Re: [Marsbar-users] [SPM] Compare 2 methods to extract %signal change in MarsBaR

[Matthew B. <mat...@gm...>]

Hi,

On Tue, Apr 24, 2012 at 3:00 AM, Ming-Tsung Tseng <d93...@nt...> wrote:
> Thanks.....but what is the difference between the values obtained by method 1 and method 2? Which one is the true %SC?

The first one is the % signal change, the second one is just the
contrast (combination of beta) values.    If you have just one HRF
regressor for your condition and just one session then the % signal
change = beta_event_1 * regressor_event1_max_height /
session_baseline, where 'regressor_event_1_max_height' is a
reconstructed regressor for and event of the duration you asked for.
So the signal change is just the beta times a scale factor.   If this
scalefactor is the same for your two events, then the contrast value
(beta2 - beta1, say) will be the same as the subtraction of the
percent signal change times a scale factor.

Best,

Matthew