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Jonas Kubilius, Daniel D. Dilks, Elizabeth S. Spelke, Nancy Kanwisher; Invariance to mirror image reversals in the Lateral Occipital Complex (LOC) and Parahippocampal Place Area (PPA). Journal of Vision 2009;9(8):968. doi: 10.1167/9.8.968.
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Electrophysiological and behavioral studies in many species (e.g., octopus, pigeon, monkey, and human) have demonstrated mirror-image confusion for objects, perhaps because left/right information is rarely important in object recognition (e.g., a cup is the same cup when seen in left or right profile). However, unlike object recognition, scene recognition and navigation crucially require left/right information; the identity and navigability of a scene are completely different when it is mirror reversed. Thus, we predicted that object representations in object-selective cortex would be invariant to left/right reversals, but scene representations in the scene-selective cortex would not be. To test for such left/right information encoding, we ran an event-related fMRI adaptation experiment. In each trial, we successively presented images of either two objects or two scenes; each pair of images was: 1) the same image (presented twice); 2) two completely different images; or 3) a scene or an object, followed by the mirror-reversed version of the same stimulus. Consistent with our prediction, preliminary results showed partial invariance to the mirror reversals in the object-selective lateral occipital cortex (LOC), to a greater extent in its anterior subregion (posterior fusiform gyrus, pFs) than its posterior subregion (LO). However, contrary to our prediction, we also found invariance to left/right orientation for scenes in the parahippocampal place area (PPA). These findings pose a challenge to hypotheses of the PPA's role in scene recognition, navigation, and reorientation.
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