While we live in and interact with a complex three dimensional world, our visual system only obtains a simplified two dimensional representation of that world. The goal of visual perception, quite possibly our most important sense, is to compute an accurate three dimensional interpretation of the world from such two dimensional images. Somewhat surprisingly, the recognition of objects from their projected images is a particularly difficult task since most images are consistent with an infinite number of interpretations. The proposed experiments will examine how observers uniquely interpret such inherently ambiguous visual images. It will be argued that image interpretation occurs through a process of constraint satisfaction. Constraints are rules derived from prior knowledge or assumptions about the world. Image interpretations inconsistent with any constraint are rejected. Given the visual system's hierarchical structure, different constraints must be utilized at different levels of analysis. To fully comprehend constraint satisfaction in image interpretation, one must study the interaction between different constraints within and across different levels of analysis. At the lowest level, the visual system must overcome the motion measurement ambiguity known as the aperture problem. Proposed psychophysical studies will examine the constraints used by humans to interpret motion locally. The visual system must then combine motion signals across different locations. To understand this process, observers will interpret stimuli viewed through multiple apertures. Higher level or more cognitive constraints will be studied through examinations of path choice in apparent motion. Taken together, these results will provide a unified understanding of visual image interpretation as well as significant insight into how the brain surmounts the inherent ambiguity of sensory information. The central problem with many visual disabilities is the increased ambiguity of the visual signal. Results from the above studies will provide important implications for how the brain normally overcomes ambiguity and therefore how one might best understand and treat increased ambiguities resulting from diseased or damaged sensory systems.
