Creating Tools

            In the past few years we have turned our attention to the problem of scientific inference. While BOLD imaging and chronometric techniques have proven to be very effective tools for identifying and localizing the components of cognition, both are intrinsically ineffective tools for understanding how these components interact. Behavioral techniques are limited because they typically only tap one aspect of processing, and do so after all interactions are complete. As a result, interactions between lexical and perceptual factors may be interpreted as top-down effects, or as the results of post-perceptual integration. Similarly, the low temporal resolution of BOLD imaging allows researchers to observe correlated patterns of interaction between localized processors, but does not support strong inferences about causal interaction because causation is a fundamentally temporal phenomenon.

 

To address these concerns, we have developed a new technique that combines the use of high spatiotemporal resolution MRI-constrained MEG/EEG imaging of brain activity and Kalman-filter based Granger causation analysis. This method has the unique ability to identify millisecond-by-millisecond causal interactions between brain regions over networks that frequently consist of more than 25 nodes. We have created a GUI-based processing stream that manages all aspects of these analyses from preprocessing of imaging data through analysis of Granger results with inferential statistics and graph theoretic visualizations.  Because our work focuses on the interaction of lexical and acoustic-phonetic processes, we have also developed a neuroanatomical model of lexical representation that draws on BOLD imaging, neuropsychology, anatomy, simulation and behavioral results. Using this model as a guide, we have used our analysis stream to examine the Ganong effect, lexical and articulatory influences on the perception of assimilated speech, categorical perception, semantic influences on speech perception, recovery from acute aphasia, sentence processing (with David Caplan), and the role of lexical factors in phonotactic repair.  

This tool, Granger Processing Stream (GPS), is available for download as well as its manual and cookbook.