Vibrotactile and Force Collaboration within 3D Virtual Environments

In a three-dimensional (3D) virtual environment (VE), proper collaboration between vibrotactile and force cues - two cues of the haptic modality - is important to facilitate task performance of human users. Many studies report that collaborations between multi-sensory cues follow maximum likelihood estimation (MLE). However, an existing work finds that MLE yields a mean and an amplitude mismatches when interpreting the collaboration between the vibrotactile and force cues. We thus proposed mean-shifted MLE and conducted a human study to investigate the mismatches. For the study, we created a VE to replicate the visual scene, the 3D interactive task, and the cues from the existing work. Our participants were biased to rely on the vibrotactile cue for their tasks, departing from unbiased reliance on both cues in the existing work. Assessments of task completion time and task accuracy validated the replication. We found that based on task accuracy MLE explained the cue collaboration to certain degrees, agreed with the existing work. Mean-shifted MLE remedied the mean mismatch, but maintained the amplitude mismatch. Further examinations revealed that the collaboration between both cues may not be entirely additive. This sheds an insight for proper modeling of the collaboration between the vibrotactile and force cues to aid interactive tasks in VEs

An exploration of grip force regulation with a low-impedance myoelectric prosthesis featuring referred haptic feedback

Abstract Background Haptic display technologies are well suited to relay proprioceptive, force, and contact cues from a prosthetic terminal device back to the residual limb and thereby reduce reliance on visual feedback. The ease with which an amputee interprets these haptic cues, however, likely depends on whether their dynamic signal behavior corresponds to expected behaviors—behaviors consonant with a natural limb coupled to the environment. A highly geared motor in a terminal device along with the associated high back-drive impedance influences dynamic interactions with the environment, creating effects not encountered with a natural limb. Here we explore grasp and lift performance with a backdrivable (low backdrive impedance) terminal device placed under proportional myoelectric position control that features referred haptic feedback. Methods We fabricated a back-drivable terminal device that could be used by amputees and non-amputees alike and drove aperture (or grip force, when a stiff object was in its grasp) in proportion to a myoelectric signal drawn from a single muscle site in the forearm. In randomly ordered trials, we assessed the performance of N=10 participants (7 non-amputee, 3 amputee) attempting to grasp and lift an object using the terminal device under three feedback conditions (no feedback, vibrotactile feedback, and joint torque feedback), and two object weights that were indiscernible by vision. Results Both non-amputee and amputee participants scaled their grip force according to the object weight. Our results showed only minor differences in grip force, grip/load force coordination, and slip as a function of sensory feedback condition, though the grip force at the point of lift-off for the heavier object was significantly greater for amputee participants in the presence of joint torque feedback. An examination of grip/load force phase plots revealed that our amputee participants used larger safety margins and demonstrated less coordination than our non-amputee participants. Conclusions Our results suggest that a backdrivable terminal device may hold advantages over non-backdrivable devices by allowing grip/load force coordination consistent with behaviors observed in the natural limb. Likewise, the inconclusive effect of referred haptic feedback on grasp and lift performance suggests the need for additional testing that includes adequate training for participants.http://deepblue.lib.umich.edu/bitstream/2027.42/116041/1/12984_2015_Article_98.pd

Haptic Sensory Feedback for Improved Interface to Smart Prosthetics.

Grip force feedback is not available in modern myoelectric upper-limb prostheses, yet its benefits are well known in object manipulation tasks performed through cable-driven body-powered prostheses. To evaluate the efficacy of grip force feedback in a myoelectric prosthesis, direct head-to-head comparisons should be made with body-powered prostheses, as well as with proposed designs that provide grip force feedback through haptic displays such as vibrotactile arrays. Direct comparisons, however, are difficult because myoelectric control for a trans-radial amputee uses residual muscles in the forearm, body-power generally refers interaction to the shoulder, and haptic displays often involve additional information encoding transformations. Currently, no unifying theory exists to cover both information encoding as well as the body part used for control or display. The work developed in this dissertation presents a systematic hypothesis-driven approach to evaluating both information encoding and body part used in the display of grip force feedback. Drawing upon principles from psychophysics, teleoperation, and sensory substitution, we use a series of human subject experiments to quantify the value of grip force feedback for an amputee wearing a trans-radial myoelectric prosthesis. Our findings demonstrate that both able-bodied individuals and amputees scale and coordinate their grip force for the anticipated weight of an object, that control and grip force feedback should be located on the same body site to improve stiffness recognition, and that grip force feedback is more useful than vision feedback in stiffness recognition through a prosthesis.PhDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/108792/1/jdelaine_1.pd