Dynamic Combination of Movement and Force for Softness Discrimination

Softness is an important source of information when interacting with remote or virtual environments (VE) via a haptic human-machine-interface. For example, in telesurgery where the surgeon operates a human-machine interface transmitting his/her actions to a robot performing actions inside the human body, tissue softness can indicate a healthy or non-healthy condition (De Gersem, 2005). Humans have no dedicated sense for perceiving softness; instead, inferring an objects compliance haptically requires the combination and integration of information from different sensory sources such as positional cues, force cues, and tactile information – see Chapter 5 for a deeper analysis of mechanisms involved in this process. For many technical systems, including above-mentioned telesurgery setups, tactile cues are not conveyed to the human operator, limiting the information available to infer softness movement and force. In direct interaction with a physical object, the gain and temporal relation of movement and force is determined by the objects mechanical impedance. A telepresence or VE system can alter the impedance by, e.g., time delay in the communication channel (Rank, Shi, & Müller, 2010; Ohnishi & Mochizuki, 2007; Pressman, Welty, Karniel, & Mussa-Ivaldi, 2007; Nisky, MussaIvaldi, & Karniel, 2008; Hirche & Buss, 2007; Rank, Shi, Müller, & Hirche, 2010; Hirche & Buss, 2012) which is found to make participants underestimate stiffness under various circumstances, see also Chapters 9 and 5. Determining the limits for