Chapter Four - A three-level qualitative model for the Ehrenstein illusion

Abstract

Hamada (1987, 1995) created the Ehrenstein patterns consisting of eight black lines (N: negative) at 45° intervals, eight white lines (P: positive), and mixed (N/P and P/N) patterns with four black and four white lines on a gray background. The apparent brightness of those background fields was the same and was darker than that of the uniform field as a control condition. The (P) pattern induced a stronger illusion than that of the (N) pattern when the gap diameter is short; however, when it is long, the (P) pattern is tending to induce weaker illusion than the (N) pattern. Hamada (2020) proposed a three-level qualitative model for the Ehrenstein illusion. There is an antagonistic process at the lower level. Linear and circular edges are detected at the middle level. The illusion occurs because at the upper level the lateral spread is blocked by the edges, and the decrease in brightness levels accordingly rises. His model claims that illusory contour formation occurs first and brightness contrast occurs later. In the illusion for mixed patterns, the brightness was offset. Furthermore, the amount of the illusion of the mixed patterns (N/P and P/N) was different, and an anisotropy of the brightness illusion was produced.