Divergence thresholds as functions of temporal separation, spatial separation, and retinal locus

Human thresholds were measured for the detection of angular divergence between straight lines using pairs of line segments. The dependence of these thresholds on temporal separation between the two lines, spatial separation, and retinal locus was assessed. Results were comparable to prior divergence thresholds obtained by Harrington and Harrington in their study of "blur patterns." In blur patterns motion parameters may be processed partly or wholly as form information rather than as motion information per se. Harrington and Harrington had used moderate blurring velocities, for which information on both motion and form were present. Observers may have been responding either to motion or to form. The study reported here used briefly presented two-line "blur patterns" with only form information. Analysis suggested that the form components of fast motion-produced blur patterns could be processed by the human visual system. Neither temporal nor spatial separation was a significant determiner of thresholds in accordance with Harrington and Harrington who found no effect of blur-line density in the range studied. Retinal locus was a factor as it was with blur patterns. Some possible mechanisms for the detection of divergence indicated by these results are discussed.