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Tim Preston, Fei Guo, Barry Giesbrecht, Miguel Eckstein; Contextual location information relevant to visual search in natural scenes is encoded in extrastriate visual cortex and the anterior intraparietal sulcus. Journal of Vision 2011;11(11):819. doi: 10.1167/11.11.819.
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Humans are highly adept at detecting objects within natural scenes taking advantage of contextual cues to increase detection and recognition performance (Oliva & Torralba, 2007). We show that both retinopically defined dorsal areas (V3d, V3A, V3B) and ventral functionally defined areas (LO, PPA) contain information able to accurately discriminate the location contextually relevant to a cued target object. Eleven observers viewed a series of natural images and determined whether a cued object was present whilst whole brain fMRI data was recorded. Trial durations were 4.86 seconds with an initial 400 ms presentation of the cue word followed by a 250 ms ISI and stimulus presentation of 250 ms. Stimuli consisted of natural scenes (640 images, 17.5° square) with targets present in 50% of the images. Critically, target absent images were selected so that a single expected location (left/right lateralized) was contextually consistent with the cued target word. Experimental runs consisted of 16 presentations of each condition with observers completing 10 runs. We used multivariate pattern analysis to assess the accuracy of discriminating the location contextually relevant to the cue word. Only object absent scenes were used to isolate effects of context from that of the target objects. Accuracy for all regions-of-interest was greater than chance for identifying the location (left vs. right) contextually relevant to the cue. Accuracies were highest in dorsal areas V3d, V3B and the anterior intraparietal sulcus. In contrast, discrimination accuracy for the location (left vs. right) which contained the most salient object within the scene (determined independently [n = 100]) showed that only higher visual areas displayed significantly greater accuracy for context relative to saliency. Our results suggest that perceptual decisions utilizing contextual information for target location involve interactions between dorsal and ventrolateral visual areas containing task-relevant information and mediating parietal cortical areas governing attention.
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