Water Level Task

Piaget and Inhelder (1956) introduced the task to study how children come to use the horizontal as a frame of reference. It has no standard set of bottles, and each study draws its own (Morawietz and colleagues 2024). Many adults also set the line tilted (Liben 1991), often in line with the bottle's frame or parallel to its bottom (Lohaus and colleagues 1996; Thomas, Lohaus and Kessler 1999); success comes from reading the line against the surroundings rather than the bottle (Barhorst-Cates and colleagues 2020). The task is used in research on spatial cognition and frames of reference, in batteries of spatial tests and in training studies. In a paper version with 12 jars, retest reliability twenty minutes apart was high in children, adolescents and young adults, with intraclass correlations of 0.78 to 0.88 (Morawietz and colleagues 2024).

The standard session has two rounds of 9 bottles, 18 settings, each round showing the upright bottle and each tilt once in its own order, in about 5 minutes; a setting gives one or three rounds. Two practice settings with the upright bottle show the true water line afterwards. Practice never shows a tilted bottle, so its feedback teaches the controls and not where water goes. The upright bottle in the test checks the controls, since its water line is level.

The main score is the mean distance of the lines from level in the tilted bottles, in degrees, the mean absolute deviation from the horizontal (Salbod 2001). The task also reports the signed error, positive when the line leans the way the bottle leans, the share of lines within 5 degrees of level and within 5 degrees of the bottle's bottom, the error at each tilt and in the upright bottle, and the time per setting. The scores are research measures and do not diagnose.