Stock-still behavior: a potential developmental marker

During the course of a pilot study of toddlers' behavior and play, the experimenters observed a previously undocumented behavior. This behavior now labeled "stock-still" behavior, was noted at the age of 17.5 months and consisted of the toddlers' standing motionless at or near the doorway of a nursery when previously they had marched, seemingly intrepid, into the room on their own. A prospective study of eight children was undertaken to test the hypothesis that this behavior reliably occurs at a set time during the child's development. Analysis of videotape footage determined that the behavior did not occur as an isolated event but instead was part of a series of one to six individual events within a window spanning two to eight weeks, during a discrete period of time from ages 15.5 months to 18.5 months. It was hypothesized that this behavior may be a developmental marker of the moment when a toddler cognitively and affectively registers the differences between "inside" and "outside," self and other and inner space and outer space. This developmental step is manifested behaviorally as the child's ability to inhibit her responses to previously compelling external stimuli. This hypothesis, as well as its limitations, is herein discussed, and additional clarifying observations are suggested.