Hi Xavier, please remember to post to the FS list. Answers below
On 12/07/2016 08:19 AM, Xavier Guell Paradis wrote:
Dear Dr. Greve, Thank you very much for your reply. I have one last question, which I think is a very basic concept that I understood wrong: If I want to compare finger tapping (for periods of 8s) vs. rest (for periods of 8s), shouldn't I enter "fingertapping" and "rest" as two conditions (i.e. two events, "ev") in Optseq?
No, you do not.
If I do this, then Optseq will generate inter-stimulus intervals, and my schedule will look more or less like this:
Fingertapping 8s NULL 1s Rest 8s NULL 4s Rest 8s NULL 2s Fingertapping 8s etc...
My question #3 made reference to this: does it make sense that "NULL" (the interstimulus interval) and "Rest" are essentially the same thing (the subject is viewing a fixation cross and not doing finger tapping)? Or should I use only one condition (Fingertapping) (i.e. only one "event", "ev"), and compare BOLD signal in the fingertapping condition with BOLD signal in the NULL condition?
I would use one condition.
I think the basic question that I am not understanding correctly is this: If one of the conditions that we want to compare is simply viewing a fixation cross, should we include this as a condition in Optseq (i.e. as an event, "ev"; which is the "Rest" in the example schedule above) or should we just use the inter-stimulus interval (NULL) as our "viewing a fixation cross" condition?
I would not include Rest as a condition in optseq
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: xaviergp@mit.edu
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:
- 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)
- 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.
- 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?
- 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: xaviergp@mit.edu
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