Neurophysiological correlates of the perceptual magnet effect in speech perception

Abstract

This study investigated the Perceptual Magnet Effect (PME) in speech perception using behavioral and Event-Related Potentials (ERP) measures. There were two primary research questions: (1) whether category goodness rating influences speech discrimination with reduced sensitivity near the prototype and increased sensitivity in the vicinity of a poor exemplar, (2) whether the PME is domain-specific to speech sounds. Twenty adult native English speakers participated in identification, goodness rating, and discrimination tasks. The stimuli were synthesized vowels for /a/ and their nonspeech analogs by systematically varying the first two formants. ERP oddball conditions included four conditions presented in a counter-balanced order with the prototypical /a/ as the standard stimuli and its variants as deviants, and a non-prototypical /a/ as the standard and its variants as deviants, as well as the nonspeech matches. Results indicated that participants rated vowel category goodness based on the F2/F1 ratio for the /a/ sounds. Mismatch negativity amplitudes in the two speech conditions aligned with PME predictions, but similar patterns were also observed in the nonspeech conditions. The findings collectively demonstrated neurophysiological evidence for the perceptual organization of within-category variations in line with PME, which may transfer to auditory processing of similar acoustic patterns in nonspeech.