Representational differences between line drawings and photographs of natural scenes: A dissociation between multi-voxel pattern analysis and repetition suppression. (August 2018) - O'Connell, Thomas P.
Abstract: Distributed representations of scene categories are consistent between color photographs (CPs) and line drawings (LDs) in the parahippocampal place area (PPA) and the retrosplenial cortex (RSC), as shown using multi-voxel pattern analysis (MVPA). Here, we used repetition suppression (RS) to further investigate the degree of representational convergence between CPs and LDs of natural scenes. MVPA and RS can capture different aspects of visual representations, and RS may prove useful in elucidating important differences in the representations of CPs and LDs of natural scenes. We performed an event-related fMRI experiment, including image-repetitions either within-type (i.e., CP to CP or LD to LD) or between-types (CP to LD, LD to CP). We found significant RS for within-type repetitions in PPA, RSC and the occipital place area (OPA), but did not observe RS for between-types repetitions. By contrast, scene categories were decodable from activity patterns evoked by both CPs and LDs using SVM classification for both within-type decoding and between-types cross-decoding. We conclude that there are representational differences between CPs and LDs in scene-selective cortex despite a category-level correspondence. Highlights: CPs and LDs of scenes are not represented as equivalent in scene-selective cortex. Between-types repetitions of CPs and LDs do not evoke repetition suppression. Scene category can be cross-decoded from activity patterns evoked by CPs and LDs. Spatially-clustered but non-identical neural populations represent CPs and LDs.