UC Berkeley

Despite decades of research, significant mysteries remain concerning two

fundamental aspects of human visual processing: how we perceive moderately complex line shapes such as letters of the alphabet, and how peripheral vision differs from foveal vision. This dissertation comprises studies that address both these topics, using experiments with letter recognition and visual "crowding"--the deleterious influence of flanking objects on identification of a target.

Letters are well-studied psychophysical stimuli that strike a balance between degenerate patterns such as Gabor patches or gratings, with more uncontrolled stimuli such as natural images. Letters contain distinct spatial features that are more straightforward to quantify than the characteristics of natural scenes, yet have a sufficient richness of information to probe the general-purpose mechanisms of object recognition.

The last decade has seen a renewed interest in perception in the peripheral visual field, with a particular emphasis on the phenomenon of crowding. Many researchers acknowledge that this curious effect provides a unique window into the process of object recognition. Since there is such a marked difference between the periphery, where crowding is potent, and the fovea, where it is nearly absent, crowding sheds light on the dichotomy between visual processing in the high resolution fovea versus the information-limited periphery. Understanding crowding may illuminate general principles of biological visual processing.