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Binocular Rivalry Stimuli Are Common but Rivalry Is Not GENERAL COMMENTARY published: 24 November 2011 HUMAN NEUROSCIENCE doi: 10.3389/fnhum.2011.00148 Binocular rivalry stimuli are common but rivalry is not Robert Paul O’Shea* Discipline of Psychology and Cognitive Neuroscience Research Cluster, School of Health and Human Sciences, Southern Cross University, Coffs Harbour, Australia *Correspondence: [email protected] A commentary on There are two problems for Arnold with These arise for regions off the location in these sorts of examples: space where images would be identical in Why is binocular rivalry uncommon? the two eyes, the horopter (Aguilonius, 1613; Discrepant monocular images in the real 1. Although it is true that one will not Panum, 1858; Ogle, 1953). Binocular rivalry world immediately experience alternations could be common off the horopter – it is Arnold, D. H. (2011). Front. Hum. Neurosci. between the blurry and sharp images, simply not noticed. 5:116. doi: 10.3389/fnhum.2011.00116 it is not true that there is no rivalry. In both situations Arnold describes, the Rather, the sharp images’ dominating tendency is for one to look at the nearby Recently Arnold (2011) asked “Why is bin- perception is a form of rivalry, well- object (Mandelbaum, 1960), bringing iden- ocular rivalry uncommon?”. He answered known from laboratory studies as per- tical sharp images onto the foveae. What is in an entertainingly written, provocative manent suppression (Ooi and Loop, needed to resolve the issue of the ecological article, for which I thank and congratulate 1994). optics of binocular vision, rather than exam- him. However, I will argue that Arnold’s 2. If one waits for long enough, the blurry ples, is for them to be quantified by sampling answer falls short in two respects and his image will alternate with the sharp ima- the images the real world presents (cf. Howe assumption that rivalry is uncommon is ges (cf. Blake, 1977). Indeed, George and Purves, 2002; Howe and Purves, 2005). correct for two reasons other than the one (1936) reported that the extremely low- Second, the eyes move about three times he discusses. stimulus-strength image of the back a second (e.g., Otero-Millan et al., 2008). Binocular rivalry is a phenomenon of of one’s closed eyelid will eventually This potentially places fresh images on human visual perception that is easy to dominate the extremely high-stimulus- each retinal region at the same rate. In the demonstrate in the laboratory by using a strength images viewed by the open eye. laboratory, these are likely to be similar to stereoscope to present one image to one eye the previous images (because rival stimuli and a different image to the other: one per- There are at least two reasons other than tend to be two-dimensional stimuli that ceives one image rather than both, and the that Arnold offered for why rivalry is not display rivalry information wherever we image one perceives alternates between the noticed outside the laboratory: look at them). But outside the laboratory, two at random (Wheatstone, 1838). First, although Arnold is correct that these images could be quite different dur- In answering the question, Arnold images of equal stimulus strength rarely fall ing each fixation, and may be identical (2011) identified two situations outside on the foveae of the two eyes, it is common for some corresponding retinal regions. the laboratory in which the view of one that images of equal stimulus strength fall on That is, any pair of corresponding reti- eye differs from that of the other for which corresponding peripheral areas of the reti- nal regions might have rival images for he claimed there is no rivalry. The first is nae. For example, as I type this on my laptop, one fixation and similar, fusible images when an object, such as the trunk of a small images of the rest of the room, several meters for the next. We know from laboratory tree, is near both eyes as we fixate on distant further from my eyes than the laptop screen, research that turning on rival images objects. The trunk projects a blurry, low- fall on the retinae below the fovea. When I briefly and turning them off for longer contrast, low-spatial-frequency (for which attend to these areas, I can see that there are prevents rivalry from occurring by creat- Arnold adopted Levelt’s, 1968, umbrella burry, diplopic images there, for example the ing fusion of the two eyes’ views (Dawson, term “stimulus strength”) image onto the vertical edge of a fireplace appears superim- 1915–1917; Kaufman, 1963; Wolfe, 1983; temporal region of the right-eye retina and posed on the horizontal edges of the bricks O’Shea and Crassini, 1984). Moreover, onto the nasal region of the left-eye retina. of the fireplace. Similarly, when I look up interspersing periods of fusion with peri- In the corresponding regions of the other at the fireplace, I can see the blurry vertical ods of rivalry tends to prevent rivalry by eye’s retina, the distant objects project dif- edge of my laptop screen crossing the blurry promoting fusion (Julesz and Tyler, 1976; ferent, sharp images. The second is when a horizontal edge of a nearby table. If I pay Buckthought et al., 2008). similar object, the tree trunk again, is closer attention to these diplopic areas, I see slow In conclusion, Arnold (2011) posed to one eye, blocking its view. The trunk pro- alternations of binocular rivalry. Laboratory an interesting question of why we do not jects a blurry image onto the fovea of that studies show that rivalry rate in peripheral notice rivalry when we look at the visual eye, and the distant objects project different, vision is much slower than in central vision world outside the laboratory. In answering sharp images onto the fovea of the other (e.g., Blake et al., 1992). it, he identified two situations in which dif- eye. In both these situations, Arnold said the The ubiquity of diplopic images away ferent strength images are projected into the sharp images dominate perception forever, from fixation was discovered by al-Haytham two eyes, and claimed that rivalry does not preventing rivalry. in the eleventh century (Alhazen, 1989). occur. I have argued, to the contrary, that: Frontiers in Human Neuroscience www.frontiersin.org November 2011 | Volume 5 | Article 148 | 1 O’Shea Why binocular rivalry is uncommon • Perception in the situations Arnold world. Front. Hum. Neurosci. 5:116. doi: 10.3389/ Ooi, T. L., and Loop, M. S. (1994). Visual suppression and identified is consistent with what we fnhum.2011.00116 its effect upon color and luminance sensitivity. Vision Blake, R. (1977). Threshold conditions for binocular Res. 34, 2997–3003. know about rivalry and offers no chal- rivalry. J. Exp. Psychol. Hum. Percept. Perform. 3, O’Shea, R. P., and Crassini, B. (1984). Binocular rivalry lenge to theory; 251–257. occurs without simultaneous presentation of rival • Different images in the two eyes are Blake, R., O’Shea, R. P., and Mueller, T. J. (1992). Spatial stimuli. Percept. Psychophys. 36, 266–276. much more common in peripheral zones of binocular rivalry in central and peripheral Otero-Millan, J., Troncoso, X. G., Macknik, S. L., Serrano- regions of the retinae than in central vision. Vis. Neurosci. 8, 469–478. Pedraza, I., and Martinez-Conde, S. (2008). Saccades Buckthought, A., Kim, J., and Wilson, H. R. (2008). and microsaccades during visual fixation, explora- vision; Hysteresis effects in stereopsis and binocular rivalry. tion, and search: foundations for a common sac- • We do not notice potential rivalry in Vision Res. 48, 819–830. cadic generator. J. Vis. 8, 1–18. http://journalofvision. peripheral vision because it is slower Dawson, S. (1915–1917). The experimental study org/8/14/21/ than in central vision and anyway we of binocular colour mixture. Br. J. Psychol. 8, Panum, P. L. (1858). Über die einheitliche Verschmelzung do not attend to it; and 510–551. verschiedenartiger Netzhauteindrucke beim Sehen mit George, R. W. (1936). The significance of the fluctuation zwei Augen. Kiel. • Movement of the eyes prevents rivalry experienced in observing ambiguous figures and in Wheatstone, C. (1838). Contributions to the physiol- from developing. binocular rivalry. J. Gen. Psychol. 15, 39–61. ogy of vision – Part the First. On some remarkable, Howe, C. Q., and Purves, D. (2002). Range image statistics and hitherto unobserved, phenomena of binocular ACKNOWLEDGMENTS can explain the anomalous perception of length. Proc. vision. Philos. Trans. R. Soc. Lond. B Biol. Sci. 128, I am grateful to Urte Roeber for commenting Natl. Acad. Sci. U.S.A. 99, 13184–13188. 371–394. Howe, C. Q., and Purves, D. (2005). Natural-scene geom- Wolfe, J. M. (1983). Influence of spatial frequency, lumi- helpfully on earlier version of this paper and etry predicts the perception of angles and line orien- nance and duration on binocular rivalry and abnor- to Derek Arnold for helpful discussion and tation. Proc. Natl. Acad. Sci. U.S.A. 102, 1228–1233. mal fusion of briefly presented dichoptic stimuli. for sharing a draft of his reply to this paper. Julesz, B., and Tyler, C. W. (1976). Neurontropy, an Perception 12, 447–456. entropy-like measure of neural correlation, in bin- ocular fusion and rivalry. Biol. Cybern. 23, 25–32. Received: 07 November 2011; accepted: 08 November 2011; REFERENCES Kaufman, L. (1963). On the spread of suppression and published online: 24 November 2011. Aguilonius, F. (1613). Opticorum libri sex. binocular rivalry. Vision Res. 3, 401–415. Citation: O’Shea RP (2011) Binocular rivalry stimuli are Philosophis juxta ac mathematicis utiles. Antwerp: Levelt, W. J. M. (1968). On Binocular Rivalry. The Hague: common but rivalry is not.
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