Contrast Influences Predominance

Rivalry predominance is defined as the percentage of total viewing time that a given rival pattern is visually dominant. Predominance of a given rival pattern depends on its stimulus strength relative to that of the competing pattern. Stimulus strength is determined by stimulus variables such as contour density, spatial frequency, stimulus motion and pattern contrast (Levelt, 1965).

Using the pairs of rival targets below, you can experience how predominance varies with contrast. View each rival pair for about a minute, paying attention to how long -- on average -- a given pattern remains dominant. According to Fox and Rasche (197?), the average duration of dominance remains more or less constant regardless of target contrast whereas the average duration of suppression varies inversely with contrast. In other words, "weak" patterns tend to remain suppressed for longer durations than do "strong" patterns. This has the effect of increasing the overall predominance of a "strong" pattern.








Predominance of a rival pattern can also be influenced by the presence of neighboring visual features, particularly when those features together with the rival pattern form a coherent, global figure (Whittle et al, 1968; Kovacs et al, 1997; Alais & Blake, 1999). There is also evidence that predominance can be modulated by "top-down" influences including the emotional content of the rival patterns (e.g., Engel, 1956). This latter possibility deserves more careful examination.

Alais, D. and Blake, R.,1999: Grouping visual features during binocular rivalry, Vision Res. 39, 4341-4353.
Engel, E., 1956: The role of content in binocular resolution, Amer. J. Psychol. 69, 87-91.
Fox, R. and Rasche, F. 1969: Binocular rivalry and reciprocal inhibition, Percept. Psychophys. 5, 215-217.
Kovács, I., Papathomas, T.V., Yang, M. and Fehér, A. 1997: When the brain changes its mind, Interocular grouping during binocular rivalry, Proc. Natl. Acad. Sci. USA 93, 15508-15511.
Whittle, P., Bloor, D. and Pocock, S. 1968: Some experiments on figural effects in binocular rivalry, Percept. Psychophys. 4, 183- 188.