Effect of acoustic features on discrimination ability in individuals with auditory neuropathy spectrum disorder: an electrophysiological and behavioral study.

PURPOSE: The present study aimed to investigate the discrimination ability for acoustic cues in individuals with auditory neuropathy spectrum disorder (ANSD) using both behavioral and neural measures and to compare the result with normal hearing individuals. METHODS: Four naturally produced syllables /ba/, /da/, /ma/ and /pa/ were used to study discrimination skills. They were combined in pairs such that the two syllables differ in acoustic features, that is place (/ba/-/da/), manner (/ba/-/ma/) and voicing (/ba/-/pa/) cues. Thirty individuals with ANSD and 30 individuals with normal hearing sensitivity were the participants. Syllable discrimination skill was assessed using behavioral (reaction time, sensitivity and D-prime) and neural (P300) measures. RESULTS: There was prolongation in latency and reduction in amplitude of P300 in individuals with ANSD compared to individuals with normal hearing sensitivity. Individuals with ANSD showed better discrimination skill for stimulus pairs differing in the manner followed by place and the least perceived was voicing information. CONCLUSION: Discrimination ability of individuals with ANSD is found to be affected as evident on behavioral and neural measures. The discrimination ability varies with acoustic features of speech.

Cortical processing of speech in individuals with auditory neuropathy spectrum disorder.

OBJECTIVE: Auditory neuropathy spectrum disorder (ANSD) is a condition where cochlear amplification function (involving outer hair cells) is normal but neural conduction in the auditory pathway is disordered. This study was done to investigate the cortical representation of speech in individuals with ANSD and to compare it with the individuals with normal hearing. DESIGN: Forty-five participants including 21 individuals with ANSD and 24 individuals with normal hearing were considered for the study. Individuals with ANSD had hearing thresholds ranging from normal hearing to moderate hearing loss. Auditory cortical evoked potentials-through odd ball paradigm-were recorded using 64 electrodes placed on the scalp for /ba/-/da/ stimulus. Onset cortical responses were also recorded in repetitive paradigm using /da/ stimuli. Sensitivity and reaction time required to identify the oddball stimuli were also obtained. RESULT: Behavioural results indicated that individuals in ANSD group had significantly lower sensitivity and longer reaction times compared to individuals with normal hearing sensitivity. Reliable P300 could be elicited in both the groups. However, a significant difference in scalp topographies was observed between the two groups in both repetitive and oddball paradigms. Source localization using local auto regressive analyses revealed that activations were more diffuses in individuals with ANSD when compared to individuals with normal hearing sensitivity. CONCLUSION: Results indicated that the brain networks and regions activated in individuals with ANSD during detection and discrimination of speech sounds are different from normal hearing individuals. In general, normal hearing individuals showed more focused activations while in individuals with ANSD activations were diffused.

Functioning of medial olivocochlear bundle in right- and left-handed individuals.

Functional symmetry of medial olivocochlear bundle (MOCB) as a function of handedness remains to be well investigated. The current study aimed to assess the functional symmetry of MOCB through contralateral inhibition of otoacoustic emissions (OAEs) in right- and left-handed individuals. Thirteen left-handed and 13 right-handed individuals in the age range of 19-25 years participated. Behavioural experiment involved measuring speech perception in noise and vocal reaction time. Physiological experiment involved measuring the contralateral inhibition of OAEs in both the ears of participants. Findings of the current study revealed lack of functional asymmetry in right- as well as left-handed individuals. Results of the current study suggest that right- as well as left-handed individuals do not demonstrate functional asymmetry at the level of descending auditory pathways unlike the higher cortical centres.

Descending auditory pathway and identification of phonetic contrast by native listeners.

The present study investigated the ability of native listeners to identify subtle phonetic contrasts in nonsense words and its relationship with the contralateral inhibition of transient evoked otoacoustic emissions (TEOAE). A group of 45 young adults with normal hearing sensitivity who were native speakers of Malayalam participated in the behavioral experiment. Phone identification score and reaction time for four phonetic pairs in nonsense words were measured for each participant. Based on the phone identification score, the participants were divided into high and low performers. Twelve participants randomly selected from each group were evaluated for contralateral inhibition of TEOAEs. Phone identification score and global contralateral inhibition amplitude of TEOAE were significantly higher and reaction time was significantly shorter in high performers than that of low performers. Significant correlation was found between the phone identification score and contralateral inhibition of TEOAE. Strength of the medial olivocochlear bundle activity explained about 30% of the variance in the phone identification scores providing evidence for the involvement of the descending auditory pathways in identifying the phonetic contrasts that are acoustically similar. These results support the emerging view that top down influences from higher centers shapes the responses of lower centers.

Temporal and speech processing skills in normal hearing individuals exposed to occupational noise.

Prolonged exposure to high levels of occupational noise can cause damage to hair cells in the cochlea and result in permanent noise-induced cochlear hearing loss. Consequences of cochlear hearing loss on speech perception and psychophysical abilities have been well documented. Primary goal of this research was to explore temporal processing and speech perception Skills in individuals who are exposed to occupational noise of more than 80 dBA and not yet incurred clinically significant threshold shifts. Contribution of temporal processing skills to speech perception in adverse listening situation was also evaluated. A total of 118 participants took part in this research. Participants comprised three groups of train drivers in the age range of 30-40 (n= 13), 41 50 ( = 13), 41-50 (n = 9), and 51-60 (n = 6) years and their non-noise-exposed counterparts (n = 30 in each age group). Participants of all the groups including the train drivers had hearing sensitivity within 25 dB HL in the octave frequencies between 250 and 8 kHz. Temporal processing was evaluated using gap detection, modulation detection, and duration pattern tests. Speech recognition was tested in presence multi-talker babble at -5dB SNR. Differences between experimental and control groups were analyzed using ANOVA and independent sample t-tests. Results showed a trend of reduced temporal processing skills in individuals with noise exposure. These deficits were observed despite normal peripheral hearing sensitivity. Speech recognition scores in the presence of noise were also significantly poor in noise-exposed group. Furthermore, poor temporal processing skills partially accounted for the speech recognition difficulties exhibited by the noise-exposed individuals. These results suggest that noise can cause significant distortions in the processing of suprathreshold temporal cues which may add to difficulties in hearing in adverse listening conditions.

Effect of Occupational Noise Exposure on Cognition and Suprathreshold Auditory Skills in Normal-Hearing Individuals.

OBJECTIVES: Adverse effects of noise exposure on hearing and cognition are well documented in the literature. Recently, it has becoming increasingly evident that noise exposure deteriorates suprathreshold auditory skills, even though the hearing sensitivity is intact. This condition is termed as cochlear synaptopathy or hidden hearing loss, which is apparent in animal models. However, equivocal findings are reported in humans. This study aimed at assessing the working memory, attention abilities, and suprathreshold hearing abilities in normal-hearing individuals with and without occupational noise exposure. We also explored the relationship between cognitive measures and suprathreshold auditory measures. DESIGN: The study participants were divided into two groups. All the participants had normal-hearing thresholds. The control group consisted of 25 individuals with no occupational noise exposure, whereas the noise exposure group had 25 individuals exposed to occupational noise of 85 dBA for a minimum period of 1 year. Working memory was assessed using auditory digit span (forward and backward), operation span, and reading span. The Erikson flanker test was used to evaluate attention abilities. The suprathreshold hearing was assessed in terms of gap detection thresholds and sentence identification in noise. RESULTS: The results showed that the noise exposure group performed poorly compared to the control group on all auditory and cognitive tasks except the reading span. CONCLUSION: The results of the study suggest that occupational noise exposure may hamper the cognitive skills and suprathreshold hearing abilities of the individual despite having normal peripheral hearing.

Pre-Attentive Neural Signatures of Auditory Spatial Processing in Listeners With Normal Hearing and Sensorineural Hearing Impairment: A Comparative Study.

Purpose This study was carried out to understand the neural intricacies of auditory spatial processing in listeners with sensorineural hearing impairment (SNHI) and compare it with normal hearing (NH) listeners using both local and global measures of waveform analyses. Method A standard group comparison research design was adopted in this study. Participants were assigned to 2 groups. Group I consisted of 13 participants with mild-moderate flat or sloping SNHI, while Group II consisted of 13 participants with NH sensitivity. Electroencephalographic data using virtual acoustic stimuli (spatially loaded stimuli played in center, right, and left hemifields) were recorded from 64 electrode sites in passive oddball paradigm. Both local (electrode-wise waveform analysis) and global (dissimilarity index, electric field strength, and topographic pattern analyses) measures were performed on the electroencephalographic data. Results Results of local waveform analyses marked the appearance of mismatch negativity in an earlier time window, relative to those reported conventionally in both the groups. The global measures of electric field strength and topographic modulations (dissimilarity index) revealed differences between the 2 groups in different time periods, indicating multiphases (integration and consolidation) of spatial processing. Further, the topographic pattern analysis showed the emergence of different scalp maps for SNHI and NH in the time window corresponding to mismatch negativity (78-150 ms), suggestive of differential spatial processing between the groups at the cortical level. Conclusions The findings of this study highlights the differential allotment of neural generators, denoting variations in spatial processing between SNHI and NH individuals.

Behavioral and Neural Correlates of Auditory n-Back Task in Adults With and Without Stuttering.

Purpose Adults with stuttering (AWS) exhibit compromised phonological working memory abilities, poor central auditory processing, and impaired auditory processing especially during overt speech production tasks. However, these tasks are sensitive to language disturbances already found in them. Thus, in this study, monosyllables were used ruling out the language effects, and auditory working memory ability was evaluated in AWS using the n-back task. In specific, the auditory sensory input of the working memory mechanism was evaluated. Method Thirty-two participants, 16 each of AWS and adults with no stuttering (AWNS), performed behavioral auditory 1-back and 2-back tasks. The long latency responses were also recorded during no-back and 2-back conditions from 64 electrode sites. Results Results revealed no significant differences between the groups in any of the behavioral parameters such as reaction time, accuracy, false alarm rate, or d'. N1 amplitude modulation was noted in AWNS, which was absent in AWS. The segmentation analysis showed a left hemisphere-oriented topographical distribution in the N2 region in AWS irrespective of conditions, whereas the scalp topography was right hemisphere-oriented with the involvement of parietal channels in AWNS. The timing differences existed between AWS and AWNS in the intervals that a topographical distribution lasted in all throughout the time window of analysis. Conclusion The results suggest altered neural pathway and hemispheric differences during auditory working memory tasks in AWS.

Gender-bias in the sensory representation of infant cry.

The auditory neural pathway in females appears to be more sensitive to the cry of an infant (De Pisapia et al., 2013; Messina et al., 2016). Cortical responses in females have shown a distinct advantage compared to males in the auditory processing of infant cry. Such gender-bias in the cortical responses might emanate either at higher levels of processing such as cognitive and emotional processing or at the lower level representation of stimulus features. We assessed for a difference if any, between the two genders, in the sensory representation of an infant's cry. We used frequency following responses (FFR) to assess the sensory representation of an infant cry. This was done in sixteen male and fifteen female non-parent adults. The FFR closely mimics the stimulus acoustics with fine temporal precision and is the measure of choice to assess the sensory encoding of sounds in the auditory system. We performed spectral analysis of the FFRs and compared the spectral magnitudes between males and females. We found significantly higher FFR spectral magnitudes in females compared to males. The gender differences found were not related to the confounding variables such as head size or differences in the volume-conducting media. By systematically controlling other influencing variables, we show that the bias in neural processing of infant cry in females emerges right at the sensory representation levels.

Functional Interplay Between the Putative Measures of Rostral and Caudal Efferent Regulation of Speech Perception in Noise.

Efferent modulation has been demonstrated to be very important for speech perception, especially in the presence of noise. We examined the functional relationship between two efferent systems: the rostral and caudal efferent pathways and their individual influences on speech perception in noise. Earlier studies have shown that these two efferent mechanisms were correlated with speech perception in noise. However, previously, these mechanisms were studied in isolation, and their functional relationship with each other was not investigated. We used a correlational design to study the relationship if any, between these two mechanisms in young and old normal hearing individuals. We recorded context-dependent brainstem encoding as an index of rostral efferent function and contralateral suppression of otoacoustic emissions as an index of caudal efferent function in groups with good and poor speech perception in noise. These efferent mechanisms were analysed for their relationship with each other and with speech perception in noise. We found that the two efferent mechanisms did not show any functional relationship. Interestingly, both the efferent mechanisms correlated with speech perception in noise and they even emerged as significant predictors. Based on the data, we posit that the two efferent mechanisms function relatively independently but with a common goal of fine-tuning the afferent input and refining auditory perception in degraded listening conditions.

Test/retest repeatability of effect contralateral acoustic stimulation on the magnitudes of distortion product ototacoustic emissions.

OBJECTIVES/HYPOTHESIS: Contralateral inhibition of distortion product otoacoustic emissions (DPOAE) has become an important tool to assess the functioning of the medial olivocochlear efferents in humans. However, before this measurement can be applied clinically, the test/retest repeatability needs to be established. Therefore, the current study aimed at evaluating intra- and intersession test/retest repeatability of contralateral inhibition of DPOAE at 2f(1) -f(2) . STUDY DESIGN: Prospective Test/Retest Reliability Study. METHODS: Contralateral inhibition of DPOAE magnitudes were measured in the right ear of 24 adult male participants. To assess the intrasession repeatability, measurements were repeated without altering the position of the DPOAE probe (single-probe-fit). To assess intersession reliability, measurements were repeated on 8 different days (multiple-probe-fit). Repeatability of inhibition of DPOAE magnitudes was evaluated by Cronbach's alpha, interclass correlations, standard error of measurement, and its 95% confidence interval and smallest detectable difference. RESULTS: DPOAE magnitudes were highly stable and repeatable across different recording sessions. However, test/retest reliability coefficients of DPOAE inhibition magnitudes were less than satisfactory for all the frequencies, in both single-probe-fit and multiple-probe-fit modes. CONCLUSIONS: Results of the present study showed that contralateral inhibition magnitudes of DPOAEs varied considerably, even though DPOAEs magnitudes remained essentially the same across different recording sessions. As reliability is an essential aspect of any clinical procedure, it is suggested that at present contralateral inhibition of DPOAEs should not be used clinically to evaluate the medial efferent system. Laryngoscope, 2012.

Distortion product otoacoustic emissions: comparison of sequential vs. simultaneous presentation of primary tones.

Distortion product otoacoustic emissions are one form of evoked otoacoustic emissions. DPOAEs provide the frequency specific information about the hearing status in mid and high frequency regions. But in most screening protocols TEOAEs are preferred as it requires less time compared to DPOAE. This is because, in DPOAE each stimulus is presented one after the other and responses are analyzed. Grason and Stadler Incorporation 60 (GSI-60) offer simultaneous presentation of four sets of primary tones at a time and checks for the DPOAE. In this mode of presentation, all the pairs are presented at a time and following that response is extracted separately whereas, in sequential mode primaries are presented in orderly fashion one after the other. In this article simultaneous and sequential protocols were used to compare the Distortion product otoacoustic emission amplitude, noise floor and administration time in individuals with normal hearing and mild sensori-neural (SN) hearing loss. In simultaneous protocols four sets of primary tones (i.e. 8 tones) were presented together whereas, in sequential presentation mode one set of primary tones was presented each time. Simultaneous protocol was completed in less than half the time required for the completion of sequential protocol. Two techniques yielded similar results at frequencies above 1000 Hz only in normal hearing group. In SN hearing loss group simultaneous presentation yielded signifi cantly higher noise floors and distortion product amplitudes. This result challenges the use of simultaneous presentation technique in neonatal hearing screening programmes and on other pathologies. This discrepancy between two protocols may be due to some changes in biomechanical process in the cochlear and/or due to higher distortion/noise produced by the system during the simultaneous presentation mode.

Prevalence and audiological characteristics in individuals with auditory neuropathy/auditory dys-synchrony.

The objectives of this study were to (a) estimate the prevalence of auditory dys-synchrony in Mysore, a city of one million population in Southern India and, (b) present the results of audiological testing of this clinical population as well as the relationship between these figures. A register-based study design was employed wherein the results of audiological tests of all patients who visited the Department of Audiology, All India Institute of Speech and Hearing between January 2000 and December 2003 were reviewed. Results showed that the prevalence of auditory dys-synchrony was around 1 in 183 in individuals with sensory neural hearing loss. Behavioural thresholds and speech identification scores were variable. Around 60% of the individuals had no measurable speech identification scores. There was no relation between the hearing thresholds and speech identification scores or between otoacoustic emissions and speech identification scores. These results indicate that auditory dys-synchrony is not an extremely rare disorder.

Functioning of olivocochlear bundle and speech perception in noise.

OBJECTIVES: To evaluate the effect of contralateral acoustic stimuli on speech identification scores and to correlate this effect to contralateral suppression of evoked otoacoustic emission. DESIGN: Ten normal-hearing children with good academic performance participated in the study. Speech identification scores were measured in quiet and with different ipsilateral signal to noise ratios in two conditions, with and without contralateral acoustic stimuli. Transient evoked otoacoustic emissions were recorded for 70 dB SPL clicks with and without contralateral acoustic stimuli. RESULTS: Findings revealed that contralateral acoustic stimuli enhanced speech perception when ipsilateral signal to noise ratios was +10 dB and +15 dB. This enhancement had significant positive correlation with contralateral suppression of OAE. CONCLUSIONS: The results of the present study support the hypothesis that medial olivocochlear bundle might aid in speech perception in noise, thereby suggesting a possible role of cochlear efferent fibers in hearing. The psychoacoustic measures can be used to evaluate the efferent auditory pathways, where it is not possible to record otoacoustic emissions.