Preferential responses to occluded objects in the human visual cortex Department of Psychology, University of Minnesota, Minneapolis, MN, USA Jay Hegdé Department of Psychology, Peking University, Beijing, China Fang Fang Department of Psychology, University of Minnesota, Minneapolis, MN, USA,& Department of Psychology, University of Washington, Seattle, WA, USA Scott O. Murray Department of Psychology, University of Minnesota, Minneapolis, MN, USA Daniel Kersten How do we see an object when it is partially obstructed from view? The neural mechanisms of this intriguing process are unclear, in part because studies of visual object perception heretofore have largely used stimuli of individual objects, such as faces or common inanimate objects, each presented alone. But in natural images, visual objects are typically occluded by other objects. Computational studies indicate that the perception of an occluded object requires processes that are substantially different from those for an unoccluded object in plain view. We studied the neural substrates of the perception of occluded objects using functional magnetic resonance imaging (fMRI) of human subjects viewing stimuli that were designed to elicit or not elicit the percept of an occluded object but were physically very similar. We hypothesized the regions that are selective for occluded objects, if they exist, will be differentially active during the two conditions. We found two regions, one in the ventral object processing pathway and another in the dorsal object processing pathway, that were significantly responsive to occluded objects. More importantly, both regions were significantly more responsive to occluded objects than to unoccluded objects, and this enhanced response was not attributable to low-level differences in the stimuli, amodal completion per se, or the behavioral task. Our results identify regions in the visual cortex that are preferentially responsive to occluded objects relative to other stimuli tested and indicate that these regions are likely to play an important role in the perception of occluded objects. Keywords: amodal completion, explaining away, object recognition, perceptual filling-in, scene understanding Citation: Hegdé, J., Fang, F., Murray, S. O., & Kersten, D. (2008). Preferential responses to occluded objects in the human visual cortex. Journal of Vision, 8(4):16, 1–16, http://journalofvision.org/8/4/16/, doi:10.1167/8.4.16. Introduction The neural mechanisms by which we perceive visual objects have long been a mystery. But recently, great strides have been made in understanding the neural mechanisms of visual object perception (see Grill-Spector & Malach, 2004). Human functional magnetic resonance imaging (fMRI) studies have revealed numerous regions of the extrastriate cortex, the part of the visual cortex involved in the higher order processing of image information. Many of the extrastriate regions are thought to be selective for various object categories. For instance, the human temporal cortex is known to contain regions selectively responsive to faces, body parts, inanimate objects, and other object categories (Grill-Spector, Knouf, & Kanwisher, 2004; Grill-Spector, Kourtzi, & Kanwisher, 2001). So far, neural mechanisms of visual object perception have been studied mainly using individual visual objects presented alone (e.g., a face, or a hammer, by itself in the absence of occlusion or background clutter). However, visual objects rarely occur in isolation in natural visual scenes. For one thing, it is common for one object to obstruct, or occlude, another in natural images. Therefore, understanding how we see occluded objects is critical to understanding how we see under natural viewing conditions. The mechanisms by which we perceive occluded objects remain poorly understood, although many studies have used stimuli that featured occluded objects (Fang & He, 2005; Lerner, Hendler, & Malach, 2002; Murray, Kersten, Olshausen, Schrater, & Woods, 2002; Olson, Gatenby, Leung, Skudlarski, & Gore, 2004; also see Discussion). One previous study that directly addressed this issue, Lerner et al. (2002), found that the responses to Journal of Vision (2008) 8(4):16, 1–16 http://journalofvision.org/8/4/16/ 1 doi: 10.1167/8.4.16 Received October 22, 2006; published April 22, 2008 ISSN 1534-7362 * ARVO