Far from being extremists in radically supporting the original formulation of the motor theory of speech perception, our hypothesis is that the motor system provides fundamental information to perceptual processing of speech sounds and that this contribution becomes fundamental to focus attention on others’ speech, particularly under adverse listening conditions or when coping with degraded stimuli. -Fadigo, NLC abstracts, 2009
Two surprises from the NLC debate between myself and Luciano Fadiga.
1. After reading his talk abstract and talking to him before the session, I thought he was going to agree that motor information at best can modulate auditory speech processing. Instead, he strongly defended a "fundamental" role for the motor system in the processing of speech sounds.
2. A majority of his arguments were not based on speech perception but came from data regarding the role of frontal systems in word-level processing ("in Broca's area there are only words"), comprehension of action semantics, syntactic processing ("Broca's region is an 'action syntax' area"), and action sequence processing.
I was expecting a more coherent argument.
The very first question during the discussion period was from someone (don't know who) who defended Luciano saying something to the effect that of course the auditory system is involved but it doesn't mean that the motor system is not fundamental. I again pointed to the large literature indicating that you don't need a motor system to perceive speech and this argues against some fundamental process. This in turn prompted the questioner to raise the dreaded Mork and Mindy argument -- something about how Mork sits by putting his head on the couch and that we understand this to be sitting but know it is not correct... I, of course, was completely defenseless and conceded my case immediately.
But seriously, when confronted with evidence that damage to the motor system doesn't produce the expected perceptional deficits, or that we can understanding actions that we cannot produce with our own motor system, it is a common strategy among mirror neuron theorists to retreat to the claim that of course many areas are involved (can you see the hands waving?). You see this all over the place in Rizzolatti's writings for example. But somehow only the motor system's involvement is "fundamental" or provides "grounding" to these perceptual processes:
“speech comprehension is grounded in motor circuits…”
-D’Ausilio, … Fadiga et al. 2009
So here is a question I would like to pose to Fadiga (or any of his co-authors):
Is speech perception grounded in auditory circuits?