The effect of visuohaptic delays on task performance and human control strategy in manual control tasks

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Currently haptic technology is being widely implemented in applications such as tele-operation. One of the main concerns are the communication delays due to the visual or haptic feedback signals traveling long distances. Also, different subsystems handling visual and haptic feedback cause modality-specific delays causing asynchrony between visual and haptic cues. It is not known how human performance and control strategy is affected by visuohaptic delays during manual control tasks, where humans are continuously controlling and observing a system. In this study an inverted pendulum balancing task served as the manual control task. Participants were required to keep the pendulum upright for 30s with various delays (0, 150, 300ms) in visual and/or haptic feedback provided by a screen and a haptic device (HapticMaster MOOG inc). The task performance was measured in fail rate (amount of failed trials) and RMS theta (root mean square of the pendulum angle measured from the upright position), while human control strategy was evaluated with reversal rate (corrections per second) and RMS xd_hand (root mean square of the hand movement speed of the human operator). The main findings are: 1) adding haptic guidance improves task performance; 2) adding haptic feedback reduces the hand movement speed and the amount of corrections made; 3) Communication delays degrade the task performance more than modality-specific delays; 4) Large delays in haptic guidance feedback evoke an aggressive control strategy. In general adding haptic guidance improves task performance with manual control tasks, however humans adapt an aggressive control strategy when large haptic delays are involved.