Abstract
In a pattern of horizontal lines containing ± 45° zigzagging phase-shifted strips, vivid illusory motion is perceived when the pattern is translated up or down at a moderate speed. Two forms of illusory motion are seen: [i] a motion “racing” along the diagonal interface between the strips and [ii] lateral (sideways) motion of the strip sections. We found the relative salience of these two illusory motions to be strongly influenced by the vertical spacing and length of the line gratings, and the period length of the zigzag strips. Both illusory motions are abolished when the abutting strips are interleaved, separated by a gap or when a real line is superimposed at the interface. Illusory motion is also severely weakened when equiluminant colored grating lines are used. Illusory motion perception is fully restored at < 20% luminance contrast. Using adaptation, we find that line-ends alone are insufficient for illusory motion perception, and that both physical carrier motion and line orientation are required. We finally test a classical spatiotemporal energy model of V1 cells that exhibit direction tuning changes that are consistent with the direction of illusory motion. Taking this data together, we constructed a new visual illusion and surmise its origin to interactions of spatial and temporal energy of the lines and line-ends preferentially driving the magnocellular pathway.
Highlights
The Italian psychologist Gaetano Kanizsa described a thin illusory contour running at right angles between two juxtaposed, phase-shifted line gratings, similar to a real line but with no physical correlate in the inducing pattern (Kanizsa, 1974)
We conclude that two kinds of illusory motion are perceived in the Serpentine Illusion, one parallel to the zigzagging illusory contour; the other parallel to the orientation of the physical line gratings
We identified the experimental conditions under which each type of illusory motion perception is optimal
Summary
The Italian psychologist Gaetano Kanizsa described a thin illusory contour running at right angles between two juxtaposed, phase-shifted line gratings, similar to a real line but with no physical correlate in the inducing pattern (Kanizsa, 1974). Patterns eliciting illusory contours have been well studied psychophysically (Spillmann and Dresp, 1995; Soriano et al, 1996; Halko et al, 2008). Von der Heydt et al (1984) and Von der Heydt and Peterhans (1989) studied the neural response of V2 units in the monkey to abutting line gratings. They found neurons that responded to these patterns to real lines (i.e., with consistent orientation selectivity). Subsequent neurophysiological, imaging, and computational modeling studies further extended the
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