Illusory Contour Strength Does Not Depend on the Dynamics Or Relative Phase of the Inducers

Jonathan D. Victor and Mary M. Conte

Vision Research 40, 3475-3483 (2000)

Abstract

We use a new objective measure of illusory contour strength, threshold reduction for aspect ratio discrimination, to examine the effect of dynamics and relative phase on the Kanizsa illusion. We found no dependence of illusory contour strength on the relative phase of flickering inducers (in phase, antiphase, or in quadrature phase) either for the standard Kanizsa square, or for modifications that facilitated or interfered with amodal completion. Comparison with a vernier acuity task indicates that the distance between the inducers, rather than the nature of the task, accounts for the insensitivity to relative phase.

Stimuli

Snapshots of the stimuli (from left to right): inducers presented in phase rotated out, antiphase rotated out, in phase rotated in, antiphase rotated in.

The basic finding

Mean threshold log aspect ratios lnr_out (circles) and lnr_in (squares) for shape discrimination with inducers presented in phase (open symbols), and in antiphase (filled symbols). Error bars represent ±2 s.e.m., calculated across subjects' individual means of lnr_out and lnr_in. There is a substantial difference in thresholds for aspect ratios when the inducers are rotated inward, but there is no difference between in-phase and antiphase conditions.