Motion assimilation for expansion/contraction and rotation and its spatial properties

In a two-frame apparent motion display, a test grating was displaced horizontally or vertically in the presence of an inducer of which component gratings made up expanding/contracting or rotational motion as a whole. In the first experiment, we demonstrated that motion assimilation did occur for the test accompanied by the two-dimensional motion of the inducer. In the second experiment, we showed that the spatial limit of motion assimilation for expansion/contraction or rotation was large, extending over at least a visual angle of 14-21 deg in diameter, but spatial summation did not occur within the limit. The results were discussed in terms of the interaction between local motion detectors and higher-order detectors which monitor global motion of the whole stimulus pattern.