“…Moreover, to exclude the possibility that significant identification was caused primarily by subject‐specific head movement patterns, we performed identification based on head motion feature only. Specifically, we calculated framewise displacement (FD) similar to fMRI studies (Ide & Li, ; Power, Barnes, Snyder, Schlaggar, & Petersen, ) for each subject in each session. For each time point t , the FD was calculated as: FD ( t ) = | Δd x ( t )| + | Δd y ( t )| + | Δd z ( t )| + r | Δα ( t )| + r | Δβ ( t )| + r | Δγ ( t )|, where ( d x , d y , d z ) and ( α , β , γ ) are the translation and rotation transformation parameters; r = 50 mm, a constant that approximates the mean distance from the cerebral cortex to the center of the head and used to covert rotations into displacement; and Δd x ( t ) = d x ( t ) − d x ( t − 1) (other parameters, i.e., d y , d z , α , β , γ , could be expressed in the same way).…”