Scanning from coarse to fine spatial scales in the human visual system after the onset of a stimulus.

The manner in which the spatial characteristics of simple discrimination tasks change with time after the onset of a stimulus were examined. The experiments measured the improvements in sensitivity to the length, orientation, curvature, and stereoscopic depth of short lines that accrue with increased exposure durations. These improvements can be consistently interpreted in terms of a change of the spatial scale of analysis from coarse to fine over a period of at least 1000 msec. Variations in visual resolution acuity over the same period are negligible, and it is concluded that the changes in spatial characteristics concern the range of spatial filters in operation. This range progressively shrinks after stimulus presentation.