Non-Colocated Kinesthetic Display Limits Compliance Discrimination in the Absence of Terminal Force Cues

An important goal of haptic display is to make available the action/reaction relationships that define interactions between the body and the physical world. While in physical world interactions reaction cues invariably impinge on the same part of the body involved in action (reaction and action are colocated), a haptic interface is quite capable of rendering feedback to a separate body part than that used for producing exploratory actions (non-colocated action and reaction). This most commonly occurs with the use of vibrotactile display, in which a cutaneous cue has been substituted for a kinesthetic cue (a kind of sensory substitution). In this paper, we investigate whether non-colocated force and displacement cues degrade the perception of compliance. Using a custom non-colocated kinesthetic display in which one hand controls displacement and the other senses force, we ask participants to discriminate between two virtual springs with matched terminal force and adjustable non-linearity. An additional condition includes one hand controlling displacement while the other senses force encoded in a vibrotactile cue. Results show that when the terminal force cue is unavailable, and even when sensory substitution is not involved, non-colocated kinesthetic displays degrade compliance discrimination relative to colocated kinesthetic displays. Compliance discrimination is also degraded with vibrotactile display of force. These findings suggest that non-colocated kinesthetic displays and, likewise, cutaneous sensory substitution displays should be avoided when discrimination of compliance is necessary for task success.