Abstract
Theoretical studies suggest that the visual system uses prior knowledge of visual objects to recognize them in visual clutter, and posit that the strategies for recognizing objects in clutter may differ depending on whether or not the object was learned in clutter to begin with. We tested this hypothesis using functional magnetic resonance imaging (fMRI) of human subjects. We trained subjects to recognize naturalistic, yet novel objects in strong or weak clutter. We then tested subjects' recognition performance for both sets of objects in strong clutter. We found many brain regions that were differentially responsive to objects during object recognition depending on whether they were learned in strong or weak clutter. In particular, the responses of the left fusiform gyrus (FG) reliably reflected, on a trial-to-trial basis, subjects' object recognition performance for objects learned in the presence of strong clutter. These results indicate that the visual system does not use a single, general-purpose mechanism to cope with clutter. Instead, there are two distinct spatial patterns of activation whose responses are attributable not to the visual context in which the objects were seen, but to the context in which the objects were learned.
Highlights
The visual system has a remarkable ability to recognize an object, despite the fact that we rarely see the same view of it twice (Figure 1A)
Our experiment essentially consisted of training the subjects off-scanner under conditions of strong or weak clutter depending on the object, and scanning the Blood oxygenation level-dependent (BOLD) responses to all objects presented under the same condition, i.e., of strong clutter (Figure 2D; Materials and Methods for details)
The clutter designations refer to the level of clutter in which a given object was seen during the training phase, and not to the level of clutter in which it was seen during the testing phase
Summary
The visual system has a remarkable ability to recognize an object, despite the fact that we rarely see the same view of it twice (Figure 1A). This ability rests on incompletely understood brain mechanisms that discount sources of variation in the images of an object and background. Discounting is necessary because images of a single object will vary due to changes in viewpoint, lighting, material reflectance, occlusion, articulation, and background (Kersten et al, 2004)
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