Yes, the first set of 20 betas (the unmodulated ones) should basically be the main effect. Note that any modulation values are first demeaned before being used to create additional regressors. So those regressors will be approximately orthogonal to the main ones, leaving the main ones to reflect the consistent, overall effect.
And to be clear, your hypothesis is that duration will affect amplitude above and beyond the amplitude of the convolution? The convolution amplitude effect has a unit height regressor for brief events (e.g. around 1s) convolving up to a height of more than 5 for long events (e.g. 12-15s+). It is not just a shape change. Just to be sure...
- rick
