A study of hysteresis in human binocular fusional ranges had been performed in order to clarify the nature of the extension of Panum's Fusional Area as demonstrated by Derek Fender and Bela Julesz (1967). Using binocular retinally stabilized images, a stimulus regime was designed to determine the size and location of Panum's Fusional Area at any given stimulus condition. This regime was employed to measure Panum's fusional area in the non-extended and in the extended conditions. The following three results were obtained. 1. The nasalward limits of Panum's fusional area and the hysteresis demonstrated by the nasalward limits do not differ significantly from the temporalward limits of Panum's fusional area and the hysteresis demonstrated by the temporalward limits. 2. A non-transient (continually presented) stimulus will fuse over a significantly wider range with a transient (flashed) stimulus than with another non-transient stimulus. Furthermore, the range of fusion for the transient stimulus is dependent upon the non-transient stimuli that are present immediately before the transient stimulus is presented. 3. The extension of Panum's fusional area, as effected by the stimulus regime of this thesis, not only includes the recruitment of retinal locations into Panum's fusional area which are not normally in Panum's fusional area, but also includes the loss from Panum's fusional area of certain retinal locations which are normally within Panum's fusional area. For all subjects, Panum's fusional area is shifted significantly. For some subjects, Panum's fusional area is stretched significantly. In some situations, the "zero disparity" retinal location may be lost from, and therefore not included within, Panum's fusional area. A new definition of "corresponding retinal points" is developed from the results of this thesis.
Daniel Bruce Diner (Wed,) studied this question.