title: Perceptual learning of degraded speech by minimizing prediction error.
abstract: Human perception is shaped by past experience on multiple timescales. Sudden and dramatic changes in perception occur when prior knowledge or expectations match stimulus content. These immediate effects contrast with the longer-term, more gradual improvements that are characteristic of perceptual learning. Despite extensive investigation of these two experience-dependent phenomena, there is considerable debate about whether they result from common or dissociable neural mechanisms. Here we test single- and dual-mechanism accounts of experience-dependent changes in perception using concurrent magnetoencephalographic and EEG recordings of neural responses evoked by degraded speech. When speech clarity was enhanced by prior knowledge obtained from matching text, we observed reduced neural activity in a peri-auditory region of the superior temporal gyrus (STG). Critically, longer-term improvements in the accuracy of speech recognition following perceptual learning resulted in reduced activity in a nearly identical STG region. Moreover, short-term neural changes caused by prior knowledge and longer-term neural changes arising from perceptual learning were correlated across subjects with the magnitude of learning-induced changes in recognition accuracy. These experience-dependent effects on neural processing could be dissociated from the neural effect of hearing physically clearer speech, which similarly enhanced perception but increased rather than decreased STG responses. Hence, the observed neural effects of prior knowledge and perceptual learning cannot be attributed to epiphenomenal changes in listening effort that accompany enhanced perception. Instead, our results support a predictive coding account of speech perception; computational simulations show how a single mechanism, minimization of prediction error, can drive immediate perceptual effects of prior knowledge and longer-term perceptual learning of degraded speech.
authors.affiliation: Medical Research Council Cognition and Brain Sciences Unit, Cambridge CB2 7EF, United Kingdom e.sohoglu@gmail.com matt.davis@mrc-cbu.cam.ac.uk.
authors.forename: Ediz
authors.initials: E
authors.lastname: Sohoglu
authors.affiliation: Medical Research Council Cognition and Brain Sciences Unit, Cambridge CB2 7EF, United Kingdom e.sohoglu@gmail.com matt.davis@mrc-cbu.cam.ac.uk.
authors.forename: Matthew H
authors.identifier: http://orcid.org/0000-0003-2239-0778
authors.initials: MH
authors.lastname: Davis
mesh_terms: D000293:Adolescent; D000328:Adult; D001931:Brain Mapping; D003198:Computer Simulation; D004569:Electroencephalography; D005260:Female; D006801:Humans; D007858:Learning / Q000502:physiology; D015225:Magnetoencephalography; D008297:Male; D008959:Models, Neurological; D064847:Multimodal Imaging; D010700:Phonetics; D013065:Speech Intelligibility; D013067:Speech Perception / Q000502:physiology*; D013702:Temporal Lobe / Q000502:physiology*; D013997:Time Factors; D055815:Young Adult
keywords: magnetoencephalography; perceptual learning; predictive coding; speech perception; vocoded speech