Irrelevant idiosyncratic acts as preparatory, confirmatory, or transitional phases in motor behaviour

Motor behaviours typically include acts that may seem irrelevant for the goal of the task. These unnecessary idiosyncratic acts are excessively manifested in certain activities, such as sports or compulsive rituals. Using the shared performance (commonness) of acts as a proxy for their relevance to the current task, we analysed motor behaviour in daily tasks, sport-related tasks, and obsessive-compulsive disorder (OCD) tasks. For each task, these motor behaviours comprised common acts that were performed by all the individuals, and idiosyncratic acts that were performed by only some individuals. In all three tasks there was a temporal section that included all the common acts (termed body). This body section was preceded by a sequence of idiosyncratic acts that we termed head, and was followed by another sequence of idiosyncratic acts that we termed tail. While both head and tail sections were relatively short in the daily tasks, the head was relatively long and the tail largely absent in sport-related tasks, which have a definite end and high stakes. In contrast, OCD behaviour had a relatively long tail. In light of these results, we suggest that the head is a preparatory phase and the tail a confirmatory phase. The head may be viewed as a warm-up phase for the pragmatic section of the task (body), and the tail as a cool-down phase. Finally, we suggest that rituals may be viewed as a descendant of pragmatic activities, which differentially feature a greater terminal phase of idiosyncratic acts in OCD, and an extended initial phase of idiosyncratic acts in sport rituals..