Discussion
MM
The present study investigated the acute cognitive effects of a mindfulness meditation session compared to an active control intervention, while controlling for possible cofounding factors related to the familiarity with this practice, the presence of an individual response, and the engagement in the intervention.The participant’s engagement in both interventions was controlled using subjective questionnaires and HR recordings. We observed high scores (>7/10) in the post-MM self-assessment questionnaire in both meditators and novices, reflecting their ability to follow the given instructions during the MM session irrespective of their previous experience with this practice. The meditators scores were however higher than those of the novices (1/10 difference, large effect size). This suggests that a previous MM experience is associated with an improved (perceived) ability to engage in the proposed intervention. The verbal exchange following the control recording also revealed that both meditators and novices were attentive during the control intervention.Irrespective of previous MM experience, the analysis of mean HR showed that both interventions slowed down the cardiovascular dynamics (lower HR, small effect size), but more so during the MM session. This latter finding is in accordance with previous studies [The used subjective and objective measures suggested that all participants, independent of whether or not they had a previous experience in MM practice, were properly engaged in both interventions. We note however a divergence between the self-assessment score and mean HR, with the former showing a statistically significant group effect, but not the latter. It could be that HR is not after all an accurate objective measure of how successfully the participants meditated.Cognitive performance was evaluated using the Stroop task. As a prerequisite, we first analyzed the number of errors which were overall negligible (less than 0.7% of the achieved trials). The number of errors was not affected by the intervention or the previous experience in MM. It was only affected by task condition, with the least errors occurring in the easiest congruent condition and the more errors in the most challenging incongruent condition (large size effect). These findings are not surprising as similar results were found in previous studies investigating the acute MM effects using the Stroop task [Regarding reaction times in Stroop task, our results showed that, compared to baseline, the participants were faster in the three conditions after both interventions (large size effect). They were additionally even faster after MM than after AL in the congruent and incongruent conditions, which supposedly reflects better selective attention, inhibition and cognitive flexibility abilities. Accordingly, our findings suggest that focusing attention on a specific object (the content of the recording in the AL, breath in the MM) may enhance the ability to select perceptual task-relevant information, and to inhibit stimuli that are not relevant to fulfill the task goal. In addition, it appears that orienting attention to the present experience, which was the specificity of the MM session, induced larger cognitive benefits. More importantly, our results suggest that both meditators and novices could show comparable acute cognitive benefits from the proposed interventions.Due to the different ways in which the Stroop task has been implemented in previous studies (computer vs. paper, number of trials, absence or presence of neutral words, kind of neutral words) and analyzed (reported outcomes and their calculation), it is not straightforward to compare our results to those reported in the available literature. While some studies reported a lack acute effects on Stroop task performance following MM (e.g., [However, in the present study, the number of used cognitive tests had to be limited since acute effects are transient and their duration is still unknown. While we used a broad spectrum task (Stroop), the lack of specific tests to assert separately the implicated processes (attention, cognitive flexibility, inhibition) is a limitation. Another limitation of the present work is the absence of a passive control intervention in addition to the AL and MM interventions. As suggested by Davidson and Kaszniak [