Wednesday, February 18, 2009

Reflections on mirror neurons and speech perception

In the very first empirical report of mirror neurons di Pellegrino, Fadiga, Gallese, & Rizzolatti (1992) noted the surface similarity between mirror neurons and the motor theory of speech perception.

[the invariance of the acoustic patterns of speech] led several authors to propose that the objects of speech perception were to be found not in the sound, but in the phonetic gesture of the speaker, represented in the brain as invariant motor commands (see Liberman and Mattingly 1985). Although our observations by no means prove motor theories of perception, nevertheless they indicate that in the premotor cortical areas there are neurons which are endowed with properties that such theories require. -di Pellegrino et al., 1992

By 1992 the motor theory of speech perception was effectively dead in the world of speech science due to extensive empirical work that undermined many of its claims. However, the discovery of mirror neurons, their interpretation as supporting action understanding, and their suggested link to speech resuscitated the motor theory of speech perception -- at least among non-speech scientists.

So does the discovery of mirror neurons in fact provide any new support for the motor theory of speech perception? This is the question we (Andre Lotto, Greg Hickok, & Lori Holt) tackled in a Trends in Cognitive Science paper that has just recently become available as an e-pub. Short answer: no. See the abstract below for a slightly longer summary, and the paper for the details.

Abstract. The discovery of mirror neurons, a class of neurons that respond when a monkey performs an action and also when the monkey observes others producing the same action, has promoted a renaissance for the Motor Theory (MT) of speech perception. This is because mirror neurons seem to accomplish the same kind of one to one mapping between perception and action that MT theorizes to be the basis of human speech communication. However, this seeming correspondence is superficial, and there are theoretical and empirical reasons to temper enthusiasm about the explanatory role mirror neurons might have for speech perception. In fact, rather than providing support for MT, mirror neurons are actually inconsistent with the central tenets of MT.


G. Pellegrino, L. Fadiga, L. Fogassi, V. Gallese, G. Rizzolatti (1992). Understanding motor events: a neurophysiological study Experimental Brain Research, 91 (1) DOI: 10.1007/BF00230027

Andrew J. Lotto, Gregory S. Hickok, Lori L. Holt (2009). Reflections on mirror neurons and speech perception Trends in Cognitive Sciences DOI: 10.1016/j.tics.2008.11.008

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