Hi
We are planning an fMRI study where each trial will involve two stimulus - the basic design would be something like this:
Cue <interval> Outcome <ITI>
We aren't particularly interested in the response to the cue, but we need to be able to deconvolve/separate it from the response to the outcome (which we are interested in). This issue is usually solved by having a jittered interval between the two stimulus. However we would also presumably need a jittered ITI to stop the response to the outcome becoming confounded with the response to the cue for the next trial.
My question is how long do these intervals need to be?
From what I've read (e.g. Huettel et al 2004) the HDR tends to be attenuated if the interval between stimuli is less than 5-7s, and studies tend therefore to use a jittered interval with an average length of 6s. However I know there are studies that show that you can distinguish responses to stimuli when they are presented as closely as 2s apart (Clark et al 98). Does anyone have any advice on what sort of timings should be used? Having 2 intervals of average 6s per trial would extend our trial time to a level where we can't really get the number of trials we would like per condition.
Thanks
Rob
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