Manipulating the relative orientation of adaptor and standard had an effect on duration estimates as revealed by ANOVA repeated measures, main effect of orientation,
F(4, 12) = 14.807,
p < 0.001, and this effect depended on the direction of motion of the standard stimulus, interaction orientation × direction,
F(4, 12) = 8.518,
p < 0.005. Also, the amount of duration compression after adaptation is significantly stronger at 18 Hz than at 3 Hz, main effect of temporal frequency,
F(1, 3) = 17.018,
p < 0.05, as can be noticed by the downward shift of both curves in
Figure 4. As in the first duration experiment, when the adaptor and standard had the same orientation (0° condition) and drifted in the opposite direction (adaptor upward, standard downward, red circles in
Figure 4), a significant duration compression is observable at 18 Hz, one-sample
t test against 0,
t(3) = −18.666,
p < 0.001, but not at 3 Hz. At 3 Hz, as the difference between the adaptor and standard orientations becomes more pronounced, the duration compression does not increase for the
downward standard direction (none of the one-sample
t tests reaches statistical significance). However, at 18 Hz, the compression for the same condition (
downward) seemed to be fairly constant across adaptor orientations (one-sample
t tests revealed statistically significant differences from 0 for all the tested orientations; all
p < 0.05). As far as the
upward standard direction is concerned (
Figure 4, blue squares), at both 3 and 18 Hz the compression was maximal for the condition in which the adaptor and standard had the same orientation and drifted in the same direction (0°), and then it progressively decreased as the adaptor was rotated away from the standard orientation. At 3 Hz, only −45° and 0° were significantly different from 0 whereas at 18 Hz compression for the −45°, 0°, and +45° adaptors were statistically significant (all
p < 0.05). We conducted four separate one-way ANOVAs to verify the existence of a quadratic trend for the two directions of motions separately at both temporal frequencies. For the
upward direction of motion, a quadratic trend was found to be significant both at 3 Hz,
F(1, 15) = 24.885,
p < 0.001, and at 18 Hz,
F(1, 15) = 5.906,
p < 0.05. However, no quadratic trend emerged for the
downward direction for either temporal frequency.