CIRCULAR TRAJECTORY FORMATION DURING BLIND LOCOMOTION - A TEST FOR PATH INTEGRATION AND MOTOR MEMORY

Eight healthy subjects were asked to walk blindfolded along circular p aths of different radii after several practice trials with vision. The ir task was to stop after completing two full revolutions. They always walked counter-clockwise (CCW) in (a) a control condition (CONTROL), including the instructions mentioned above, (b) with the further instr uction to count backwards in twos (MENTAL), (c) with the instruction t o count loudly (LOUD). The movement of two markers lying along the hea d naso-occipital axis was recorded by means of an ELITE system. Total walked distance (DISTANCE), total head turning angle (ANGLE) and avera ge radius (RADIUS) of the trajectories performed were measured. All su bjects were able to perform approximately circular trajectories. They consistently overshot the ideal radius independently of the condition and circle size, undershot the total angle and overshot total distance . The LOUD condition induced greater errors in the performance but onl y on total distance (P<0.05). A strong correlation was found between t he errors in radius and total distance but not between distance and to tal angle. Principal components analysis suggested that radius and dis tance share a common source of errors while total angle produced indep endent errors. The results indicate that (a) circular trajectories can be generated starting from spatial and/or motor memory, without the a id of visual information; (b) the task needs some attentional control and does not involve simple automatic processing of afferent informati on; (c) different sensory information or different processing modes ar e probably involved in the estimation of the curvature and length of t he walked path on the one hand, and of the total rotation angle on the other.