Brain responses to auditory and visual stimulus offset: shared representations of temporal edges.
ABSTRACT Edges are crucial for the formation of coherent objects from sequential sensory inputs within a single modality. Moreover, temporally coincident boundaries of perceptual objects across different sensory modalities facilitate crossmodal integration. Here, we used functional magnetic resonance imaging in order to examine the neural basis of temporal edge detection across modalities. Onsets of sensory inputs are not only related to the detection of an edge but also to the processing of novel sensory inputs. Thus, we used transitions from input to rest (offsets) as convenient stimuli for studying the neural underpinnings of visual and acoustic edge detection per se. We found, besides modality-specific patterns, shared visual and auditory offset-related activity in the superior temporal sulcus and insula of the right hemisphere. Our data suggest that right hemispheric regions known to be involved in multisensory processing are crucial for detection of edges in the temporal domain across both visual and auditory modalities. This operation is likely to facilitate cross-modal object feature binding based on temporal coincidence.
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ABSTRACT: Understanding how the brain extracts and combines temporal structure (rhythm) information from events presented to different senses remains unresolved. Many neuroimaging beat perception studies have focused on the auditory domain and show the presence of a highly regular beat (isochrony) in "auditory" stimulus streams enhances neural responses in a distributed brain network and affects perceptual performance. Here, we acquired functional magnetic resonance imaging (fMRI) measurements of brain activity while healthy human participants performed a visual task on isochronous versus randomly timed "visual" streams, with or without concurrent task-irrelevant sounds. We found that visual detection of higher intensity oddball targets was better for isochronous than randomly timed streams, extending previous auditory findings to vision. The impact of isochrony on visual target sensitivity correlated positively with fMRI signal changes not only in visual cortex but also in auditory sensory cortex during audiovisual presentations. Visual isochrony activated a similar timing-related brain network to that previously found primarily in auditory beat perception work. Finally, activity in multisensory left posterior superior temporal sulcus increased specifically during concurrent isochronous audiovisual presentations. These results indicate that regular isochronous timing can modulate visual processing and this can also involve multisensory audiovisual brain mechanisms.Cerebral Cortex 04/2012; · 8.31 Impact Factor
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ABSTRACT: Rhythm is a central characteristic of music and speech, the most important domains of human communication using acoustic signals. Here, we investigated how rhythmical patterns in music are processed in the human brain, and, in addition, evaluated the impact of musical training on rhythm processing. Using fMRI, we found that deviations from a rule-based regular rhythmic structure activated the left planum temporale together with Broca's area and its right-hemispheric homolog across subjects, that is, a network also crucially involved in the processing of harmonic structure in music and the syntactic analysis of language. Comparing the BOLD responses to rhythmic variations between professional jazz drummers and musical laypersons, we found that only highly trained rhythmic experts show additional activity in left-hemispheric supramarginal gyrus, a higher-order region involved in processing of linguistic syntax. This suggests an additional functional recruitment of brain areas usually dedicated to complex linguistic syntax processing for the analysis of rhythmical patterns only in professional jazz drummers, who are especially trained to use rhythmical cues for communication.Cerebral Cortex 11/2012; · 8.31 Impact Factor
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ABSTRACT: Multisensory events in our natural environment unfold at multiple temporal scales over extended periods of time. This functional magnetic resonance imaging study investigated whether the brain uses transient (onset, offset) or sustained temporal codes to effectively integrate incoming visual and auditory signals within the cortical hierarchy. Subjects were presented with 1) velocity-modulated radial motion, 2) amplitude-modulated sound, or 3) an in phase combination of both in blocks of variable durations to dissociate transient and sustained blood oxygen level-dependent responses. Audiovisual interactions emerged primarily for transient onset and offset responses highlighting the importance of rapid stimulus transitions for multisensory integration. Strikingly, audiovisual interactions for onset and offset transients were dissociable at the functional and anatomical level. Low-level sensory areas integrated audiovisual inputs at stimulus onset in a superadditive fashion to enhance stimulus salience. In contrast, higher order association areas showed subadditive integration profiles at stimulus offset possibly reflecting the formation of higher order representations. In conclusion, multisensory integration emerges at multiple levels of the cortical hierarchy using different temporal codes and integration profiles. From a methodological perspective, these results highlight the limitations of conventional event related or block designs that cannot characterize these rich dynamics of audiovisual integration.Cerebral Cortex 04/2011; 21(4):920-31. · 8.31 Impact Factor