ABSTRACT

This chapter explores the spatial characteristics of the Straddle Effect in order to elaborate on its hypothesized explanation, the contrast-comparison process. It looks at regions of the visual field occupied by spatial texture or forms or patterns. The chapter shows that when the spatial characteristics of the adapt and test patterns were identical, there was always a Straddle Effect. But when the adapt and test patterns differed in orientation, phase, or position, the Straddle Effect was much diminished. This diminishing was not because performance on the Straddle test patterns improved. In the long ages of evolution, eyes occasionally saw a blank, unchanging part of the visual field, for example, a large region of blue sky. A change that produces a ringing output is easy to detect in any number of ways, but it is hard to know the direction of change because that requires knowing whether the first excursion was up or down.