Self-selection refers to the fact that certain kinds of people may be drawn to certain kinds of lifestyles or practices (including participation in human research). When the effects of those lifestyles/practices are observed scientifically, they are confounded with myriad other factors which also characterize that group. For example, in the context of meditation studies, it is possible that meditation in the realm of 10-50,000 hours has beneficial effects, but is also difficult to prove the important factor is not all other characteristics of such avid meditators (for example, their tendency to sleep soundly or to drink green tea, etc).
A recent study in PNAS by Tang et al. begins to address this concern by reporting results from the random assignment of 40 subjects to an active control group learning stress-reduction techniques, and another 40 subjects to an experimental group undergoing 5 daily 20-minute sessions of a “integrative body-mind training” program targeting the same “body relaxation, breathing practice, mental imagery and mindfulness” abilities as meditation, absent attentional control, known to be distractingly difficult for novice meditators.
Outcomes on intelligence, attention, mood, and stress were assessed (with Raven’s progressive matrices, Posner et al’s attentional network test, a scale called the Profile of Mood States, and cortisol & secretory IgA, respectively).
Despite a lack of pre-training differences between groups, the meditation training was associated with:
- significantly greater improvements in attention than the control group, only in terms of the ability of subjects to quickly resolve conflict; the ability to maintain alertness or to orient attention was unimproved;
- marginally larger improvements in intelligence, as assessed by Raven’s (p=.086)
- reduction in the stress evoked by a cognitive challenge (as evaluated after 3 minutes of mental arithmetic and then another 20 minute session of training)
- broad improvements in mood, including increased positive mood and decreased negative moods.
Whereas the current study found improvements only in conflict resolution on the ANT, work by Jha et al with expert meditators found improvements only on the other two components of the ANT. Critically, however, Jha et al included subjects who were interested in meditation; maybe this capacity is resistant to training among those with a prior interest in meditation, perhaps because they are already quite good at it (a ceiling effect). Alternatively, meditation’s effects on conflict resolution could be more immediate but also more impermanent than those on the other subsystems, yielding an effect here but not in the longer term study of Jha et al.
See also the coverage at MindUpdate.