Dear SPMers,
I’m analyzing an event-related working memory task with three levels of wm-load and two groups (placebo vs. verum), the conditions are:
1. Baseline (fixation-cross)
2. wm-load 1
3. wm-load 2
4. wm-load 3
To compare groups on the second level I used a full-factorial design (factors: group (2-levels) x load (3-levels).
My questions:
1. I ran the analysis with con-images (wm-load 1-Baseline / wm-load2-Baseline / wm-load3-Baseline) and beta-images (from load1 / load2 / load3). The analyses reveal different results. Which analysis reveals the most reliable results?
2. Both analyses reveal a main effect of group, however no group x load interaction. How can I be sure, that the effects are working-memory specific? Would it be valid the mask the contrast of the main group effect with the main effect of task?
3. For a more sensitive analysis I’m planning to compute the contrast for:
1/3 wm-load 1 + 1/3 wm-load2 + 1/3 wm-load3 vs baseline for the whole sample. Than compute a 1-sample t-test with these contrast images. Significant clusters from this analysis are thought to represent the working memory networks. In a next step individual beta values will be extracted using these significant clusters as ROIs. Does this analysis lead to valid results?
Thanks in advance & kind regards,
Ben
|