Rick,
I haven't fixed a limit of 6 seconds between stimuli, but from reading a couple papers that have utilized an event-related design, they seem to limit their ISIs to 1, 2, or 3 TRs. Each of my stimuli will last 2 seconds (yes, my TR = 2 secs). My experiment will have 3 conditions, call them A, B, and C, and I want to present them completely randomly. My basic question is, in between each presentation of A, B, or C do I need an ISI or can I go directly from one stimuli to the next? I guess, I'm asking the definition of jittering. I thought jittering meant to simply randomize the ISI, such that in some cases it could be 1 TR, 2 TRs, 3 TRs etc...In as slow design there is roughly a 15 second ISI, correct? And in a fast design the ISI can be shortened to 2 seconds, correct? But, in a fast design you can have a fixed ISI, say 2 seconds, or a fixed ISI of 6 seconds, whatever you want. Isn't jittering randomizing the length of that ISI instead of keeping it fixed? I feel as though what you are saying is that you can have an ISI of zero if that's what RSFgen is calling for. I just thought that you always needed some sort of ISI, with the shortest being 1 TR and the longest being however long you wanted, but never could it be 0 seconds. Does my question make sense? Thanks a lot for your help.
-Andy