differ from controls. The influence of the mold on elevation responses was largest on the ipsilateral side, and declined systematically with azimuth towards the side of the free ear. Near the midsagittal plane the elevation responses were clearly affected by the mold, suggesting a systematic binaural interaction in the neural computation of perceived elevation that straddles the midline. A quantitative comparison of responses from the unilateral mold, the bilateral mold and control condition provided evidence that the fusion process can be described by binaural weighted averaging. Two different conceptual schemes are discussed that could underlie the observed responses.

Acoustic Stimulation↗

PubMed1997

Design of two syllabic nonlinear multichannel signal processors and the results of speech tests in noise.

OBJECTIVE: Multichannel syllabic compressors have not yet shown clear advantages for speech perception. New multichannel syllabic nonlinear processors are designed and evaluated in this study to test whether they enhance speech perception scores. DESIGN: Nonsense consonant-vowel-consonant words have been processed in real time with two syllabic nonlinear methods in nine different frequency channels: 1) 30 dB of speech information is mapped into the residual dynamic range (DR) of the subjects with hearing impairment using either compression or expansion; 2) speech levels above the rms level are compressed with a ratio of 3:1, and input levels below the rms level are mapped into the reduced DR of the subjects. The overall frequency spectrum of speech is tilted with more high-frequency output for this condition. The two syllabic nonlinear processors were compared with two linear reference systems (one of them with the same spectral tilt as the second nonlinear condition) for seven hearing-impaired subjects. RESULTS: On average, the syllabic nonlinear processors show scores similar to one of the linear systems. The linear reference with tilt has, on average, 3% higher scores, mainly due to improved vowel identification. CONCLUSIONS: No negative effects were shown on average for the syllabic nonlinear processors, but no positive effects were demonstrated either. Tilting of the overall speech spectrum was advantageous.

Adult↗

PubMed2002

The effects of spatial separation in distance on the informational and energetic masking of a nearby speech signal.

Although many studies have shown that intelligibility improves when a speech signal and an interfering sound source are spatially separated in azimuth, little is known about the effect that spatial separation in distance has on the perception of competing sound sources near the head. In this experiment, head-related transfer functions (HRTFs) were used to process stimuli in order to simulate a target talker and a masking sound located at different distances along the listener's interaural axis. One of the signals was always presented at a distance of 1 m, and the other signal was presented 1 m, 25 cm, or 12 cm from the center of the listener's head. The results show that distance separation has very different effects on speech segregation for different types of maskers. When speech-shaped noise was used as the masker, most of the intelligibility advantages of spatial separation could be accounted for by spectral differences in the target and masking signals at the ear with the higher signal-to-noise ratio (SNR). When a same-sex talker was used as the masker, the intelligibility advantages of spatial separation in distance were dominated by binaural effects that produced the same performance improvements as a 4-5-dB increase in the SNR of a diotic stimulus. These results suggest that distance-dependent changes in the interaural difference cues of nearby sources play a much larger role in the reduction of the informational masking produced by an interfering speech signal than in the reduction of the energetic masking produced by an interfering noise source.

Adult↗

PubMed2005

Vowel perception by noise masked normal-hearing young adults.

This study examined vowel perception by young normal-hearing (YNH) adults, in various listening conditions designed to simulate mild-to-moderate sloping sensorineural hearing loss. YNH listeners were individually age- and gender-matched to young hearing-impaired (YHI) listeners tested in a previous study [Richie et al., J. Acoust. Soc. Am. 114, 2923-2933 (2003)]. YNH listeners were tested in three conditions designed to create equal audibility with the YHI listeners; a low signal level with and without a simulated hearing loss, and a high signal level with a simulated hearing loss. Listeners discriminated changes in synthetic vowel tokens /I e epsilon alpha ae/ when Fl or F2 varied in frequency. Comparison of YNH with YHI results failed to reveal significant differences between groups in terms of performance on vowel discrimination, in conditions of similar audibility by using both noise masking to elevate the hearing thresholds of the YNH and applying frequency-specific gain to the YHI listeners. Further, analysis of learning curves suggests that while the YHI listeners completed an average of 46% more test blocks than YNH listeners, the YHI achieved a level of discrimination similar to that of the YNH within the same number of blocks. Apparently, when age and gender are closely matched between young hearing-impaired and normal-hearing adults, performance on vowel tasks may be explained by audibility alone.

Acoustic Stimulation↗

PubMed1992

Speech pattern hearing aids for the profoundly hearing impaired: speech perception and auditory abilities.

A family of prototype speech pattern hearing aids for the profoundly hearing impaired has been compared to amplification. These aids are designed to extract acoustic speech patterns that convey essential phonetic contrasts, and to match this information to residual receptive abilities. In the first study, the presentation of voice fundamental frequency information from a wearable SiVo (sinusoidal voice) aid was compared to amplification in 11 profoundly deafened adults. Intonation reception was often better, and never worse, with fundamental frequency information. Four subjects scored more highly in audio-visual consonant identification with fundamental frequency information, five performed better with amplified speech, and two performed similarly under these two conditions. Five of the 11 subjects continued use of the SiVo aid after the tests were complete. A second study examined a laboratory prototype compound speech pattern aid, which encoded voice fundamental frequency, amplitude envelope, and the presence of voiceless excitation. In five profoundly deafened adults, performance was better in consonant identification when additional speech patterns were present than with fundamental frequency alone; the main advantage was derived from amplitude information. In both consonant identification and connected discourse tracking, performance with appropriately matched compound speech pattern signals was better than with amplified speech in three subjects, and similar to performance with amplified speech in the other two. In nine subjects, frequency discrimination, gap detection, and frequency selectivity were measured, and were compared to speech receptive abilities with both amplification and fundamental frequency presentation. The subjects who showed the greatest advantage from fundamental frequency presentation showed the greatest average hearing losses, and the least degree of frequency selectivity. Compound speech pattern aids appear to be more effective for some profoundly hearing-impaired listeners than conventional amplifying aids, and may be a valuable alternative to cochlear implants.

Adult↗

PubMed2001

Systematic distortions of auditory space perception following prolonged exposure to broadband noise.

Perceptual distortions referred to as aftereffects may arise following exposure to an adapting sensory stimulus. The study of aftereffects has a long and distinguished history [Kohler and Wallach, Proc. Am. Philos. Soc. 88, 269-359 (1944)] and a range of aftereffects have been well described in sensory modalities such as the visual system [Barlow, in Vision: Coding and Efficiency (Cambridge University Press, Cambridge, 1990)]. In the visual system these effects have been interpreted as evidence for a population of cells or channels specific for certain features of a stimulus. However there has been relatively little work examining auditory aftereffects, particularly in respect of spatial location. In this study we have examined the effects of a stationary adapting noise stimulus on the subsequent auditory localization in the vicinity of the adapting stimulus. All human subjects in this study were trained to localize short bursts of noise in a darkened anechoic environment. Adaptation was achieved by presenting 4 min of continuous noise at the start of each block of trials and was maintained by a further 15-s noise burst between each trial. The adapting stimulus was located either directly in front of the subject or 30 degrees to the right of the midline. Subjects were required to determine the location of noise burst stimuli (150 ms) in the proximity of the adapting stimulus following each interstimulus period of adaptation. Results demonstrated that following adaptation there was a general radial displacement of perceived sound sources away from the location of the adapting stimulus. These data are more consistent with a channel-based or place-based process of sound localization rather than a simple level-based adaptation model. A simple "distribution shift" model that assumes an array of overlapping spatial channels is advanced to explain the psychophysical data.

Adult↗