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?

 

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?

 

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)

 

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?

 

Thank you very much,

Xavier Guell.