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Recurrent bottom-up and top-down interactions in multisensory object processing
Naci, L., HENSON, R.N.A., Taylor, K., & Tyler, L
15th Cognitive Neuroscience Society Annual Meeting
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This research asks how the brain combines low-level features processed in remote sensory cortices to create /meaningful/ multisensory object representations. Models of visual object processing typically assume a feedforward system in which increasingly complex visual features are processed in the hierarchically organized ventral object processing stream. The integration of multisensory inputs into meaningful object representations additionally involves frontal and antero-medial temporal cortex (Taylor et al., 2006). Here we test the feedforward hypothesis, contrasting it with an alternate hypothesis in which object processing is viewed as an interactive, iterative feedforward and feedback process (Bar et al., 2006). To determine how the key regions involved in the meaningful multisensory integration interact with each other over time, we carried out an EEG study. Subjects performed a one-back same/different audio-visual identity task on auditory, visual, and audio-visual stimuli. We used coherence analysis to investigate any large-scale cortical interactions during multisensory processing that would be expressed as synchronized oscillations between our regions of interests. We found a recurrent pattern of induced coherence in the /?/ range (4-7 Hz) between (a) frontal and antero-temporal regions and (b) antero-temporal and occipital regions at 150-500 ms, suggesting frontal facilitation of antero-temporal activity, and antero-temporal facilitation of subsequent processing in the visual regions. The theta rhythm has been associated with mnemonic processing and long-range synchronization between distant cortical regions (von Stein & Sarnthein 2000). Our results suggest that the integration of multisensory inputs into meaningful object representations involves the recurrent interaction of top-down and bottom-up processes.