Electrophysiological correlates of selective speech adaptation.

Selective speech adaptation refers to the phenomenon where repeated exposure to identical speech sounds temporarily reduces sensitivity to that sound. We used EEG to track the time-course of this effect. Participants were first exposed to the Dutch vowels /e/ or /ø/ and subsequently identified ambiguous sounds halfway between these phonemes. In over 90 % of the trials, the ambiguous speech sounds were perceived as the opposite phoneme to the one they were repeatedly exposed to. This perceptual shift was linked to late EEG deviations, starting around 575 ms after sound onset, which were primarily located in the left superior temporal gyrus. These findings highlight a strong link between the perceptual interpretation of ambiguous phonemes and late brain potentials. As selective speech adaptation can occur at various levels within the auditory processing hierarchy, the observed EEG effects likely reflect activity at a higher-order cortical stage involved in resolving perceptual ambiguity.