Masked Speech Reception Thresholds Research Articles

Effect of reverberation and informational masking on speech perception by adolescents and young adults with cochlear implants

Children with severe to profound hearing loss fitted with cochlear implants (CIs) can develop speech with degraded auditory inputs. Little is known about how speech perception by CI users who developed speech through electrical hearing is affected by realistic reverberation—a source of additional degradation in acoustic inputs to the CI speech processor. Moreover, how these young CI users handle competing maskers with high informational masking, such as two-talker babble, in speech-in-noise perception is not well characterized. Both reverberation and competing maskers are relevant factors in everyday classroom listening scenarios. In this work, we studied a cohort of adolescents and young adults with early fitting of CIs. Speech reception thresholds (SRTs) were measured in five types of maskers: speech-shaped noise (SSN), SSN modulated by a speech envelope, two-talker babble in English and in French, and time-reversed two-talker English babble. SRTs from each masker type were repeated in an anechoic condition and two reverberation conditions mimicking a classroom meeting classroom acoustics standard versus a lecture hall. When compared with a group of age-matched normal-hearing listeners, young CI users showed steeper increase of masked SRTs by increasing reverberation but comparable release from informational masking. [Work supported by the Hearing Health Foundation.]

Benefits from different types of acoustic beamforming in bilateral cochlear-implant listeners

Acoustic beamforming improves speech reception in noise at the cost of removing spatial cues. Recently, novel approaches have been proposed for enhancing speech reception via beamforming while preserving sound localization by reintroducing natural binaural cues to the beamformer output. It is, however, unclear whether such a hybrid approach will improve performance for bilateral cochlear-implant (BICI) listeners because they receive little benefit from natural spatial cues. Here, effects of beamforming on masked speech reception thresholds (SRTs) were determined in BICI and normal-hearing (NH) listeners for a standard single-channel beamformer and a new triple-beamformer comprising a diotic central beam, -40 deg left-ear-only beam, and + 40 deg right-ear-only beam [Jennings and Kidd, JASA 143, 1743]. Speech targets and maskers were co-located (0 deg) or maskers were symmetrically separated at ±30 deg or ±90 deg. Natural binaural listening, single-channel beamformer, and triple-beamformer conditions were tested. Both beamformers were better than natural cues. For BICI listeners, single-channel beamforming improved SRTs by 5 (±30 deg) and 15 dB (±90 deg). SRTs for the triple-beam were best for NH but were 5 dB worse than the single-channel beam for BICI listeners. These preliminary findings suggest beamforming provides significant spatial release from masking for BICI listeners but assessing overall benefit, including localization, awaits further study.

Effect of response context and masker type on word recognition in school-age children and adults.

In adults, masked speech recognition improves with the provision of a closed set of response alternatives. The present study evaluated whether school-age children (5-13 years) benefit to the same extent as adults from a forced-choice context, and whether this effect depends on masker type. Experiment 1 compared masked speech reception thresholds for disyllabic words in either an open-set or a four-alternative forced-choice (4AFC) task. Maskers were speech-shaped noise or two-talker speech. Experiment 2 compared masked speech reception thresholds for monosyllabic words in two 4AFC tasks, one in which the target and foils were phonetically similar and one in which they were dissimilar. Maskers were speech-shaped noise, amplitude-modulated noise, or two-talker speech. For both experiments, it was predicted that children would not benefit from the information provided by the 4AFC context to the same degree as adults, particularly when the masker was complex (two-talker) or when audible speech cues were temporally sparse (modulated-noise). Results indicate that young children do benefit from a 4AFC context to the same extent as adults in speech-shaped noise and amplitude-modulated noise, but the benefit of context increases with listener age for the two-talker speech masker.

Factors affecting the development of speech recognition in steady and modulated noise.

This study used a checkerboard-masking paradigm to investigate the development of the speech reception threshold (SRT) for monosyllabic words in synchronously and asynchronously modulated noise. In asynchronous modulation, masker frequencies below 1300 Hz were gated off when frequencies above 1300 Hz were gated on, and vice versa. The goals of the study were to examine development of the ability to use asynchronous spectro-temporal cues for speech recognition and to assess factors related to speech frequency region and audible speech bandwidth. A speech-shaped noise masker was steady or was modulated synchronously or asynchronously across frequency. Target words were presented to 5-7 year old children or to adults. Overall, children showed higher SRTs and smaller masking release than adults. Consideration of the present results along with previous findings supports the idea that children can have particularly poor masked SRTs when the speech and masker spectra differ substantially, and that this may arise due to children requiring a wider speech bandwidth than adults for speech recognition. The results were also consistent with the idea that children are relatively poor in integrating speech cues when the frequency regions with the best signal-to-noise ratios vary across frequency as a function of time.

Benefits of Acoustic Beamforming for Solving the Cocktail Party Problem.

The benefit provided to listeners with sensorineural hearing loss (SNHL) by an acoustic beamforming microphone array was determined in a speech-on-speech masking experiment. Normal-hearing controls were tested as well. For the SNHL listeners, prescription-determined gain was applied to the stimuli, and performance using the beamformer was compared with that obtained using bilateral amplification. The listener identified speech from a target talker located straight ahead (0° azimuth) in the presence of four competing talkers that were either colocated with, or spatially separated from, the target. The stimuli were spatialized using measured impulse responses and presented via earphones. In the spatially separated masker conditions, the four maskers were arranged symmetrically around the target at ±15° and ±30° or at ±45° and ±90°. Results revealed that masked speech reception thresholds for spatially separated maskers were higher (poorer) on average for the SNHL than for the normal-hearing listeners. For most SNHL listeners in the wider masker separation condition, lower thresholds were obtained through the microphone array than through bilateral amplification. Large intersubject differences were found in both listener groups. The best masked speech reception thresholds overall were found for a hybrid condition that combined natural and beamforming listening in order to preserve localization for broadband sources.

Development and Preliminary Evaluation of a Pediatric Spanish–English Speech Perception Task

The purpose of this study was to develop a task to evaluate children's English and Spanish speech perception abilities in either noise or competing speech maskers. Eight bilingual Spanish-English and 8 age-matched monolingual English children (ages 4.9-16.4 years) were tested. A forced-choice, picture-pointing paradigm was selected for adaptively estimating masked speech reception thresholds. Speech stimuli were spoken by simultaneous bilingual Spanish-English talkers. The target stimuli were 30 disyllabic English and Spanish words, familiar to 5-year-olds and easily illustrated. Competing stimuli included either 2-talker English or 2-talker Spanish speech (corresponding to target language) and spectrally matched noise. For both groups of children, regardless of test language, performance was significantly worse for the 2-talker than for the noise masker condition. No difference in performance was found between bilingual and monolingual children. Bilingual children performed significantly better in English than in Spanish in competing speech. For all listening conditions, performance improved with increasing age. Results indicated that the stimuli and task were appropriate for speech recognition testing in both languages, providing a more conventional measure of speech-in-noise perception as well as a measure of complex listening. Further research is needed to determine performance for Spanish-dominant listeners and to evaluate the feasibility of implementation into routine clinical use.

Effects of Age and Hearing Impairment on the Ability to Benefit From Temporal and Spectral Modulation

At poor signal-to-noise ratios, speech understanding may depend on the ability to combine speech fragments that are distributed across time and frequency. The goal of this study was to determine the effects of development and hearing impairment on this ability. Listeners in the present study included adults and children with normal hearing and with hearing impairment. The children with normal hearing included a younger group (aged 4.6-6.9 yr, N = 10) and an older group (aged 7.3-11.1 yr, N = 11). The adults with normal hearing were aged 19 to 27 yr (N = 10). Adults (aged 19-54 yr, N = 9) and children (aged 7.2-10.7 yr, N = 8) with hearing impairment were also tested. The two groups with hearing impairment had comparable mild/moderate bilateral sensorineural hearing impairment. Masked speech reception thresholds for sentences were determined in a baseline condition of steady speech-shaped noise and in noise that was temporally modulated, spectrally modulated, or both temporally and spectrally modulated. The results of normal-hearing listeners indicated higher masked speech reception thresholds for children than adults in steady noise. Adults and children showed the same magnitude of masking release for spectral modulation. Adults showed more masking release than the younger children for temporal modulation and showed more masking release than both the younger and older children for combined temporal/spectral modulation. Comparing normal-hearing and hearing-impaired listeners, the hearing-impaired listeners had higher masked speech reception thresholds in the steady noise condition and reduced masking release in the modulated noise conditions. Neither the two-way interaction between age and hearing impairment nor the three-way interaction between age, hearing impairment, and masking configuration was significant. Although the reduced masking release for temporal modulation shown by the younger children with normal hearing could be a result of poor temporal resolution, it more likely reflects inefficient use of speech cues in temporal gaps or factors stemming from higher signal-to-noise ratios required by children in the baseline condition. The reduced masking release for combined temporal/spectral modulation demonstrated by both the younger and older children with normal hearing may indicate that children in the age range tested here have some difficulty in combining speech information that is distributed across temporal and spectral gaps. Hearing impairment was associated with higher thresholds and reduced masking release in all modulation conditions. Children with hearing impairment showed the poorest performance of any group, consistent with additive effects of hearing loss and development.

Erratum: “Speech reception by listeners with real and simulated hearing impairment: Effects of continuous and interrupted noise” [J. Acoust. Soc. Am. 128, 342–359 (2010)

Figures ​Figures55​566​677 of the original version of this paper erroneously omitted some of the descriptive material that assists in understanding the data presented. These amended figure captions provide clarification of these figures. Figure 5 Measurements of masked speech-reception thresholds (dB SPL) in 30 dB SPL continuous background noise types for Unaided (top panel) and NAL-RP aided (bottom panel) listening conditions. In each panel, the dB SPL threshold is plotted for the 10 HI listeners ... Figure 6 Measurements of masked speech-reception thresholds (S∕N) in four different background noise types for Unaided and NAL-RP aided listening conditions. In each panel, S∕N is plotted for a given HI listener (light gray) and for the corresponding ... Figure 7 Masking release (MR) as a function of noise level in Unaided and in NAL-RP aided listening conditions. In each panel, MR is plotted for a given HI listener (light gray) and for the corresponding AM-SIM (medium gray) and NAM-SIM (dark gray) groups. The ...

Prior listening in rooms improves speech intelligibility

Although results from previous studies have demonstrated that the acoustic effects of a single reflection are perceptually suppressed after repeated exposure to a particular configuration of source and reflection, the extent to which this dynamic echo suppression might generalize to speech understanding in room environments with multiple reflections and reverberation is largely unknown. Here speech intelligibility was measured using the coordinate response measure corpus both with and without prior listening exposure to a reverberant room environment, which was simulated using virtual auditory space techniques. Prior room listening exposure was manipulated by presenting either a two-sentence carrier phrase that preceded the target speech, or no carrier phrase within the room environment. Results from 14 listeners indicate that with prior room exposure, masked speech reception thresholds were on average 2.7 dB lower than thresholds without exposure, an improvement in intelligibility of over 18 percentage points on average. This effect, which is shown to be absent in anechoic space and greatly reduced under monaural listening conditions, demonstrates that prior binaural exposure to reverberant rooms can improve speech intelligibility, perhaps due to a process of perceptual adaptation to the acoustics of the listening room.

Acceptable Noise Level as a Measure of Directional Hearing Aid Benefit

An acceptable noise level (ANL) procedure for measuring hearing aid directional benefit was compared with masked speech reception threshold (SRT) and front-to-back ratio (FBR) procedures. ANL is the difference between the most comfortable listening level and the maximum accepted background noise level while listening to speech. Forty adult subjects wearing their own binaural hearing aids were evaluated in omnidirectional and directional modes. The subjects were fitted with a variety of hearing aids by clinical audiologists, independent of the study. For each procedure, speech and noise were presented through loudspeakers located at 0 degrees and 180 degrees azimuth, respectively. Mean ANL (3.5 dB), SRT (3.7 dB), and FBR (2.9 dB) directional benefits were not significantly different. The ANL and masked SRT benefits were significantly correlated. The ANL appears to be a quick, clinician/user friendly procedure for measuring hearing aid directional benefit.

Binaural sluggishness in the perception of tone sequences and speech in noise.

The binaural system is well-known for its sluggish response to changes in the interaural parameters to which it is sensitive. Theories of binaural unmasking have suggested that detection of signals in noise is mediated by detection of differences in interaural correlation. If these theories are correct, improvements in the intelligibility of speech in favorable binaural conditions is most likely mediated by spectro-temporal variations in interaural correlation of the stimulus which mirror the spectro-temporal amplitude modulations of the speech. However, binaural sluggishness should limit the temporal resolution of the representation of speech recovered by this means. The present study tested this prediction in two ways. First, listeners' masked discrimination thresholds for ascending vs descending pure-tone arpeggios were measured as a function of rate of frequency change in the NoSo and NoSpi binaural configurations. Three-tone arpeggios were presented repeatedly and continuously for 1.6 s, masked by a 1.6-s burst of noise. In a two-interval task, listeners determined the interval in which the arpeggios were ascending. The results showed a binaural advantage of 12-14 dB for NoSpi at 3.3 arpeggios per s (arp/s), which reduced to 3-5 dB at 10.4 arp/s. This outcome confirmed that the discrimination of spectro-temporal patterns in noise is susceptible to the effects of binaural sluggishness. Second, listeners' masked speech-reception thresholds were measured in speech-shaped noise using speech which was 1, 1.5, and 2 times the original articulation rate. The articulation rate was increased using a phase-vocoder technique which increased all the modulation frequencies in the speech without altering its pitch. Speech-reception thresholds were, on average, 5.2 dB lower for the NoSpi than for the NoSo configuration, at the original articulation rate. This binaural masking release was reduced to 2.8 dB when the articulation rate was doubled, but the most notable effect was a 6-8 dB increase in thresholds with articulation rate for both configurations. These results suggest that higher modulation frequencies in masked signals cannot be temporally resolved by the binaural system, but that the useful modulation frequencies in speech are sufficiently low (<5 Hz) that they are invulnerable to the effects of binaural sluggishness, even at elevated articulation rates.

Effect of reducing slow temporal modulations on speech reception

The effect of reducing low-frequency modulations in the temporal envelope on the speech-reception threshold (SRT) for sentences in noise and on phoneme identification was investigated. For this purpose, speech was split up into a series of frequency bands (1/4, 1/2, or 1 oct wide) and the amplitude envelope for each band was high-pass filtered at cutoff frequencies of 1, 2, 4, 8, 16, 32, 64, or 128 Hz, or infinity (completely flattened). Results for 42 normal-hearing listeners show: (1) A clear reduction in sentence intelligibility with narrow-band processing for cutoff frequencies above 64 Hz; and (2) no reduction of sentence intelligibility when only amplitude variations below 4 Hz are reduced. Based on the modulation transfer function of some conditions, it is concluded that fast multichannel dynamic compression leads to an insignificant change in masked SRT. Combining these results with previous data on low-pass envelope filtering (temporal smearing) [Drullman et al., J. Acoust. Soc. Am. 95, 1053-1064 (1994)] shows that at 8-10 Hz the temporal modulation spectrum is divided into two equally important parts. Vowel and consonant identification with nonsense syllables were studied for cutoff frequencies of 2, 8, 32, 128 Hz, and infinity, processed in 1/4-oct bands. Results for 12 subjects indicate that, just as for low-pass envelope filtering, consonants are more affected than vowels. Errors in vowel identification mainly consist of reduced recognition of diphthongs and of durational confusions. For the consonants there are no clear confusion patterns, but stops appear to suffer least. In most cases, the responses tend to fall into the correct category (stop, fricative, or vowel-like).

The effect of frequency-selective attenuation on the speech-reception threshold of sentences in conditions of low-frequency noise

Within a study on the merits of a multichannel automatic gain control in hearing aids, the effect of frequency-selective amplification on the masked speech-reception threshold (SRT) for sentences is measured in conditions of seriously disturbing low-frequency noise, with the effect of wideband amplification as a reference. Speech and noise are both spectrally shaped according to the bisector line of the listener's dynamic-range of hearing, but with the noise in a single octave band (0.25-0.5 or 0.5-1 kHz) increased by 20 dB relative to this line. The increase of noise level is steady state in the first experiment, and time varying in the second experiment. Results for 12 normal-hearing and 12 hearing-impaired listeners indicate that, in both experiments, frequency-selective compression of the signal in the octave band with the 20-dB increase of noise is more beneficial than wideband compression. For the hearing-impaired group, wideband compression does not give any systematic change in intelligibility. Frequency-selective compression in steady-state conditions may, for both groups of listeners, give a decrease of masked SRT (relative to a condition without compression) of up to 4 dB for a compression factor of 100%. Roughly comparable effects are seen for frequency-selective compression in time-varying conditions. The superiority of frequency-selective over wideband compression is attributed to a more effective reduction of upward spread of masking.

Speech-reception Threshold in Noise for Hearing-impaired Listeners in Conditions with a Varying Amplitude-Frequency Response.

In a study on the effects of a frequency-dependent automatic gain control in hearing-aids, two experiments were carried out with hearing-impaired listeners. In the first experiment, the effect of varying the amplitude-frequency response on the speech-reception threshold (SRT) of sentences presented in noise was studied. The noise had the same spectrum as the long-term average spectrum of the sentences. Results suggest that the amplitude-frequency response may vary within a range from, roughly, -3 to +10 dB/oct relative to the bisector of the dynamic range, without giving an increase in SRT larger than 2 dB. In the second experiment, the effect on masked SRT of adjusting the amplitude-frequency response to situations of seriously interfering low-frequency noise was studied. Again, the noise had a spectrum identical with the long-term average spectrum of the sentences, but this time the noise level in one octave band was increased by 20 dB. Preliminary results indicate that a selective attenuation of the signal in the band containing the extra noise may give a decrease of masked SRT up to 4.5 dB.

The effect of varying the amplitude-frequency response on the masked speech-reception threshold for sentences in conditions with low-frequency noise

Within a study on the merits of a frequency-dependent automatic gain control in hearing aids, the beneficial effect of adapting the amplitude-frequency response to situations of seriously interfering low-frequency noise is studied. For 12 normal-hearing and 12 hearing-impaired listeners, the masked speech-reception threshold (SRT) for sentences is measured. The noise has a spectrum identical to the long-term average spectrum of the sentences, but with its level in one octave band raised by a constant 20 dB in the first experiment, and slowly increasing by 20 dB during sentence presentation in the second experiment. Results indicate that, in conditions with steady-state noise, selective attenuation of the signal in the band containing the extra noise gives an improvement of speech intelligibility in terms of speech-to-noise ratio of up to about 4 dB for both the normal-hearing and hearing-impaired group. In conditions with time-varying noise, a similar improvement was observed for both groups.

The effect of varying the amplitude-frequency response on the masked speech-reception threshold of sentences for hearing-impaired listeners.

In an evaluation of frequency-dependent automatic gain-control systems in hearing aids, the effect of varying the amplitude-frequency response on the speech-reception threshold (SRT) for sentences in noise is studied for 20 hearing-impaired listeners. The noise has a spectrum identical to the long-term average spectrum of the sentences. Speech and noise are shaped by the same amplitude-frequency response; their spectra are varied relative to the bisector of the individual's dynamic range. In four experimental conditions, the effect of a steady-state amplitude-frequency response is studied. Steepening the negative spectral slope of speech and noise appears to cause an increase of masked SRT, possibly due to increased effect of upward spread of masking. The effect of a single transition of the amplitude-frequency response between 10 and -10 dB/oct halfway through the sentence seems to be related to the effect for the fixed -10-dB/oct condition. Two transition times are tested. For a transition time of 0.25 s, the SRT is only a little higher than for 1 s. The results suggest that the amplitude-frequency response may be varied in time without having a detrimental effect on the masked SRT of sentences for hearing-impaired listeners as long as strongly negatively sloping spectra are avoided.

The effect of varying the amplitude-frequency response on the masked SRT for sentences in hearing-impaired listeners

A multichannel gain-control hearing aid, in which the frequency-dependent amplification is adapted automatically to the fluctuations of the incoming signal,. may optimally deliver speech to an impaired ear. Such a system requires that the speech-reception threshold (SRT) in noise is, within limits, unaffected by dynamic variations in the amplitude-frequency response of the hearing aid. For normal-hearing listeners, van Dijkhuizen et al. [J. Acoust. Soc. Am. 81, 465–496 (1987)] found that the masked SRT for sentences is remarkably resistant to dynamic variations in the slope of the amplitude-frequency response when it shaped both speech and noise. In this experiment, we studied corresponding conditions for hearing-impaired listeners. Again, the amplitude-frequency response shaped both speech and noise and thus left speech-to-noise ratios untouched. The results obtained so far also indicate that, for hearing-impaired listeners, dynamic variations of the amplitude-frequency response do not affect the SRT.

The effect of varying the slope of the amplitude-frequency response on the masked speech-reception threshold of sentences.

Within the framework of a study on the merits of a frequency-dependent automatic gain control in hearing aids, the effect of varying the slope of the amplitude-frequency response on the speech-reception threshold (SRT) for sentences in noise was studied for normal-hearing listeners. Speech and noise were both subjected to the same amplitude-frequency response. In the first experiment, the effect of a constant slope was investigated (20 listeners). Over a range of about -7 to +10 dB/oct, the SRT in noise remained constant. In the second experiment, a single change in the slope of the amplitude-frequency response was introduced halfway through the sentence. The effect of varying the transition time over a range down to 0.125 s appeared to be very small. In the third experiment, the slope varied continuously with range and variation frequency (0.25-2 Hz) as the parameters. The masked SRT increased gradually with variation frequency. The results indicate that the masked SRT for sentences is remarkably resistant to dynamic variations in the slope of the amplitude-frequency response.

Influence of pulsed masking on the threshold for spondees.

The changes in masking for spondee words that result from varying both the level and the interruption rate of a white-noise masker were studied with 14 normal hearing subjects and 14 subjects with sensorineural hearing loss diagnosed as resulting from cochlear otosclerosis. The masker was a white noise and was presented monaurally at either 90 dB sound-pressure level (SPL) or 30 dB sensation level (SL). It was either continuous or was pulsed at rates of 1, 10, or 100/sec with 50% duty cycle. During the burst-off half of each cycle, the noise was either dropped 14 dB in level or was fully interrupted. The masked speech reception threshold (SRT) was not improved re the masked SRT in continuous noise when the 30 dB SL masker was pulsed 100 times/sec. Reduction in masking was observed under all other circumstances of cycling the noise. This reduction was more pronounced when the noise was completely interrupted rather than only modulated by 14 dB, when the masker was at its higher level (90 dB SPL as opposed to 30 dB SL), and when the masker was interrupted at the slowest rate [1 interruption per second (ips)]. During equivalent conditions, the reduction in masking was greater for normal-hearing subjects than for those with cochlear otosclerosis. Appreciable residual masking (re SRT in quiet) persisted across the range of all parameters of noise level, modulation depth, cycling rate, and type of subject encompassed during the present study. This last finding appears to be contradictory to some of the results from earlier studies but not to others. This discrepancy, along with other aspects of the present findings, are discussed.