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Zusammenfassung:
To form an accurate percept of the environment the brain integrates sensory signals weighted by their relative reliabilities (Ernst and Banks, 2002). Indeed, recent neurophysiological research has demonstrated that activity of multisensory MSTd neurons during a heading task is modulated by changes in cue reliability in line with predictions of optimal integration (Fetsch et al., 2012). Moreover, top-down influences like task-relevance modulate multisensory perception (Bertelson and Radeau, 1981). The current study investigated how the human brain integrates audiovisual signals into spatial representations depending on their relative reliability and task-relevance. Using fMRI, we characterized how these integration processes emerged along the visual and auditory processing hierarchies. Subjects (N = 5) were presented with synchronous audiovisual signals that were spatially congruent or discrepant at 4 positions along the azimuth. We manipulated visual reliability (low vs. high) and task-relevance (auditory vs. visual-selective localization). Multivariate decoding of spatial information from fMRI data revealed that multisensory influences on spatial representations were present already at the primary cortical level and progressively increased along the cortical hierarchies. Likewise, the influence of task-relevance increased. Most prominently, the intraparietal sulcus integrated audiovisual signals weighted by their relative reliabilities and task-relevance. Further, IPS showed the greatest correlation with participant’s behavioral crossmodal bias. Collectively, the results suggest that IPS forms a spatial priority map (Bisley and Goldberg, 2010) by integrating sensory signals weighted by their bottom-up reliability and top-down task-relevance.
