Do Monocular Tilt and Spatial Frequency Aftereffects Induce the Binocular Perception of Inclination and Slant?

Prolonged viewing of a set of tilted lines can affect the perceived orientation of a second set of lines with a different physical orientation (tilt AE). Similarly, prolonged viewing of a set of lines of a particular spatial periodicity can affect the perceived periodicity of a second set of lines with a different physical periodicity (spatial frequency shift AE). We investigated whether a binocular difference resulting from monocular tilt or spatial-frequency aftereffects could induce the perception of 3-D inclination or slant, respectively. Observers adapted to monocular patterns (5 deg in diameter) arranged in a vertical ‘dumbbell’ configuration in dichoptic alternation. The adapting patterns differed in either orientation (±6.25° or ±11.25°) or in spatial frequency (±0.5 or ±0.75 octaves) from a test surface comprising vertical lines at 4 cycles deg⁻¹. The period of adaptation was 3 mins. Observers judged whether the test surface appeared to (i) form a convex or concave hinge in depth (after adaptation to tilt) or (ii) to slant in opposite directions about a vertical axis (after adaptation to periodicity). Using a relative slant/inclination judgment may be more sensitive than depth matching or nulling of a single surface (eg Sloane and Blake, 1987 Perception & Psychophysics 42 569 – 575). Our results suggest that (i) differences in perceived periodicity in separate monocular images do not induce the impression of stereoscopic slant [confirming the results of Sloane and Blake (1987)] and (ii) differences in perceived orientation in separate monocular images do not induce an impression of stereoscopic inclination.