“In other words, flow is a state of arousal, but it is accompanied not by the shallow respiration characteristic of mental effort but rather by the deep respiration typical of joyous states. This is compatible with our proposal that the flow state is the result of an interaction between positive affect and attention.”
in B. Bruya (ed.) Effortless attention: a new perspective in the cognitive science of attention and action.
Compliance has been a delicate subject in psychological research: how do we know whether the participant will follow protocol in a truthful and accurate manner? A lot of ingenious ways of control this have been created, but if the task is hard and burdensome, it is more likely that participants will fail to comply fully. The Experience Sampling Method (ESM), and others alike, are frequently demanding, and require the researcher to work with participants towards increasing motivation and compliance with protocol (even when a reward is given). These methods require answering questionnaires whenever participants are prompted, several times a day, usually during one week. The content of the questionnaire and the amount of times the participant is prompted to answer during each day, depend on the design of the study. However, regardless of having to answer four or eight times a day, it still disrupts daily life; even if that is not intended. By adding physiological measures to the ESM, researchers are also able to find associations between physiological and psychological functioning; but at the cost of loosing not only rates of compliance, but volunteers. This happens because the procedure becomes even more demanding, and it can cause some distress due to social self-awareness when taking physiological samples.