Abstract
Even though auditory training exercises for humans have been shown to improve certain perceptual skills of individuals with and without hearing loss, there is a lack of knowledge pertaining to which aspects of training are responsible for the perceptual gains, and which aspects of perception are changed. To better define how auditory training impacts brain and behavior, electroencephalography (EEG) and magnetoencephalography (MEG) have been used to determine the time course and coincidence of cortical modulations associated with different types of training. Here we focus on P1-N1-P2 auditory evoked responses (AEP), as there are consistent reports of gains in P2 amplitude following various types of auditory training experiences; including music and speech-sound training. The purpose of this experiment was to determine if the auditory evoked P2 response is a biomarker of learning. To do this, we taught native English speakers to identify a new pre-voiced temporal cue that is not used phonemically in the English language so that coinciding changes in evoked neural activity could be characterized. To differentiate possible effects of repeated stimulus exposure and a button-pushing task from learning itself, we examined modulations in brain activity in a group of participants who learned to identify the pre-voicing contrast and compared it to participants, matched in time, and stimulus exposure, that did not. The main finding was that the amplitude of the P2 auditory evoked response increased across repeated EEG sessions for all groups, regardless of any change in perceptual performance. What’s more, these effects are retained for months. Changes in P2 amplitude were attributed to changes in neural activity associated with the acquisition process and not the learned outcome itself. A further finding was the expression of a late negativity (LN) wave 600–900 ms post-stimulus onset, post-training exclusively for the group that learned to identify the pre-voiced contrast.
Highlights
Long before the effects of auditory deprivation and stimulation on the brain were known, audiologists used auditory training exercises as a way to help people compensate for hearing loss (Carhart, 1960)
SUMMARY AND CONCLUSIONS The purpose of this study was to determine if enhanced auditory evoked P2 activity is a biomarker of learning
The question is relevant to the study of auditory rehabilitation in that neurophysiological correlates of auditory training are needed to better understand the mechanisms of action presumed to be involved when using training as an intervention approach for people with and without hearing loss
Summary
Long before the effects of auditory deprivation and stimulation on the brain were known, audiologists used auditory training exercises as a way to help people compensate for hearing loss (Carhart, 1960). The motivation for such exercises stemmed from the fact that adults and children with hearing loss often needed help in dealing with their speech perception deficits that remained after being fit with hearing aid amplification devices (Boothroyd, 2010). We focus on auditory perceptual training as a means of exploring the human capacity to learn so that brain plasticity can be optimized in ways that enhance the rehabilitation of people with hearing loss. Previous studies have shown that training-related changes in neural activity precede changes in auditory perception (Tremblay et al, 1998; Atienza et al, 2002) non-invasive physiological measures might provide an opportunity to monitor and optimize intervention efforts in people with different types of hearing loss
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