Dimberg fixed the intertrial intervals in his standard procedure in the article "facial electromyography and emotional reactions" at 25-45 s. This is generally used in studies of facial reactions by EMG. What is the justification of this choice ?
Thank you. I found even 8750 ms in one study, and I wonder if the minimum value which allows the return to the baseline state is known. Is there new standard procedure that specifies these settings?
Yes, 25 to 45s ISI is from the 'standard procedure' Dimberg suggested.
I didn't see another 'standard procedure'. If you found 8750ms and the stimuli is similar to what you will use, go ahead. In my opinion, It's closer to minimal. In My pilot test with dynamic facial stimuli, 4000ms was too closer.
25s even sounds far too long to me, but depends on how long of that is stimuli. EMG signals are fast to disappear when face stimuli are removed. using good dynamic video clips, i find that 2-3s baseline fixation cross is more than enough. if you use 25s you risk serious attentional artefacts (boredom). best to map out the signal average of a few people across 500ms trial bins to see when it drops exactly for your stimuli.
Yes, 25s is too long for 5s of stimulus presentation, and specially if each stimulus must be exposed 6 times. Thank you both for the advice !
In the same context, are there recommendations for what must be shown during the intertrial interval ? I think about a grey screen and a 500 ms fixation point.
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