The brain must interpret an incoming visual signal in order to form a perception of the outside world. The most obvious step in this interpretation -- the translation from light into a neuronal code -- occurs in the retina, with each subsequent stage of visual processing providing a further refinement of this visual signal. In general, this processing cascade leads to a perception of the world that would seem to be an adequate representation of the original image. However, it is not uncommon for the brain to misrepresent the image that is presented to the eyes, often resulting in what is known as a visual illusion. Even beyond well-known illusions, many studies have shown that much of normal vision is in fact based on an inaccurate and/or inadequate representation of the physical stimulus presented to the eyes. Studies of the manner in which the brain misrepresents the visual scene will lead to a greater understanding of the way in which we see. The proposed research was designed to determine whether the neuronal activity in different brain areas corresponds better to the physical stimulus presented to the eyes, or the subject's perception of this image. For this purpose, our investigations will focus primarily on a region of the brain that has been shown to respond specifically to the visual image of a face. The functional specificity of this region will allow us to contrast its activation under conditions in which face and/or non-face images are presented but may not be perceived as such. In each experiment, the superior temporal and spatial resolution of high field (4 Tesla) functional magnetic resonance imaging will allow us to compare the time course of brain activity with the behavioral measures of visual perception in individual subjects. The results of these experiments will allow us to better understand the processing cascade that leads to visual perception.
