I have a question about comparing two tasks with significantly different mean reaction times (1946ms vs. 2341ms). A reviewer brought up the point that it is unclear whether differences found using our current analysis (using fixed duration and impulse convolved with the double-gamma HRF and temporal derivative) are due to magnitude differences or simply caused by temporal offsets/differences in task duration. While we have reason to believe our region of interest is not sensitive to variability in RT, I agree that this needs to be addressed and want to make sure I go about this in a satisfactory way.
I've looked through previous posts and it seems one approach is to include an RT regressor (with either variable duration or impulse). If this modulated regressor is included, would I be safe in interpreting significant regions resulting from contrasts of the original (unmodulated) regressors as likely reflecting differences of response magnitude between the tasks? Further, would it make sense to run the same contrasts on modulated regressors in order to obtain an RT-sensitive map, which could then be used as an exclusive mask for the unmodulated contrasts?
It seems that the above may be useful to do regardless, I might not be able to make specific conclusions about whether my current results are due to magnitude differences or temporal offset. In order to do this, would it make sense to use FIR basis functions and examine how the tasks differ within each time bin? Or alternatively, generating average peri-stimulus plots for each condition and examining those for differences?.
I understand that there is probably no "correct" answer, but I would greatly appreciate any input as to what kind of interpretations can be made from the varous approaches.
Thank you for your help,