The Effect of Activating the Medial Olivocochlear Fibers on Cochlear Distortions in Humans

The function of the medial olivocochlear (MOC) fibers has been investigated extensively in animals, and far less in humans. A possible function of the MOC efferents is protection against loud sounds. The aim of this study is to investigate a potential tool for evaluating the MOC reflex clinically in humans. Cochlear microphonic (CM) and the associated distortions were measured while activating the MOC fibers for an extended period of time. CM was recorded in 16 normal hearing young adults using 500 Hz toneburst at 80 dB nHL. Recording of CM was conducted every three minutes for a time-block of 18-minutes. Four total 18-minute time-blocks were recorded, two without contralateral broadband noise (CBBN) [condition (1)] and two with 50 dB SPL CBBN [condition (2)]. The CM responses were subjected to fast-Fourier transform to obtain the amplitude of the primary frequency (F1=500Hz), and the second (2F1=1000Hz) and the third (3F1=1500Hz) harmonics. A repeated-measures ANOVA was completed on the amplitude of F1, 2F1, and 3F1, and post-hoc analysis was utilized using LSD. There is approximately 21% increase in the F1 amplitude as a result of presenting CBBN, which is significant (p<0.01). There is a significant change in 2F1 (p<0.01) and 3F1 (p<0.01) amplitudes as a result of presenting the CBBN. The current study shows that the activation of the MOC fibers results in enhancement of the CM response. Furthermore, the results show that activation of the MOC fibers causes modulation of 2F1 and 3F1 of the CM response. The resulting changes of the CM distortions are in agreement with the proposed model of adjusting the operating point of the cochlear amplifier as a result of activating the MOC fibers. These results support the use of CM measurement as an objective measure for evaluating the MOC reflex clinically

The North Texas Daily, April 26, 1989

Article discussing the successes of the first class of Texas Academy of Mathematics and Science students, and th difficulties they had in adjusting to living away from home

The Effect of Activating the Olivocochlear Bundle Ipsilaterally and Contralaterally on Cochlear Microphonic in Humans

The current study was designed to investigate the effect of activating the crossed and uncrossed medial olivocochlear bundle (MOCB) in humans to better understand the function of the efferent system. Cochlear microphonic (CM) for 0.5 and 2.0 kHz tone burst (TB) was recorded in 17 female subjects (20-30 years old) while activating the crossed or uncrossed MOCB. Activation of the MOCB was completed at three levels of broadband noise (BBN) (40, 50, and 60 dBSPL). CM amplitude was recorded without presenting BBN as a baseline. Then, CM amplitude was recorded while presenting BBN ipsilaterally or contralaterally at the different BBN levels. The change in CM amplitude was measured by subtracting the without-BBN condition from the with-BBN condition. Enhancement/suppression of the CM amplitude was observed when the BBN was presented. Greater change in CM amplitude was observed when 0.5 kHz TB was used compared to 2.0 kHz. Greater change in CM amplitude was observed when the uncrossed fibers were activated (contralateral activation) compared to the crossed fibers (ipsilateral activation). For the BBN level, 50 dBSPL seemed to have the greatest effect on the CM amplitude. The current results support the theory that the MOCB modulates the outer hair cells, which could help explain the function of the efferent system

The Role of the Medial Olivocochlear Reflex in Acceptable Noise Level in Adults

Abstract Background The acceptable noise level (ANL) is a measurement used to quantify how much noise a person is willing to accept while listening to speech. ANL has been used to predict success with hearing aid use. However, physiological correlates of the ANL are poorly understood. One potential physiological correlate is the medial olivocochlear reflex (MOCR), which decreases the output of the cochlea and is thereby expected to increase noise tolerance. Purpose This study investigates the relationship between contralateral activation of the MOCR and tolerance of background noise. Research Design This study recruited 22 young adult participants with normal hearing. ANL was measured using the Arizona Travelogue recording under headphones presented at the most comfortable level (MCL) with and without multitalker babble noise. The MOCR strength was evaluated in all participants by measuring the cochlear microphonic (CM) with and without 40 dB sound pressure level contralateral broadband noise (CBBN). Data Analysis The CM observed in response to a 500-Hz tone was measured with and without CBBN, and changes in response to fast Fourier transform amplitude at 500 Hz were used as an indicator of the MOCR effect. The ANL was calculated by subtracting the maximum acceptable background noise level from the MCL. Participants were divided into two groups based on their ANL: low-ANL (ANL &lt; 7 dB) and moderate-ANL (ANL ≥ 7 dB). An independent samples t-test was used to compare CM enhancement between low-ANL and moderate-ANL groups. Additionally, Pearson's correlation was used to investigate the relationship between the ANL and the MOCR effect on the CM. Results The results indicated that presentation of CBBN increased the CM amplitude, consistent with eliciting the MOCR. Participants in the low-ANL group had significantly larger CM enhancement than moderate-ANL participants. The results further revealed a significant correlation between the ANL and the MOCR effect on the CM. Conclusion This study suggests that a stronger MOCR, as assessed using CM enhancement, is associated with greater noise tolerance. This research provides a possible objective measure to predict background tolerance in patients and adds to our understanding about the MOCR function in humans.</jats:p

Effect of Abstract Phonemic Complexity on Mismatch Negativity Amplitude

PURPOSE: Mismatch negativity (MMN) reflects a preperceptual neurophysiological response that is generated subconsciously due to the interruption of a memory trace of ongoing sensory events in the environment. It has been widely used by researchers to understand complex perceptual mechanisms. Furthermore, it has been recommended as an objective tool to investigate disorders related to auditory cognition in hearing aid and cochlear implant users. Many researchers suggest that utilizing a larger acoustic difference between standard and deviant stimuli within the oddball paradigm will lead to a more robust MMN response. The purpose of the present study is to examine if increasing the abstract phonemic contrast between standard and deviant stimuli in the oddball paradigm leads to a more robust MMN response. METHODS: Fourteen young female adults participated in the present study. To ensure that the MMN response was elicited by phonemic and not acoustic differences in the stimuli, a one-to-many ratio was created for the abstract phonemic features while controlling the acoustic features when designing the oddball paradigm as described by Phillips et al. (2000). MMN amplitude was measured at the Cz and Fz electrodes in two conditions, with two trials in each condition. In condition 1, the standards and deviants differed by one distinctive feature: voicing in trial 1 (/tӕ/ was standard and /dӕ/ was deviant) and place of articulation in trial 2 (/bӕ/ was standard and /dӕ/ was deviant). In condition 2, the standards and deviants differed across two distinctive features: voicing and place of articulation. In trial 1, /pӕ/ was standard and /dӕ/ was deviant; in trial 2, /dӕ/ was standard and /pӕ/ was deviant. RESULTS: MMN amplitudes elicited by two distinctive features were significantly larger than MMN amplitudes elicited by one distinctive feature (p \u3c 0.001). Trials 1 and 2 in each condition showed no statistical difference, and they were repeatable and highly correlated. Recordings from the Cz and Fz electrodes showed no statistical difference and were highly correlated and similar in morphology. CONCLUSION: It is known in the literature that increasing acoustic complexity elicits a more robust MMN. The present study showed that this assumption can be extended to abstract phonemic complexity. Increasing the phonemic complexity by utilizing more distinctive features in the oddball paradigm increased the amplitude and robustness of the MMN