i believe it is the other way around. The 4th colum is the temporal
derivative of the parametric modulator,
Luke Stoeckel wrote:
> When using the parametric modulation option for a 1st level analysis of an
> event-related design, our design matrix does not appear as we expected.
> We are using an HRF + temporal derivative to model brain activation in
> response to to 4 conditions with a parametric modulator (e.g., reaction
> time). For each onset time within a condition, there is an associated
> parametric modulator value. The resulting design matrix consisted of 4
> columns per condition. Why are there 4 columns? I guess we might have
> expected 3 columns per condition. Does the 4th column correspond to the
> parametric modulation of the temporal derivative?