The discrimination of differences in duration of a thermal reinforcement

The sides of a contour square appear successively when context lines are presented one before and one after the square. As the interstimulus interval (ISI) between lines and square is increased to 140 msec, reports of succession increase. If the sides of the square are presented successively and interpart interval (IPI) varied by a single staircase method in order to determine a succession threshold, the average magnitude of this threshold varies as a function of ISI, decreasing up to 140 msec lSI. Each S, however, shows a maximum decrease in threshold between 80 and 120 msec. Reports of this illusion are not dependent on beta movement of either context lines or square.