Effect of Auditory and Visual Distracters on Brainstem Encoding of Speech

Abstract

The present study was taken up to measure the effect of auditory and visual distracters on the brainstem encoding of speech. Speech evoked auditory brainstem responses were recorded in fifteen normal hearing adults for synthetically generated /da/ presented to the right ear in four experimental conditions- Baseline, with meaningful auditory distracter stimulus, with non-meaningful auditory distracter stimulus and with visual distracter stimulus. The transient response obtained was visually analyzed to note down the latency and amplitude of wave V and A. whereas frequency following response was subjected to FFT to derive the magnitude of response at F0, H2 and H3 and H4. The results revealed that there is no main effect of condition on the latencies and amplitudes of wave V and A. However, the spectral magnitude of the third harmonic centred around 343Hz reduces in the test ear when a meaningful distracter is presented in the auditory modality. Such an influence was not present with non-meaningful auditory distracter or the visual distracter. Based on the findings of the present study it can be inferred that the semantic load of the distracter stimuli has a significant influence on the activation of the corticofugal regulation and in turn on the brainstem encoding of speech.