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Chris Paffen, Ryota Kanai; Numbers with higher magnitude have higher perceptual strength during binocular rivalry. Journal of Vision 2009;9(8):287. doi: 10.1167/9.8.287.
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© ARVO (1962-2015); The Authors (2016-present)
It has been suggested that human number processing is part of a common cortical system of magnitude processing (Walsh, 2003). According to this idea, the visual system should recruit the same processing structures when confronted with stimuli of different contrast or luminance, as when confronted with numerical information.
In the current study we use a perceptual phenomenon known to reveal abstract magnitude processing properties of low-level features such as contrast and luminance. During binocular rivalry, perception alternates between dissimilar images presented dichoptically. Of particular interest here is the fact that increasing the contrast (or luminance) of only one of the dissimilar images will increase its perceptual dominance. We hypothesize that if numbers are processed by a common mechanism for magnitude processing, numbers of different magnitude should conform lawfully to this contrast-rule of binocular rivalry.
We presented images of the numbers 2, 4, 6 or 8 to one eye, while presenting a meaningless shape (#) to the other eye. Observers continuously indicated which of the two (the number or the #) was dominant in perception during trials lasting one minute. Importantly, the images used were spatially filtered such that there were no differences in contrast and Fourier-energy.
The results of our study reveal that numbers conform lawfully to the contrast-rule: increasing the magnitude of a digit increased its predominance. Control experiments ruled out the possibility that low-level images features not related to the magnitude of a number were responsible for this result. We conclude that the processing of numbers shares at least some processing structures involved in the analysis of magnitude.
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