Neuroscience Letters 418 (2007) 60–65 Visual exteroceptive information provided during obstacle crossing did not modify the lower limb trajectory Chris K. Rhea, Shirley Rietdyk ∗ Department of Health and Kinesiology, 800 West Stadium Ave., Purdue University, West Lafayette, IN 47906, United States Received 27 July 2006; received in revised form 14 February 2007; accepted 27 February 2007 Abstract The roles of visual exteroception (information regarding environmental characteristics) and exproprioception (the relation of body segments to the environment) during gait adaptation are not fully understood. The purpose of this study was to determine how visual exteroception regarding obstacle characteristics provided during obstacle crossing modified foot elevation and placement with and without lower limb-obstacle visual exproprioception (manipulated with goggles). Visual exteroceptive information was provided by an obstacle cue – a second obstacle identical to the obstacle that was stepped over – which was visible during crossing. Ten subjects walked over obstacles under four visual conditions: full vision with no obstacle height cue, full vision with an obstacle height cue, goggles with no obstacle height cue and goggles with an obstacle height cue. Obstacle heights were 2, 10, 20 and 30 cm. The presence of goggles increased horizontal distance (distance between foot and obstacle at foot placement), toe clearance and toe clearance variability. The presence of the obstacle height cue did not alter horizontal distance, toe clearance or toe clearance variability. These observations strengthen the argument that it is the visual exproprioceptive information, not visual exteroceptive information, that is used on-line to fine tune the lower limb trajectory during obstacle avoidance. © 2007 Elsevier Ireland Ltd. All rights reserved. Keywords: Visual information; Visual exteroception; Visual exproprioception; Obstacle avoidance; Gait; Gait adaptations; Locomotion Environmental visual cues and cues of one’s self in relation to the environment are used for the planning and control of human movement [1,3]. Visual information during obstacle crossing can be used in a feedforward or on-line manner [5]. Feedfor- ward refers to the use of visual information that was viewed before obstacle crossing, while on-line refers to the use of visual information available during obstacle crossing. A robust finding during obstacle avoidance is that the view of the lower limb as it crosses an obstacle is an important factor in controlling the lower limb trajectory [5,9]. Information of the body relative to the environment is termed visual exproprioception, which is distinguished from visual exteroception, information of environ- mental characteristics, such as height or color of an obstacle [3]. Researchers have manipulated visual exproprioception with the use of goggles (termed visual interference) that act as blinders to remove vision of the lower limbs, and this manipulation resulted in increased horizontal distance (the horizontal distance of the ∗ Corresponding author. Tel.: +1 765 496 6703; fax: +1 765 496 1239. E-mail address: srietdyk@purdue.edu (S. Rietdyk). foot relative to the obstacle), toe clearance (vertical distance between the toe and obstacle when toe is over the obstacle) [5,9] and toe clearance variability [9]. The increased toe clearance variability may reflect the absence of fine-tuning when visual sensory information is not available [5,7]. For example, if it is true that the trajectory is modified during swing as a function of visual information, the absence of visual information will result in a more variable response. A series of studies have demonstrated the effect of visual information on toe clearance measures. When crossing with the trail limb the obstacle is behind the subject, so visual input regarding the obstacle and the limb is unavailable, and toe clear- ance variability of the trail limb is higher than the lead limb [7]. Similarly, when vision of the lead limb and obstacle is obstructed two steps prior to crossing, toe clearance variability also increases [5]. Lead limb elevation, but not trail limb ele- vation, decreased when full vision was restored during obstacle crossing [4] and sudden changes in obstacle height were accom- modated by increased limb elevation [8]. With this rich set of experiments, it is clear that lead limb elevation is controlled by visual information. However, it is not clear if the control is 0304-3940/$ – see front matter © 2007 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2007.02.063