1. Neural Bases of the Motor Theory of Speech Perception
Tyler Perrachione
HST.722 / 9.044J
11/1/2007

2. The Speech Chain(s)

3. Acoustic Variability and Phonological Invariance
Formant trajectories
Aspiration following sibilants
Coarticulation
Intra/inter-speaker variation
Syllable position

4. Bonuses from Motor Theory
Parsimonious w/r/t a unified system for production and perception
Accounts for mapping between highly variable acoustic signal and invariant phonological percepts
Consistent with perception as internal representation of distal events

5. Why is the Motor Theory Always the Alternative Theory?
Lack of direct behavioral evidence
Putatively less computationally efficient
Less intuitive
Skepticism about theories that are “too big”
Haskins labs are a bunch of crackpots

6. New Evidence - fMRI
Hearing speech activation overlaps regions of activation during the production of speech
(Wilson et al., 2004 Nat. Neurosci.)

7. New Evidence - fMRI
Lip regions of motor cortex more active during perception of /p/, tongue regions more active during perception of /t/
(Pulvermüller et al., 2006, PNAS)

8. New Evidence - TMS
Stimulation of prefrontal cortex impairs speech, not nonspeech, perception (Meister et al. 2007, Current Biology)
Dissociable loci of phonological and semantic processing in IFG (Gough et al. 2005, J. Neurosci).
Combined PET and TMS to locate speech perception modulation in IFG (Watkins & Paus, 2004, J. Cog. Neuro)
Enhanced motor-evoked potential when listening to speech vs nonspeech (Watkins et al. 2003, Neuropsychologia)

9. Relation to Other Topics
Somatic & auditory integration in DCN for spatial location perception => sensory & motor integration in IFG for speech perception
Stuttering and production / perception feedback loop
Putative human mirror-neuron system
Lateralization of speech-language processes

10. Why Discuss Motor Theory?
Sensorimotor integration in perception has implications beyond speech:
Conspecific identification, theory of mind, internal world models / simulations
Implications for diagnosis and treatment of speech-sound disorders
Broader perspective on nature of speech / language integration and evolution