PowerPoint Presentation - Group Analysis with AFNI

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å-amean: Estimates the mean for every level of factor ÔaÕ (collapsed across factor ÔbÕ) and provides a t-statistic for the null hypothesis, Ho: mean = 0

íIn this example, the mean percent signal change for each stimulus condition type is averaged across subjects on a voxel-by-voxel basis

íFor example:

Mean Percent Signal Change at Voxel ÒxÓ

Subject (b)

4.1%

3.8%

4.5% Þ

M = 4.13%

Stim Cond (a)

3.2%

2.5%

2.8% Þ

M = 2.83%

4.6%

4.1%

4.9% Þ

M = 4.53%

1.7%

2.0%

1.1% Þ

M = 1.60%

íAllows you to determine if the percent signal change in a voxel is significantly different from zero. If so, appears as colored activation blobs