Laughter abolishes binocular rivalry

Binocular rivalry is an increasingly popular technique for the study of consciousness, which changes quasi-regularly during rivalry, despite the unchanging sensory stimuli presented to each eye. For example, if a small patch of horizontal stripes is presented constantly to the fovea of one eye and a small patch of vertical stripes is similarly presented constantly to the fovea of the other eye, most subjects experience an alternation between stimuli rather than a simultaneous mixed percept of both.

Binocular rivalry was induced, superimposed on normal viewing, using liquid crystal shutters and a short persistence monitor, which produced a one degree circular patch of horizontal gratings to the right eye and an identical patch of vertical gratings in the same location for the left eye. The subject signalled with key presses the three possible perceptual states that alternated with each other, namely horizontal, vertical and mixed percept (where horizontal and vertical were simultaneously visible).

The present study builds on an incidental observation that laughter stopped the rivalry alternations between horizontal and vertical and induced the mixed percept instead. A physical explanation for this effect was ruled out by using stabilised imagery in the form of retinal after-images of the rivalling gratings. Under conditions of retinal stabilisation, laughter also produced the mixed percept.

The results are discussed in the light of recent work that indicates the inadequacy of low-level explanation of rivalry, with laughter being another complex multi-level contribution to the neural basis of rivalry, along with other aspects of mood. The results are discussed in relation to the interesting literature on the neurology and postulated functions of laughter.