Bosky,
No, the 3 column format supports an effect strength value, not just 1s
or 0s. The format is interpreted as follows:
Column 1: event onset time (secs)
Column 2: event period (secs)
Column 3: event value (i.e. can vary continuously)
If you're describing an experiment with different stimulus strengths
then you could hard code the strengths in EV waveform amplitudes
however this would not be very flexible. This is probably best done by
using separate EVs for each and using appropriately chosen contrast
values to investigate the relationship between stimulus and response.
In this case your 3 column files have a value of 1 for each "event"
then if you expect EV1, EV2 and EV3 to be progressively (linearly)
stronger in response then a -1 0 1 contrast can be used to test for it.
On 30 Aug 2005, at 17:51, Bosky wrote:
> Dear List,
>
> Could someone help me understand how in the 3 column format for full
> model setup , the last number or the strength affects the analysis. I
> assume it can take only 0 or 1 as input. How does one decide which
> strength to apply? If for example in a single session, I have multiple
> EVs whose strengths are different, then should I be defining the lower
> strength EV as 0 ( in a 3 column text file) and the higher strength EV
> as 1?The study design that I am tring to analyse is an event related
> one:
>
> The EVs are as follows:
>
> There are 3 phases to the experiment:
> Phase 1 : where two colors are presented red and blue
> EV1= Red Phase1
> EV2 = Red Phase 1
> Phase 2: Where few reds are coupled with an auditory stimuli:
> EV3: Red + auditory stimuli
> EV4: Red Phase 2
> EV5:Blue Phase 2
> Phase 3: Where no auditory stimuli are coupled to the colors
> EV6: Red
> EV7:Blue
> Right now I have set all the EVs to strength '1' , but EV3 is
> definitely stronger than the other EVs. What should I do in this case?
> Thanks in advance,
> Bosky
>
> Laboratory for the Study of Emotion and Cognition,
> Department of Biomedical Engineering
> Stony Brook University,
> New York, 11790
> Phone- 631-444-8405/ 631-444-7868
>
>
--
Cheers, Dave
Dave Flitney, IT Manager
Oxford Centre for Functional MRI of the Brain
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URL: http://www.fmrib.ox.ac.uk/~flitney
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