How do we hear ourselves while we're speaking? 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 the act of speaking suppresses the normal response to speech sounds in auditory cortex and associated regions. Previous studies by Dr. John F. Houde suggest that this suppression reflects a comparison between actual auditory input and a prediction of that auditory input. Based on these initial studies, Dr. Houde and colleagues developed a model, derived from modern control theory, for how auditory feedback is processed during speech production. With support of NSF, Dr. Houde is testing this model by using whole-head magnetic source imaging (MSI) to monitor activity in auditory cortex as speakers respond to brief perturbations of their auditory feedback. Prior studies have shown that such speech perturbations cause compensatory responses in speech motor output. In this project, researchers are first determining whether auditory cortex is part of the neural circuitry mediating these compensatory responses by examining how variations in speaker's perturbation responses are correlated with activity in auditory cortex. Their next step is determining if their model of feedback processing explains the responses previously observed in auditory cortex. A key concept of the model is that auditory feedback does not directly affect speech motor output. Instead, incoming feedback is compared with an internally-generated prediction of the expected feedback, with the resulting feedback prediction error used to control speech output. The research tests whether the responses of auditory cortex to feedback perturbations are consistent with this model.
This project is important not only for understanding the neural circuits linking speech perception and production. This project involves using state-of-the art MSI methods to test predictions of an engineering control theory model of speech feedback processing. The research team is trained in the speech research, engineering control theory, signal processing, neuroscience and magnetic source imaging methods needed to conduct this research. The project will enable students and postdocs involved to gain experience in functional neuroimaging as well as learn about control theory concepts - an area of knowledge important for understanding motor control but usually neglected in the education of neuroscience, bioengineering and cognitive science students. And although this research is focused on speech motor control, its research emphasizes the importance of studying perception in conjunction with production to understand general problems in motor control and motor dysfunctions.
