Thanks for your interest
Here is the paradigm in more detail
letter presented until a speeded 3AFC response is made based on the letter's identity and then is cleared
stimulus onset asynchrony of 50, 11 245 or 542 ms following onset of letter
tone presented, speeded 2AFC response to the tone required
must respond to letter before tone

e.g.
H - wait for response
SOA of 50 ms
high tone presented - may make speeded response after response to letter
end of trial

The idea is that responses to the tone will be slower when the SOA is shorter. I will also be adding a difficulty manipulation to the tone task (high or low loudness) but I can work this out later.