Schematic view of the luminance ramps of primers and targets.

<p>In the first task of Experiment 1, the two frames were filled in with a 100 ms onset asynchrony, such that the sequence was unambiguously perceived. Subjects were instructed to press the response button on the same side as the first square. In the second task of Experiment 1 only one frame was filled in, and subjects were told to press the button on the side of the filled-in square.