Among the types of the introduced augmented sensory feedback, haptic feedback is the one that can deliver tangible feedbacks, e.g., force, stretch, or vibration, to users' body parts. A haptic lever is one of the most commonly-used interfaces providing a force feedback to attract the user toward the safer or the desired directions while driving a power-wheelchair (Crespo and Reinkensmeyer, 2008; Marchal-Crespo et al., 2010a; Yoon et al., 2017) or assisting target-pointing/hitting tasks (Powell and O'Malley, 2012; Fisher et al., 2015; Patton and Huang, 2016). Vibrators or skin-stretchers have also been used to provide tactile stimulations for postural sway improvement (Gopalai and Senanayake, 2011; Pan and Hur, 2016; Pan et al., 2017), trunk sway improvement (Davis et al., 2010; Lee et al., 2012), target acquisition and pointing (Bark et al., 2010; Hsieh et al., 2014; Kaul and Rohs, 2016), balance training (Spelmezan et al., 2009; Nanhoe-Mahabier et al., 2012), gait function learning (Shull et al., 2011; Sienko et al., 2013). Several devices have been developed to provide realistic three dimensional tactile sensation to the user, e.g., touching a flat surface, grasping a virtual object, and tipping a surface or an object (Chinello et al., 2012; Prattichizzo et al., 2013; Pacchierotti et al., 2015).
Although there exist many investigations about the effect of haptic sensory augmentation, the benefit from the haptic sensory augmentation is still debatable. It has been known that the performance improvement under haptic guidance depends on the user's age and initial skill level (Marchal-Crespo et al., 2010b). Specifically, haptic guidance is more suitable for the novice subjects than the skilled subjects, and the significant improvement could be observed mostly for the for young adults compared to the elderly adults (Cesqui et al., 2008; Milot et al., 2010; Marchal-Crespo et al., 2010b). A critical drawback of the haptic guidance that has been reported is that the haptic guidance can improve the user's performance mostly for the simple motor tasks, e.g., pointing or reaching tasks; in contrast, its benefits tend to degrade for more complex motor tasks, e.g., driving tasks, learning motions in sport activity (Todorov, 2004; Rauter et al., 2010; Marchal-Crespo et al., 2012). All of these issues have been observed in our previous research where subjects drove a virtual power-wheelchair without colliding against obstacles under haptic guidance (Yoon and Hur, 2016). Considering that elderly adults are usually novice drivers, the observed inconsistency of performance improvement across the elderly adults impeded extending our methods for power-wheelchair guidance to the elderly adults.
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To overcome these issues and advance state-of-the-arts in both multiple haptic modalities and haptic guidance for the elderly adults, we propose a haptic joystick combined with a custom-designed wearable skin-stretcher to more effectively guide the elderly adults while driving a power-wheelchair. The objectives of this study are (i) to examine the synergistic effects between two haptic sensory feedback modalities, i.e., force feedback to the hand and cutaneous skin stretch feedback on the steering forearm, (ii) and observe if the synergistic effects are consistent throughout various scenarios. Our hypothesis is that these two simultaneous feedbacks can provide more reliable and informative sensory cues for the improved driving performance in the elderly population. This is plausible because the additional skin stretch feedback can provide more reliable guidance on the supination/pronation of the forearm, which plays an important role in the rider's power-wheelchair control. To the best of authors' knowledge, combining force feedback and cutaneous skin stretch feedback for elderly subjects to improve power-wheelchair control has not been considered.
The anatomy of the wearable skin-stretcher: Front view (A) and Rear view (B). The entire length can be adjusted by the number of Module II with respect to the subject's forearm thickness.
Third, we found a significant main effect of augmented sensory feedback on M3 [p = 0.001, F(3, 42) = 7.27]. Pairwise comparison yielded two significant differences between FC vs. NA (p = 0.039), and FC vs. C (p = 0.026), indicating that the combined sensory feedbacks significantly reduced the deviation of the driving trajectory from the reference compared with no sensory augmentation or cutaneous skin-stretch only (Figure 11C).
Further investigation on M3 (i.e., deviation from the reference trajectory) under FC shows the feasibility of positive synergistic effect between force feedback and cutaneous skin stretch feedback. For the proposed guidance approach, the artificially-generated (software-generated) reference trajectory was invisible to the human subjects. In M3, C, and F separately didn't show any effect even though F seemed to have smaller mean value compared to C. However, the combined FC could effectively minimize the deviation of their driving trajectory from the reference, suggesting synergistic sensory augmentation from both F and C (see Figure 11C).
Even though it's not the scope of this study, it will be interesting to look into the effect of multiple modalities on the performance indices. It was reported that different modalities have different effects on the performance indices (Wang et al., 2011; Ronsse et al., 2011). For example, auditory alertness helped enhance the driving performance whereas visual feedback alone did not (Wang et al., 2011). Even though multiple modalities can be useful in enhancing the driving performance, haptic modality can have more direct effects on the improvement since visual or auditory modalities are already heavily used while conducting the tasks (Scott and Gray, 2008; Wang et al., 2011; Yoon et al., 2017). In our study, other modalities, e.g., vision or audition, were not included than haptic modalities. As reported in the result section, force feedback and skin stretch feedback have different effects in enhancing the performance indices even though both synergistically enhanced the performance. It will be interesting to investigate how other modalities, e.g., vision or audition, can influence the synergistic behavior. In addition, it will be worth examining the way both of force feedback and skin stretch feedback are integrated to maximize the enhancement. 2ff7e9595c
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