Cite as:
Kitaoka A, Ashida H, 2002, "An anomalous motion illusion based upon signal delay" Perception 31 ECVP Abstract Supplement

An anomalous motion illusion based upon signal delay

A Kitaoka, H Ashida

We found a new anomalous motion illusion, which looks like the Ouchi illusion but is different in the direction of illusory motion. In the Ouchi illusion, we see an illusory motion in a direction perpendicular to a retinal slip, whereas the direction of this new illusion is the same as the retinal slip. In a series of experiments, we ascertained lightness contrast to be the critical factor. Low-contrast random dots showed longer signal delays than high-contrast ones, irrespective of their average luminance or contrast polarity. Within low-contrast patterns, 'dark' ones showed longer delays than 'light' ones. This illusion can be regarded as an extension of the Hess effect, which is characterised by signal delays shown by low-contrast, 'dark' patterns. Since the Hess effect is known as the monocular manifestation of the Pulfrich effect, we examined whether illusory motion in depth could be observed when low-contrast and high-contrast 'light' patterns were binocularly fused and moved horizontally. Under these conditions, observers rarely reported illusory motion in depth. Possible explanations of this discrepancy are discussed.

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