User:Eugene M. Izhikevich/Proposed/Monocular rivalry
Dr. Robert O'Shea accepted the invitation on 9 September 2008 (self-imposed deadline: 9 March 2009).
This article is based on one I and others wrote for Wikipedia (see http://en.wikipedia.org/wiki/Monocular_rivalry). Figure 1 also comes from that Wikipedia article.
Monocular rivalry is a phenomenon of human visual perception that occurs when two different images are optically superimposed. During prolonged viewing, one image becomes clearer than the other for a few moments, then the other image becomes clearer than the first for a few moments. These alternations in clarity continue at random for as long as one looks. Occasionally one image will become exclusively visible and the other image invisible.
In Figure 1, one image is a set of blurry green lines, a green grating, and the other is a red grating. To experience monocular rivalry, one must look steadily at one point of the figure. It might take 10, or 20, or even 30 seconds before one will see anything other than a plaid, but eventually one grating will appear to be clearer than the other for a second or so. It might appear clearer by appearing as if superimposed above the other or by appearing to have higher contrast than the other. Then its clarity will wane and the other will appear clearer than the first. Occasionally one grating will be all that is visible and occasionally the other grating will be all that is visible. Sometimes, at transitions, one will briefly see irregular composites of the two gratings (such as the red and green gratings superimposed but with one or two bars of the green grating invisible).
Theories of monocular rivalry fall into two broad classes. Some researchers argue that monocular rivalry is explained by similar mechanisms underlying binocular rivalry or other multistable phenomena. Others argue that monocular rivalry is an epiphenomenon of eye movements and afterimages, involving adaptation. It is likely that both theories are correct: monocular rivalry shows both high-level, multistability properties and low-level, adaptation properties.
History of monocular rivalry
According to Tong (2001) monocular rivalry was discovered by Helmholtz (1866/1924). It was independently discovered, and named, by Breese (1899). He used images similar to those in Figure 1:
Rivalry of colors was perceptible. Neither disappeared entirely: but at times the red would appear very distinctly while the green would fade; then the red would fade and the green appear distinctly. The two sets of lines showed the same fluctuation, keeping pace with the changing of the intensities of the colors. Sometimes one of them would disappear altogether. This rivalry of the color and of the lines was much slower than the rivalry in binocular vision. (p. 43)
Breese called the phenomenon monocular rivalry to distinguish it from binocular rivalry, a similar phenomenon in which the different images are presented to opposite eyes. McDougall (1906) discovered monocular rivalry of afterimages but neither called it that nor connected it with Breese's work. This neglect of monocular rivalry continued until it was independently rediscovered by Sindermann and Lüddeke (1972) and by Campbell and Howell (1972). Campbell and Howell called the phenomenon monocular pattern alternation, but Campbell called it monocular rivalry in later papers, and that is the term that has stuck, even though the phenomenon does not require monocular viewing. Maier, Logothetis, and Leopold (2005) have started calling the phenomenon pattern rivalry.
Attention on monocular rivalry again waned for more than a decade after Georgeson and Phillips (1980) argued it was an epiphenomenon of eye movements and afterimages (see below). But it revived after Andrews and Purves (1997) showed that monocular-rivalry alternations could synchronize with binocular-rivalry alternations in an adjacent part of the visual field.
Theories of monocular rivalry
Breese (1899) proposed that monocular rivalry is mediated by the same mechanisms that mediate binocular rivalry. According to Breese, these involve inhibition, attention, satiation, and fatigue. A similar theory was adopted by those researching monocular rivalry in the 1970s and after the 1990s. For example, O'Shea (1998) proposed that identical neural elements are involved in the two phenomena. In the case of binocular rivalry, presenting vertical contours to one eye and horizontal contours to the other weakly stimulates two sets of binocular cells--ones with vertical as their preferred orientation and others with horizontal as their preferred orientation. In the case of monocular rivalry, presenting vertical contours to one eye and horizontal contours to the same eye moderately stimulates the same two sets of binocular cells. For both phenomena, reciprocal inhibition between these two set of cells could yield dominance of one and suppression of the other; adaptation of the active set of cells could yield alternations.
Maier, Logothetis, and Leopold (2005) took the similarity between the monocular and binocular rivalry even further by proposing that they both represent the action of a general mechanism for resolving ambiguity. This tied both phenomena to other multistable phenomena, including reversible perspective figures such as the Necker cube and Rubin's face-vase figure.
Georgeson and Phillips (1980) on the other hand proposed that monocular rivalry arises from afterimages and eye movements. They argued that with gratings, prolonged fixation of the stimuli builds up a negative afterimage that will tend to cancel the real images, making both invisible (a form of neural adaptation). An eye movement at right angles to one grating of one half of the period of the grating will make the afterimage reinforce that original image, making it spring into visibility while the other grating remains invisible. A correct eye movement at right angles to the second grating will make it visible and leave the first invisible. Random eye movements, therefore, could be responsible for the random fluctuations in clarity and visibility of the two images.
Although afterimages and eye movements must contribute to monocular rivalry, they cannot be a complete explanation for at least four reasons: First, it occurs with stimuli other than gratings for which afterimages would not cancel or reinforce the original images (e.g., Sindermann & Lüddeke, 1972). Second, it occurs when the stimuli themselves are afterimages; these cannot be cancelled or reinforced by eye movements (Crassini & Broerse, 1982). Third, sometimes a perceptual alternation occurs after an eye movement in the wrong direction for Georgeson and Phillips's explanation (Bradley & Schor, 1988). Fourth, visibility of an irregular composite of the two images (e.g., Sindermann & Lüddeke, 1972) cannot be explained by eye movements. To be explained by cancellation of afterimages, such composites impossibly require that different parts of the retina move in different directions.
Recent developments in monocular rivalry
- Andrews and Purves (1997)
- van Ee et al.
- MR suppression depth
- MR between complex images
- Other hallmarks of BR shared by MR.
- Blind spot
- Filling in
- Motion-induced blindness
- Troxler's effect
Andrews, T. J., & Purves, D. (1997). Similarities in normal and binocularly rivalrous viewing. Proceedings of the National Academy of Sciences of the United States of America, 94, 9905-9908.
Bradley, A., & Schor, C. (1988). The role of eye movements and masking in monocular rivalry. Vision Research, 28, 1129-1137.
Breese, B. B. (1899). On inhibition. Psychological Monographs, 3, 1-65.
Campbell, F. W., & Howell, E. R. (1972). Monocular alternation: A method for the investigation of pattern vision. Journal of Physiology, 225, 19P-21P.
Crassini, B., & Broerse, J. (1982). Monocular rivalry occurs without eye movements. Vision Research, 22, 203-204.
Leopold, D. A., & Logothetis, N. K. (1999). Multistable phenomena: Changing views in perception. Trends in Cognitive Sciences, 3(7), 254-264.
Maier, A., Logothetis, N. K., & Leopold, D. A. (2005). Global competition dictates local suppression in pattern rivalry. Journal of Vision, 5, 668-677.
Sindermann, F., & Lüddeke, H. (1972). Monocular analogues to binocular contour rivalry. Vision Research, 12, 763-772.
Tong, F. (2001). Competing theories of binocular rivalry: A possible resolution. Brain and Mind, 2, 55-83.