I have a learning experiment with this basic design (cue -> predict using scale -> outcome -> fixation). The whole trial lasts for about 7 seconds. There are 16 different cues in one epoch and I decided that I need 20 epochs (at max) at two stages (10 for stage 1 and 10 for stage 2).
I plan to use this for an fMRI study later on but based on very few pilot (behavioral) data I see that subjects get tired and their attention deteriorates after about 20 minutes as reflected by the number of missed trials and the bad performance (predictions get worse).
Do you have any suggestions on how to make subjects more engaged?