See below.Best Regards,Donald McLaren, PhDOn Thu, Aug 20, 2015 at 9:59 AM, Joelle Zimmermann <[log in to unmask]> wrote:Hi SPMers,I have a couple of questions about parametric modulators. I'd appreciate thoughts about any/all of them :-)
1) When entering a parametric modulator at the first-level, where I have one condition with 10 onsets, am I expected to have 10 parametric modulator values? (ie one per onset)? The PM values I want to enter are behavioural performance values, and indeed I have 1 performance value per onset, so logically this would make sense, I am just not sure what the program expects.PMs are meant to modulate each trial, thus you need to have 1 value per trial.2) Can I use raw behavioural performance scores as covariates? These performance scores are all numbers between 0 and 1. Or is some adjustment to the values advised?As long as you think the BOLD response changes linear over the range of performance, no adjustment is necessary. The program should remove the mean from the values.3) MOST IMPORTANTLY: What's the difference between adding behavioural performance as a parametric modulator, and adding it as a regressor?Regressors aren't convolved with the HRF.JoelleThanks in advance,