Purpose: Efferent auditory system has an inhibitory function in the auditory system, and has been hypothesized to improve speech perception in noise. The function of efferent auditory system can be measured non-invasively using suppression of otoacoustic emissions (OAEs). OAEs are very small amplitude sounds generated in the cochlea by motile function of outer hair cells, and activation of the efferent system reduces the amplitude of OAEs, referred as suppression of OAEs. Several studies have been carried out by various investigators to understand the role of efferent auditory pathways during auditory processing. These investigations have used white noise, narrowband noise, pure-tones, modulated tones, etc., to activate the efferent system. However, in real-life situation, these noises are seldom found, hence the findings of above investigations may not be readily generalized to real-life situations. Hence, the present study was carried out to investigate the effect of real-life noise signals on the suppression of OAEs. Method: A total of 19 young adults aged between 18 and 23 years participated in the study. Transient evoked otoacoustic emissions (TEOAEs) were recorded with and without suppressor signal in contralateral ear conditions. Suppressor signals included white noise, amplitude-modulated noise, and real-life noise signals. The amount of suppression elicited by these noise signals were measured and compared across the noise conditions. Results: Findings of present study shows the largest suppression of TEOAE for white noise. In contrast, speech babble elicited least suppression of TEOAE compared to other noise signals used in the present investigation. For amplitude-modulated noise, the amount of suppression increased with modulation frequency of noise. Among real-life noise signals, the suppression was largest for cafeteria noise compared with traffic noise. Conclusion: Real-life noise signals used in the present study also elicited suppression, but the amount of suppression was found to be variable depending on the type of noise.

The aim of the present study was to investigate the effect of stimulus polarity on speech evoked auditory brainstem response (ABR). In order to accomplish it, speech evoked ABR was recorded with various stimulus polarities from 17 normally hearing adults. The result of the study shows differential effect of stimulus polarity on components of speech evoked ABR. Latency of peaks for onset, sustained and offset responses of speech evoked ABR were found to be not significantly different across stimulus polarities. In contrast, the amplitude of first formant and high frequency components was found to be significantly reduced for alternating polarity compared to single polarity, while amplitude of fundamental frequency response was not affected by polarity of the stimuli. Thus speech evoked ABR may be recorded using single polarity rather than using alternating polarities.

Objective: To investigate the effect of pre-transition duration on acoustic change complex (ACC) for speech and tonal stimulus. Design: Cortical potentials were recorded for consonant-vowel syllable and tonal complex stimuli with varying pre-transition durations. Study sample: Ten individuals (three male and seven female) in the age range from 18 to 26 years, with normal hearing sensitivity, participated in the study. Results: The results revealed that a minimum pre-transition duration of 100 ms for tonal stimulus (with spectral change) and 80 ms for consonant-vowel syllable is necessary in order to elicit ACC. The latency of N1¹ and P2¹, which is the response for change within the ongoing stimulus, increased with increase in pre-transition duration. The amplitude of the evoked responses did not show any significant change. Conclusions: It was found that minimum pre-transition duration required in eliciting ACC for speech and non-speech stimulus is not same. The speech stimulus required lesser duration of pre-transition than non-speech stimulus. Further studies regarding the acoustic aspects of sound on CAEP in isolation are warranted.

P300 has been studied with a variety of stimuli. However, the nature of P300 has not been investigated for deviant stimuli which change its characteristics from standard stimuli after a period of time from onset. Nine young adults with normal hearing participated in the study. The P300 was elicited using an oddball paradigm, the probability of standard and deviant stimuli was 80% and 20% respectively. Six stimuli were used to elicit P300, it included two pure-tones (1,000 Hz and 2,000 Hz) and four tone-complexes (tones with frequency changes). Among these stimuli, 1,000 Hz tone served as standard while others served as deviant stimuli. The P300 was recorded in five separate blocks, with one of the deviant stimuli as target in each block. Electroencephalographic was recorded from electrode sites Fz, Cz, C3, C4, and Pz. Latency and amplitude of components of the cortical auditory evoked potentials were measured at Cz. Waveforms obtained in the present study shows that, all the deviant stimuli elicited obligatory P1-N1-P2 for stimulus onset. 2,000 Hz deviant tone elicited P300 at a latency of 300 ms. While, tone-complexes elicited acoustic change complex (ACC) for frequency changes and finally elicited P300 at a latency of 600 ms. In addition, the results showed shorter latency and larger amplitude ACC and P300 for rising tone-complexes compared to falling tone-complexes. Tone-complexes elicited distinct waveforms compared to 2,000 Hz deviant tone. Rising tone-complexes which had an increase in frequency elicited shorter latency and larger amplitude responses, which could be attributed to perceptual bias for frequency changes.

OBJECTIVE: The present study was carried out to compare the consonant perception of young and middle-aged adults in quiet and noisy listening conditions. MATERIALS and METHODS: Twenty-nine adults aged between 18 and 55 years old participated in the study, and were separated into two groups based on their age: Group I, comprising 15 young adults aged between 18 and 40 years old, and Group II, comprising 14 middle-aged adults aged between 41 and 55 years old. All the participants had normal hearing sensitivity in both ears. RESULTS: Consonant perception was better in favorable listening conditions for both young and middle-aged adults. Comparison of the consonant identification scores of young and middle-aged adults showed significantly poorer scores among middle-aged adults in both quiet and noisy listening conditions. CONCLUSION: The findings of the present study reveal that middle-aged adults have small but significant consonant perception difficulties compared to younger adults in quiet and noisy listening conditions.

Objective: This study examined the effects of bilingualism and multilingualism on supra-threshold auditory processing abilities in children. Design: Cross-sectional study. Study sample: Ninety children participated in the study, based on the number of languages they know children were assigned into three groups, i.e. monolingual, bilingual and multilingual. Amplitude modulation detection threshold, gap detection threshold, pitch discrimination threshold and spectral ripple discrimination threshold were measured. Results: Results showed superior supra-threshold auditory processing abilities among multilingual and bilingual children than monolingual children. The results further showed that, the supra-threshold auditory processing of multilingual children was better than bilingual children. Conclusion: This finding suggests that knowledge of multiple languages improves supra-threshold auditory processing abilities. This study adds to the growing body of literature supporting the superior supra-threshold auditory processing abilities among bilingual and multilingual individuals.