Effects of biofeedback on secondary-task response time and postural stability in older adults
Highlights
► We study the effects of biofeedback on secondary task performance during standing. ► Older adults use torso-based vibrotactile feedback to minimize their body sway. ► Biofeedback improves postural metrics even while a secondary task is performed. ► Biofeedback decreases performance on secondary task.
Introduction
A frequent explanation for the decrease in postural sway observed with vibrotactile feedback devices is that these devices augment intact native sensory inputs, giving the user more information about body position with respect to gravity [1], [2], [3], [4], [5], [6], [7], [8]. The cues delivered by vibrotactile feedback provide an external reference of verticality and are similar to those considered responsible for the improvement in balance observed when a user lightly touches a cane [9]. Research in dual-tasking, however, has suggested that the improved balance afforded by light touch and other traditional mobility aids may come at the cost of increased cognitive load and decreased secondary task performance [10], [11]. On the other hand, studies augmenting other sensory modalities have yielded encouraging results under dual-task conditions. For example, Downs demonstrated that using a hearing aid, which amplifies auditory input, not only increases performance on speech discrimination (primary task), but also improves performance on a secondary task [12]. In that study subjects were told to turn off a light, as quickly as possible, that turned on randomly throughout the trial. Downs posited that hearing aids reduce the cognitive demands of the primary task and allow subjects to allocate more attention to the secondary task.
Increased cognitive load presents a particular challenge for older adults as they show not only increased postural sway under such conditions [13], [14], [15], [16] but also decreased secondary task performance [13], [17]. This exhibited decrease in dual-task performance for older adults is often attributed to decreased sensory information [14], [17], suggesting that sensory augmentation may be beneficial. However, if there is a corresponding increase in cognitive load when using sensory augmentation, vibrotactile feedback may further decrease dual-task performance.
A recent gait study by Verhoeff et al. used two different secondary tasks, one motor (carrying a tray with cups of water) and the other cognitive (counting backwards by 7 s), to evaluate the ability of older adults to use multi-modal feedback (tactors, audio alarms, and lights) during dual-tasking [6]. For the motor task trials, trunk sway velocities decreased when feedback was provided. This reduction, however, was confounded by a significant increase in trial time (i.e., subjects took longer to complete the dual-task trials); lower gait velocities may have contributed to the decrease in trunk sway velocities. For the cognitive task trials, gait showed no improvements although cognitive task performance improved. However, the longer length of the dual-task trials could have inflated the improvements observed in secondary task performance.
Recognizing that separate investigations have reported opposite findings for the influence of sensory augmentation on cognitive load, the aim of this study was to assess the effects of vibrotactile feedback on dual-tasking for older adults by using standing balance and response time tasks. We first compare balance metrics with and without feedback during secondary tasks to determine if older adults can effectively use vibrotactile feedback while multitasking. We then analyze the response times of the secondary task with and without feedback to quantify the attentional demands of feedback.
Section snippets
Participants
Ten (6 male and 4 female) community-dwelling older adults ranging in age from 68 to 80 (74 ± 4.3 years) volunteered to take part in the study. The Institutional Review Board at the University of Michigan approved the experimental protocol and informed consent was obtained from each subject in conformance with the Helsinki Declaration. In order to participate, subjects were required to be free of any central neurologic or musculoskeletal dysfunction and not suffering from frequent back or lower
Postural metrics
Fig. 2 shows the results of the PZ analysis. There was a significant interaction between feedback and secondary task. To confirm that subjects were still able to use vibrotactile feedback to increase PZ while performing a secondary task, data were first separated into three groups by secondary task. In all three conditions PZ increased significantly for feedback-on trials in comparison with feedback-off trials (verbal: +13.6%, p < 0.001; push-button: +10.1%, p = 0.007; no secondary task: +28.9%, p <
Postural metrics
The results demonstrate that when feedback was provided, subjects significantly increased PZ and decreased RMS of tilt even when dual-tasking. There was also an increase in PZ when feedback was off and secondary tasks were performed. This is in line with previous work [13] which has shown that when both the postural and secondary tasks are minimally demanding, posture improves. The secondary task distracts individuals away from the postural task and prevents them from focusing too much
Conclusions
Older adults constitute a compelling subject population because they have mild to moderate losses in sensory, cognitive, and motor function, yet they can benefit from extrinsic cues of body position with respect to gravity. Of particular interest is whether or not balance performance will worsen when simultaneously using feedback and performing a secondary task. In this study we demonstrate that older adults are able to improve postural metrics even when performing a secondary task, but find
Conflict of interest statement
The authors have no conflict of interest to disclose.
Acknowledgements
This work was supported by the National Science Foundation's CAREER program (RAPD-0846471, funded under the American Recovery and Reinvestment Act of 2009) and the National Institute on Aging Michigan Claude Pepper Older Americans Independence Center (AG08808 and AG024824). We would like to acknowledge Linda Nyquist and Janet Kemp for their assistance with subject recruitment and testing, Dan Ursu for his assistance with protocol development and data analysis, and Shu Chen for her assistance
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