Cortical responses to feedback perturbations during speaking: a magnetic source imaging study
John F. Houde
Otolaryngology – Head
and Neck Surgery, UCSF,
Understanding how speech perception interacts with speech production is a longstanding issue that has classically been investigated by looking at how altering auditory feedback affects speech. Recently, however, the advent of functional neuroimaging methods has allowed a new approach to the issue: examining how producing speech affects the neural processes serving auditory perception. Several studies have shown that speaking suppresses the normal response to speech sounds in auditory cortex and associated regions. Our own studies suggest that this suppression reflects a comparison between actual auditory input and a prediction of that auditory input (Houde et al., 2002). Based on these initial studies, we have developed a model, derived from modern control theory, for how auditory feedback is processed during speech production. Here, we test this model by using whole-head magnetic source imaging (MSI) to monitor activity in auditory cortex as speakers compensate for brief perturbations of the pitch or amplitude of their speech. Prior studies have shown that such speech perturbations cause compensatory responses in speech motor output (Burnett et al., 1998; Heinks-Maldonado & Houde, 2005). In the speaking session of the experiment, subjects phonated the neutral schwa vowel while sitting in the MSI scanner. At roughly 1.2 second intervals, they experienced 400ms perturbations of the pitch or amplitude of their audio speech feedback. In the listening session of the experiment, subjects passively listened to playback of their audio feedback in the speaking session. Our preliminary results reveal that in most subjects making significant compensations for the feedback perturbations, we find areas in the vicinity of auditory cortex in both hemispheres that have greater responses to the perturbations during speaking than during passive listening. These results advance our understanding of the neural mechanisms by which speech perception affects speech production. Support Contributed By: NSF Cognitive Neurosicence program, NIH grant R01DC4855, and the Whitaker Foundation