How to realize overlap in a masked priming experiment?

[Leon]

eprime，hello！
             I am using E-prime 1.1 to do a masked priming experiment. I dont know how to realize a overlap. Fox example: the prime during 20ms, and the mask during 50 ms,how to let the mask occur when the prime has occured 10ms? demonstrated like this:
|----prime-----|
        |----mask--------------|
It's seems like the only way is to make three pictures: a prime, a mask, and a picture of prime+mask. That means I have to make two procedures(overlap or not) in order to adjust the SOA systemicly. Is it right?
             Thank you in advance.

Best Wish!
 				
　　　　　　　　　　　　　　                    Leon
　　　　　　　　　　　　　                    　liuch at psych.ac.cn
　　　　　　　　　　　　　　　                  　　2002-12-03
===========================
Institute of Psychology
Chinese Academy of Science
Tel: 86-10-64850862
Zip: 100101
===========================