Constraining Eye Movements While Redirecting Walking Trajectories in Healthy Young Adults

1. INTRODUCTION • Significant differences in relative segment timing were only observed in Free Gaze Ipsilateral Foot Contact 2 (IFC2) Turn Offset • Turning around a corner or redirecting the walking trajectory is executed using a specific motor strategy (or steering synergy) where the eyes and head rotate to the new direction first, followed by the body and feet [1] • In a previous study, it was found that when participants were presented a simulated 900 turn while they stepped in place, the steering synergy was evoked [2] • In a follow up study, when the participants were asked to fix their eye position, the steering synergy was not observed [3] • These observations lead to the hypothesis that eye redirection is critical to whole body turning strategies Eyes Head Trunk Pelvis p = 0.096 90˚ p = 0.429 Trial End Position *p < 0.001 p = 0.221 Constraining Eye Movements While Redirecting Walking Trajectories in Healthy Young Adults *p = 0.009 Ipsilateral Foot Contact 1 (IFC1) Turn Onset Time in ms PURPOSE • The purpose of this research was to extend these previous findings into real world walking and turning situations • The goal of this study was to investigate the effects of constraining eye movements on real world walking and turning in healthy young adults • Hypothesized that constraining eye movement would alter the sequence and timing of head, trunk and leg reorientation to the new walking direction Fixed Gaze Free Gaze Trial Start Position Figure 3. Timing (Mean ± SD) of reorientation of eyes, head, trunk and pelvis with respect to IFC1 illustrating intersegment timing in Free Gaze and Fixed Gaze conditions Figure 1. Schematic of right turning trial illustrating turning stride, and definition of turn onset and offset for segment timing analysis RESULTS DISCUSSION • Significant difference in onset of reorientation of segments was observed between Fixed Gaze and Free Gaze (p < 0.001; Fig. 2) • Individual segment analysis revealed significant difference in onset of reorientation between Fixed Gaze and Free Gaze for eyes, head, and thorax segments • Results support that constraining eye movements, while making a change in walking direction, alters the sequence and timing of head and trunk reorientation to the new direction of travel (Fig. 2 & 3) • In turning trials where the eye position was constrained to a fixed point, participants displayed an ‘en bloc’ movement strategy, where all body segments moved together (Fig. 3) • These findings suggest that the oculomotor system is intrinsically linked to systems that control axial body segment reorientation • Limitation was learning effect which limited the real world turning behavior in a few participants. • Inefficiency in steering in certain clinical populations (such as Parkinson’s Disease) could be attributable to deficits in visual redirection, an area of research that as of yet has been largely untouched • Weare currently analyzing data from Parkinsonian participants METHODS V.N. Pradeep Ambati1, Nicholas G. Murray1 , Fabricio Saucedo2, Douglas Powell3 ,Rebecca Reed-Jones2 1Interdisciplinary Health Sciences PhD Program; 2Department of Kinesiology; The University of Texas at El Paso, El Paso, TX 3School of Education, Health and Human Performance, Fairmont State University, Fairmont, WV • 9 healthy young adults between the ages of 18-30 years were recruited for this study • Whole body kinematics were captured using motion capture (120 Hz, Vicon, San Francisco, CA) • Eye movement was recorded using an ASL Eye Tracker system (120 Hz, ASL Eye-Trac 6, Applied Science Laboratories, Bedford, MA) • Participants performed 30 walking trials (straight, right turn, and left turn) randomly presented in two experimental conditions (Free Gaze and Fixed Gaze) • Analysis of segment movement focused on rotation about the yaw (vertical) axis. Eye data focused on horizontal eye in head angular displacement. Straight walking trials were used as control trials and ensemble averaged • Onset of segment and eye reorientation in the turning trials was determined with respect to first foot contact of the transition stride (IFC1; Fig. 1) • Repeated measures ANOVA compared onset time of each segment (dependent variable) between the different gaze conditions (independent variable) *p < 0.001 *p < 0.001 *p = 0.034 p = 0.322 Free Gaze Fixed Gaze Time in ms REFERENCES 1.Patla AE, Adkin A, Ballard T. (1999). Online steering: coordination and control of body center of mass, head and body reorientation. Exp Brain Res. 129; 629-634 2.Reed-Jones RJ, Hollands MA, Reed-Jones JG, Vallis LA. (2009). Visually evoked whole-body turning response during stepping in place in a virtual environment. Gait and Posture. 30; 317-321. 3.Reed-Jones RJ, Reed-Jones J, Vallis LA, Hollands M. (2009). The effects of constraining eye movements on visually evoked steering responses during walking in a virtual environment. Exp Brain Res.197; 357-367. Eyes Head Trunk Pelvis Figure 2. Timing (Mean ± SD) of reorientation of eyes, head, trunk and pelvis with respect to IFC1 in Free Gaze and Fixed Gaze conditions For reprints email: rjreedjones@utep.edu