Consonant perception with linear and compression amplification

The consonant perception of 15 subjects with mild to moderate sensorineural hearing loss was evaluated using linear amplification and two different types of compression amplification. A specially modified hearing aid was used which allowed for variation of the amplifier input/output function in three steps, such that the compression ratio could be set to 1 (linear), 1.3 or 1.8. The Nonsense Syllable Test (NST) was recorded through the aid in quiet and in two different noise conditions (four-talker babble and a background noise with sharp intermittent sounds), and replayed to the listeners through headphones. No differences in consonant perception were found between the different types of amplification in the quiet condition. In the babble condition, consonant perception was significantly better with linear amplification than with either form of compression. In the sharp noise condition, there was no difference in performance between linear amplification and compression amplification with the ratio of 1.8. Consonant perception was adversely affected, however, by the compression and amplification with the ratio of 1.3 in this condition. Overall NST results and results for particular classes of consonants are discussed.     

Auditory perception with level-dependent hearing protectors. The effects of age and hearing loss

Auditory perception with hearing protectors was assessed in three groups of subjects, two with normal hearing, but differing in age, and one with moderate bilateral sensorineural hearing loss. Individuals were tested with the ears unoccluded, and fitted with each of two level-dependent ear muffs and their conventional level-independent counterparts. One of the former devices provided limited amplification. In each of these five ear conditions, the threshold of audibility for one-third octave noise bands centered at 500, 1,000, 2,000 and 4,000 Hz, consonant discrimination, and word recognition were measured in quiet and in a continuous impulse noise background. The results showed that the attenuation of sounds (i.e. the difference between protected and unoccluded thresholds) in quiet did not vary as a function of age or hearing loss for any of the four protectors. In noise, the difference between protected and unoccluded listening was close to zero, as long as hearing was normal. With hearing loss as a factor, there was a significant increment in the protected threshold, the amount determined by the device. Word recognition in quiet was adversely affected in normal-hearing listeners by the three attenuating devices but improved in noise relative to unoccluded listening. Amplification had a deleterious effect for both consonant discrimination and word recognition in noise. In hearing-impaired listeners, speech perception was impeded by all four muffs but less so in quiet with limited amplification.     

Preferred hearing-aid frequency responses in simulated listening environments

This study was designed to determine if an adaptive strategy could be used to select frequency/gain characteristics that would be considered appropriate across a variety of listening environments. In Experiment I, the test-retest reliability of the paired comparison procedure used in Experiment II was assessed in quiet for nine subjects and in speech noise for six subjects. For both conditions, results revealed mean standard deviations of < 3 dB from 200 through 4000 Hz. In Experiment II, four subjects selected frequency/gain characteristics for five different listening environments (quiet, speech noise, quiet conference room, reverberant lecture hall, and reverberant lecture hall in noise). In general, subjects did not tend to select different frequency/gain characteristics across the five simulated environments used in this study. When differences in frequency responses were observed, they tended to be alterations in overall gain rather than changes in relative frequency response. Findings support additional evaluation in more diverse listening environments, possibly with systems that incorporate nonlinear signal processing.     

Benefits of linear amplification and multichannel compression for speech comprehension in backgrounds with spectral and temporal dips

People with cochlear hearing loss have markedly higher speech-receptions thresholds (SRTs) than normal for speech presented in background sounds with spectral and/or temporal dips. This article examines the extent to which SRTs can be improved by linear amplification with appropriate frequency-response shaping, and by fast-acting wide-dynamic-range compression amplification with one, two, four, or eight channels. Eighteen elderly subjects with moderate to severe hearing loss were tested. SRTs for sentences were measured for four background sounds, presented at a nominal level (prior to amplification) of 65 dB SPL: (1) A single female talker, digitally filtered so that the long-term average spectrum matched that of the target speech; (2) a noise with the same average spectrum as the target speech, but with the temporal envelope of the single talker; (3) a noise with the same overall spectral shape as the target speech, but filtered so as to have 4 equivalent-rectangular-bandwidth (ERB) wide spectral notches at several frequencies; (4) a noise with both spectral and temporal dips obtained by applying the temporal envelope of a single talker to speech-shaped noise [as in (2)] and then filtering that noise [as in (3)]. Mean SRTs were 5-6 dB lower (better) in all of the conditions with amplification than for unaided listening. SRTs were significantly lower for the systems with one-, four-, and eight-channel compression than for linear amplification, although the benefit, averaged across subjects, was typically only 0.5 to 0.9 dB. The lowest mean SRT (-9.9 dB, expressed as a speech-to-background ratio) was obtained for noise (4) and the system with eight-channel compression. This is about 6 dB worse than for elderly subjects with near-normal hearing, when tested without amplification. It is concluded that amplification, and especially fast-acting compression amplification, can improve the ability to understand speech in background sounds with spectral and temporal dips, but it does not restore performance to normal.     

Development and evaluation of a procedure for fitting multi-channel compression hearing aids

Hearing aids with multi-channel compression are often fitted on the basis of loudness scaling data obtained using narrow bands of noise or tones. Here, we report the development and evaluation of an alternative fitting procedure based on the use of speech signals. The parameters of the hearing aid (the gains in each channel for high and low input levels) are adjusted adaptively under computer control on the basis of the listener's responses. The goal is that speech at 85 dB SPL should be judged as 'loud', speech at 60 dB SPL should be judged as 'quiet', and speech at both levels should be judged as 'neither tinny nor boomy'. The procedure was evaluated using a two-channel compression hearing aid, the remote control of which allowed two programs to be stored. One program was based on our fitting procedure. The other was either based on the manufacturer's recommended full fitting procedure (which included loudness scaling with bands of noise), or was based on the audiogram alone, using the manufacturer's algorithm. After an acclimatization period of at least two weeks, subjects were then asked to fill in a questionnaire about their experiences with the two programs in different listening situations. The results generally indicated a preference for the program based on our adaptive fitting procedure. We also conducted laboratory measurements of speech intelligibility, in quiet and in a background of a single competing talker. These showed no clear difference between programs, although scores overall were very high. We conclude that our adaptive procedure gives very satisfactory results in everyday life. Parameter values giving good comfort also give good intelligibility. The procedure typically takes between five and 10 minutes per ear, which is quicker than most loudness scaling procedures.     

Aided speech recognition abilities of adults with a severe or severe-to-profound hearing loss

Adults with severe or severe-to-profound hearing losses constitute between 11% and 13.5% of the hearing-impaired population. A detailed investigation of the speech recognition of adults with severe (n = 20) or severe-to-profound (n = 14) hearing loss was conducted at The University of Melbourne. Each participant took part in a series of speech recognition tasks while wearing his or her currently fitted hearing aid(s). The assessments included closed-set tests of consonant recognition and vowel recognition, combined with open-set tests of monosyllabic word recognition and sentence recognition. Sentences were presented in quiet and in noise at +10 dB SNR to replicate an environment more typical of everyday listening conditions. Although the results demonstrated wide variability in performance, some general trends were observed. As expected vowels were generally well perceived compared with consonants. Monosyllabic word recognition scores for both the adults with a severe hearing impairment (M = 67.2%) and the adults with a severe-to-profound hearing impairment (M = 38.6%) could be predicted from the segmental tests, with an allowance for lexical effects. Scores for sentences presented in quiet showed additional linguistic effects and a significant decrease in performance with the addition of background noise (from 82.9% to 74.1% for adults with a severe hearing loss and from 55.8% to 34.2% for adults with a severe-to-profound hearing loss). Comparisons were made between the participants and a group of adults using a multiple-channel cochlear implant. This comparison indicated that some adults with a severe or severe-to-profound hearing loss may benefit from the use of a cochlear implant. The results of this study support the contention that cochlear implant candidacy should not rely solely on audiometric thresholds.     

Effect of low-frequency gain reduction on speech recognition and its relation to upward spread of masking

Speech recognition was measured in listeners with normal hearing and in listeners with sensorineural hearing loss under conditions that simulated hearing aid processing in a low-pass and speech-shaped background noise. Differing amounts of low-frequency gain reduction were applied during a high-frequency monosyllable test and a sentence level test to simulate the frequency responses of some commercial hearing aids. The results showed an improvement in speech recognition with low-frequency gain reduction in the low-pass noise, but not in the speech-shaped background noise. Masking patterns also were obtained with the two background noises at 70 and 80 dB SPL to compare with the speech results. There was no correlation observed between the masking results and the improvement in speech recognition with low-frequency gain reduction.     

Speech enhancement based on a sinusoidal model

Sinusoidal modeling is a new procedure for representing the speech signal. In this approach, the signal is divided into overlapping segments, the Fourier transform computed for each segment, and a set of desired spectral peaks is identified. The speech is then resynthesized using sinusoids that have the frequency, amplitude, and phase of the selected peaks, with the remaining spectral information being discarded. Using a limited number of sinusoids to reproduce speech in a background of multi-talker speech babble results in a speech signal that has an improved signal-to-noise ratio and enhanced spectral contrast. The more intense spectral components, assumed to be primarily the desired speech, are reproduced, whereas the less intense components, assumed to be primarily background noise, are not. To test the effectiveness of this processing approach as a noise suppression technique, both consonant recognition and perceived speech intelligibility were determined in quiet and in noise for a group of subjects with normal hearing as the number of sinusoids used to represent isolated speech tokens was varied. The results show that reducing the number of sinusoids used to represent the speech causes reduced consonant recognition and perceived intelligibility both in quiet and in noise, and suggests that similar results would be expected for listeners with hearing impairments.     

Speaking clearly for the hard of hearing IV: Further studies of the role of speaking rate

The contribution of reduced speaking rate to the intelligibility of "clear" speech (Picheny, Durlach, & Braida, 1985) was evaluated by adjusting the durations of speech segments (a) via nonuniform signal time-scaling, (b) by deleting and inserting pauses, and (c) by eliciting materials from a professional speaker at a wide range of speaking rates. Key words in clearly spoken nonsense sentences were substantially more intelligible than those spoken conversationally (15 points) when presented in quiet for listeners with sensorineural impairments and when presented in a noise background to listeners with normal hearing. Repeated presentation of conversational materials also improved scores (6 points). However, degradations introduced by segment-by-segment time-scaling rendered this time-scaling technique problematic as a means of converting speaking styles. Scores for key words excised from these materials and presented in isolation generally exhibited the same trends as in sentence contexts. Manipulation of pause structure reduced scores both when additional pauses were introduced into conversational sentences and when pauses were deleted from clear sentences. Key-word scores for materials produced by a professional talker were inversely correlated with speaking rate, but conversational rate scores did not approach those of clear speech for other talkers. In all experiments, listeners with normal hearing exposed to flat-spectrum background noise performed similarly to listeners with hearing loss.     

Speech intelligibility in noise with fast compression hearing aids

The effect of fast (syllabic) compression with overshoot reduction was studied in moderately hearing-impaired and in severely hearing-impaired listeners in quiet and in noisy situations. A test battery of daily masking noises was selected using multidimensional scaling techniques. Four relevant noises were selected: a multi-talker babble, the noise in an industrial plant, in a printing office and a city-noise background. The speech measurements show that only selected patients benefit from syllabic compression, i.e. listeners with a poor speech discrimination score. The effect in noisy surroundings was tested at the critical signal-to-noise ratio of each patient, showing whether they benefited from compression in the most critical condition or not. It turns out that the effect depends largely on the speech discrimination score and the modulation of the noise signal. When the speech discrimination score is good, compression tends to impair the results. When the speech discrimination score is poor, compression helps if the noise is modulated.     

Listening to discourse in distracting settings: The effects of aging.

Younger and older adults listened to discourse in quiet and in conversational noise, before answering questions concerning the material. Some questions required listeners to recall specific details; others were of a more integrative nature. When the listening situation was adjusted for individual differences in hearing, younger and older adults were equally adept at remembering the gist of the passages in both quiet and in two levels of noise. The two age groups also did not differ with respect to memory for specific details when listening in quiet or in a moderate level of noise, even when required to perform a concurrent task. Only at the loudest noise level did younger adults tend to recall more detail than older adults. However, when no adjustments were made to compensate for the poorer hearing of older adults (all participants tested under identical listening conditions), older adults could not recall as much detail as younger adults, either in quiet or in noise. The results indicate that the speech-comprehension difficulties of older adults primarily reflect declines in hearing rather than in cognitive ability. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of angiotensin II, endothelin-1, and nitric oxide in HgCl2-induced acute renal failure

Although multichannel compression systems are quickly becoming integral components of programmable hearing aids, research results have not consistently demonstrated their benefit over conventional amplification. The present study examined two confounding factors that may have contributed to this inconsistency in results: alteration of temporal information and audibility of speech cues. Recognition of linearly amplified and multichannel-compressed speech was measured for listeners with mild-to-severe sensorineural hearing loss and for a control group of listeners with normal hearing. In addition to the standard speech signal, which provided both temporal and spectral information, the listener's ability to use temporal information in a multichannel compressed signal was directly tested using a signal-correlated noise (SCN) stimulus. This stimulus consisted of a time-varying speech envelope modulating a two-channel noise carrier. It preserved temporal cues but provided minimal spectral information. For each stimulus condition, short-term level measurements were used to determine the range of audible speech. Multichannel compression improved speech recognition under conditions where superior audibility was provided by the two-channel compression system over linear amplification. When audibility of both linearly amplified and multichannel-compressed speech was maximized, the multichannel compression had no significant effect on speech recognition score for speech containing both temporal and spectral cues. However, results for the SCN stimuli show that more extreme amounts of multichannel compression can reduce use of temporal information.     

Telephone communication with in-the-ear hearing aids using acoustic and electromagnetic coupling

The purpose of this study was to determine whether telephone communication was improved with electromagnetic coupling for in-the-ear hearing aid users with mild to moderate hearing losses. Each user adjusted his hearing aid gain to the level he determined to be best for telephone communication with each coupling method. Under these conditions, average word recognition scores in quiet and average high-frequency output levels measured at the tympanic membrane were not different for each coupling method. The ability to tolerate background noise was also studied. Background noise tolerance was not different for the two coupling methods. However, significantly greater levels of background noise were tolerated when telephone side-tone feedback was eliminated regardless of coupling method.     

Reliability of monosyllabic discrimination tests in white noise for differentiating among hearing aids

In spite of criticism, monosyllabic discrimination tests are widely employed for hearing aid selection. The current study was designed to investigate the following questions: (1) How reliable is aided speech discrimination of monosyllables in a background of white noise? (2) Can differences among hearing aids be reliably demonstrated by measuring intelligibility of monosyllables in a background of white noise? and (3) Do hearing aids interact with hearing loss? Twenty subjects with mild-moderate sensorineural hearing losses participated in two experimental sessions. Four hearing aids were evaluated using the NU-6 monosyllables in a background of white noise (s/n = +20 dB). Since the standard deviation of the test-retest differences was 6%, differences between aids were not considered significant unless they exceeded 12%. An interaction between subjects and hearing aids was found; that is, the best aid for one person was not the best for all. Measuring monosyllabic word intelligibility in a background of white noise does not reliably identify a single best aid. However, one or more inferior aids were consistently eliminated in 80% of the subjects.     

An adaptive noise canceller for hearing aids using two nearby microphones

An adaptive noise cancellation scheme based on two-stage adaptive filtering as proposed by Van Compernolle [Proceedings of the IEEE International Conference on Acoustics, Speech and Signal Processing (IEEE, New York, 1990)] was tested for two identical directional microphones mounted in an endfire configuration within a single behind-the-ear (BTE) hearing aid. Speech intelligibility tests were carried out with two normal hearing subjects and three hearing aid users with moderate hearing losses, in a realistic test environment using open set words and sentences. A significant improvement, on average more than 5 dB, of speech reception threshold (SRT) in background noise was obtained.     

Linking injection drug users to medical services: role of street outreach referrals

OBJECTIVE: The study was designed to assess the effects of background noise level on the detection and localization of speech. DESIGN: The phrase "Where is this?" was presented either in quiet or in a diffuse noise field, through loudspeakers arranged in a 360 degrees azimuth array. The noise conditions included 11 signal to noise ratios (SNRs) ranging from -18 dB SNR to +12 dB SNR in 3 dB increments. Seventeen normal-hearing subjects, aged 18 to 29, participated in the study. RESULTS: Results revealed that in all listening conditions the signal was most easily detected when presented through a loudspeaker positioned at 90 degrees or 270 degrees azimuth. Although the actual level for 50% detection varied as a function of loudspeaker location and SNR, 85% and 100% of all presentations of the signal were detected at -9 dB and -6 dB SNR, respectively. Localization accuracy improved as the SNR increased, ranging from 18% accuracy at -18 dB SNR to 89% at +12 dB SNR. Localization accuracy in quiet was 95%. The data are discussed in reference to patterns of responses at each loudspeaker location. CONCLUSIONS: Detection of the target signal deteriorated as background noise level increased and was dependent on the source location of the incoming signal, as expected. Localization accuracy of the target signal was highly dependent on the SNR and spatial location of the signal source. Detection and localization accuracy data were found to be repeatable across test sessions and response patterns were found to be symmetrical on the right and left sides of the horizontal plane.     

Self-reported hearing problems in daily life throughout adulthood

The authors assessed age differences on self-reported hearing problems on the performance of auditory tasks in the natural environment. The Your Hearing questionnaire was administered to 265 respondents (aged 20-94 years). Both the degree and variability of self-reported hearing problems were found to increase significantly with age, including those associated with listening to speech under conditions of background noise, the perception of normal and distorted speech, and the perception of short segments of speech and the perception of high-pitched sounds. Experienced hearing problems were greater for Ss who judged their hearing as being of poor quality. Findings suggest that self-report measures can provide valuable insights into the impact of age-related hearing disability on daily life that are not provided by more traditional laboratory-based studies.     

Acoustic differences, listener expectations, and the perceptual accommodation of talker variability.

Two talkers' productions of the same phoneme may be quite different acoustically, whereas their productions of different speech sounds may be virtually identical. Despite this lack of invariance in the relationship between the speech signal and linguistic categories, listeners experience phonetic constancy across a wide range of talkers, speaking styles, linguistic contexts, and acoustic environments. The authors present evidence that perceptual sensitivity to talker variability involves an active cognitive mechanism: Listeners expecting to hear 2 different talkers differing only slightly in average pitch showed performance costs typical of adjusting to talker variability, whereas listeners hearing the same materials but expecting a single talker or given no special instructions did not show these performance costs. The authors discuss the implications for understanding phonetic constancy despite variability between talkers (and other sources of variability) and for theories of speech perception. The results provide further evidence for active, controlled processing in real-time speech perception and are consistent with a model of talker normalization that involves contextual tuning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pathology of lung cancer

The aim of this study was to assess the repeatability of the program-usage in everyday listening situations. A blind field test was used. The Widex Quattro (WQ) system served as a model for multiple memory hearing aids (linear amplification) Eleven experienced WQ wearers (41-73 years) with mild to moderate, recruiting, cochlear hearing losses participated. Eight of them regularly used all four available programs (all used at least three programs). The participants stated in duplicate the best hearing aid program in 15 real-world listening situations. The percentage of subjects who selected identical programs (repeatability) surpassed the level corresponding to pure guess under almost all listening conditions (14). Maximum repeatability (100%) was achieved by the five subjects who visited an industrial environment twice. Interestingly, the repeatability exceeded 70% in demanding listening situations such as: party, conversation in group, etc. Support for this high repeatability was given by a distinct improvement in the mean aided speech-to-noise threshold (3.7 dB, p < 0.005).     

Tributyrin induces growth inhibitory and differentiating effects on HT-29 colon cancer cells in vitro

HINT list equivalency was examined using 24 listeners between 60 and 70 years old who had sensorineural hearing impairment. A Greco-Latin square design was used to ensure that each list was presented an equal number of times per condition. Four conditions were tested: (1) speech in quiet, (2) speech in 65 dBA noise with noise at 0 degrees azimuth, (3) speech in 65 dBA noise with noise at 90 degrees azimuth, and (4) speech in 65 dBA noise with noise at 270 degrees azimuth. Speech materials were always presented at 0 degrees azimuth. Overall mean scores ranged from 29.9 dBA for the quiet condition to 63.4 dBA for the noise at 0 degrees azimuth condition. A significant difference was found between Lists 13 and 16 only. This was attributed to audibility differences among the listeners. Therefore, the 25 HINT lists should be considered equivalent for older populations with similar hearing impairment. The HINT lists can be used for relative measures, such as comparison of aided versus unaided sentence SRTs or comparison of 2 different hearing aids.