On 12/06/2016 04:57 PM, Xavier Guell Paradis wrote: > > Dear FS team, > > We are designing an fMRI experiment that has to include one motor, one > cognitive and one affective task. We would like to use a rapid > event-related design because we want to do MVPA to classify patients > vs controls. We have 4 questions regarding Optseq: > > 1) We are designing a task where subjects either rest (while viewing a > fixation cross) or tap their right index finger (while viewing a > fixation cross surrounded by a green circle). Does it make sense, for > a rapid-event related design, to make subjects tap their right index > finger for 8 seconds or rest for 8 seconds, or should we decrease the > number of seconds? > From an analysis standpoint, that is fine. optseq will set the number of seconds for the rest period (you can set the bounds with --tnullmin and --tnullmax) > > 2) We have a similar question for a task where subjects view images > which are either happy, scary or neutral. Each image lasts 1.5s. We > would like to group images in groups of 4 so that the emotional > response is more intense (if we are interested in making the subject > feel happiness we would prefer that subjects see 4 consecutive happy > images, rather than one happy image and then one scary image and then > one happy image). Therefore, we have groups of 4 images and each group > lasts 6s (4x1.5s). Does it make sense, for a rapid-event related > design, to consider that each stimulus lasts 6 seconds (this includes > 4 images of 1.5s of the same emotional category); or should we > decrease the number of seconds; or simply present each image of 1.5s > individually? > Again, ok. > > 3) We are designing a task where subjects either rest (while viewing a > fixation cross) or tap their right index finger (while viewing a > fixation cross surrounded by a green circle). Optseq generates > jittered inter-stimulus intervals, and during inter-stimulus intervals > subjects will view a fixation cross and rest. Does it make sense that > subjects are seeing the same thing in the “rest” condition and in the > inter-stimulus intervals? (in both cases, a fixation cross is shown in > the screen and subjects are resting) > Isn't this the same as #1? I guess I don't understand how you plan to analyze your data. Is some of the rest different than other parts of the rest? > > 4) We are designing a go/nogo task where subjects have to press a > button only when a stimulus of a particular shape (square or circle) > and color (yellow or purple) is presented. Each stimulus is presented > for 2s. We would like to change the instructions every 12 stimuli, and > we would like to change the instructions 3 times. To change the > instructions, we would have to show text to the subjects for 15 > seconds explaining the new instructions (e.g. “press the button when > you see a purple square”). Is there any way to include the > instructions in Optseq; or should we run Optseq for 12 stimuli, keep > the best 4 schedules, and then include a 30 seconds pause between each > schedule of 12 stimuli to allow the hemodynamic response to return to > baseline while presenting the new instructions? > There is not a way to include the instructions in optseq. I would keep the best 12-stimulus sequences from optseq. You don't need to wait 30 sec, 15 sec should be ok > > Thank you very much, > > Xavier Guell. > > > > Xavier Guell Paradis, M.D. > Visiting Scientist > Massachusetts Institute of Technology > McGovern Institute for Brain Research > Office: 46-4033A > Phone: (617) 324-4355 > Email: [email protected] > > > _______________________________________________ > Freesurfer mailing list > [email protected] > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
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