Sriram Boothalingam

Influence of the stimulus presentation rate on medial olivocochlear system assays

Click evoked otoacoustic emissions (CEOAEs) are commonly used both in research and clinics to assay the medial olivocochlear system (MOC). Clicks presented at rates >50 Hz in the contralateral ear have previously been reported to evoke contralateral MOC activity. However, in typical MOC assays, clicks are presented in the ipsilateral ear in conjunction with MOC elicitor (noise) in the contralateral ear. The effect of click rates in such an arrangement is currently unknown. A forward masking paradigm was used to emulate typical MOC assays to elucidate the influence of ipsilateral click presentation rates on MOC inhibition of CEOAEs in 28 normal hearing adults. Influence of five click rates (20.83, 25, 31.25, 41.67, and 62.5 Hz) presented at 55 dB peSPL was tested. Results indicate that click rates as low as 31.25 Hz significantly enhance contralateral MOC inhibition, possibly through the activation of ipsilateral and binaural MOC neurons with potential contributions from the middle ear muscle reflex. Therefore, click rates ≤25 Hz are recommended for use in MOC assays, at least for 55 dB peSPL click level.

Cochlear Delay and Medial Olivocochlear Functioning in Children with Suspected Auditory Processing Disorder

Behavioral manifestations of processing deficits associated with auditory processing disorder (APD) have been well documented. However, little is known about their anatomical underpinnings, especially cochlear processing. Cochlear delays, a proxy for cochlear tuning, measured using stimulus frequency otoacoustic emission (SFOAE) group delay, and the influence of the medial olivocochlear (MOC) system activation at the auditory periphery was studied in 23 children suspected with APD (sAPD) and 22 typically developing (TD) children. Results suggest that children suspected with APD have longer SFOAE group delays (possibly due to sharper cochlear tuning) and reduced MOC function compared to TD children. Other differences between the groups include correlation between MOC function and SFOAE delay in quiet in the TD group, and lack thereof in the sAPD group. MOC-mediated changes in SFOAE delay were in opposite directions between groups: increase in delay in TD vs. reduction in delay in the sAPD group. Longer SFOAE group delays in the sAPD group may lead to longer cochlear filter ringing, and potential increase in forward masking. These results indicate differences in cochlear and MOC function between sAPD and TD groups. Further studies are warranted to explore the possibility of cochlea as a potential site for processing deficits in APD.

Effect of contralateral acoustic stimulation on cochlear tuning measured using stimulus frequency and distortion product OAEs

Abstract Objective: To study whether a change in cochlear tuning, measured using OAEs, could be detected due to contralateral activation of the efferent system using broadband noise. Design: Cochlear tuning measures based on SFOAE phase gradients and SFOAE-2TS ‘Q’ were used to test this hypothesis. SFOAE magnitude and phase gradient were measured using a pure-tone sweep from 1248 to 2496 Hz at 50 dB SPL. 2TS curves of SFOAE were recorded with a suppressor frequency swept from 1120 to 2080 Hz at 50 dB SPL. DPOAE f2-sweep phase gradient was also obtained to allow comparisons with the literature. All three assays were performed across with- and no-CAS conditions. Study sample: Twenty-two young, normal-hearing adults. Results: CAS did not produce a statistically significant change in the tuning metric in any of the OAE methods used, despite producing significant reductions in the OAE magnitude. Conclusion: It is unknown whether this insensitivity to CAS is due to an insensitivity of these three measures to cochlear mechanical tuning. The results suggest that any changes in tuning induced by CAS that may occur are small and difficult to detect using the OAE measurement paradigms used here.

Influence of 100Hz amplitude modulation on the human medial olivocochlear reflex.

It is well known that medial olivocochlear system (MOC) activity causes inhibition of cochlear amplification that can be measured using otoacoustic emissions (OAEs). The temporal characteristics of this MOC inhibitory effect are still not well understood. Two experiments were performed to further explore a previously reported enhancement in MOC inhibition of OAEs by a broadband noise (BBN) elicitor modulated at 100Hz (AM-BBN). In experiment I, MOC inhibition was measured for toneburst (1 and 2kHz presented at 41.67Hz) and stimulus-frequency (0.96-1.92kHz) OAEs for two elicitor conditions, BBN and AM-BBN (100% modulation depth [MD]), in 27 young normal hearing adults. In experiment II, tonebursts were presented at 50Hz instead of 41.67Hz to test if the previously reported enhancement of the MOC response to 100Hz AM-BBN is specific to a 50Hz toneburst presentation rate. All elicitors caused significant reduction of both TB- and SF-OAE amplitude. AM-BBN evoked the same OAE inhibition compared to BBN in both experiments. This pattern was consistent across OAE types, and toneburst presentation rates. Results suggest that the MOC is not especially sensitive to 100Hz AM-BBN; instead, AM dips in noise energy likely reduce its effectiveness in evoking MOC activity due to temporal energy integration.

Efferent Modulation of Stimulus Frequency Otoacoustic Emission Fine Structure.

Otoacoustic emissions, sounds generated in the inner ear, have become a convenient non-invasive tool to examine the efferent modulation of cochlear mechanics. Activation of the medial olivocochlear (MOC) efferents has been shown to alter the magnitude of these emissions. When the effects of efferent activation on the detailed spectral structures of these emissions have been examined, a shift of the spectral patterns toward higher frequencies has been reported for distortion product and spontaneous otoacoustic emissions. Stimulus frequency otoacoustic emissions (SFOAEs) have been proposed as the preferred emission type in the study of efferent modulation due to the simplicity of their production leading to the possibility of clearer interpretation of results. The effects of efferent activation on the complex spectral patterns of SFOAEs have not been examined to the best of our knowledge. We have examined the effects of activating the MOC efferents using broadband noise in normal-hearing humans. The detailed spectral structure of SFOAEs, known as fine structure, was recorded with and without contralateral acoustic stimulation. Results indicate that SFOAEs are reduced in magnitude and their fine structure pushed to higher frequencies by contralateral acoustic stimulation. These changes are similar to those observed in distortion product or spontaneous otoacoustic emissions and behavioral hearing thresholds. Taken together with observations made about magnitude and phase changes in otoacoustic emissions and hearing thresholds upon contralateral acoustic stimulation, all changes in otoacoustic emission and hearing threshold fine structure appear to be driven by a common set of mechanisms. Specifically, frequency shifts in fine structure patterns appear to be linked to changes in SFOAE phase due to contralateral acoustic stimulation.

Psychological Work Environment and Professional Satisfaction Among Indian Audiologists

Objective : The study examined self-reported work environment and professional satisfaction among Indian audiologists. Method : A cross-sectional online survey was conducted using the demand-control-support questionnaire (DCSQ), a short version of the effort-reward-imbalance (ERI) questionnaire and open-ended questions to explore professional issues. Seventy-one Indian audiologists participated in the survey. Results : No association was found between demographic factors (i.e., gender, education, work type, and work settings) and the DCSQ and ERI sub-scales. Using the demand control model, 14% of audiologists reported working in a high-stress psychological work environment. Using the ERI ratio to estimate the imbalance between efforts and reward, it was observed that 72% of the participants experienced unfavourable working situations where the reward did not correspond to the effort made. Audiologists identified various professional issues including ‘lack of awareness of the profession among public’ and ‘unethical practice by other professionals and unqualified people is a concern’, and also made some suggestions on how to overcome them. Conclusions : The results suggest that a high percentage of audiologists perceive to be practising in high effort-low reward working conditions in comparison with audiologists in other countries such as Sweden. Further work is required to understand, and possibly overcome various professional concerns raised by audiologists.

Effects of Auditory Attention on Otoacoustic Emissions

In humans, auditory efferent control of the cochlea has been implicated in sharpening of frequency tuning, improved detection of signals in noise, and the ability to switch the focus of auditory attention. However, it remains unknown whether the modulation of efferent activity during an auditory attention task depends on the degree of task difficulty. This study aimed to compare the suppression of otoacoustic emissions (OAEs), an objective measure of auditory efferent activation, during a lexical decision task with varying degrees of difficulty, compared with passive auditory listening. Ten normal-hearing 18-35 year-olds were assessed using monosyllabic words and non-words presented in a natural or noise-vocoded (less intelligible) condition. The participants were instructed to press a button every time they heard a non-word. Simultaneously, click evoked-OAEs were obtained from the contralateral ear to the speech stimuli with a probe in the external ear canal. Preliminary results showed that OAEs amplitud...