Dear Francis,
Please forgive the delay in replying. I've been on Holdiay.
......
> There are a number of ways forward. First you could model both the
> behavioural effects and the response to task preformance per se and
> then the interaction between these. You could model all the
> behavioural variables togther after some suitable orthogonalization
> (and interactions among them).
FIRSTLY, LETS SAY I PROCEED WITH THE FIRST OPTION YOU SUGGEST AND I
DECIDE ON 3 BEHAVIOURAL MEASURES (E.G. ERROR, REACTION TIME, AND
MOVEMENT DISTANCE). I WOULD CARRY OUT THE ANALYSIS (AS I SET OUT IN MY
ORIGINAL EMAIL ABOVE -USER DEFINED OPTION ETC.)
<underline>SEPARATELY</underline> FOR EACH OF THE BEHAVIOURAL VARIABLE.
IS CARRING OUT SEPARARTE ANALYSIS CORRECT OR SHOULD (CAN) I CARRY OUT
THE ANALYSES FOR ALL THREE VARIABLES AT THE SAME TIME ? IF I CAN, HOW
DOES SPM 96 PROMPT ME FOR THE SECOND AND THIRD BEHAVIOURAL VARIABLE ?
Parametric regressors such as yours are entered as 'User specified'
covariates. Simply type 3 when prompted for '# of waveforms or
conditions'. I would analyse all regresors together.
SECONDLY, REGARDING THE INTERACTION BETWEEN THESE VARIABLES. HOW DO I
ACTUALLY CARRY OUT TESTING FOR INTERACTIONS IN SPM96?
You simply create a new covariate that is the product of the mean
corrected covariates subtending the interaction. For example if A and
B were vectors with two variables in them, the interaction AxB is
simply AxB = spm_detrend(A,0).*spm_detrend(B,0);
......
> Yes. To say that activation has increased you would have to model a
> task x error interaction.
MY QUESTIONS HERE ARE RELATED TO THOSE (NEW) AT 2 ABOVE. HOW WOULD I
MODEL SUCH A TASK X ERROR INTERACTION ? WOULD THIS INVOLVE LET'S SAY,
AN ANALYSIS BASED ON A DELAYED BOX CAR DESIGN FOR THE TASK PER SE
(BASED THE SCANNING DESIGN I USED -BASELINE-LEARNING PERIOD-BASELINE)
AND THEN CARRYING OUT AN ANALYSIS BASED ON THE USER SPECIFIED OPTION,
USING THE ERROR VALUE? I AM GUESSING HERE.
Yes absolutely. In this instance the box-car would be A above and the
error rate B.
I hope this helps - Karl
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