Double Fusion Does Not Occur in Panum's Limiting Case: Evidence from Orientation Disparity

Abstract

When two lines of different orientations are combined in regular stereograms, the orientation of the resulting line is different from those of the monocular lines. In this study we investigate the percept elicited by orientation disparity in Panum's limiting case. A variant of Panum's limiting case was designed to include orientation disparity. The single line in one half-image tilted leftwards. One of the double lines in the other half-image was parallel to the single line, while the other one tilted rightwards with obliquity one third that of the single line. In this stimulus configuration, if the single line in one half-image fuses with both lines in the other half-image at the same time, both of the two lines perceived after fusion should tilt leftwards. If double fusion does not happen, the two lines should tilt leftwards and rightwards respectively. The results of this study are in agreement with the latter prediction, which implies that double fusion does not occur in this variant of Panum's limiting case.

The matching rule of Panum’s limiting case and its influencing factors

“…Previous studies have disputed the depth mechanism in Panum's limiting case (Mckee et al, 1995;Gillam and Nakayama, 1999;Frisby, 2001;Wang et al, 2001;Howard and Rogers, 2012). In the present study, we revealed the matching rule of Panum's limiting case resulted from fast alternative matching, and the position of fixation could influence the matching results.…”

“…It should be noted that if the presentation time of the stimulus is limited and the position of fixation is fixed during the presentation of the stimulus, the speed of fast alternative matching between features in different eyes would be slowed down. In this case, participants could perceive the order of fast alternative matching and be able to correctly report the perceptual results (Frisby, 2001;Wang et al, 2001). However, if the presentation time of the stimulus is unlimited and the position of fixation is not fixed, the speed of fast alternative matching between features in different eyes would be too fast for the participant to be aware of the order of the fast alternative matching.…”

“…In real scenes, if two opaque objects in different positions in front and behind are both at the same level as the sight line of one of the observer's eyes, then the eye can only see one object between objects due to occlusion and the other eye can see two objects (Gettys and Harker, 1967). After binocular fusion, the observer can perceive two objects with depth (Nakayama and Shimojo, 1990;Nakamizo et al, 1994;Wang et al, 2001;Tsirlin et al, 2012;DöVencioğlu et al, 2013). For the past few decades, although Panum's limiting case has attracted a great deal of attention, the matching rule of corresponding features in Panum's limiting case still needs to be further illustrated (Anderson, 1994;Shimono et al, 1999;Frisby, 2001;Wang et al, 2001;Gillam et al, 2003;Cook and Gillam, 2004;Li et al, 2017).…”

“…After binocular fusion, the observer can perceive two objects with depth (Nakayama and Shimojo, 1990;Nakamizo et al, 1994;Wang et al, 2001;Tsirlin et al, 2012;DöVencioğlu et al, 2013). For the past few decades, although Panum's limiting case has attracted a great deal of attention, the matching rule of corresponding features in Panum's limiting case still needs to be further illustrated (Anderson, 1994;Shimono et al, 1999;Frisby, 2001;Wang et al, 2001;Gillam et al, 2003;Cook and Gillam, 2004;Li et al, 2017).…”

Last but Not Least

“…Limited understanding of Panum's limiting case Wang et al's (2001) report in this issue is an elegant and careful study of a variant of Panum's limiting case (PLC) which leads them to conclude that double fusion does not occur in that particular PLC configuration. Their study prompts me to present a demonstration, and some variants of it, that I have used in teaching for many years.…”