Colour maps sources

Discussions
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Hi Francois,

I have been working on the ttest analysis on my data. I wondered whether there is an option to do an individual independent ttest that takes sign into account. So, if for example, the sign is positive in the awake condition and is negative in the drowsy condition at the same timepoint, this will still yield a significant pvalue on an awake vs drowsy ttest? From what I have read, the ttests in brainstorm do not take sign into account and only compare the amplitude of absolute values?

Thanks for your help,
Corinne

Statistics: Single subject

  • A = B : Parametric or non-parametric
    • Compute source maps for each trial (constrained, no normalization).
    • Parametric or non-parametric two-sample t-test, independent, two-tailed.
      Identifies correctly where and when the conditions are different ( sign not meaningful ).
    • Directionality : Additional step to know which condition has higher values.
      Compute the difference of rectified averages: |avg(Ai)|-|avg(Bi)|
      Combine the significance level (t-test) with the direction (difference): See details.

Statistics: Group analysis, within subject

  • |A| = |B| : Parametric or non-parametric
    • First-level statistic : Rectified and normalized subject averages.
      Proceed as in Average: Group analysis to obtain two averages per subject: Ai and Bi.
    • Second-level statistic : Parametric or non-parametric two-sample t-test, paired, two-tailed.
    • This test does not consider the sign difference within a subject, and therefore cannot detect correctly when A and B have opposite signs. Works well and indicates which condition has higher values when A and B have the same sign within a subject.