Seeing the articulatory gestures of the speaker significantly enhances speech perception. Findings from recent neuroimaging studies suggest that activation of the speech motor system during lipreading enhance speech perception by tuning, in a top-down fashion, speech-sound processing in the superior aspects of the posterior temporal lobe. Anatomically, the superior-posterior temporal lobe areas receive connections from the auditory, visual, and speech motor cortical areas. Thus, it is possible that neuronal receptive fields are shaped during development to respond to speech-sound features that coincide with visual and motor speech cues, in contrast with the anterior/lateral temporal lobe areas that might process speech sounds predominantly based on acoustic cues. The superior-posterior temporal lobe areas have also been consistently associated with auditory spatial processing. Thus, the involvement of these areas in audiovisual speech perception might partly be explained by the spatial processing requirements when associating sounds, seen articulations, and one’s own motor movements. Tentatively, it is possible that the anterior “what” and posterior “where / how” auditory cortical processing pathways are parts of an interacting network, the instantaneous state of which determines what one ultimately perceives, as potentially reflected in the dynamics of oscillatory activity.
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