Neurobiology of Language -
New Post-Doc: Alexis Hervais-Adelman
It is now widely understood that speech perception does not proceed in an exclusively serial manner, with sound being mapped onto prelexical representations, which in turn are mapped to words, and ultimately to meaning. On the contrary, mechanisms of expectation and prediction are constantly at work, and enable us to fill in missing information based on our explicit and implicit a priori knowledge of language and the world. These top-down processes are of critical importance to the comprehension of acoustically-degraded speech, in which the input signal is harder to match than usual to an existing template. Not only is this helpful in situations where the incoming signal is suboptimal, it is also of great importance to individuals who suffer from a hearing impairment, whether they use auditory prostheses or not.
A growing body of research suggests that, in addition to more abstract linguistic mechanisms, one compensation mechanism in the face of acoustically-degraded speech is the recruitment of the speech-motor system. Recent work indicates that articulatory-motor brain areas are causally involved in speech comprehension. Support for this is particularly strong in studies of degraded speech perception and of syllable or phoneme-identification. It seems likely that articulatory-motor regions are most heavily recruited when the input signal is sub-optimal and insufficient information can be retrieved from other sources (which can collectively be thought of as “context”) to restore intelligibility. My goal is to investigate these mechanisms, with particular emphasis on elucidating the role of articulatory-motor structures in supporting speech comprehension. I will address this using a variety of techniques, including MRI to examine the neuroanatomical correlates of degraded speech perception ability, and transcranial electrical stimulation to more directly examine the nature of the top-down signals generated by the articulatory-motor system.