Codes for visual shape perception and the contribution of depth information

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Visual shape perception is fundamental for effective interactions with our environment and to recognize objects. This proposal is part of our ongoing long-term project of uncovering how the human visual system processes and represents shape information. Our previous studies have shown that two representation formats (or codes) are involved in the perception of simple shapes. One is based on global shape features such as aspect ratio, curvature, or symmetry. Another is based on the visible surfaces of the object that are delimited by its edges. Two main goals of this proposal concern these codes. Specifically, we wish to establish, for a variety of global shape properties, whether their representation is invariant to depth rotations and if so, what is the depth information required to support this invariance. Regarding the surface code, the proposed experiments will examine to what degree it is distinct from a representation of shape that exclusively rests on its edges, and whether it is invariant to rotations on the picture plane and in depth. A third main goal of this proposal is to explore the perception and representation of complex objects; i.e. those that can be segmented in two or more parts. Our previous investigation of complex objects has shown that their perception involves two separate mechanisms, one concerned with the shape of parts and another with their spatial arrangement, or configuration. We now propose to examine whether the representation of parts in complex objects uses the same global feature and surface codes we have demonstrated for simple objects. We will also examine the perception of the configuration of complex objects. Specifically, we will examine the properties of objects that make the perception of configuration more or less difficult as well as the factors that affect our capacity to discriminate objects on their configuration.