Neural Correlates of Human Echolocation of Path Direction during Walking
Echolocation can be used by blind and sighted humans to navigate their environment. The current study investigated the neural activity underlying processing of path direction during walking. Brain activity was measured with fMRI in three blind echolocation experts, and three blind and three sighted novices. During scanning, participants listened to binaural recordings that had been made prior to scanning while echolocation experts had echolocated during walking along a corridor which could continue to the left, right, or straight ahead. Participants also listened to control sounds that contained ambient sounds and clicks, but no echoes. The task was to decide if the corridor in the recording continued to the left, right, or straight ahead, or if they were listening to a control sound. All participants successfully dissociated echo from no echo sounds, however, echolocation experts were superior at direction detection. We found brain activations associated with processing of path direction (contrast: echo vs. no echo) in superior parietal lobule (SPL) and inferior frontal cortex in each group. In sighted novices, additional activation occurred in the inferior parietal lobule (IPL) and middle and superior frontal areas. Within the framework of the dorso-dorsal and ventro-dorsal pathway proposed by Rizzolatti and Matelli (2003), our results suggest that blind participants may automatically assign directional meaning to the echoes, while sighted participants may apply more conscious, high-level spatial processes. High similarity of SPL and IFC activations across all three groups, in combination with previous research, also suggest that all participants recruited a multimodal spatial processing system for action (here: locomotion).