Path integration is a navigation process in which self-velocity and self-acceleration over time are integrated to update one's positions. The sensory inputs used in path integration are classified into internal and external information. The internal information consists of physical senses from the vestibular system and kinesthetic sense (proprioception and efference copy). The external information is primarily a visual one, obtained from the optic flow. In Experiment 1, participants were asked to point out the start points after traveling 3 paths (containing 3, 5 or 7 turns & legs) in body-based (Internal) or vision-based (External) path integration tasks. Performance in Internal was better than that in External, particularly in the path with 5 turns & legs. In Experiment 2, participants learned the relative locations of 3 points along the path in both Internal and External and were tested on the basis of the pointing accuracy between points. Performance in Internal was more accurate than that in External only when tracing back on the path was needed to estimate directions. The results suggested that the internal information is vital to update the homing direction at turns where we are prone to lose it and helps us to acquire survey knowledge by providing homing directions.
