The Journal of neuroscience : the official journal of the Society for Neuroscience
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Face-to-face communication challenges the human brain to integrate information from auditory and visual senses with linguistic representations. Yet the role of bottom-up physical (spectrotemporal structure) input and top-down linguistic constraints in shaping the neural mechanisms specialized for integrating audiovisual speech signals are currently unknown. Participants were presented with speech and sinewave speech analogs in visual, auditory, and audiovisual modalities. ⋯ In addition to this "ventral" processing stream, a "dorsal" circuitry encompassing posterior STS/STG and left inferior frontal gyrus differentially integrated audiovisual speech and SWS signals. Indeed, dynamic causal modeling and Bayesian model comparison provided strong evidence for a parallel processing structure encompassing a ventral and a dorsal stream with speech intelligibility training enhancing the connectivity between posterior and anterior STS/STG. In conclusion, audiovisual speech comprehension emerges in an interactive process with the integration of auditory and visual signals being progressively constrained by stimulus intelligibility along the STS and spectrotemporal structure in a dorsal fronto-temporal circuitry.