Preliminary stiffness perception assessment for a tele-palpation haptic interface

Palpation of patients is a common type of examination that is carried out by physicians for the early diagnosis of abnormalities in abdomens. In the ReMeDi project, a system for tele-palpation is developed. The system includes a diagnostician haptic interface which renders the abdomen of the remote patient. For the design of such a haptic interface, we investigate how the stiffness of a tissue layer is perceived by a human when mediated by a high-performance haptic interface acting in a simulated teleoperation loop. In our setup, the participants interacted with a haptic interface that displayed on their hands a force proportional to the stiffness of two layers that were compressed. The participants had to discriminate whether they were pushing on one or two layers of tissue. The stiffness of the first layer (k1) was used as a baseline, whereas the stiffness of the second layer (k2) varied. We investigated the just noticeable difference (JND) in the tissues stiffness that the participants could perceive. The stiffness JND was investigated by varying the thickness and the stiffness of the first layer. Moreover, we simulated the teleoperation loop by including a delay and damping in the interaction of the user with the virtual tissues. The preliminary results show that the estimated JND is higher with respect to direct interaction with real objects. Our study is in line with the finding that delay is detrimental to stiffness detection. Moreover, we found that higher baseline stiffness, as well as a thicker first tissue layer, help the stiffness discrimination. From this study, we hypothesize that enhancing the feedback to the doctors is crucial to help them making correct diagnoses.