Illusory Contour-motion Arising from Translating Terminators

Periodic grating patterns were created by phase shifting or eliminating vertical columns of a fine line carrier grating oriented 45 deg. Motion was created by translating the patterns parallel to the carrier grating. This veridical motion was seen when terminators (i) were created in low-frequency carriers; (ii) terminated short lines; and (iii) moved slowly. In the complementary conditions an illusory contour-motion was seen perpendicular to the orientation of the terminator-defined contours. A model involving a competition between second-layer filters (encoding the orientation and motions of the terminator defined contours) and double endstopped mechanisms (signalling the presence of terminators) was developed and found to be in quantitative agreement with these data. Experiments with plaids composed of two such patterns were generally consistent with the results of the one-dimensional cases. Coherent "subjective contour plaid" motion was almost always seen when the two subjective contours had the same orientation and were perfectly phase aligned.