Informational Masking in Listeners with Sensorineural Hearing Loss

Measures of energetic and informational masking were obtained from 46 listeners with sensorineural hearing loss. The task was to detect the presence of a sequence of eight contiguous 60-ms bursts of a pure tone embedded in masker bursts that were played synchronously with the signal. The masker was either a sequence of Gaussian noise bursts (energetic masker) or a sequence of random-frequency 2-tone bursts (informational masker). The 2-tone maskers were of two types: one type that normally tends to produce large amounts of informational masking and a second type that normally tends to produce very little informational masking. The two informational maskers are called "multiple-bursts same" (MBS), because the same frequency components are present in each burst of a sequence, and "multiple-bursts different" (MBD), because different frequency components are presented in each burst of a sequence. The difference in masking observed for these two maskers is thought to occur because the signal perceptually segregates from the masker in the MBD condition but fuses with the masker in MBS. In the present study, the effectiveness of the MBD masker, measured as the signal-to-masker ratio at masked threshold, increased with increasing hearing loss. In contrast, the signal-to-masker ratio at masked threshold for the MBS masker changed much less as a function of hearing loss. These results suggest that sensorineural hearing loss interferes with the ability of the listener to perceptually segregate individual components of complex sounds. The results from the energetic masking condition, which included critical ratio estimates for all listeners and auditory filter characteristics for a subset of the listeners, indicated that increasing hearing loss also reduced frequency selectivity at the signal frequency. Overall, these results suggest that the increased susceptibility to masking observed in listeners with sensorineural hearing loss is a consequence of both peripheral and central processes.     

Stable release of BDNF from the fibroblast cell line NIH3T3 grown on silicone elastomers enhances survival of spiral ganglion cells in vitro and in vivo

Humans and other animals often communicate acoustically in noisy social groups, in which the background noise generated by other individuals can mask signals of interest. When listening to speech in the presence of speech-like noise, humans experience a release from auditory masking when target and masker are spatially separated. We investigated spatial release from masking (SRM) in a free-field call recognition task in Cope's gray treefrog (Hyla chrysoscelis). In this species, reproduction requires that females successfully detect, recognize, and localize a conspecific male in the noisy social environment of a breeding chorus. Using no-choice phonotaxis assays, we measured females' signal recognition thresholds in response to a target signal (an advertisement call) in the presence and absence of chorus-shaped noise. Females experienced about 3 dB of masking release, compared with a co-localized condition, when the masker was displaced 90° in azimuth from the target. The magnitude of masking release was independent of the spectral composition of the target (carriers of 1.3 kHz, 2.6 kHz, or both). Our results indicate that frogs experience a modest degree of spatial unmasking when performing a call recognition task in the free-field, and suggest that variation in signal spectral content has small effects on both source identification and spatial unmasking. We discuss these results in the context of spatial unmasking in vertebrates and call recognition in frogs.     

The relationship between MOC reflex and masked threshold

Otoacoustic emission (OAE) amplitude can be reduced by acoustic stimulation. This effect is produced by the medial olivocochlear (MOC) reflex. Past studies have shown that the MOC reflex is related to listening in noise and attention. In the present study, the relationship between strength of the contralateral MOC reflex and masked threshold was investigated in 19 adults. Detection thresholds were determined for 1000-Hz, 300-ms tone presented simultaneously with one repetition of a 300-ms masker in an ongoing train of masker bursts. Three masking conditions were tested: 1) broadband noise 2) a fixed-frequency 4-tone complex masker and 3) a random-frequency 4-tone complex masker. Broadband noise was expected to produce energetic masking and the tonal maskers were expected to produce informational masking in some listeners. DPOAEs were recorded at fine frequency intervals from 500 to 4000 Hz, with and without contralateral acoustic stimulation. MOC reflex strength was estimated as a reduction in baseline level and a shift in frequency of DPOAE fine-structure maxima near 1000-Hz. MOC reflex and psychophysical testing were completed in separate sessions. Individuals with poorer thresholds in broadband noise and in random-frequency maskers were found to have stronger MOC reflexes.     

The effect of perceived spatial separation on informational masking of Chinese speech

The effect of perceived spatial separation, induced by the precedence effect, on release from noise or speech masking was investigated. Listeners were asked to orally repeat Chinese nonsense sentences, which were spoken by a female talker and presented by both the left (-45 degrees) and right (+45 degrees) loudspeakers, when maskers, which were either speech-spectrum noise sounds or Chinese nonsense sentences spoken by two other female talkers, were presented by the same two loudspeakers. Delays between identical sounds presented over the two loudspeakers were used to control the perceived locations of the target (right only) and masker (right, center, or left). The results show that perceived 45 degrees and 90 degrees separations of target speech from masking speech led to equivalently marked improvement in speech recognition, even though the degree of improvement was smaller than that reported in [J. Acoust. Soc. Am. 106 (1999) 3578 (using English nonsense speech)]. When the masker was noise, however, perceived separation only marginally improved speech recognition. These results indicate that release from informational masking, due to perceived target/masker spatial separation induced by the precedence effect, also occurs for tonal Chinese speech. Compared to the 45 degrees perceived within-hemifield separation, the 90 degrees perceived cross-hemifield separation does not produce further unmasking.     

Directional benefit in the presence of speech and speechlike maskers

Recent research suggests that omnidirectional hearing aids are relatively ineffective at improving speech understanding in everyday conversational speech settings when the background noise contains both energetic and informational masking components. Energetic masking refers to situations where the peripheral (or neural) activity of the target is less than that of the masker, thus making the target inaudible. In contrast, informational masking effects, in this paper, refer to additional masking effects that are not energetic in nature. The current study evaluated the benefits of directional technology in the presence of background noises that contained both energetic and informational masking components. Aided speech recognition (in both omnidirectional and directional modes) was assessed in the presence of three types of maskers (forward and reversed speech and speech-modulated noise) that varied in the amount of informational masking they were expected to produce. Study results showed significant directional benefit in all conditions. This finding suggests that in everyday conversational speech environments, directional technology is equally efficacious regardless of the magnitude of informational masking present in the background noise. In addition, study findings suggest that the semantic information present in the masking speech may play only a limited role in contributing to informational masking in everyday environments.     

Aging and speech-on-speech masking

OBJECTIVES: A common complaint of many older adults is difficulty communicating in situations where they must focus on one talker in the presence of other people speaking. In listening environments containing multiple talkers, age-related changes may be caused by increased sensitivity to energetic masking, increased susceptibility to informational masking (e.g., confusion between the target voice and masking voices), and/or cognitive deficits. The purpose of the present study was to tease out these contributions to the difficulties that older adults experience in speech-on-speech masking situations. DESIGN: Groups of younger, normal-hearing individuals and older adults with varying degrees of hearing sensitivity (n = 12 per group) participated in a study of sentence recognition in the presence of four types of maskers: a two-talker masker consisting of voices of the same sex as the target voice, a two-talker masker of voices of the opposite sex as the target, a signal-envelope-modulated noise derived from the two-talker complex, and a speech-shaped steady noise. Subjects also completed a voice discrimination task to determine the extent to which they were able to incidentally learn to tell apart the target voice from the same-sex masking voices and to examine whether this ability influenced speech-on-speech masking. RESULTS: Results showed that older adults had significantly poorer performance in the presence of all four types of maskers, with the largest absolute difference for the same-sex masking condition. When the data were analyzed in terms of relative group differences (i.e., adjusting for absolute performance) the greatest effect was found for the opposite-sex masker. Degree of hearing loss was significantly related to performance in several listening conditions. Some older subjects demonstrated a reduced ability to discriminate between the masking and target voices; performance on this task was not related to speech recognition ability. CONCLUSIONS: The overall pattern of results suggests that although amount of informational masking does not seem to differ between older and younger listeners, older adults (particularly those with hearing loss) evidence a deficit in the ability to selectively attend to a target voice, even when the masking voices are from talkers of the opposite sex. Possible explanations for these findings include problems understanding speech in the presence of a masker with temporal and spectral fluctuations and/or age-related changes in cognitive function.     

Evoked response narrow-band noise masking patterns in the chinchilla

Narrow-band noise masking patterns were measured at 0.5, 1, 2 and 4 kHz in the chinchilla using the auditory evoked response from the inferior colliculus. At low masker levels, the masking profiles were symmetrical and centered on the masker. However, as masker level increased, the masking profiles spread predominantly toward the high frequencies. The masking profiles obtained at 0.5 and 1 kHz, exhibited a broad plateau extending 1-2 octaves above the masker at the highest masker level (70 dB SPL) whereas those obtained at 2 and 4 kHz showed a peak. In contrast to tone-on-tone masking profiles, none of the narrow-band noise masking profiles contained a low-threshold notch on the high frequency side of the masker. The evoked response masking profiles obtained in the chinchilla were slightly wider, but qualitatively similar to those measured psychophysically in humans. Thus, the evoked response narrow-band noise masking profiles may provide a convenient way of evaluating the spread of masking in difficult-to-test subjects.     

Behaviour of delayed evoked otoacoustic emission under forward masking paradigm.

The behaviour of delayed evoked otoacoustic emission (DEOAE) has been studied in normally hearing adults under a conventional forward-masking paradigm, and subjective measurements were carried out additionally for comparison. The clicks served as signals and the noise bursts were used as masker. In different experimental sets, signal and masker intensity, masker duration, and the interval between masker and maskee were altered. At masker levels corresponding to the subjective post-masking threshold of the clicks, the DEOAE was unaffected, i.e. had no noticeable alteration, compared with click stimulation without masking. Even at higher masker levels the inaudible clicks elicited clearly discernible DEOAEs. The forward-masking detection threshold of DEOAE ('DEOAE post-masking threshold') was reached at masker levels approximately 35 dB above the subjective post-masking threshold. The gap between subjective and DEOAE post-masking threshold vis-à-vis the masker level was also evident at different masker durations and different time intervals between masker and maskee. Central neural and peripheral receptor mechanisms are suggested to be the constituents of the masking phenomenon. The neural mechanism is involved at low masker levels. The receptor mechanism effectively joins the neural one at masker levels exceeding the threshold of psychoacoustic masking. The progressive increase in the number of auditory units from the periphery to the centre in the hearing system, linked with an increase in inhibition, can help to explain these effects.     

Evoked potential tone-on-tone masking patterns in the chinchilla

Tone-on-tone masking patterns were measured in the chinchilla using the auditory evoked response from the inferior colliculus. The masker was a 2 kHz continuous tone presented at one of five levels from 20 to 70 dB SPL. The evoked response was elicited with tone bursts presented over a wide range of frequencies. Masking was defined as the difference between evoked response thresholds measured in the presence of the masker versus quiet. At low masker levels, the masking profile was symmetrical and centered around 2 kHz. However, as masker level increased, masking spread toward the high frequencies. Furthermore, at masker levels above 50 dB SPL, a low-threshold notch occurred above the masker. The masking profiles obtained with the evoked response are in good agreement with those obtained psychophysically.     

Adding irrelevant information to the content prime reduces the prime-induced unmasking effect on speech recognition

Presenting the early part of a nonsense sentence in quiet improves recognition of the last keyword of the sentence in a masker, especially a speech masker. This priming effect depends on higher-order processing of the prime information during target-masker segregation. This study investigated whether introducing irrelevant content information into the prime reduces the priming effect. The results showed that presenting the first four syllables (not including the second and third keywords) of the three-keyword target sentence in quiet significantly improved recognition of the second and third keywords in a two-talker-speech masker but not a noise masker, relative to the no-priming condition. Increasing the prime content from four to eight syllables (including the first and second keywords of the target sentence) further improved recognition of the third keyword in either the noise or speech masker. However, if the last four syllables of the eight-syllable prime were replaced by four irrelevant syllables (which did not occur in the target sentence), all the prime-induced speech-recognition improvements disappeared. Thus, knowing the early part of the target sentence mainly reduces informational masking of target speech, possibly by helping listeners attend to the target speech. Increasing the informative content of the prime further improves target-speech recognition probably by reducing the processing load. The reduction of the priming effect by adding irrelevant information to the prime is not due to introducing additional masking of the target speech.     

Informational masking in normal-hearing and hearing-impaired listeners

The present study aimed to test whether central, across-channel, informational auditory processing abilities are altered by hearing loss. The informational masking effect exerted on a 1 kHz tone-pip by a simultaneous four-tone masker, whose spectral content changed within as well as across trials, was measured in the left and right ears of normal-hearing subjects and hearing-impaired subjects with either symmetrical or asymmetrical hearing loss between the two ears. In the subjects with normal-hearing or symmetrical hearing loss, the level of the masker was set to 40 dB SL in each ear, in the subjects with asymmetrical hearing loss, the masker was set to 40 dB SL in the best ear and loudness-balanced in the other ear. The results failed to reveal significant differences in informational masking between normal-hearing and hearing-impaired subjects. However, in subjects with asymmetric hearing loss, less informational masking was observed in the ear with the more elevated absolute thresholds than in the opposite ear. Since the latter finding can be explained in terms of across-ear differences in loudness recruitment, it is suggested that central, across-channel, informational processing abilities are not substantially different in hearing-impaired than in normal-hearing ears.     

Evoked otoacoustic emission: behaviour under the forward masking paradigm.

The behaviour of evoked otoacoustic emission (EOAE) has been studied in normally hearing adults under the conventional forward masking paradigm. The clicks and tone pips served as signals, and the noise bursts were used as maskers. At noise burst levels, defined as psychoacoustic masking thresholds of signals (postmasking threshold), attenuation of EOAEs was just noticeable but did not occur in all records. The EOAEs were not completely eliminated even at noise levels exceeding the post-masking threshold by 30 dB. Central or neural and peripheral or receptor mechanisms are suggested to be the constituents of the masking phenomenon. The receptor mechanism effectively joins the neural one at masker levels, well exceeding the thresholds of psychoacoustic masking. The increase in masker duration and decrease in interval between masker and signal seem to accentuate the neural mechanism. As a result, the difference between masker levels, leading to psychoacoustic masking of the signal and having marked attenuating effects upon the EOAEs, respectively, is increased.     

Continuum of impulsiveness caused by auditory masking

OBJECTIVE: Impulsivity is a hallmark of attention deficit/hyperactivity disorder (ADHD). Various auditory masking procedures can quantify the impulsivity caused by distracting background sounds. This study compares the impulsiveness and distraction caused by informational masking (unpredictable tones) with previously published data on central masking (contralateral noise) in children with and without ADHD. METHODS: Twenty-six normal and 14 children diagnosed as having ADHD (combined type), all between the ages of 7 and 13, indicated whether they heard a 512-ms, 500-Hz pure tone in a single-interval task under conditions of informational masking and in quiet. The masker consisted of 10 randomly selected frequencies between 1,000 and 2,500 Hz presented simultaneously at an overall level of 60 dB SPL. A maximum-likelihood method estimated thresholds and false alarm rates. RESULTS: There were no differences due to ADHD in thresholds or false alarm rates either with informational masking or in quiet. With informational masking, normal children had high false alarm rates, similar to those from children with ADHD under central masking. With informational masking, all children tended to say a stimulus was present when it was not. CONCLUSIONS: All children behave impulsively under some conditions. Pediatric patients with attention disorders can thus be reassured that impulsiveness with unpredictable background sounds is normal, to some extent. Response biases of children with ADHD may only diverge from normal in situations where distracting external stimuli have an intermediate level of predictability. A previous study showed that with central masking, children with ADHD are more impulsive than normal. There appears to be a limit to the uncertainty in auditory masking that can be tolerated by children. Children with ADHD become impulsive at lower levels of uncertainty than normal. Increasing the predictability of distracting background sounds may thus improve the performance of children with ADHD. Informational masking may, for normal listeners, mimic something of what it is like to have an attention deficit. ADHD can be profitably studied with auditory tasks.     

Asymmetry of masking in the European starling: behavioural auditory thresholds

Psychophysical studies of simultaneous masking with human observers exhibit an asymmetry in the amount of masking that depends on the relative bandwidths of signals and maskers. For noise bands up to the bandwidth of one auditory filter, masked auditory thresholds are considerably lower when the bandwidth of the signal exceeds that of the masker compared to the reversed condition. We investigate asymmetry of masking in an animal model, that will allow to study the mechanisms associated with the asymmetry of masking effect. European starlings (Sturnus vulgaris) were trained in a Go/NoGo paradigm to report the detection of a 500 ms noise signal centred in a 700 ms noise masker. Signals and maskers with centre frequencies of 2 kHz had bandwidths of 4 Hz or 256 Hz. Thresholds for detecting the 256 Hz wide-band signal in a 4 Hz narrow-band masker were considerably lower compared to detecting the 4 Hz narrow-band signal in a 256 Hz wide masker and compared to all other conditions. The asymmetry of masking in starlings was on average 15 and 17 dB for 40 and 70 dB SPL overall masker level, respectively. Our animal model thus proved perceptual abilities similar to human subjects. The results are discussed with respect to the importance of both intensity and temporal cues for signal detection.     

Informational Masking in Normal-hearing and Hearing-impaired Listeners

The present study aimed to test whether central, across-channel, informational auditory processing abilities are altered by hearing loss. The informational masking effect exerted on a 1 kHz tone-pip by a simultaneous four-tone masker, whose spectral content changed within as well as across trials, was measured in the left and right ears of normal-hearing subjects and hearing-impaired subjects with either symmetrical or asymmetrical hearing loss between the two ears. In the subjects with normal-hearing or symmetrical hearing loss, the level of the masker was set to 40 dB SL in each ear, in the subjects with asymmetrical hearing loss, the masker was set to 40 dB SL in the best ear and loudness-balanced in the other ear. The results failed to reveal significant differences in informational masking between normal-hearing and hearing-impaired subjects. However, in subjects with asymmetric hearing loss, less informational masking was observed in the ear with the more elevated absolute thresholds than in the opposite ear. Since the latter finding can be explained in terms of across-ear differences in loudness recruitment, it is suggested that central, across-channel, informational processing abilities are not substantially different in hearing-impaired than in normal-hearing ears.     

The effect of otitis media with effusion on perceptual masking

OBJECTIVE: To determine the effect of otitis media with effusion (OME) on perceptual masking (a phenomenon in which spondee threshold for a 2-talker masker is poorer than for a speech-shaped noise masker). DESIGN: Longitudinal testing over a 1-year period following insertion of tympanostomy tubes, using clinical and normal-hearing control groups. SUBJECTS: Forty-seven children having a history of OME were tested. Possible testing intervals were just before the placement of tympanostomy tubes, and up to 3 separate occasions after the placement of the tubes. An age-matched control group of 19 children was tested. METHODS: A perceptual masking paradigm was used to measure the ability of the listener to recognize a spondee in either a speech-shaped noise or a 2-talker masker background. The masker was either continuous or gated on and off with the target spondee. RESULTS: In gated masking conditions, children with a history of normal hearing showed only slight perceptual masking, but the children with a history of OME showed relatively great perceptual masking before surgery and up to 6 months following surgery. In continuous masking conditions, both groups of children showed relatively great perceptual masking and did not differ significantly from each other in this respect either before or after surgery. However, before surgery, the OME group showed higher thresholds in both the 2-talker and speech-shaped noise maskers. CONCLUSIONS: In agreement with previous psychoacoustical findings, the relatively great perceptual masking in gated conditions shown by children with OME history may reflect a general deficit in complex auditory processing.     

Spondee recognition in a two-talker masker and a speech-shaped noise masker in adults and children

OBJECTIVE: The objective of the study was to examine developmental effects for perceptual masking due a two-talker masker. Both continuous and gated maskers were employed in order to determine the importance of masker continuity for perceptual masking. DESIGN: A repeated measures design compared the spondee recognition performance of adults and children using both a speech-shaped noise and a two-talker masker. The masker was either presented continuously, or was gated on and off at about the same time as the target spondee. The ages of the listeners were 19 to 48 yr (adults) and 5 to 10 yr (children). RESULTS: The results for the continuous masker indicated higher thresholds for the two-talker masker than for the speech-shaped noise masker. This effect was greater in the children than in the adults. In the gated masking condition, the greater masking effect associated with the two-talker masker was either diminished (children) or eliminated (adults). CONCLUSIONS: These results suggest a masking effect for two-talker speech competition that is greater in children than in adults. Perceptual masking is greater for continuous than for gated masking.     

Human frequency-following responses to binaural masking level difference stimuli

Binaural masking level difference is the behavioral threshold difference between a diotic condition (SoNo) and a dichotic condition with a 180 degrees interaural phase delay of either the signal (SpiNo) or the masker (SoNpi). Threshold disparity is partially related to coincidence-detecting units in the medial superior olive that are sensitive to low-frequency binaural stimuli with interaural phase differences. Previous surface evoked potential studies report significant latency and amplitude differences to SpiNo stimuli with respect to SoNo stimuli in the P1-N1 auditory event related potential, but no study has reported physiologic masking level differences in a brain stem evoked potential. The human frequency-following response (FFR) represents activity from low-frequency, phase locking neural units in the upper brainstem. Unmasked FFRs to 500 Hz tone bursts and masked FFRs using a 1.5 kHz low-pass masker were recorded from nine normal-hearing adult subjects. Significant reduction in FFR amplitude occurred in the SoNo condition, re the So condition, with masker intensities near the psychoacoustic SoNo masking level. Significant FFR amplitude recovery was observed for both the SoNpi and SpiNo conditions. These results support the role of phase-locked neural activity in brainstem mechanisms involved in perceptual masking release.     

Auditory Enhancement in Cochlear-Implant Users Under Simultaneous and Forward Masking

Auditory enhancement is the phenomenon whereby the salience or detectability of a target sound within a masker is enhanced by the prior presentation of the masker alone. Enhancement has been demonstrated using both simultaneous and forward masking in normal-hearing listeners and may play an important role in auditory and speech perception within complex and time-varying acoustic environments. The few studies of enhancement in hearing-impaired listeners have reported reduced or absent enhancement effects under forward masking, suggesting a potentially peripheral locus of the effect. Here, auditory enhancement was measured in eight cochlear-implant (CI) users with direct stimulation. Masked thresholds were measured under simultaneous and forward masking as a function of the number of masking electrodes, and the electrode spacing between the maskers and the target. Evidence for auditory enhancement was obtained under simultaneous masking, qualitatively consistent with results from normal-hearing listeners. However, no significant enhancement was observed under forward masking, in contrast to earlier results with normal-hearing listeners. The results suggest that the normal effects of auditory enhancement are partially but not fully experienced by CI users. To the extent that the CI users’ results differ from normal, it may be possible to apply signal processing to restore the missing aspects of enhancement.     

Measurements of monopolar and bipolar current spreads using forward-masking with a fixed probe

Abstract

Objectives

This research employed a forward-masking paradigm to estimate the current spread of monopolar (MP) and bipolar (BP) maskers, with current amplitudes adjusted to elicit the same loudness. Since the spatial separation between active and return electrodes is smaller in BP than in MP configurations, the BP current spread is more localized and presumably superior in terms of speech intelligibility. Because matching the loudness requires higher current in BP than in MP stimulation, previous forward-masking studies show that BP current spread is not consistently narrower across subjects or electrodes within a subject.

Methods

The present forward-masking measures of current spread differ from those of previous studies by using the same BP probe electrode configuration for both MP and BP masker configurations, and adjusting the current levels of the MP and BP maskers so as to match them in loudness. With this method, the estimate of masker current spread would not be contaminated by differences in probe current spread. Forward masking was studied in four cochlear implant patients, two females and two males, with speech recognition scores higher than 50%; that is, their auditory-nerve survival status was more than adequate to carry out the experiments.

Results

The data showed that MP and BP masker configurations produce equivalent masking patterns (and current spreads) in three participants. A fourth participant displayed asymmetrical patterns with enhancement rather than masking in some cases, especially when the probe and masker were at the same location.

Discussion

This study showed equivalent masking patterns for MP and BP maskers when the BP masker current amplitude was increased to match the loudness of the MP masker, and the same BP probe configuration is used with both maskers. This finding could help to explain why cochlear implant users often fail to accrue higher speech intelligibility benefit from BP stimulation.