Illusory depth from moving subjective figures and neon colour spreading

Abstract

If a pattern of concentric circles, interrupted so as to produce the perception of a subjective bar extending from the centre to the periphery of the pattern, was slowly rotated in a plane perpendicular to the line of sight, observers reported seeing the bar slanted in depth and moving over complete and stationary concentric circles. When the interrupted concentric circles were completed by red segments--thereby giving rise to a neon colour-spreading effect--observers reported seeing a reddish bar, which sometimes appeared to be slanted in depth, moving behind the plane of the concentric circles. A combination of the two patterns was found to originate a compelling percept of a unitary bar slanted in depth: part of the bar (the subjective half) appeared to be located in front of its inducing elements, whereas the other part (the neon-like half) appeared to continue behind them. When translatory instead of rotary motion was used, the bars did not look slanted in depth: however, the neon bar appeared either behind or in front of the inducing lines, depending on the luminance contrast between the segments and the inducing lines themselves.