Have no response as a response

[Sukh]

I am programming an experiment in which people have to detect the onset of a peripheral stimulus, while fixating a central stimulus. I need to add in some catch trials in whcih no peripheral stimulus occurs and to which people DO NOT respond. I looked at the help section on how to program "no response" as a response and keep track of whether the response was correct or not, but could not get the program to work properly. Does anyone with more experience with DirectRT know how to program a no response trial and to determine whether in fact there was no response (a correct response) or whether the person accidently hit a button (an incorrect response). I am very new to DirectRT and this is the first experiment i am programming so your help would be very much appreciated! Thanks