Spatial Release From Masking in Children: Effects of Simulated Unilateral Hearing Loss

The purpose of this study was twofold: 1) to determine the effect of an acute simulated unilateral hearing loss on children’s spatial release from masking in two-talker speech and speech-shaped noise, and 2) to develop a procedure to be used in future studies that will assess spatial release from masking in children who have permanent unilateral hearing loss. There were three main predictions. First, spatial release from masking was expected to be larger in two-talker speech than speech-shaped noise. Second, simulated unilateral hearing loss was expected to worsen performance in all listening conditions, but particularly in the spatially separated two-talker speech masker. Third, spatial release from masking was expected to be smaller for children than for adults in the two-talker masker

Release from masking: Behavioral and physiological masking level differences

Binaural hearing offers several advantages over monaural hearing and is believed to be one factor that is involved in the ability to understand speech in background noise. Binaural hearing involves analysis of interaural timing and intensity differences in signals arriving at the two ears which provides listeners with sound localization cues as well as signal in noise detection. When sounds arrive at each ear at slightly different times, there may be a release from the effects of background noise, allowing listeners to detect softer sounds in noise. Masking Level Differences (MLDs) have been widely used to evaluate behavioral binaural processing. However, the literature inconsistently reports a release from masking in physiological responses. The purposes of this study were 1) to establish the feasibility of measuring physiological masking level differences using the frequency-following response (FFR), and 2) to characterize the relationship between behavioral and physiological measures of masking level differences (MLDs). Fourteen young adults (ages 21-26) with clinically normal hearing sensitivity participated in this study. Stimuli for behavioral and physiological conditions were 500 Hz tonebursts presented in one-third octave narrowband noise. Three phase conditions were tested: SoNo, SoNπ, and SπNo. Behavioral MLDs were assessed using an adaptive 2AFC procedure. Physiological MLDs were assessed using the frequency-following response, an auditory evoked potential reliant on phase-locked neural activity. FFR analysis focused on amplitude measures. Speech-in-noise understanding was also tested using the Words-in-Noise test (WIN). Behavioral MLDs were 8.29 dB (std. dev = 4.09) for SoNπ and 10.03 dB (std. dev = 4.96) for the SπNo condition. Physiological MLDs did not indicate a robust release from masking, especially for the SπNo condition. Correlations between behavioral and physiological MLDs were not significant. However, FFR amplitude differences between having the signal, or 500 Hz tone, in phase between the ears (e.g., SoNo) and 180° out of phase (i.e., SπNo) predicted behavioral SπNo MLDs. These findings may help to clarify which scalp-recorded auditory evoked potentials reflect binaural processing in humans and report the first brainstem auditory evoked potentials in humans that can predict behavioral masking level differences

Reverberation limits the release from informational masking obtained in the harmonic and binaural domains

A difference in fundamental frequency (ΔF0) and a difference in spatial location (ΔSL) are two cues known to provide masking releases when multiple speakers talk at once in a room. Situations were examined in which reverberation should have no effect on the mechanisms underlying the release from energetic masking produced by these two cues. Speech reception thresholds using both unpredictable target sentences and the coordinate response measure followed a similar pattern. Both ΔF0s and ΔSLs provided masking releases in the presence of non-speech maskers (matched in excitation pattern and temporal envelope to speech maskers) which, as intended, were robust to reverberation. Larger masking releases were obtained for speech maskers, but critically, they were affected by reverberation. The results suggest that reverberation either limits the amount of informational masking there is to begin with, or affects its release by ΔF0s or ΔSLs

Entwurf eines Hörtests zur Bestimmung des Comodulation Masking Release bei Cochlea Implantat-Trägern

Normal hearing (NH) listeners commonly perform better when listening to speech in modulated than in steady state maskers. This improvement is often labeled as a “release of masking”. Cochlear-implant (CI) listeners generally don’t receive a masking release in speech perception tests and the reasons are indistinct. This study for the first time investigates the comodulation masking release, an underlying psychoacoustic effect, in a flanking band setup acoustically in CI users. The focus of the experiments was, if CI users can use across-frequency cues to improve signal detection in (co-)modulated interfering noise. The test bases upon a forced choice paradigm to determine detection thresholds of a sinusoidal signal in fluctuating maskers. The maskers consisted of one or five amplitude modulated narrow noise-bands. The masking noise-bands were either incoherently or coherently modulated (comodulated). The difference of the detection threshold of the sinusoidal signal in these two conditions is defined as comodulation masking release (CMR). Two parameters of the masking noise complex were varied: the bandwidth/modulation frequency and the spectral alignment. 18 NH and 28 CI users participated in this study. The measured detection thresholds in CI users were highly reproducible. In contrast, the inter-individual standard deviation was higher for CI users compared to NH. Nevertheless, CMR in CI users was significant (p<0.01). The results clearly show that CI users can benefit from across-frequency cues and achieve a significant CMR under the described test conditions. So, the basis for a release of masking in speech perception tests in CI users seems to exist

Age-related deficits in dip-listening evident for isolated sentences but not for spoken stories

Fluctuating background sounds facilitate speech intelligibility by providing speech ‘glimpses’ (masking release). Older adults benefit less from glimpses, but masking release is typically investigated using isolated sentences. Recent work indicates that using engaging, continuous speech materials (e.g., spoken stories) may qualitatively alter speech-in-noise listening. Moreover, neural sensitivity to different amplitude envelope profiles (ramped, damped) changes with age, but whether this affects speech listening is unknown. In three online experiments, we investigate how masking release in younger and older adults differs for masked sentences and stories, and how speech intelligibility varies with masker amplitude profile. Intelligibility was generally greater for damped than ramped maskers. Masking release was reduced in older relative to younger adults for disconnected sentences, and stories with a randomized sentence order. Critically, when listening to stories with an engaging and coherent narrative, older adults demonstrated equal or greater masking release compared to younger adults. Older adults thus appear to benefit from ‘glimpses’ as much as, or more than, younger adults when the speech they are listening to follows a coherent topical thread. Our results highlight the importance of cognitive and motivational factors for speech understanding, and suggest that previous work may have underestimated speech-listening abilities in older adults

Informational masking release in children and adults

This study assessed informational masking and utilization of cues to reduce that masking in children aged 4–9 years and in adults. The signal was a train of eight consecutive tone bursts, each at 1 kHz and 60 ms in duration. Maskers were comprised of a pair of synchronous tone-burst trains, with randomly chosen frequencies spanning 200–5000 Hz, with a protected region 851–1175 Hz. In the reference condition, maskers were eight bursts in duration, with a fixed frequency within intervals. Experiment 1 tested two monotic masking release conditions: within-interval randomization of masker burst frequency and the introduction of leading masker bursts. Experiment 2 examined masking release in which the signal was presented to one ear and masking components were presented to both ears (masker components in the contralateral ear were 10 dB higher than those in the ipsilateral ear). Both adults and children demonstrated a significant informational masking effect, with children showing a larger effect on average. Both groups also showed significant release from masking in the two monotic conditions, although children received somewhat less benefit from the masking release cues. The binaural condition supported a moderate release from informational masking in adults, but resulted in increased informational masking in children

Effects of Simulated and Profound Unilateral Sensorineural Hearing Loss on Recognition of Speech in Competing Speech

OBJECTIVES: Unilateral hearing loss (UHL) is a condition as common as bilateral hearing loss in adults. Because of the unilaterally reduced audibility associated with UHL, binaural processing of sounds may be disrupted. As a consequence, daily tasks such as listening to speech in a background of spatially distinct competing sounds may be challenging. A growing body of subjective and objective data suggests that spatial hearing is negatively affected by UHL. However, the type and degree of UHL vary considerably in previous studies. The aim here was to determine the effect of a profound sensorineural UHL, and of a simulated UHL, on recognition of speech in competing speech, and the binaural and monaural contributions to spatial release from masking, in a demanding multisource listening environment. DESIGN: Nine subjects (25 to 61 years) with profound sensorineural UHL [mean pure-tone average (PTA) across 0.5, 1, 2, and 4 kHz = 105 dB HL] and normal contralateral hearing (mean PTA = 7.2 dB HL) were included based on the criterion that the target and competing speech were inaudible in the ear with hearing loss. Thirteen subjects with normal hearing (19 to 60 years; mean left PTA = 4.1 dB HL; mean right PTA = 5.5 dB HL) contributed data in normal and simulated "mild-to-moderate" UHL conditions (PTA = 38.6 dB HL). The main outcome measure was the threshold for 40% correct speech recognition in colocated (0\ub0) and spatially and symmetrically separated (\ub130\ub0 and \ub1150\ub0) competing speech conditions. Spatial release from masking was quantified as the threshold difference between colocated and separated conditions. RESULTS: Thresholds in profound UHL were higher (worse) than normal hearing in separated and colocated conditions, and comparable to simulated UHL. Monaural spatial release from masking, that is, the spatial release achieved by subjects with profound UHL, was significantly different from zero and 49% of the magnitude of the spatial release from masking achieved by subjects with normal hearing. There were subjects with profound UHL who showed negative spatial release, whereas subjects with normal hearing consistently showed positive spatial release from masking in the normal condition. The simulated UHL had a larger effect on the speech recognition threshold for separated than for colocated conditions, resulting in decreased spatial release from masking. The difference in spatial release between normal-hearing and simulated UHL conditions increased with age. CONCLUSIONS: The results demonstrate that while recognition of speech in colocated and separated competing speech is impaired for profound sensorineural UHL, spatial release from masking may be possible when competing speech is symmetrically distributed around the listener. A "mild-to-moderate" simulated UHL decreases spatial release from masking compared with normal-hearing conditions and interacts with age, indicating that small amounts of residual hearing in the UHL ear may be more beneficial for separated than for colocated interferer conditions for young listeners

TASTE ABATEMENT AND CHARACTERIZATION OF DISPERSIBLE TABLETS OF ARTEMETHER PREPARED BY HOT MELT EXTRUSION

Objective: The aim of this study was to formulate and evaluate a taste-masked formulation using hot melt extrusion approach for artemether.Methods: Taste masking of artemether was done by preparing solid dispersion with coating polymer kollicoatsmartseal 30D using hot melt extrusion. The prepared solid dispersion was subjected to taste masking evaluation like sensory evaluation parameters against five levels set for taste evaluation using artemether as control standard along with in vitro release studies in simulated salivery fluid. After taste evaluation of solid dispersion was subjected to the formulation of dispersible tablets by direct compression method. The final taste masking evaluation of dispersible tablets of solid dispersion containing artemether were done by a sensory evaluation panel of nine members along with in vitro release study in simulated salivary and gastric fluid.Results: The percent drug content was found 35.09±0.06 % in solid dispersion. The drug excipients compatibility studies performed with the help of FTIR instrument and DSC that indicates there were no interactions between drug and polymers. Solid dispersions (1:1, 1:2, 1:3 drug polymer ratio) of artemether were evaluated by sensory evaluation panel from which 1:3 drug: polymer solid dispersion was found more palatable. Release rate study in simulated salivary fluid shown no release but shows release of drug in simulated gastric fluids which indicates that the drug was taste masked. The optimized batch of dispersible tablets (F1) were subjected for evaluation parameters like dispersion time (70±1.90), wetting time (63±1.86), etc. Dissolution studies of optimized formulation indicated that the polymer does not allow drug to release in simulated salivery pH 6.8 but shows immediate release in simulated gastric pH which also confirms taste masking efficiency of polymer. Final optimized F1 batch evaluated for taste masking evaluation by sensory evaluation panel using pure drug as control standard found to be palatable.Conclusion: It may be concluded that kollicoatsmartseal 30D could mask the taste of the drug in salivary pH and shows drug release at gastric pH which confirms its efficiency for taste masking

Masking Release for Igbo and English

In this research, we explored the effect of noise interruption rate on speech intelligibility. Specifically, we used the Hearing In Noise Test (HINT) procedure with the original HINT stimuli (English) and Igbo stimuli to assess speech reception ability in interrupted noise. For a given noise level, the HINT test provides an estimate of the signal-to-noise ratio (SNR) required for 50%-correct speech intelligibility. The SNR for 50%-correct intelligibility changes depending upon the interruption rate of the noise. This phenomenon (called Masking Release) has been studied extensively in English but not for Igbo – which is an African tonal language spoken predominantly in South Eastern Nigeria. This experiment explored and compared the phenomenon of Masking Release for (i) native English speakers listening to English, (ii) native Igbo speakers listening to English, and (iii) native Igbo speakers listening to Igbo. Since Igbo is a tonal language and English is a non-tonal language, this allowed us to compare Masking Release patterns on native speakers of tonal and non-tonal languages. Our results for native English speakers listening to English HINT show that the SNR and the masking release are orderly and consistent with other English HINT data for English speakers. Our result for Igbo speakers listening to English HINT sentences show that there is greater variability in results across the different Igbo listeners than across the English listeners. This result likely reflects different levels of ability in the English language across the Igbo listeners. The masking release values in dB are less than for English listeners. Our results for Igbo speakers listening to Igbo show that in general, the SNRs for Igbo sentences are lower than for English/English and Igbo/English. This means that the Igbo listeners could understand 50% of the Igbo sentences at SNRs less than those required for English sentences by either native or non-native listeners. This result can be explained by the fact that the perception of Igbo utterances by Igbo subjects may have been aided by the prediction of tonal and vowel harmony features existent in the Igbo language. In agreement with other studies, our results also show that in a noisy environment listeners are able to perceive their native language better than a second language. The ability of native language speakers to perceive their language better than a second language in a noisy environment may be attributed to the fact that: a) Native speakers are more familiar with the sounds of their language than second language speakers. b) One of the features of language is that it is predictable hence even in noise a native speaker may be able to predict a succeeding word that is scarcely audible. These contextual effects are facilitated by familiarity.National Institutes of Health (U.S.) (Grant R01 DC00117

Novel Microelectromechanical Systems Image Reversal Fabrication Process Based on Robust SU-8 Masking Layers

This paper discusses a novel fabrication process that uses a combination of negative and positive photoresists with positive tone photomasks, resulting in masking layers suitable for bulk micromachining high-aspect ratio microelectromechanical systems (MEMS) devices. MicroChem\u27s negative photoresist Nano™ SU-8 and Clariant\u27s image reversal photoresist AZ 5214E are utilized, along with a barrier layer, to effectively convert a positive photomask into a negative image. This technique utilizes standard photolithography chemicals, equipment, and processes, and opens the door for creating complementary MEMS structures without added fabrication delay and cost. Furthermore, the SU-8 masking layer is robust enough to withstand aggressive etch chemistries needed for fabrication research and development, bulk micromachining high-aspect ratio MEMS structures in silicon substrates, etc. This processing technique was successfully demonstrated by translating a positive photomask to an SU-8 layer that was then utilized as an etching mask for a series of trenches that were micromachined into a silicon substrate. In addition, whereas the SU-8 mask would normally be left in place after processing, a technique utilizing Rohm and Haas Microposit™ S1818 as a release layer has been developed so that the SU-8 masking material can be removed post-etching