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Involvement of motor cortex in speech perception

Involvement of motor cortex in speech perception. Riikka Möttönen Department of Experimental Psychology University of Oxford. Yes Motor theory of speech perception (Liberman et al., 1967) Speech perception and production mechanisms are tightly linked No Auditory theories

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Involvement of motor cortex in speech perception

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  1. Involvement of motor cortex in speech perception Riikka Möttönen Department of Experimental Psychology University of Oxford

  2. Yes Motor theory of speech perception (Liberman et al., 1967) Speech perception and production mechanisms are tightly linked No Auditory theories Speech sounds are processed as any other sounds Humans and other animal process speech sounds using similar auditory mechanisms Is speech perception embodied?

  3. Transcranial Magnetic Stimulation (TMS) A tool to modulate normal functioning of brain areas in a controlled manner Based on electromagnetic induction (Faraday’s law)

  4. Stimulating the hand and lip representations in the primary motor (M1) cortex HAND Motor Evoked Potentials = MEPs 1 mV MEP TMS- pulse 50 ms MEP LIP First dorsal interrossius Orbicularis oris

  5. Hearing and seeingspeech enhances excitability of the lip area in the left M1 cortex Lip area in Left M1 Lip area in Right M1 Hand area in Left M1 Watkins et al. (2003)

  6. Does the motor cortex contribute to speech perception?

  7. Speech sounds are highly variable Kuhl, 2004

  8. Categorical perception of speech sounds • Identification • Discrimination

  9. ExperimentalDesign Tasks: • Identification (Id) • Discrimination (Di) • Low-frequency repetitive TMS (rTMS): • 0.6 Hz for 15 min • Monophasic pulses • Over lip or hand area of left M1 • Sub-threshold intensity (active motor threshold) Möttönen and Watkins, 2009, J Neurosci

  10. TMS-induced disruptions in the motor cortex • Low-frequency rTMS • Suppressed excitability of the targeted area in M1 15 min after before 7 min after Möttönen and Watkins, 2009

  11. Speech sounds • Experiment 1: • 8-step continuum from ‘ba’ to ‘da’ • 8-step continuum from ‘ka’ to ‘ga’ b / p d / t g / k

  12. Categorical perception of speech sounds Category boundary • Identification • Discrimination Across-category pairs Möttönen and Watkins, 2009, J Neurosci

  13. Identification: • Disruption of the lip representation reduced the slope of the ‘ba’-’da’ boundary (p < 0.05) • no effects on positions of category boundaries • Discrimination: • Disruption of the lip representation reduced the proportion of “different” responses to ‘ba’-’da’ across-category pairs (p < 0.001) • no effects on discrimination of within-category pairs InfluencesofTMS-induced motor disruptionsoncategoricalperception Möttönen and Watkins, 2009, J Neurosci

  14. Speech sounds • Experiment 1: • 8-step continuum from ‘ba’ to ‘da’ • 8-step continuum from ‘ka’ to ‘ga’ • Experiment 2: • 8-step continuum from ‘pa’ to ‘ta’ • 8-step continuum from ‘da’ to ‘ga’ b / p d / t g / k

  15. Identification: • Disruption of the lip representation reduced the slope of the ‘ba’-’da’ boundary (p < 0.05) • no effects on positions of category boundaries • Discrimination: • Disruption of the lip representation reduced the proportion of “different” responses to ‘pa’- ‘ta’ across-category pairs (p < 0.001) • no effects on discrimination of within-category pairs InfluencesofTMS-induced motor disruptionsoncategoricalperception Möttönen and Watkins, 2009, J Neurosci

  16. Summary and Conclusions • Representations of articulators in the left M1 cortex contribute to categorical perception of speech sounds • The motor system generates internal motor models of speaker’s articulatory movements during speech perception Möttönen and Watkins, 2009, J Neurosci

  17. Open questions • Does motor cortex contribute to • early stages of speech processing in the auditory cortex? • later “task-dependent” stages of speech processing? • Are these motor influences • automatic? • dependent on attention?

  18. Does the motor cortex contribute to early auditory processing of speech sounds ?- combined TMS and EEG

  19. Mismatch Negativity (MMN) • can be recorded using EEG and MEG • is elicited by infrequent changes in the sound sequence • peaks 100-200 ms after the change • generated in the auditory cortex • automatic Do TMS-induced disruptions in the left M1 cortex suppress MMN responses to changes in speech sounds?

  20. Sound sequence • Oddball: Da Da Da Ga Da Da Da Da Da Ba Da Da Da... 80% 10% 10% Möttönen, Dutton and Watkins (in prep)

  21. Experimental Design Möttönen, Dutton and Watkins (in prep)

  22. Experiment 1:TMS-induced disruption of the lip representation suppressed MMN responses to ‘ba’ and ‘ga’ POST < PRE: 166-188 ms (p< 0.05) POST < PRE: 170-210 ms (p< 0.05) MMN = Response to deviant sounds minus Response to standard sounds Responses were bandpass filtered 1-30 Hz and referenced to the left and right mastoids. Möttönen, Dutton and Watkins (in prep)

  23. Are these effects specific to the stimulation site?Does TMS over the hand area suppress MMN responses?

  24. Experiment 2: TMS-induced disruption of the hand representation did not suppress MMN responses to ‘ba’ and ‘ga’ Responses were bandpass filtered 1-30 Hz and referenced to the left and right mastoids. Möttönen, Dutton and Watkins (in prep)

  25. Summary “Speech motor cortex” modulates early automatic discrimination of speech sounds Disruption of the lip, but not hand, representation suppressed MMNs Not specific to articulatory features of speech sounds MMNs to both lip- and tongue-articulated sounds were suppressed Does TMS over the lip representation suppress processing of any kind of acoustic changes in speech sounds? Möttönen, Dutton and Watkins (in prep)

  26. Are these effects specific to phonetic changes in speech sounds?Does disruption of lip area suppress processing of any kind of acoustic changes in speech sounds?

  27. Experiment 3 • Oddball: Da Da Da Da Da Da Da Da Da Da Da Da Da... 80% 10% Duration change + 70 ms 10% Intensity change - 6dB Möttönen, Dutton and Watkins (in prep)

  28. Experiment 3:Effects of TMS-induced disruption of the lip representation on MMN responses to acoustic changes in speech sounds POST < PRE: 148-170 ms & 186-202 ms (p< 0.05) Responses were bandpass filtered 1-30 Hz and referenced to the left and right mastoids. Möttönen, Dutton and Watkins (in prep)

  29. Is this effect specific to speech?Does disruption of the lip area suppress MMN responses to changes in tones?

  30. Experiment 4 • Oddball: ♪ ♪ ♪ ♪ ♪ ♪ ♪ ♪ ♪ ♪ 80% 10% Duration change + 70 ms 10% Intensity change - 6dB Möttönen, Dutton and Watkins (in prep)

  31. Experiment 4:TMS-induced disruption of the lip representation did not suppress MMN responses to changes in tones Responses were bandpass filtered 1-30 Hz and referenced to the left and right mastoids. Möttönen, Dutton and Watkins (in prep)

  32. P < 0.01 P < 0.05 P < 0.05 The MMN mean amplitudes were calculated as the mean voltage across a 40-ms window centred at the peak latency in the grand-average response at FCZ.

  33. Conclusions Motor representations of articulators contribute to discrimination of speech sounds The auditory system interacts with the motor system at early stages of speech processing Interaction supports discrimination of speech sounds even when they are outside the focus of attention Attention may however modulate this interaction Combination of TMS and EEG is a powerful tool to investigate auditory-motor speech processing with high temporal resolution Combination of TMS and MEG

  34. Thank you Kate Watkins Rebekah Dutton Julia Erb Rowan Boyles Jennifer Chesters Mervyn Hardiman Dorothy Bishop

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