Dear Dorian and Donald,
yes, you're absolutely right. I should have made it clearer, I don't want to simply account for different durations, I also want to explore/statistically test them in the manner of a parametric modulator. Basically I want to obtain beta values for the PM of one condition and then simulate the neural activations adjusted to a different RT and compare this to a second condition (= can the differences between two conditions be fully explained by RT difference). The standard PM works on the amplitude though. For my purpose it would be better to modulate the length and not the amplitude (length can directly be linked to RT, assuming a constant process from stimulus appearance to button press).
It seems this is possible with some extra code, as partly shown here http://wagerlab.colorado.edu/wiki/doku.php/help/fmri_help/fmri_statistical_models/parametric_modulation, but I'm not sure. And I would like to here some opinions on this approch.
Best,
Helmut
|