Distinguishing left from right: A large-scale investigation of left-right confusion in healthy individuals.

The ability to distinguish left from right has been shown to vary substantially within healthy individuals, yet its characteristics and mechanisms are poorly understood. In three experiments, we focused on a detailed description of the ability to distinguish left from right and the role of individual differences, and further explored the potential underlying mechanisms. In Experiment 1, a questionnaire concerning self-reported left-right identification (LRI) and strategy use was administered. Objective assessment was used in Experiment 2 by means of vocal responses to line drawings of a figure, with the participants' hands in a spatially neutral position. In Experiment 3, the arm positions and visibility of the hands were manipulated to assess whether bodily posture influences left-right decisions. Results indicate that 14.6% of the general population reported insufficient LRI and that 42.9% of individuals use a hand-related strategy. Furthermore, we found that spatial alignment of the participants' arms with the stimuli increased performance, in particular with a hand-related strategy and females. Performance was affected only by the layout of the stimuli, not by the position of the participant during the experiment. Taken together, confusion about left and right occurs within healthy population to a limited extent, and a hand-related strategy affects LRI. Moreover, the process involved appears to make use of a stored body representation and not bottom-up sensory input. Therefore, we suggest a top-down body representation is the key mechanism in determining left and right, even when this is not explicitly part of the task.