Hi Nancy,
Here is an input file that I used in my thesis study. The file starts out with 16 practice trials followed by four blocks of varying contrasts (the non-practice trials were randomized within and between blocks). For each trial, the cross was displayed for 1000 ms, followed by the probes for 500 ms, followed by the dot, which remained on the screen until a response was made. I hope this helps (late as it may be),
Paul