Neural Bases of the Motor Theory of Speech Perception

Tyler PerrachioneHST.722 / 9.044J

11/1/2007

tkp@mit.edu

The Speech Chain(s)

Acoustic Variability and Phonological Invariance

• Formant trajectories• Aspiration following

sibilants• Coarticulation• Intra/inter-speaker

variation• Syllable position

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

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

New Evidence - fMRI

• Hearing speech activation overlaps regions of activation during the production of speech

(Wilson et al., 2004 Nat. Neurosci.)

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)

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)

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

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