Figure 3.

Plot of Lateralization Indices (LI) computed for each participant in the easy and hard condition (left). The data show highly correlated (r = 0.83, n = 20, p = < 0.0001) LIs. The LIs are computed by averaging the CBFV difference in a window, here 2 s, around the absolute peak value in the analysis window, here 2–15 s post task onset. This means that, when LIs for two conditions or tasks are compared, the peak values do not have to coincide. The right hand graph shows the position of the windows that are the basis for the LI analysis: in the majority of cases LIs derive from similar positions between 10 and 15 s after task onset; for three individuals (A–C) peak LI values were found toward the end of the hard task conditions, but at the beginning of the “easy” conditions (arrows in right plot); for another three participants LIs were computed for relatively early responses (around 4 s) in both tasks. We argue that for a meaningful correlation analysis, matching time windows should be considered.