Item

Abstract

Haptic feedback systems can be designed to assist vehicular steering by sharing manual control with the human operator. For example, direct haptic feedback (DHF) forces, that are applied over the control device, can guide the operator towards an optimized trajectory, which he can either augment, comply with or resist according to his preferences. DHF has been shown to improve performance (Olivari et al. submitted) and increase safety (Tsoi et al. 2010). Nonetheless, the human operator may not always benefit from the haptic support system. Depending on the amount of the haptic feedback, the operator might demonstrate an over- reliance or an opposition to this haptic assistance (Forsyth and MacLean 2006). Thus, it is worthwhile to investigate how different levels of haptic assistance influence shared control performance. The current study investigates how different gain levels of DHF influence performance in a compensatory tracking task. For this purpose, 6 participants were evenly divided into two groups according to their previous tracking experience. During the task, they had to compensate for externally induced disturbances that were visualized as the difference between a moving line and a horizontal reference standard. Briefly, participants observed how an unstable aircraft symbol, located in the middle of the screen, deviated in the roll axis from a stable artificial horizon. In order to compensate for the roll angle, participants were instructed to use the control joystick. Meanwhile, different DHF forces were presented over the control joystick for gain levels of 0, 12.5, 25, 50 and 100 . The maximal DHF level was chosen according to the procedure described in (Olivari et al. 2014) and represents the best stable performance of skilled human operators. The participants’ performance was defined as the reciprocal of the median of the root mean square error (RMSE) in each condition. Figure 1a shows that performance improved with in- creasing DHF gain, regardless of experience levels. To evaluate the operator’s contribution, relative to the DHF contribution, we calculated the ratio of overall performance to estimated DHF performance without human input. Figure 1b shows that the subject’s contribution in both groups decreased with increasing DHF up to the 50 condition. The contribution of experienced subjects plateaued between the 50 and 100 DHF levels. Thus, the increase in performance for the 100 condition can mainly be attributed to the higher DHF forces alone. In contrast, the inexperienced subjects seemed to completely rely on the DHF during the 50 condition, since the operator’s contribution approximated 1. However, this changed for the 100 DHF level. Here, the participants started to actively contribute to the task (operator’s contribution [1). This change in behavior resulted in performance values similar to those of the experienced group Our findings suggest that the increase of haptic support with our DHF system does not necessarily result in over-reliance and can improve performance for both experienced and inexperienced subjects.