Abstract
The use of naturalistic stimuli to probe sensory functions in the human brain is gaining increasing interest. Previous imaging studies examined brain activity associated with the processing of cinematographic material using both standard “condition-based” designs, as well as “computational” methods based on the extraction of time-varying features of the stimuli (e.g. motion). Here, we exploited both approaches to investigate the neural correlates of complex visual and auditory spatial signals in cinematography. In the first experiment, the participants watched a piece of a commercial movie presented in four blocked conditions: 3D vision with surround sounds (3D-Surround), 3D with monaural sound (3D-Mono), 2D-Surround, and 2D-Mono. In the second experiment, they watched two different segments of the movie both presented continuously in 3D-Surround. The blocked presentation served for standard condition-based analyses, while all datasets were submitted to computation-based analyses. The latter assessed where activity co-varied with visual disparity signals and the complexity of auditory multi-sources signals. The blocked analyses associated 3D viewing with the activation of the dorsal and lateral occipital cortex and superior parietal lobule, while the surround sounds activated the superior and middle temporal gyri (S/MTG). The computation-based analyses revealed the effects of absolute disparity in dorsal occipital and posterior parietal cortices and of disparity gradients in the posterior middle temporal gyrus plus the inferior frontal gyrus. The complexity of the surround sounds was associated with activity in specific sub-regions of S/MTG, even after accounting for changes of sound intensity. These results demonstrate that the processing of naturalistic audio-visual signals entails an extensive set of visual and auditory areas, and that computation-based analyses can track the contribution of complex spatial aspects characterizing such life-like stimuli.
Highlights
Three-dimensional movies are becoming popular both for cinema projections as well as for home-based entertainment
The condition-based analysis showed an effect of 3D in right anterior superior parietal lobule (SPL), where subsequent computation-based analyses revealed an influence of absolute disparity
In Exp 2 we found a positive co-variation between absolute disparity and the BOLD signal in V3A (Fig. 3A, left panel), with activation extending dorsally to the posterior SPL and ventrally in the fusiform gyrus
Summary
Three-dimensional movies are becoming popular both for cinema projections as well as for home-based entertainment. One concerns the distance in depth between two locations in space, while the other relates to the surface geometry of 3D shapes [9]. The former, referred as ‘‘absolute disparity’’, is deduced from the interocular distance and vergence angles [10]. The latter defines the ‘‘disparity gradient’’, which corresponds to the spatial offsets on the surface of 3D objects or at the boundary of objects at different depths
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