Dear SPM experts,
I would like to hear your opinion about parametric modulation across conditions. Within SPM modulators are linked to specific conditions. But it would be possible to build a modulator across conditions by setting up another model in which several conditions are collapsed into one and forward the resulting timecourse into another model as a standard regressor.
I'm aware of problems that might arise (like activation for condition A is higher than for condition B, so what does the modulator do), but still I think this approach might be useful. Imagine something like presenting stimuli to the left and to the right. There might well be differences in early visual areas, but a parametric modulator across conditions might be helpful to include some rating involving higher-order perception and/or decision-related processes not fixed to visual quadrants.
What do you think? Thanks!
Helmut
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