Fig. 1: The sequential metacontrast paradigm (SQM).
A central line is presented, followed by pairs of flanking lines, eliciting the percept of two diverging motion streams. Participants are instructed to attend to one of the motion streams (here, the right one) and report the perceived direction of the offset. If one of the lines in the stream is offset (e.g., the central line or a later flanking line), the entire stream is perceived as offset, even though the other lines are, in fact, straight. If both the central and a flanking line are offset, the two offsets integrate, if separated by less than about 300 ms, depending on the observer2: if the two offsets are in opposite directions, they cancel each other out before reaching consciousness; if they are in the same direction, the offset direction is perceived at increased performance levels. Note that the colors are only used for illustration. In the real experiment, all lines were white on a black background.
