P. Wenderoth et al., DIRECT EVIDENCE FOR COMPETITION BETWEEN LOCAL AND GLOBAL MECHANISMS OF 2-DIMENSIONAL ORIENTATION ILLUSIONS, Perception, 22(3), 1993, pp. 273-286
Orientation illusions induced by two-dimensional stimuli, such as squa
re outline frames or plaids, have been more or less adequately account
ed for in terms of repulsion of the vertical test stimulus from the ax
is of symmetry nearest vertical of the inducing stimulus, whether that
axis is real or virtual. Recently, data have been obtained which dire
ctly suggest a more complex mechanism: one in which the observed illus
ion is the sum of all effects-complementary and antagonistic-induced b
y all axes flanking vertical which are sufficiently close to vertical
to exert a significant effect. Experiments are reported in which this
latter ypothesis was directly tested by using nonorthogonal plaid comp
onent gratings and varying the real-axis orientations while a virtual
plaid axis remained fixed in orientation at 10-degrees from vertical.
The data indicate that the real component gratings modulate the virtua
l-axis effect.