Response to Lynch et al: On measuring head motion and effects of head molds during fMRI.

We recently presented evidence indicating limited efficacy of custom-molded headcases in reducing head motion in two naturalistic experimental contexts - passive movie watching, and speaking in the scanner (Jolly et al., 2020). In a commentary on this work, Lynch et al (2020) present additional data that support the original findings of (Power et al., 2019) and raise several potential issues with our recent work. We appreciate the opportunity to address these criticisms and raise additional points that should be considered when interpreting these conflicting findings. We do not believe that their criticisms diminish the value of our work, but instead, along with this reply, help better elucidate the key factors researchers should consider to make the most informed choice about their own research protocols.