Abstract
Studying how we retrace our way in darkness provides a means of understanding the internal representations we use during navigation. In adults, path integration in darkness is influenced by previously presented visual information that conflicted with actual motion (Tcheang et al, PNAS, 2011, 108(3): 1152-7). Here we used immersive virtual reality to isolate visual and motor cues during encoding of a path in children and adults, and examined whether the cues' relative contributions to the stored path representation reflect optimal integration. Eighteen adults and fifteen 10-11-year-old children were guided along a two-leg path in darkness (motor-only), in a virtual room (visual-motor), or they watched a pre-recorded walk in the virtual room while standing still (visual-only). Participants then reproduced the path in darkness. By fitting bivariate normal distributions we obtained a measure of the dispersion of the end-points (variable error) and of their distances from the correct end point (constant error). While adults performed similarly across all three conditions, 10-11-year-old children reduced their variable error when encoding in the bimodal condition, indicating integration of cues. Both adults and children showed greater constant error in the visual-only condition than the motor-only (although significantly greater in adults than children), while the constant error for the visual-motor was intermediate between these two. A significant inverse correlation between visual-motor constant error and number of trials indicated that with only 10 repetitions children learnt to better combine the two cues. These results indicate that 10-11 year-old children can learn to optimally combine visual and motor information to encode a path. Adults' inability to do this could reflect their complete reliance on internal motion-related information because of its greater perceived reliability and relevance to the task. This suggests that the representations we use to navigate in darkness change significantly during the lifespan.
