Sensory Gating in the Auditory System: Classical and Novel Stimulus Paradigms.

PURPOSE: Sensory gating is a phenomenon where the cortical response to the second stimulus in a pair of identical stimuli is inhibited. It is most often assessed in a conditioning-testing paradigm. Both active and passive neuronal mechanisms have been implicated in sensory gating. The present study aimed to assess if sensory gating is caused by an active neural mechanism associated with stimulus redundancy. METHOD: The study was carried out on 20 young neurotypical adults. We assessed the gating phenomenon using identical and nonidentical stimuli pairs presented in an electrophysiological conditioning-testing paradigm. We hypothesized that the novel stimulus in the nonidentical stimulus pair would not exhibit the sensory gating effects (reduction in the amplitude of cortical potentials to the second stimuli in the pair), owing to stimulus novelty. RESULTS: Contrary to our expectations, the response analyses of the cortical auditory evoked potentials revealed that adults gated repetitive and novel stimuli similarly. CONCLUSIONS: The findings are discussed in relation to the significance of methodological factors in evaluating sensory gating. We believe that additional research using oddball presentation of novel stimuli along with appropriate analysis methods is necessary before drawing any conclusions on the mechanisms underlying sensory gating.

Speech Perception in Noise and Medial Olivocochlear Reflex: Effects of Age, Speech Stimulus, and Response-Related Variables.

PURPOSE: The role of the medial olivocochlear system in speech perception in noise has been debated over the years, with studies showing mixed results. One possible reason for this could be the dependence of this relationship on the parameters used in assessing the speech perception ability (age, stimulus, and response-related variables). METHODS: The current study assessed the influence of the type of speech stimuli (monosyllables, words, and sentences), the signal-to-noise ratio (+5, 0, -5, and -10 dB), the metric used to quantify the speech perception ability (percent-correct, SNR-50, and slope of the psychometric function) and age (young vs old) on the relationship between medial olivocochlear reflex (quantified by contralateral inhibition of transient evoked otoacoustic emissions) and speech perception in noise. RESULTS: A linear mixed-effects model revealed no significant contributions of the medial olivocochlear reflex to speech perception in noise. CONCLUSION: The results suggest that there was no evidence of any modulatory influence of the indirectly measured medial olivocochlear reflex strength on speech perception in noise.