Hi Gang,

thank you for your useful reply. One more question:

In case of –stim_times_AM2, (only one regressor for simplicity) instantaneous percent signal change (PSC) for one subject should be computed as:
(Beta coef of the first regressor)+(beta coef of the second regressor)x(instantaneous valence - mean valence of that subject)
If this is correct, since valence is a function of time (in the sense that at different times pictures with different valence are presented), PSC (the second term in particular) is a function of valence. More: it is a linear function of valence, with the beta coef of the second regressor being the slope.

In group analysis should I apply 3dttest with –base1 0 and –set2 the list of sub-briks of all subjects corresponding to the beta coef of the second regressor (but it is not PSC!)? If the result is not statistically significant does it mean that BOLD response is not modulated by emotional valence?

Is there a way to compute PSC and use it to run group analysis? Does it make any difference compared to the approach described above?


Thank you,

Silvia