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Matthew Lowe, Jason Rajsic, Susanne Ferber, Dirk Walther; Category discrimination of early electrophysiological responses reveals the time course of natural scene perception. Journal of Vision 2017;17(10):311. doi: https://doi.org/10.1167/17.10.311.
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Humans have the remarkable ability to categorize complex scenes within a single glance. Which properties of scenes make this feat possible, and what is the time course of this process? Neural representations of scene categories for line drawings and colour photographs have been shown to elicit similar responses in scene-selective cortex. Together with previous investigations highlighting the importance of surface features for scene identification, these results suggest that both structure and surface features play an integral role in perceiving and understanding our environment. Within the spatial domain, these features may be closely interwoven in the human brain. Within the temporal domain, however, they may elicit distinct patterns along a hierarchy of visual processing. To investigate these questions, the present study used electroencephalography (EEG) to examine the time course of scene processing (beach; city; forest; highway; mountain; office) for colour photographs and line drawings (stimulus-type) in the human visual system. Participants (N=16) performed a blocked scene-memorization task during observation of colour photographs and line drawings. An initial event-related potential (ERP) analysis revealed dissociable response patterns across scene categories over the occipital pole for early visually-evoked components P1 and P2. Furthermore, line drawings evoked an overall higher P1 amplitude, while colour photographs evoked a higher P2 peak. Additional differences across stimulus-type were distributed throughout cortex. To investigate these response patterns in greater detail, we performed an analysis examining the grand-averaged correlations for within-category versus across-category discriminations during the time course of scene processing. This analysis revealed that significant discriminations of scene categories in line drawings emerge earlier (~80ms) than colour photographs (~100ms). Critically, these findings provide evidence that basic-level categorization of scenes can occur earlier in visual processing than object-class detection (e.g., animal detection), and further suggest that differences in visual feature processing emerge across the temporal domain for natural scene perception.
Meeting abstract presented at VSS 2017
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