Hello,

I am running an experimental paradigm where the subject decides how long a visual stimulus is going to persist on the screen on a trial-by-trial basis, usually from a minimum of 3 s to a maximum of 30 s.
I wish to use a separate regressor for each event. I first ran 3dDeconvolve using:

-stim_times 1 '1D: 15' 'BLOCK(13.7,1)' -stim_label s1
-stim_times 2 '1D: 45' 'BLOCK(6.4,1)' -stim_label s2
-stim_times 3 '1D: 75' 'BLOCK(5.5,1)' -stim_label s3
-stim_times 4 '1D: 105' 'BLOCK(3,1)' -stim_label s4

and so on. Then I realized that the instruction 'BLOCK(time,1)' forces the peak value of the basis function to be 1 and therefore the beta weights are affected by the duration of the stimuli. Therefore, I ran another ANOVA identical to the first except for the ",1" option, in order to obtain "comparable" beta weights between events of different durations:

-stim_times 1 '1D: 15' 'BLOCK(13.7)' -stim_label s1
-stim_times 2 '1D: 45' 'BLOCK(6.4)' -stim_label s2
-stim_times 3 '1D: 75' 'BLOCK(5.5)' -stim_label s3
-stim_times 4 '1D: 105' 'BLOCK(3)' -stim_label s4

However, I obtain exactly the same results as with BLOCK(time,1). What's wrong either in my analysis or in my understanding of the option BLOCK(.)?

Thank you very much for your help,

Silvia