Do not turn your head when estimating the distance: influence of head rotation on distance judgement

According to the mental number line (MNL) concept, people mentally represent numbers along a line with smaller values on the left and greater on the right. Embodied cognition theory assumes that MNL is activated by postural bias and in turn affects cognitive processes; for example, research shows that quantitative estimates are smaller when participants' bodies are leaning to the left than to the right. In this study, we tested whether distance estimation in the natural environment is influenced by head rotation. Outdoors, participants gave verbal reports about egocentric distances while keeping their head turned left, turned right, or in the straight-ahead position. Results showed that distance estimates were greater when participants rotated their head right as compared to left. Additionally, we tested whether the MNL is activated by camera-based image movement indicating that the camera is rotating left or right. Participants estimated distances in videos recorded with camera rotation, and the videos were viewed without any postural bias; estimates were similar for camera rotating left and right. The study thus demonstrates that proprioceptive information seems to be necessary for activation of the MNL, which in turn influences verbal distance estimation in the outdoor space.