Abstract
Phonetic discrimination learning is an active perceptual process that operates under the influence of cognitive control mechanisms by increasing the sensitivity of the auditory system to the trained stimulus attributes. It is assumed that the auditory cortex and the brainstem interact in order to refine how sounds are transcribed into neural codes. Here, we evaluated whether these two computational entities are prone to short-term functional changes, whether there is a chronological difference in malleability, and whether short-term training suffices to alter reciprocal interactions. We performed repeated cortical (i.e., mismatch negativity responses, MMN) and subcortical (i.e., frequency-following response, FFR) EEG measurements in two groups of participants who underwent one hour of phonetic discrimination training or were passively exposed to the same stimulus material. The training group showed a distinctive brainstem energy reduction in the trained frequency-range (i.e., first formant), whereas the passive group did not show any response modulation. Notably, brainstem signal change correlated with the behavioral improvement during training, this result indicating a close relationship between behavior and underlying brainstem physiology. Since we did not reveal group differences in MMN responses, results point to specific short-term brainstem changes that precede functional alterations in the auditory cortex.
Highlights
Auditory Research Group Zurich (ARGZ), Division Neuropsychology, Institute of Psychology, University of Zurich, Zurich, Switzerland
Both short-20, 21 and long-term[22,23,24] training protocols consisting in discriminating phonemes manipulated in formant transitions[20, 22, 23] or syllables varying in VOT21, 24, have reliably been shown to induce causal changes in the auditory cortex, as reflected by a modification of auditory-evoked potentials’ (AEPs) strength
Long-lasting training protocols have more often been associated with neural facilitation[22,23,24], whereas short-term ones have been shown to induce both facilitation[20] and adaptation[18, 20, 21]
Summary
Russo et al.[11] as well as Song and colleagues[12] made use of long-term training protocols consisting of learning to distinguish vowels manipulated in terms of pitch, and consistently revealed increased phase-locking to the fundamental frequency (i.e., f0) of the trained stimulus Even though these results fundamentally contribute to a better understanding of the subcortical neural computations underlying phonetic discrimination learning, there are several open questions that need to be addressed more deeply. The present work aimed at contributing to a better understanding of the neural operations underlying short-term phonetic discrimination learning at both the processing level of the brainstem and the auditory cortex. We re-evaluated the influence of short-term phonetic discrimination training on neural facilitation and adaptation
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