Cerebral Cortex, Vol. 12, No. 10, 1031-1039,
October 2002
© 2002 Oxford University Press
Dynamics of Cortico-subcortical Cross-modal Operations Involved in Audio-visual Object Detection in Humans
INSERM U280, Mental Processes and Brain Activation, 151 Cours Albert Thomas, 69003 Lyon, France
Address correspondence to Alexandra Fort, INSERM U280, 151 Cours Albert Thomas, 69424 Lyon cedex 03, France. Email: fort{at}lyon.inserm.fr.
Very recently, a number of neuroimaging studies in humans have begun to investigate the question of how the brain integrates information from different sensory modalities to form unified percepts. Already, intermodal neural processing appears to depend on the modalities of inputs or the nature (speech/non-speech) of information to be combined. Yet, the variety of paradigms, stimuli and technics used make it difficult to understand the relationships between the factors operating at the perceptual level and the underlying physiological processes. In a previous experiment, we used event-related potentials to describe the spatio-temporal organization of audio-visual interactions during a bimodal object recognition task. Here we examined the network of cross-modal interactions involved in simple detection of the same objects. The objects were defined either by unimodal auditory or visual features alone, or by the combination of the two features. As expected, subjects detected bimodal stimuli more rapidly than either unimodal stimuli. Combined analysis of potentials, scalp current densities and dipole modeling revealed several interaction patterns within the first 200µs post-stimulus: in occipito-parietal visual areas (45–85µs), in deep brain structures, possibly the superior colliculus (105–140µs), and in right temporo-frontal regions (170–185µs). These interactions differed from those found during object identification in sensory-specific areas and possibly in the superior colliculus, indicating that the neural operations governing multisensory integration depend crucially on the nature of the perceptual processes involved.
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