The goal of this research is to understand how we see what we see: how does the brain analyze the light falling on the retina of the eye to encode a world full of objects, people and things? During the past year we have continued to focus on the effect of position changes on visual object recognition. It is typically assumed that visual object recognition is independent of position in the visual field, that our ability to recognize an object is unaffected by changes in the position of that object. Indeed, some models of object recognition propose that the brain produces an abstract visual representation of an object that is independent of its specific position or size, for example, which is then available to interact with semantic or conceptual knowledge. In a series of behavioral experiments we have now shown that small changes in position do in fact have a large impact on object recognition. These results suggest that the visual system does not contain completely abstract representations of objects. However, to confirm these findings we have now completed a functional magnetic resonance imaging (fMRI) study to determine the effect of position changes on the activity elicited in regions of the brain thought critical for object recognition. In agreement with the behavioral results, we found that the patterns of activity elicited by viewing objects were specific to the position in which those objects were presented. These findings provide important insights into object recognition in the brain and suggest that current models of cortical visual processing do not accurately reflect the underlying mechanisms. We are also completing a study investigating how we recognize different body parts (our own and others). Previous fMRI studies have identified a region of the brain that responds more when people view body parts (e.g. legs, arms, feet) than when they view objects (e.g. chair, car, hammer). Although it has been suggested that this brain region may be important for our ability to recognize bodies, no study has shown that this region contains information about different body parts. In an fMRI experiment, we are investigating brain activity in this brain region while participants view images of different body parts in different positions in the visual field, taken from perspectives corresponding either to a view of their own body or to a view of someone elses body. We find that this body-selective region of the brain contains information about individual body parts (e.g. hand, arm) including where that body part is in space, and from which side of the body. These results suggest that the body-selective region of the visual cortex contains very specific representations of the body. Elucidating how the brain enables us to recognize objects, faces and bodies provides important insights into the nature of our internal representations of the world around us. Understanding these representations is vital in trying to determine the underlying deficits in many mental health disorders.
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