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Martijn E. Wokke, H. Steven Scholte, Victor A. F. Lamme; Figure-ground signals in early and object specific visual areas: A combined fMRI, EEG and rTMS study. Journal of Vision 2010;10(7):1218. doi: 10.1167/10.7.1218.
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© ARVO (1962-2015); The Authors (2016-present)
Two processes can be discriminated when distinguishing a figure from its background: boundary detection and surface segregation. The neural origin and temporal dynamics of these two processes are still much disputed. In this study we used motion and texture defined stimuli that differentiate between edge detection and surface segregation. In order to investigate the function of networks involved in figure-ground segregation, we combined online rTMS and EEG and disrupted processing in nodes of distinct visual networks (dorsal vs. ventral). For motion defined stimuli rTMS/EEG results indicate that rTMS alters figure-ground related processes differentially depending on whether the dorsal (V5/MT) or ventral (Lateral Occipital [LO]) network was stimulated. The data suggest that disrupting V5/MT impairs surface segregation but not edge detection. This behavioral effect was reflected in interrupted feedback signals to occipital areas as measured by EEG. However, disrupting LO has the opposite effect, it enhances surface segregation and boosts feedback signals to occipital areas. To interpret the rTMS/EEG results, BOLD-MRI was measured in both areas. fMRI data showed that V5/MT differentiates between edge detection and surface segregation for motion defined stimuli, while LO does not. For texture defined stimuli no differentiation was found between edge detection and surface segregation in both areas. In general, the rTMS/EEG and fMRI data suggest a battle of resources between the dorsal and ventral stream in the process of figure-ground segregation. When the stream that is less involved in this process becomes disrupted, the stream that is more involved can become more dominant, resulting in better performance and enhanced feedback signaling to occipital areas.
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