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PubMed1999

Evaluation of spectral enhancement in hearing aids, combined with phonemic compression.

In this study, the separate and combined effects on speech perception of compensation of the reduced dynamic range by compression and compensation of the reduced frequency resolution by spectral enhancement is investigated. The study has been designed to compare the effects of signal processing on monosyllabic consonant-vowel-consonant words for hearing-impaired listeners in conditions of quiet, fluctuating noise, and continuous noise. Speech perception of spectrally enhanced speech was compared with unprocessed speech. In addition, a comparison was made between combinations of spectrally enhanced speech and two types of phonemic compression. In the past, the definition "syllabic compressor" is often used to indicate fast compressors. However, the time constants of the fast compressors used in this study are so short that syllabic has become an inappropriate term. Moreover, intelligibility tests were performed in which scores were acquired of monosyllabic words, and their constituent "phonemic" parts. Therefore, the definitions "phoneme" and phonemic will be used throughout this paper. In one condition, spectral enhancement produced significant improvements for vowel perception. But, this was counteracted by deterioration of the consonant scores for all but one subject. In general, the best overall scores for consonant-vowel-consonant words were obtained in the unprocessed condition. After the spectral enhancement, a single-channel phonemic compressor added no improvement. There are indications that a multichannel phonemic compressor and spectral enhancement have opposite effects, because the scores for this combination are, in general, the lowest.

Adolescent↗
PubMed1993

Auditory pattern perception in the profoundly hearing impaired and lipreading of Dutch phonemes.

Successful rehabilitation of the profoundly hearing impaired by means of a speech-processing hearing aid requires integration of auditory and visual speech information. In two studies we investigated (1) which perceptual dimensions play a role in processing various auditory patterns by profoundly hearing-impaired subjects, and (2) which Dutch consonants and vowels can be identified by the average lipreader. One of the important cues in auditory pattern discrimination seems to be the presence of temporal fluctuations (beats) in the signal, resulting from two closely placed frequency components. However, this feature is confounded with the perception of loudness. A second cue used by some subjects is the presence of high-frequency peaks. In lipreading, at least three groups of consonants and three vowel groups may be distinguished; phonemes within a group cannot be discriminated from each other. Important features for both consonants and vowels are degree of lip opening and lip activity (movement or rounding). These results suggest how the auditory speech signal might be coded so as to provide supplementary information to speechreading.

Acoustic Stimulation↗
PubMed1992

Fitting multichannel-compression hearing aids.

Multichannel hearing aids have been introduced recently in clinical practice. In this paper, some advantages and disadvantages of multichannel hearing aids are discussed. The advantages include an improved use of compression. However, the number of settings will be larger in multichannel hearing aids and exact knowledge of the goal to be pursued by compression is more necessary than ever. Inexactness of the definitions of these goals may have been a reason for the contradictory results in the studies on multichannel compression. A number of requirements must be fulfilled for a successful application of multichannel compression. One of these is detailed knowledge about the perception of suprathreshold signals. For that reason, an extension of the battery of tests commonly used in rehabilitative audiology is necessary. Another requirement is that the fitting strategy is determined by the purpose of applying compression. The objectives will be different for compression limiting and syllabic compression. A fitting procedure used in clinical practice has to take into account some limitations in the fitting time available. A number of possible fitting tools are discussed. Two strongly different fitting strategies for the same commercially available three-channel compression aid illustrate fundamental differences in fitting philosophy.

Audiometry, Pure-Tone↗
PubMed2002

Improving the classroom listening skills of children with Down syndrome by using sound-field amplification.

Many children with Down syndrome have fluctuating conductive hearing losses further reducing their speech, language and academic development. It is within the school environment where access to auditory information is crucial that many children with Down syndrome are especially disadvantaged. Conductive hearing impairment which is often fluctuating and undetected reduces the child's ability to extract the important information from the auditory signal. Unfortunately, the design and acoustics of the classroom leads to problems in extracting the speech signal through reduced speech intensity due to the increased distance of the student from the teacher in addition to masking from excessive background noise. One potential solution is the use of sound-field amplification which provides a uniform amplification to the teacher's voice through the use of a microphone and loudspeakers. This investigation examined the efficacy of sound-field amplification for 4 children with Down syndrome. Measures of speech perception were taken with and without the sound-field system and found that the children perceived significantly more speech in all conditions where the sound-field system was used (p < .0001). Importantly, listening performance with the sound-field system was not affected by reducing the signal-to-noise ratio through increasing the level of background noise. In summary, sound-field amplification provides improved access to the speech signal for children with Down syndrome and as a consequence leads to improved classroom success.

Amplifiers, Electronic↗
PubMed1990

Infants' perception of timbre: classification of complex tones by spectral structure.

Infants 7 to 8.5 months of age were tested for their discrimination of timbre or sound quality differences in the context of variable exemplars. They were familiarized with a set of complex tones with specified spectral structure; members of the set varied in fundamental frequency, intensity, or duration. Infants were then tested for their detection of tones that contrasted in spectral structure but were similar in other respects. They successfully differentiated the two spectral structures in the context of these variations, indicating that they can classify tonal stimuli on the basis of timbre. When the stimuli were organized into arbitrary categories, infants were unable to differentiate these categories, indicating that their performance with nonarbitrary categories was not attributable to memorization of the familiarized set.

Female↗
PubMed2001

Accenting and detection of timing variations in tone sequences: different kinds of accents have different effects.

The effect of intensity and pitch accents on the perception of timing was examined in two experiments using a signal detection procedure. Analyses of sensitivity and response bias revealed opposite effects of intensity and pitch accents under similar conditions. Time intervals preceding intensity accents were perceived as longer, but time intervals preceding pitch accents were perceived as shorter. These results showed that listeners found it easier to detect timing variations that were contrary to expectations, as compared with variations that were consistent with expectations. In the present case, listeners should have expected shorter time intervals before intensity accents and longer intervals before pitch accents. The fact that the effects were observed with stimuli that had minimal musical structure demonstrated the contribution of psychoacoustic factors to such phenomena.

Attention↗
PubMed1993

A reexamination of duplex perception evoked by intensity differences.

Duplex perception is a term used to describe the simultaneous evocation of phonetic and nonphonetic percepts, a phenomenon held by some to reveal the operation of a specialized module for phonetic perception. In a widely cited experiment by Whalen and Liberman (1987), duplex percepts were created by replacing the third format transition in a synthetic syllable with a sinusoidal tone glide and manipulating the level of the glide relative to the rest of the syllable. We discuss this study, and report four experiments. The first two made a systematic estimate of the "duplexity threshold"--the tone glide level at which a chirp-like sound could be heard as well as the speech-like syllable. In the third and fourth experiments, we used the results of the first to repeat and extend the experimental procedures in the original Whalen and Liberman study. We discuss the differences in outcome, and conclude that our results may be explained without the need to invoke a specialized phonetic module.

Attention↗
PubMed1994

[Social support, disability, coping with stress and personality markers in patients with subjective chronic aural tinnitus and a clinical control group].

The inhibition of physiological habituation in patients with chronic aural tinnitus extends from the level of cellular processing to psychologic and psychosocial determinants. The following hypotheses were tested in 32 patients with chronic tinnitus and 30 patients of a comparable clinical control group: tinnitus patients differ concerning (1) the perception of social support, (2) a disposition to psychosomatic diseases, (3) coping with stress and (4) certain personality traits. Standard psychological tests were used as well as a detailed examination of at least 30 minutes. Results showed that the tinnitus patients statistically perceived less social support and more social distress compared to the control group. They also showed significantly poorer results in coping with stress. Increased social distress in a number of cases resulted in noticeable decompensation. Additionally, a disposition to psychosomatic disorders increased, so that conflicts arising expressed themselves in various functional diseases. In most cases psychiatric exploration showed a vocational or familial overcharge. In patients experiencing decompensation, close cooperation with a psychotherapist is required.

Adaptation, Psychological↗
PubMed1996

The Doppler illusion: the influence of dynamic intensity change on perceived pitch.

Four studies illustrate a new auditory illusion associated with the Doppler effect and demonstrate a new influence of dynamic intensity change on perceived pitch. Experiment 1 confirmed the existence of a popular belief that the pitch of a moving sound source rises as the source approaches. Because there is no corresponding rise in frequency, the authors refer to the perceived pitch rise as the Doppler illusion. Experiment 2 confirmed that the effect occurs perceptually, so the belief in a "naive principle" of physics has a perceptual basis. Experiment 3 confirmed the effect does not occur under matched static conditions. Experiment 4 showed that the influence of dynamic intensity change on perceived pitch occurs outside the realm of Doppler stimuli. The findings support a dynamic dimensional interaction of pitch and loudness, with marked differences in the perception of pitch and loudness under static and dynamic conditions.

Adult↗
PubMedDate not supplied

Hearing at low and infrasonic frequencies.

The human perception of sound at frequencies below 200 Hz is reviewed. Knowledge about our perception of this frequency range is important, since much of the sound we are exposed to in our everyday environment contains significant energy in this range. Sound at 20-200 Hz is called low-frequency sound, while for sound below 20 Hz the term infrasound is used. The hearing becomes gradually less sensitive for decreasing frequency, but despite the general understanding that infrasound is inaudible, humans can perceive infrasound, if the level is sufficiently high. The ear is the primary organ for sensing infrasound, but at levels somewhat above the hearing threshold it is possible to feel vibrations in various parts of the body. The threshold of hearing is standardized for frequencies down to 20 Hz, but there is a reasonably good agreement between investigations below this frequency. It is not only the sensitivity but also the perceived character of a sound that changes with decreasing frequency. Pure tones become gradually less continuous, the tonal sensation ceases around 20 Hz, and below 10 Hz it is possible to perceive the single cycles of the sound. A sensation of pressure at the eardrums also occurs. The dynamic range of the auditory system decreases with decreasing frequency. This compression can be seen in the equal-loudness-level contours, and it implies that a slight increase in level can change the perceived loudness from barely audible to loud. Combined with the natural spread in thresholds, it may have the effect that a sound, which is inaudible to some people, may be loud to others. Some investigations give evidence of persons with an extraordinary sensitivity in the low and infrasonic frequency range, but further research is needed in order to confirm and explain this phenomenon.

Acoustics↗
PubMed1980

Intensity perception. X. Effect of preceding stimulus on identification performance.

This article describes some results on the effect of the preceding stimulus on performance in an intensity-identification experiment with feedback. Based on previous research and our own subjective experiences as listeners, we had expected that sensitivity would increase when the intensities of the preceding and current stimuli were close together. The results of our experiments show, however, that this is not the case: sensitivity is indepenent of the preceding stimulus. The fact that the response variance tends to decrease when the intensities of the preceding and current stimuli are close together is found to be caused solely by sequential effects in response bias. These findings create an interesting puzzle concerning the mechanism by which feedback improves sensitivity in identification. Apparently, the most obvious hypothesis--namely, that the feedback enables the previous stimulus to be used as a standard for judging the current stimulus--is false.

Acoustic Stimulation↗
PubMed1992

Time perception: effects of sex and sound intensity on scales of subjective duration.

Six women and six men reproduced ten time intervals varying in logarithmic steps between 1.3 and 20 s. The durations were indicated by white noise of 10, 25, 40 and 55 dB SL, different sound intensities in different sessions. It was found that (i) greater sound intensity entails shorter reproductions, and (ii) reproductions by male observers are shorter than those by female, although for both (i) and (ii) there is an interaction with the standard durations. The data were treated in accordance with the "parallel-clock model" (Eisler, 1975), whereby the parameters of the psychophysical power function are determined from duration reproduction data. As in previous experiments (Eisler, 1975), the data showed a break in the function entailing two segments. The effect of sound intensity could be attributed to the exponent, which was lower for stronger noise, and the effect of sex to the weight coefficient of the upper relative to the lower segment of the psychophysical function, the coefficient being lower for men.

Adult↗
PubMed1990

The role of single-channel cues in synchrony perception: the summed waveform.

Human observers are able to discriminate between simultaneously presented bands of noise having envelopes that are identical (synchronous) rather than statistically independent (asynchronous). The possibility that the detection of envelope synchrony is based on cues available in a single critical band, rather than on a simultaneous comparison of envelopes extracted via independent critical bands, is examined. Two potential single-channel cues were examined, both relying on the assumption that information present in the envelope of the summed bands is available to the listener. One such single-channel cue is the rms of the envelope of the summed waveform; the envelope is more deeply modulated for the summed synchronous bands than for the summed asynchronous bands. The second cue examined was envelope regularity; the envelope of the summed synchronous bands has periodic envelope minima, while the summed asynchronous bands exhibit aperiodic envelope minima. Psychophysical results suggest that such within-channel cues may be both available to, and utilized by, the listener when the component bands are separated by less than one-third of an octave.

Attention↗
PubMed1990

The inability of young children to reproduce intensity differences in musical rhythms.

A musical rhythm can be described in terms of both its temporal and its dynamic structure. However, although 6-year-old children are able to perceive and reproduce simple temporal structures, even 8-year-olds rarely reproduce intensity differences. Four experiments on the perception and reproduction of musical rhythms by 5- to 8-year-old children demonstrate that even though dynamic structure is clearly dominated by its temporal support, intensity differences play a role in reinforcing the temporal structure. The inability of children to reproduce intensity differences appears to be due neither to an inability to control the intensity of their tap responses nor to the fact that they cannot perceive such changes in intensity. Rather, the results seem best interpreted in terms of the allocation of attentional resources. With simple stimulus material (Experiments 1-3), the children focused on temporal information, and only when the processing of temporal information was mastered did they have "enough attention left" to direct it to intensity differences (Experiment 2). With more complex orchestral music (Experiment 4), attention was primarily allocated to the dynamic structure.

Attention↗
PubMed2006

Differences in responses from the cochleae and central nervous systems of females with low versus high acceptable noise levels.

Studies of acceptable noise level (ANL) consistently report large intersubject variability in acceptance of background noise while listening to speech. This variability is not related to age, gender, hearing sensitivity, type of background noise, speech perception in noise performance, or efferent activity of the medial olivocochlear pathway. An exploratory study was conducted to determine if differences in aggregate responses from the peripheral and central auditory system can account for intersubject variability in ANL. Click-evoked otoacoustic emissions (CEOAEs), binaural auditory brainstem responses (ABRs), and middle latency responses (MLRs) were measured in females with normal hearing with low (n = 6) versus high (n = 7) ANLs. Results of this preliminary study indicate no differences between the groups for CEOAEs or waves I or III of the ABR. Differences between the two groups emerge for the amplitudes of wave V of the ABR and for the Na-Pa component of the MLR, suggesting that physiological variations arising from more central regions of the auditory system may mediate background noise acceptance.

Acoustic Stimulation↗
PubMed1978

Comparison of normal and impaired hearing. II. Frequency analysis, speech perception.

Frequency analysis covers two separate listening tasks, one involving frequency discrimination, the other frequency selectivity. Discrimination refers to the ability to distinguish one frequency from another. Selectivity refers to the ability to hear one frequency in the presence of other frequencies. Selectivity is critical to the understanding of speech which comprises sounds containing many different frequencies. To understand speech easily, the listener must be able to analyze speech sounds into their component frequencies, especially formants. The hard-of-hearing person is probably less able to make that analysis, but we know surprisingly little about either discrimination or selectivity in hearing impairment. Existing evidence does suggest that both discrimination and selectivity are reduced in cochlear impairment so that such patients need a bigger frequency difference to discriminate between two tones and they have a wider critical band. A widened critical band would be expected to make it very difficult for the severely impaired person to understand speech under all listening conditions; it would make it difficult for the moderately impaired person to understand speech in a noisy background, unless the signal-to-noise ratio is improved as is possible by appropriate amplitude compression in hearing aids.

Audiometry, Pure-Tone↗
PubMed1991

Periodicity and pitch perception.

There has been experimental evidence pointing to at least two pitch mechanisms, the first involving low-order harmonics that are resolved along the basilar membrane, and the second a periodicity mechanism that depends only on the repetition rate of the time waveform on the basilar membrane. If this time waveform is derived from repeated bursts of sinusoidal tone, the second mechanism might be the sole pitch mechanism. It is found that this can be so up to rates as high as 250 bursts of 4978-Hz tone per second. The stimuli used are periodic patterns of equally spaced tone bursts, with either successive tone bursts in the same phase, or every fourth tone burst 180 degrees out of phase with respect to the rest. Up to a critical transitional rate of tone bursts a second, the two sequences sound exactly the same, despite their different fundamental frequencies and frequency separation of harmonics. Critical rate data are given for sinusoidal bursts of seven different frequencies. Critical rates appear to be closely related to the critical bandwidth. Pitch matching appears to be consistent with these observations; it is on rate below the critical rate and can be on fundamental frequency above the critical rate.

Attention↗
PubMed2005

Effects of stimulation rate, mode and level on modulation detection by cochlear implant users.

In cochlear implant (CI) patients, temporal processing is often poorest at low listening levels, making perception difficult for low-amplitude temporal cues that are important for consonant recognition and/or speech perception in noise. It remains unclear how speech processor parameters such as stimulation rate and stimulation mode may affect temporal processing, especially at low listening levels. The present study investigated the effects of these parameters on modulation detection by six CI users. Modulation detection thresholds (MDTs) were measured as functions of stimulation rate, mode, and level. Results show that for all stimulation rate and mode conditions, modulation sensitivity was poorest at quiet listening levels, consistent with results from previous studies. MDTs were better with the lower stimulation rate, especially for quiet-to-medium listening levels. Stimulation mode had no significant effect on MDTs. These results suggest that, although high stimulation rates may better encode temporal information and widen the electrode dynamic range, CI patients may not be able to access these enhanced temporal cues, especially at the lower portions of the dynamic range. Lower stimulation rates may provide better recognition of weak acoustic envelope information.

Acoustic Stimulation↗