Small-angle attraction in the tilt illusion

Abstract

The tilt illusion (TI) describes the phenomenon in which a surround inducer grating of a particular orientation influences the perceived orientation of a central test grating. Typically, inducer-test orientation differences of 5 to 40 degrees cause the test orientation to appear shifted away from the inducer orientation (i.e. repulsion). For orientation differences of 60 to 90 degrees, the inducer typically causes the test grating orientation to appear shifted toward the inducer orientation, termed here “large-angle” attraction. Both repulsion and large-angle attraction effects have been observed in contrast-modulated as well as luminance-modulated grating patterns. Here, we show that a secondary, “small-angle” 0 to 10 degrees attraction effect is observed in contrast-modulated and orientation-modulated gratings, as well as in luminance-modulated gratings that are relatively low in spatial frequency, low in contrast, or contain added texture. The observed small-angle attraction, which can exceed in magnitude that of the repulsion and large-angle attraction effects, is dependent on the spatial phase relationship between the inducer and test, being maximal when in-phase. Both small-angle attraction and repulsion effects are reduced when a gap is introduced between the test and inducer. Our findings suggest that small-angle attraction in the TI is a result of assimilation of the inducer pattern into the receptive fields of neurons sensitive to the test.

Stereoscopic slant contrast revisited

“…Analogous to stereo slant contrast is the well-known tilt illusion, in which an oriented surround pattern (such as a grating) causes a repulsive shift in the perceived orientation of a differently-oriented central test pattern ( Akgöz, Gheorghiu, & Kingdom, 2022 ; Blakemore, Carpenter, & Georgeson, 1970 ; Clifford, 2014 ; Schwartz, Sejnowski, & Dayan, 2009 ). The standard explanation of the tilt illusion is that orientation-selective channels sensitive to the surround inhibit via divisive normalization same-orientation-selective channels sensitive to the test, resulting in a shift in central tendency of the population of channel responses in the test in a direction away from that of the surround.…”