to some extent the issue of missing columns is addressed by the contrast
manager batch option "Condition/session based" t-contrast. There, you
can specify contrast weight per contrast weight, where in terms of
condition#, basis fcn#, modulation# etc you want to place this weight.
This solution does not yet cover all possible causes of missing columns,
but may already be helpful.
Am Montag, den 14.04.2008, 14:01 +0200 schrieb Paul Smeets:
> Dear all,
> I'm struggling with the use of parametric modulation in my design. I
> have 3 conditions (stimuli), the response to which I want to modulate
> with a subjective rating that was obtained after every stimulus (6
> ratings per stimulus per session).
> I have two similar questions:
> 1) If my parameter values do not change during the session (which
> happens sometimes for one of the stimuli), SPM leaves out the
> 'modulation column(s)' (admittedly, there is nothing to modulate). I
> guess this is a feature, but it is inconvenient for generating multiple
> batch jobs because it changes the number of columns in the design
> matrix, rendering my pre-specified contrasts useless. Could this be
> turned off somehow?
> 2) Essentially the same thing occurs for higher order modulation: a 2nd
> order modulation column is only included when the parameter value
> changes at least twice. I understand that for fitting a quadratic curve
> rather than a line one needs more than 2 different parameter values,
> however, I would still want to have one column for 1st order modulation
> (by 'parameter' ) and one for 2nd order modulation (by 'parameter
> squared'), regardless of my parameter values. This might reflect my lack
> of understanding of how parametric modulation is performed in SPM but,
> could this be done somehow?
> Thank you, regards,
> PS I plan to do an analysis with all three stimuli merged into one
> condition; then I will have enough variation in my parameter values not
> to encounter the issues mentioned above.
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