Simple line drawings suffice for functional MRI decoding of natural scene categories
- aDepartment of Psychology, The Ohio State University, Columbus, OH 43210;
- bDepartment of Computer Science, Stanford University, Stanford, CA 94305;
- cBeckman Institute, University of Illinois at Urbana–Champaign, Urbana, IL 61801; and
- dDepartment of Psychology, University of Illinois at Urbana–Champaign, Champaign, IL 61820
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Edited by Anne Treisman, Princeton University, Princeton, NJ, and approved April 22, 2011 (received for review October 22, 2010)

Abstract
Humans are remarkably efficient at categorizing natural scenes. In fact, scene categories can be decoded from functional MRI (fMRI) data throughout the ventral visual cortex, including the primary visual cortex, the parahippocampal place area (PPA), and the retrosplenial cortex (RSC). Here we ask whether, and where, we can still decode scene category if we reduce the scenes to mere lines. We collected fMRI data while participants viewed photographs and line drawings of beaches, city streets, forests, highways, mountains, and offices. Despite the marked difference in scene statistics, we were able to decode scene category from fMRI data for line drawings just as well as from activity for color photographs, in primary visual cortex through PPA and RSC. Even more remarkably, in PPA and RSC, error patterns for decoding from line drawings were very similar to those from color photographs. These data suggest that, in these regions, the information used to distinguish scene category is similar for line drawings and photographs. To determine the relative contributions of local and global structure to the human ability to categorize scenes, we selectively removed long or short contours from the line drawings. In a category-matching task, participants performed significantly worse when long contours were removed than when short contours were removed. We conclude that global scene structure, which is preserved in line drawings, plays an integral part in representing scene categories.
Footnotes
- ↵1To whom correspondence should be addressed. E-mail: bernhardt-walther.1{at}osu.edu.
Author contributions: D.B.W., B.C., E.C., D.M.B., and L.F.-F. designed research; D.B.W., B.C., and E.C. performed research; B.C. contributed new reagents/analytic tools; D.B.W. analyzed data; and D.B.W., D.M.B., and L.F.-F. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1015666108/-/DCSupplemental.
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