The role of mirror neurons in speech perception and action word semantics

Abstract

The discovery of mirror neurons in the macaque monkey has ignited intense interest in motor theories of cognition, including speech and language. Here we examine two such claims, that the perception of speech sounds critically depends on motor representations of speech gestures (the motor theory of speech perception) and that the representation of action-related semantic knowledge critically depends on motor representations involved in performing actions. We conclude that there is strong evidence against the claim that speech perception critically depends on the motor system and that there is no conclusive evidence in support of the view that the motor system supports action semantics. We propose instead that motor-related activity during perceptual processes stem from spreading activation in sensory-motor networks that are critical for speech and language production.

Keywords:

• Mirror neurons
• Speech perception
• Action semantics
• Aphasia

Acknowledgements

This work was supported by NIH grants R01 DC03681 & R01 DC009659.

Notes

¹This result also argues for bilateral organization of the speech perception system in auditory regions because left hemisphere deactivation, which included not only the motor speech system but also left auditory regions (Hickok & Poeppel, 2000, 2004, 2007). Note, one cannot appeal to bilateral organization of a motor speech perception system because the motor speech systems was functionally deactivated in patients with left anesthesia; i.e., they were completely mute at testing. See also lesion evidence in text.

²A similar color-matching task was used as a control and showed no effect of stimulation. The authors argue that this result rules out post-perceptual task effect. However, this interpretation relies on pure insertion logic (i.e., that there is no interaction between stimulus type and task), which may not be valid (Friston et al., 1996).

³For example, if my lips are tingling I may be more likely to guess a lip-related sound when I am presented with a partially ambiguous stimulus. Perhaps clever subjects developed a response strategy for ambiguous stimuli based on sensory effects of the stimulation!

⁴Wernicke's ideas on concept formation invoke Hebbian principles decades before Hebb (Gage & Hickok, 2005).