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Joseph Borders, Birken Noesen, Assaf Harel; Electrophysiological Evidence for the Tripartite Organization of the Ventral Stream by Animacy and Object Size. Journal of Vision 2018;18(10):1146. doi: https://doi.org/10.1167/18.10.1146.
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© ARVO (1962-2015); The Authors (2016-present)
One recurrent finding in the neuroimaging of vision is category-selective regions in occipitotemporal cortex (OTC). It is still unclear, however, how object information is organized in OTC. Konkle and Caramazza (2013) suggested that object representations in OTC are organized based on their animacy and real-world size. These two dimensions, they argue, do not operate independently, but rather interact; small and large inanimate objects are represented in separate OTC regions, while in contrast, animate objects are grouped together irrespective of their size. We investigated the early neurophysiological signatures of this organizational principle by asking whether the N1, a category-selective event-related potential (ERP) component, is differentially affected by animacy and size. We recorded ERPs from participants while they viewed object images from four categories spanning animacy (Inanimate: roller-skate, motorbike; Animate: cow, butterfly) and size (Large: motorbike, cow; Small: roller-skate, butterfly) dimensions. To ensure active categorization of the objects along all dimensions, participants were asked to categorize the objects based on their size and animacy (as well as based on physical properties, as a control condition). We found that the combined effect of animacy and size can be observed as early as 170ms post-stimulus onset. Specifically, there was a significant interaction effect on N1 amplitude reflecting the organizational principle suggested by Konkle and Caramazza: N1 amplitude in right posterior lateral regions was more negative for animate than inanimate objects, and critically, size had an effect on N1 amplitude which was evident only for inanimate objects. A more negative response was recorded in response to large objects compared to the small objects. Together, these data support previous neuroimaging findings suggesting object representations in OTC are represented based on their animacy and size, and, importantly, indicate that this organizational principle can be observed in a relatively early stage along the visual processing hierarchy.
Meeting abstract presented at VSS 2018
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