Redwood Neuroscience
Title: Neural network interactions in speech perception
D'Esposito Lab
University of California,
Berkeley
Abstract:
Watching a speaker’s mouth movements improves comprehension, both
for normal listeners in noisy environments and especially for the
hearing-impaired. Several brain regions have repeatedly been implicated
in crossmodal speech tasks: left superior
temporal sulcus, intraparietal
sulcus, V5 complex, and several frontal cortical
areas. There is however little evidence to distinguish these areas
functionally -- for instance whether their role is in sensory processing
(evaluating spatiotemporal proximity) or specifically in perceptual
fusion. In an event-related fMRI study, eleven
human subjects were presented with nonsense vowel-consonant-vowel audiovisual
utterances. The auditory and visual parts of the stimuli occurred either
simultaneously or offset in time. Subjects responded with a button press
to indicate whether they experienced audiovisual stimuli as fused or not.
We evaluated the BOLD (blood oxygenation level dependent) sensitivity of crossmodally responsive regions to changes in the subject’s
percept regardless of stimulus coincidence, and to changes in stimulus
coincidence regardless of the subject’s percept. Many crossmodal
areas, such as superior temporal sulcus, were more
consistently involved in perceptual fusion. Other areas, such as the
anterior insula, were more involved with evaluating
the spatiotemporal proximity of speech stimuli, regardless of a subject’s
percept. Differential network interactions among these regions demonstrate
how low-level sensitivity to the physical properties of stimuli may become
manifest in the experience of perceptual fusion.