Neural correlates of boundary extension during visual imagination

People typically remember seeing a greater expanse of a scene than was visible in a studied close-up (boundary extension, BE). Multivoxel pattern analysis was used to test the neural correlates of BE. Classifiers were trained using a whole-brain searchlight method to discriminate between close-up and wider-angle versions of 16 scenes during repeated perceptual exposures. Earlier, each subject studied either the close or wide version of each scene and then visually imagined it from memory. If a brain region reflects BE, then unlike classification during perception, visual images of close views should sometimes be misclassified as wide (capturing false memory beyond the view), whereas visual images of wide views should be correctly classified. BE-consistent patterns during imagery were found in high-level visual regions, including posterior superior parietal cortex. This pattern did not reflect a brain-wide bias toward better classification of wider-angle views: the pattern reversed (better classification of close views) in the early visual cortex, presenting a novel distinction between early and late visual representations in imagery. We propose that this method reflects active maintenance of boundary-extended scene representations in memory and that it holds promise as a general purpose tool for decoding false memory in the brain.