Impaired Depth Perception and Restricted Pitch Head Movement Increase Obstacle Contacts When Dual-Tasking in Older People

Background. Trips are the largest contributor to falls in older people, yet little is known about the underlying physiological mechanisms for safe obstacle negotiation. The aims of the study were to determine (i) the effect of a secondary visual task on obstacle contacts when older people negotiated an obstacle course and (ii) physiological factors associated with obstacle contacts. Methods. Thirty community-living adults aged 65 years and older walked along a I 4.5-m walkway containing 21 obstacles with and without a secondary task. The secondary task required participants to call out a series of letters presented in front of them at head height and the suit of a playing card framed on the sidewall. Obstacle contacts, secondary task errors, eye peak-to-peak pitch amplitude and head peak-to-peak pitch amplitude (PA-H), and head angle in pitch were measured. Participants also completed assessments of sensorimotor function and balance. Results. Compared with the obstacle-only trials, participants performed the dual-task trials more slowly (p<.001), contacted more obstacles (p=.032), showed greater PA-H (p<.001), and an extended head position (p<.001). Most participants also made secondary task errors. Regression analysis revealed that depth perception was the only significant determinant of obstacle contacts (explaining 20.6% of the variance) in the obstacle-only task and that depth perception and PA-H were independent and significant determinants of obstacle contacts (explaining 42.3% of the variance) in the dual task. Results. Compared with the obstacle-only trials, participants performed the dual-task trials more slowly (p<.001), contacted more obstacles (p=.032), showed greater PA-H (p<.001), and an extended head position (p<.001). Most participants also made secondary task errors. Regression analysis revealed that depth perception was the only significant determinant of obstacle contacts (explaining 20.6% of the variance) in the obstacle-only task and that depth perception and PA-H were independent and significant determinants of obstacle contacts (explaining 42.3% of the variance) in the dual task. Conclusion. The findings demonstrate the importance of depth perception and head movement for safe negotiation of obstacles in older people and suggest that depth perception in particular should form part of fall risk assessments.