The timing between both stimuli is taken from a uniform distribution ranging between 0 and 3 seconds.
Histogram of all reaction times:
The point near zero is in fact a false positive (I pushed the key before seeing the second stimulus, but it appeared between my decision and the actual push).
Reaction time (y) versus time between the two stimuli (x):
There is a trend of longer latency for smaller time between stimuli. However, my feeling is not the one of “increasing prior”, but that early stimuli arrive “before expected”, surprising me. Obviously, more experiments are needed.