The effects of age and cochlear hearing loss on temporal fine structure sensitivity, frequency selectivity, and speech reception in noise

Temporal fine structure (TFS) sensitivity, frequency selectivity, and speech reception in noise were measured for young normal-hearing (NHY), old normal-hearing (NHO), and hearing-impaired (HI) subjects. Two measures of TFS sensitivity were used: the "TFS-LF test" (interaural phase difference discrimination) and the "TFS2 test" (discrimination of harmonic and frequency-shifted tones). These measures were not significantly correlated with frequency selectivity (after partialing out the effect of audiometric threshold), suggesting that insensitivity to TFS cannot be wholly explained by a broadening of auditory filters. The results of the two tests of TFS sensitivity were significantly but modestly correlated, suggesting that performance of the tests may be partly influenced by different factors. The NHO group performed significantly more poorly than the NHY group for both measures of TFS sensitivity, but not frequency selectivity, suggesting that TFS sensitivity declines with age in the absence of elevated audiometric thresholds or broadened auditory filters. When the effect of mean audiometric threshold was partialed out, speech reception thresholds in modulated noise were correlated with TFS2 scores, but not measures of frequency selectivity or TFS-LF test scores, suggesting that a reduction in sensitivity to TFS can partly account for the speech perception difficulties experienced by hearing-impaired subjects.     

Effects of age and mild hearing loss on speech recognition in noise

Using an adaptive strategy, the effects of mild sensorineural hearing loss and adult listeners' chronological age on speech recognition in babble were evaluated. The signal-to-babble ratio required to achieve 50% recognition was measured for three speech materials presented at soft to loud conversational speech levels. Four groups of subjects were tested: (1) normal-hearing listeners less than 44 years of age, (2) subjects less than 44 years old with mild sensorineural hearing loss and excellent speech recognition in quiet, (3) normal-hearing listeners greater than 65 with normal hearing, and (4) subjects greater than 65 years old with mild hearing loss and excellent performance in quiet. Groups 1 and 3, and groups 2 and 4 were matched on the basis of pure-tone thresholds, and thresholds for each of the three speech materials presented in quiet. In addition, groups 1 and 2 were similar in terms of mean age and age range, as were groups 3 and 4. Differences in performance in noise as a function of age were observed for both normal-hearing and hearing-impaired listeners despite equivalent performance in quiet. Subjects with mild hearing loss performed significantly worse than their normal-hearing counterparts. These results and their implications are discussed.     

Proportional frequency compression of speech for listeners with sensorineural hearing loss.

This study examined proportional frequency compression as a strategy for improving speech recognition in listeners with high-frequency sensorineural hearing loss. This method of frequency compression preserved the ratios between the frequencies of the components of natural speech, as well as the temporal envelope of the unprocessed speech stimuli. Nonsense syllables spoken by a female and a male talker were used as the speech materials. Both frequency-compressed speech and the control condition of unprocessed speech were presented with high-pass amplification. For the materials spoken by the female talker, significant increases in speech recognition were observed in slightly less than one-half of the listeners with hearing impairment. For the male-talker materials, one-fifth of the hearing-impaired listeners showed significant recognition improvements. The increases in speech recognition due solely to frequency compression were generally smaller than those solely due to high-pass amplification. The results indicate that while high-pass amplification is still the most effective approach for improving speech recognition of listeners with high-frequency hearing loss, proportional frequency compression can offer significant improvements in addition to those provided by amplification for some patients.     

Fundamental frequency is critical to speech perception in noise in combined acoustic and electric hearing

Cochlear implant (CI) users have been shown to benefit from residual low-frequency hearing, specifically in pitch related tasks. It remains unclear whether this benefit is dependent on fundamental frequency (F0) or other acoustic cues. Three experiments were conducted to determine the role of F0, as well as its frequency modulated (FM) and amplitude modulated (AM) components, in speech recognition with a competing voice. In simulated CI listeners, the signal-to-noise ratio was varied to estimate the 50% correct response. Simulation results showed that the F0 cue contributes to a significant proportion of the benefit seen with combined acoustic and electric hearing, and additionally that this benefit is due to the FM rather than the AM component. In actual CI users, sentence recognition scores were collected with either the full F0 cue containing both the FM and AM components or the 500-Hz low-pass speech cue containing the F0 and additional harmonics. The F0 cue provided a benefit similar to the low-pass cue for speech in noise, but not in quiet. Poorer CI users benefited more from the F0 cue than better users. These findings suggest that F0 is critical to improving speech perception in noise in combined acoustic and electric hearing.     

Monosyllabic word recognition at higher-than-normal speech and noise levels

The effects of intensity on monosyllabic word recognition were studied in adults with normal hearing and mild-to-moderate sensorineural hearing loss. The stimuli were bandlimited NU#6 word lists presented in quiet and talker-spectrum-matched noise. Speech levels ranged from 64 to 99 dB SPL and S/N ratios from 28 to -4 dB. In quiet, the performance of normal-hearing subjects remained essentially constant in noise, at a fixed S/N ratio, it decreased as a linear function of speech level. Hearing-impaired subjects performed like normal-hearing subjects tested in noise when the data were corrected for the effects of audibility loss. From these and other results, it was concluded that: (1) speech intelligibility in noise decreases when speech levels exceed 69 dB SPL and the S/N ratio remains constant; (2) the effects of speech and noise level are synergistic; (3) the deterioration in intelligibility can be modeled as a relative increase in the effective masking level; (4) normal-hearing and hearing-impaired subjects are affected similarly by increased signal level when differences in speech audibility are considered; (5) the negative effects of increasing speech and noise levels on speech recognition are similar for all adult subjects, at least up to 80 years; and (6) the effective dynamic range of speech may be larger than the commonly assumed value of 30 dB.     

The effects of hearing loss on the contribution of high- and low-frequency speech information to speech understanding. II. Sloping hearing loss

The speech understanding of persons with sloping high-frequency (HF) hearing impairment (HI) was compared to normal hearing (NH) controls and previous research on persons with "flat" losses [Hornsby and Ricketts (2003). J. Acoust. Soc. Am. 113, 1706-1717] to examine how hearing loss configuration affects the contribution of speech information in various frequency regions. Speech understanding was assessed at multiple low- and high-pass filter cutoff frequencies. Crossover frequencies, defined as the cutoff frequencies at which low- and high-pass filtering yielded equivalent performance, were significantly lower for the sloping HI, compared to NH, group suggesting that HF HI limits the utility of HF speech information. Speech intelligibility index calculations suggest this limited utility was not due simply to reduced audibility but also to the negative effects of high presentation levels and a poorer-than-normal use of speech information in the frequency region with the greatest hearing loss (the HF regions). This deficit was comparable, however, to that seen in low-frequency regions of persons with similar HF thresholds and "flat" hearing losses suggesting that sensorineural HI results in a "uniform," rather than frequency-specific, deficit in speech understanding, at least for persons with HF thresholds up to 60-80 dB HL.     

The effects of hearing loss on the contribution of high- and low-frequency speech information to speech understanding

The speech understanding of persons with "flat" hearing loss (HI) was compared to a normal-hearing (NH) control group to examine how hearing loss affects the contribution of speech information in various frequency regions. Speech understanding in noise was assessed at multiple low- and high-pass filter cutoff frequencies. Noise levels were chosen to ensure that the noise, rather than quiet thresholds, determined audibility. The performance of HI subjects was compared to a NH group listening at the same signal-to-noise ratio and a comparable presentation level. Although absolute speech scores for the HI group were reduced, performance improvements as the speech and noise bandwidth increased were comparable between groups. These data suggest that the presence of hearing loss results in a uniform, rather than frequency-specific, deficit in the contribution of speech information. Measures of auditory thresholds in noise and speech intelligibility index (SII) calculations were also performed. These data suggest that differences in performance between the HI and NH groups are due primarily to audibility differences between groups. Measures of auditory thresholds in noise showed the "effective masking spectrum" of the noise was greater for the HI than the NH subjects.     

Sentence reception in noise from one versus two sources: effects of aging and hearing loss

Sentence reception thresholds (SRTs) and babble detection thresholds (BDTs) were measured for signals presented from loudspeakers located at 0 deg and 90 deg azimuth. In addition, the S/B ratios necessary to achieve SRT in the presence of a 12-talker babble were determined under three conditions in which the speech and babble were presented from the same or spatially separated loudspeakers. In the first experiment, normal-hearing subjects were tested on two occasions. The results were highly reliable, with standard errors of the test-retest differences of less than 1dB for all conditions. In the second experiment, SRTs, BDTs, and S/B ratios were measured for three normal-hearing groups (less than or equal to 39, 40-54, and greater than or equal to 55 years) and for a fourth group with presbycusis (greater than or equal to 55 years). Presbycusics had higher SRTs and BDTs than all other groups regardless of age, and the oldest normals had higher thresholds than younger subjects. Presbycusics required higher S/B ratios than any of the normal groups, and the oldest normal group needed a higher S/B ratio compared to the youngest group. All groups demonstrated a significant advantage in S/B ratio when the sentences and babble sources were spatially separated compared to when they were presented from the same loudspeaker. There was no significant difference in the magnitude of advantage due to spatial separation of speech and noise between the normal groups regardless of age, but the presbycusics had significantly smaller advantages than all normals.(ABSTRACT TRUNCATED AT 250 WORDS)     

噪声对单耳语言可懂度的影响

单耳通信时,周边噪声对语言可懂度产生影响。针对信号侧语音信号强度70dB时,研究3种不同类型噪声下,干扰侧不同强度噪声和信号侧不同信噪比情况的语言可懂度。实验结果表明:当信号侧信噪比大于某一阈值时,干扰侧噪声对可懂度不产生显著影响,该阈值同噪声类型有关;而在信号侧低信噪比的情形下,干扰侧适当强度噪声可提高信号侧语言可懂度,最佳干扰噪声级为78—82dB,过大的干扰侧噪声级导致可懂度下降。基于心理声学和生理学的初步机理发现:噪声环境下的语音识别中,对侧耳中耳肌肉伸缩对噪声感知的抑制提高了信号侧语言可懂度。     

Intensity-time tradeoff for constant hearing loss with high sound levels

The tradeoff relation between exposure intensity and duration for constant hearing loss was investigated in two series of experiments using Mongolian gerbils. The gerbils were exposed to a 1/3 octave band of noise at 2.5 kHz. In the first series animals were exposed to 120 dB SPL for 1 h, to 126 dB SPL for 15 min, and to 126 dB SPL for 3.75 min. In the second series, shorter durations were used: 120 dB SPL for 15 min, 126 dB SPL for 3.75 min, and 126 dB SPL for 56 s. The hearing thresholds were determined behaviorally immediately before exposure and 6 weeks after exposure. The results suggest that the intensity-time tradeoff for the investigated intensity interval is between 1.5 and 3 dB per halving of the duration.     

Relations among temporal acuity, hearing loss, and the perception of speech distorted by noise and reverberation

Eight normal listeners and eight listeners with sensorineural hearing losses were compared on a gap-detection task and on a speech perception task. The minimum detectable gap (71% correct) was determined as a function of noise level, and a time constant was computed from these data for each listener. The time constants of the hearing-impaired listeners were significantly longer than those of the normal listeners. The speech consisted of sentences that were mixed with two levels of noise and subjected to two kinds of reverberation (real or simulated). The speech thresholds (minimum signal-to-noise ratio for 50% correct) were significantly higher for the hearing-impaired listeners than for the normal listeners for both kinds of reverberation. The longer reverberation times produced significantly higher thresholds than the shorter times. The time constant was significantly correlated with all the speech threshold measures (r = -0.58 to -0.74) and a measure of hearing threshold loss also correlated significantly with all the speech thresholds (r = 0.53 to 0.95). A principal components analysis yielded two factors that accounted for the intercorrelations. The factor loadings for the time constant were similar to those on the speech thresholds for real reverberation and the loadings for hearing loss were similar to those of the thresholds for simulated reverberation.     

Localization in speech mixtures by listeners with hearing loss

The ability of listeners with bilateral sensorineural hearing loss to localize a speech source in a multitalker mixture was measured. Five simultaneous words spoken by different talkers were presented over loudspeakers in a small room, and listeners localized one target word. Errors were significantly larger in this group compared to a control group with normal hearing. Localization of the target presented alone was not different between groups. The results suggest that hearing loss does not impair spatial hearing per se, but degrades the spatial representation of multiple simultaneous sounds.     

Contribution of frequency modulation to speech recognition in noise

Cochlear implants allow most patients with profound deafness to successfully communicate under optimal listening conditions. However, the amplitude modulation (AM) information provided by most implants is not sufficient for speech recognition in realistic settings where noise is typically present. This study added slowly varying frequency modulation (FM) to the existing algorithm of an implant simulation and used competing sentences to evaluate FM contributions to speech recognition in noise. Potential FM advantage was evaluated as a function of the number of spectral bands, FM depth, FM rate, and FM band distribution. Barring floor and ceiling effects, significant improvement was observed for all bands from 1 to 32 with the additional FM cue both in quiet and noise. Performance also improved with greater FM depth and rate, which might reflect resolved sidebands under the FM condition. Having FM present in low-frequency bands was more beneficial than in high-frequency bands, and only half of the bands required the presence of FM, regardless of position, to achieve performance similar to when all bands had the FM cue. These results provide insight into the relative contributions of AM and FM to speech communication and the potential advantage of incorporating FM for cochlear implant signal processing.     

Spectral and threshold effects on recognition of speech at higher-than-normal levels

To examine spectral and threshold effects for speech and noise at high levels, recognition of nonsense syllables was assessed for low-pass-filtered speech and speech-shaped maskers and high-pass-filtered speech and speech-shaped maskers at three speech levels, with signal-to-noise ratio held constant. Subjects were younger adults with normal hearing and older adults with normal hearing but significantly higher average quiet thresholds. A broadband masker was always present to minimize audibility differences between subject groups and across presentation levels. For subjects with lower thresholds, the declines in recognition of low-frequency syllables in low-frequency maskers were attributed to nonlinear growth of masking which reduced "effective" signal-to-noise ratio at high levels, whereas the decline for subjects with higher thresholds was not fully explained by nonlinear masking growth. For all subjects, masking growth did not entirely account for declines in recognition of high-frequency syllables in high-frequency maskers at high levels. Relative to younger subjects with normal hearing and lower quiet thresholds, older subjects with normal hearing and higher quiet thresholds had poorer consonant recognition in noise, especially for high-frequency speech in high-frequency maskers. Age-related effects on thresholds and task proficiency may be determining factors in the recognition of speech in noise at high levels.     

Coherent effects in inverse compton scattering in the high frequency region

The conditions under which a cooperative emission from different friges occurs in the scattering between a relativistic electron beam and two interfering laser beams are discussed. In particular, the conditions to have an electron grating are discussed.     

Suppression of localization effects by the high frequency field and the nyquist noise

It is shown that strong inelastic processes are not necessary for suppression of localization effects in disordered conductors. The influence of an external high frequency electric field on quantum corrections to conductivity is considered. Relatively weak fields are found to suppress localization. Thermal electromagnetic fluctuations act in the same way. These fluctuations lead to new dependences of localization effects in films and wires on temperature, impurity concentration and transversal size of the sample.     

The relationship between frequency selectivity and pitch discrimination: sensorineural hearing loss

This study tested the relationship between frequency selectivity and the minimum spacing between harmonics necessary for accurate fo discrimination. Fundamental frequency difference limens (fo DLs) were measured for ten listeners with moderate sensorineural hearing loss (SNHL) and three normal-hearing listeners for sine- and random-phase harmonic complexes, bandpass filtered between 1500 and 3500 Hz, with fo's ranging from 75 to 500 Hz (or higher). All listeners showed a transition between small (good) fo DLs at high fo's and large (poor) fo DLs at low fo's, although the fo at which this transition occurred (fo,tr) varied across listeners. Three measures thought to reflect frequency selectivity were significantly correlated to both the fo,tr and the minimum fo DL achieved at high fo's: (1) the maximum fo for which fo DLs were phase dependent, (2) the maximum modulation frequency for which amplitude modulation and quasi-frequency modulation were discriminable, and (3) the equivalent rectangular bandwidth of the auditory filter, estimated using the notched-noise method. These results provide evidence of a relationship between fo discrimination performance and frequency selectivity in listeners with SNHL, supporting "spectral" and "spectro-temporal" theories of pitch perception that rely on sharp tuning in the auditory periphery to accurately extract fo information.