Publication in: Fall 2023 Issue

Neural Correlates of Perceptual Learning of Sine Wave Speech
David Bortolotto
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Faculty Mentor(s):
Michael Neelon
Abstract / Summary:
The present study investigates the changes in electroencephalogram (EEG) responses that occur when listeners learn to perceive sine-wave speech (SWS) as clearly intelligible speech. SWS is an artificial acoustic signal made by reducing the complex amplitude and frequency changes of natural speech to several time-varying sinusoids (Remez, 2008). Typically, listeners begin to hear speech in SWS after exposure to the original speech recording on which it is based. Our study attempts to extend the reported finding of an event-related potential (ERP) called the “Perceptual Awareness Negativity” (PAN) that may occur when listeners start hearing SWS as speech rather than as unidentifiable electronic noise (Dykstra et al, under review). At the start of each session, participants listened to SWS, pure-tones, and spectrally rotated control (SR) words and responded when they heard any sounds repeat. Following this, participants completed a speech training phase in which SWS and natural speech tokens were paired together. After speech training participants repeated the initial phase yet this time with updated speech awareness. Behavioral results show that 80% (25/31) of participants did not hear speech content in the first phase of exposure to SWS, but reported hearing SWS as speech after training. ERPs were analyzed for the presence of a left-lateralized fronto-central negativity in the 200-300 ms post-stimulus time range similar to that of the PAN. Behavioral results confirmed the perceptual experience of learning to hear SWS as speech after proper exposure. A negative shift in the grand-averaged ERP was observed in subjects hearing SWS as speech after speech training between blocks 1 and 2 (i.e., non-noticers). At the same time, no similar negative shift was observed across blocks for these same listeners in the ERPs to spectrally-rotated control sounds, indicating the absence of a PAN for stimuli not perceived as speech
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