Coarse to fine dynamics of monocular and binocular processing in human pattern vision.

Biological image processing has been hypothesized to adopt a coarse to fine strategy: the image is initially analyzed at a coarse spatial scale, and this analysis is then used to guide subsequent inspection at a finer scale. Neurons in visual cortex often display response characteristics that are consistent with this hypothesis for both monocular and binocular signals. Puzzlingly, measurements in human observers have failed to expose similar coarse to fine dynamics for human pattern vision, questioning the applicability of direct parallels between single neurons and perception. We performed a series of measurements using experimental protocols that were specifically designed to examine this question in more detail. We were able to confirm that, when the analysis is restricted to the linear properties of the perceptual process, no coarse to fine dynamics were evident in the data. However, when the analysis was extended to nonlinear descriptors, a clear coarse to fine structure emerged that consisted of two processes: an early nonlinear process operating on a coarse spatial scale followed by a linear process operating on a fine spatial scale. These results potentially serve to reduce the gap between the electrophysiological and behavioral findings.