Abstract
Incompatible patterns viewed by each of the two eyes can provoke binocular rivalry, a competition of perception. Levelt’s first law predicts that a highly visible stimulus will predominate over a less visible stimulus during binocular rivalry. In a behavioural study, we made a counterintuitive observation: high visibility patterns do not always predominate over low visibility patterns. Our results show that none of Levelt’s binocular rivalry laws hold when luminance-modulated (LM) patterns compete with contrast-modulated (CM) patterns. We discuss visual saliency, asymmetric feedback, and a combination of both as potential mechanisms to explain the CM versus LM findings. Competing orthogonal LM stimuli do follow Levelt’s laws, whereas only the first two laws hold for competing CM stimuli. The current results provide strong psychophysical evidence for the existence of separate processing stages for LM and CM stimuli.
Highlights
Binocular rivalry, generated by presenting incompatible stimuli separately to each eye, is a powerful tool to investigate visual perception as it can evoke alternating perception over time without any changes to the physical environment[1,2,3]
The visibility levels for CM gratings are relatively low, we suggest in the discussion, why it is unlikely that the fourth law would hold even if hypothetically higher visibility levels could be tested for CM vs. CM gratings
Our previous results reveal the presence of very few exclusive percepts and predominantly superimposition during binocular rivalry between competing orthogonal CM gratings, which support this idea as well[9,10]
Summary
Binocular rivalry, generated by presenting incompatible stimuli separately to each eye, is a powerful tool to investigate visual perception as it can evoke alternating perception over time without any changes to the physical environment[1,2,3]. The reader may experience binocular rivalry by looking at the gratings in Fig. 1A held at a distance of approximately 40 cm. Classical laws of binocular rivalry predict that the vertical grating of high visibility will predominate perception. This relationship between stimulus visibility and perception during binocular rivalry is described by Levelt’s first law[2,4]. Levelt’s four laws are based upon findings when the competing patterns were defined by variations in luminance. The first, second, and third laws as stated above describe the effects of varying interocular differences in stimulus strength, for example by changing the contrast of one stimulus, whereas the fourth law describes the impact of binocular stimulus strength variations. Correspondence and requests for materials should be addressed to J.S. (email: jan.skerswetat@ anglia.ac.uk) www.nature.com/scientificreports/
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