Hi,
Pretty much - you just need two regressors - one is the sin(a*t) and the
other is cos(a*t). The relative values of the coefficients (parameter
estimates)
for these then encodes the phase. That is:
tan(phase angle) = parameter estimate for cos() / parameter
estimate for sin()
which comes from: sin(a*t + phi) = sin(a*t)*cos(phi) +
cost(a*t)*sin(phi)
Note that the temporal derivative of sin(a*t) is a*cos(a*t), but I
wouldn't
use that as the factor in front is quite crucial and you need to know
exactly how the derivative has been scaled. Instead I would just turn
the
temporal derivative off and explicitly make a cosine regressor with the
correct amplitude.
All the best,
Mark
On 21 May 2009, at 19:31, Michael Scheel wrote:
> Dear fsl experts,
>
> i have data from a retinotopic mapping experiment - and I want to
> analyse it using the so called 'travelling wave method', i.e. a
> rotating checkerboard wedge, that jumps 45 degr. every 4 sec. After
> 32 sec it has fully rotated and starts again. Therefore the stimulus
> I'd choose is a sinusoid wave with a period of 32 sec. My question
> is how to get a retinotopic map using fsl, i.e. how do I extract the
> phase information - is this the same as the temporal derivative.
>
> Thanks, Michael
>
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