title: Cortical processing of degraded speech sounds: effects of distortion type and continuity.
abstract: Human speech perception is highly resilient to acoustic distortions. In addition to distortions from external sound sources, degradation of the acoustic structure of the sound itself can substantially reduce the intelligibility of speech. The degradation of the internal structure of speech happens, for example, when the digital representation of the signal is impoverished by reducing its amplitude resolution. Further, the perception of speech is also influenced by whether the distortion is transient, coinciding with speech, or is heard continuously in the background. However, the complex effects of the acoustic structure and continuity of the distortion on the cortical processing of degraded speech are unclear. In the present magnetoencephalography study, we investigated how the cortical processing of degraded speech sounds as measured through the auditory N1m response is affected by variation of both the distortion type (internal, external) and the continuity of distortion (transient, continuous). We found that when the distortion was continuous, the N1m was significantly delayed, regardless of the type of distortion. The N1m amplitude, in turn, was affected only when speech sounds were degraded with transient internal distortion, which resulted in larger response amplitudes. The results suggest that external and internal distortions of speech result in divergent patterns of activity in the auditory cortex, and that the effects are modulated by the temporal continuity of the distortion.
authors.affiliation: Brain and Mind Laboratory, Department of Biomedical Engineering and Computational Science, Aalto University School of Science, Espoo, Finland. ismo.miettinen@aalto.fi
authors.forename: Ismo
authors.initials: I
authors.lastname: Miettinen
authors.forename: Paavo
authors.initials: P
authors.lastname: Alku
authors.forename: Santeri
authors.initials: S
authors.lastname: Yrttiaho
authors.forename: Patrick J C
authors.initials: PJ
authors.lastname: May
authors.forename: Hannu
authors.initials: H
authors.lastname: Tiitinen
mesh_terms: D000328:Adult; D001303:Auditory Cortex / Q000502:physiology*; D005260:Female; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D010700:Phonetics; D013067:Speech Perception / Q000502:physiology*; D013997:Time Factors; D055815:Young Adult