title: Cortical encoding of aperiodic and periodic speech sounds: evidence for distinct neural populations.
abstract: Most speech sounds are periodic due to the vibration of the vocal folds. Non-invasive studies of the human brain have revealed a periodicity-sensitive population in the auditory cortex which might contribute to the encoding of speech periodicity. Since the periodicity of natural speech varies from (almost) periodic to aperiodic, one may argue that speech aperiodicity could similarly be represented by a dedicated neuron population. In the current magnetoencephalography study, cortical sensitivity to periodicity was probed with natural periodic vowels and their aperiodic counterparts in a stimulus-specific adaptation paradigm. The effects of intervening adaptor stimuli on the N1m elicited by the probe stimuli (the actual effective stimuli) were studied under interstimulus intervals (ISIs) of 800 and 200 ms. The results indicated a periodicity-dependent release from adaptation which was observed for aperiodic probes alternating with periodic adaptors under both ISIs. Such release from adaptation can be attributed to the activation of a distinct neural population responsive to aperiodic (probe) but not to periodic (adaptor) stimuli. Thus, the current results suggest that the aperiodicity of speech sounds may be represented not only by decreased activation of the periodicity-sensitive population but, additionally, by the activation of a distinct cortical population responsive to speech aperiodicity.
authors.affiliation: Department of Signal Processing and Acoustics, Aalto University School of Electrical Engineering, P.O. Box 13000, FI-00076 AALTO, Finland. santeri.yrttiaho@tkk.fi
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
authors.forename: Paavo
authors.initials: P
authors.lastname: Alku
mesh_terms: D000161:Acoustic Stimulation; D000222:Adaptation, Physiological / Q000502:physiology; D002540:Cerebral Cortex / Q000166:cytology* / Q000502:physiology*; D003627:Data Interpretation, Statistical; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D009474:Neurons / Q000502:physiology*; D013060:Speech; D013067:Speech Perception / Q000502:physiology*; D055815:Young Adult