Also, to ensure that framewise displacement was not related to our outcome measures, we calculated the mean frame-to-frame displacement (FD) (Power et al., 2012) for the remaining frames and matched our participants, such that there was no significant difference in this variable between controls and children with ADHD. FD was calculated as a scalar quantity using a formula that sums the values for framewise displacement in the six rigid body parameters (FDi=|Δdix|+|Δdiy|+|Δdiz|+|Δαi|+|Δβi|+|Δγi|, where Δdix =d(i−1)x −dix, and similarly for the other five rigid body parameters) (Power et al., 2012). There was no relationship between mean FD and measures of delay discounting of rewards (n=122; r=−0.13; p=0.14), and for the comparison analysis, the groups were matched by mean FD for the remaining frames.
