SPEECH SOUND PROCESSING IN AUDITORY CORTEX

Project: Research project

Project Details

Description

DESCRIPTION: (Adapted from the Applicant's Abstract.) The overall
objective of this project is to employ electrophysiological responses to
human speech sounds within monkey primate auditory cortex (AI) as a model
of neural mechanisms that underlie cortical processing of acoustic and
phonetic features of speech. Using multicontact electrodes, three
complementary techniques will be used to examine the activity from neuronal
ensembles; multiple unit activity (MUA), auditory evoked potentials (AEPs)
and the derived current source density (CSD). CSD analysis delineates the
temporal and laminar distribution of the current sources and sinks that
reflect net synaptic excitation and inhibition whereas phasic MUA patterns
provide information on changes in the net firing rate of neurons in the
vicinity of the recording electrodes. The neuronal ensemble responses will
also be compared to single unit recordings to evaluate relationships
between these procedures. These studies will define the obligatory
auditory cortical evoked responses elicited by speech stimuli and form the
basis for future comparisons with responses associated with discriminative
task requirements, Speech sound processing will be defined in terms of the
spatio-temporal pattern theory of complex sound encoding, which states that
complex sounds are uniquely encoded in the overall response patterns
generated within auditory cortex. Thus, the different response patterns of
MUA and transmembrane currents elicited by synthetic consonant-vowel (CV)
syllables that differ in their specific vowels, consonant place of
articulation and onset of voicing will be defined and related to the
acoustic parameters of the stimuli and to the laminar, tonotopic, binaural
column and ampliotopic organizations of AI. Response differences between
thalamocortical fibers and cortical cells within different laminae will be
compared to delineate the transformations that occur in the response at
successive levels of cortical processing. Modulation of the response
patterns induced by formant interactions and by changes in stimulus
intensity will be assessed. The applicability of findings for synthetic
speech sounds to naturally produced syllables will be determined. The
relative importance of changing formant transitions versus constant formant
onsets in the neural encoding of consonants will be assessed. The
hypothesis that the discrete encoding of the onsets of the unvoiced and
voiced portions of stop CV syllables defines the psychoacoustic boundary
demarcating the perception of these two classes of consonants will be
tested. Finally, the relationship of the intracortical responses to AEPs
recorded over the cortical convexity will be determined to define those
aspects of the intracortical processing that are reflected at the cortical
surface. These relationships will serve as a model for the neural events
that underlie the scalp recorded human AEPs to speech, and in so doing,
will increase our understanding of both normal and pathological speech
processing.
StatusFinished
Effective start/end date8/1/907/31/91

Funding

  • National Institute on Deafness and Other Communication Disorders

ASJC

  • Sensory Systems
  • Speech and Hearing
  • Cognitive Neuroscience
  • Developmental Neuroscience
  • Acoustics and Ultrasonics

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