A vertical test grating appears tilted away from a surrounding inducing grating which is 15°from vertical (repulsion effect) but towards an inducer 75°from vertical (attraction effect). This is the tilt illusion (TI) and similar effects occur when inducing and test stimuli are presented successively (tilt after-effect or TAE). When it was reported [Wolfe, J. (1984). Vision Research, 24, 1959-1964] that large repulsion TAEs occurred with short test flashes, Wolfe postulated that either there are distinct mechanisms which process brief and longer duration stimuli; or that there are distinct mechanisms which are not primarily concerned with duration but are differentially responsive to temporal parameters, amongst several others. Other evidence that TI attraction effects are not modulated by test flash duration resulted in an hypothesis that repulsion and attraction effects are mediated by transient and sustained mechanisms, respectively [Wenderoth, P., van der Zwan, R., and Johnstone, S. (1989). Perception, 18, 715-728]. We demonstrate that large repulsion TIs can be induced when parameters other than duration are manipulated, including contrast and spatial frequency but that these parameters fail to modulate attraction TIs. These results are consistent with some previous hypotheses regarding the origin of repulsion and attraction effects and with Wolfe's latter hypothesis but do not support the view that the two effects are processed, respectively, by transient and sustained mechanisms.
- Spatial frequency
- Tilt illusion