Haptic perception of viscous friction of rotary switches

Viscous friction or damping for rotatory switches is a mechanical parameter for the torque caused by the angular velocity and crucial to human haptic perception. The detection threshold (DT) and just noticeable difference (JND) for this mechanical parameter was measured. The JND was determined for a standard stimulus of 2 mNms. The DT and JND were investigated for two knob sizes and under the presence or absence of an additional task. In the single-task experimental setup the haptic experiment was the only task. In the dual-task experimental setup the Lane Change Test (LCT) was used as additional task. The results indicate that both the DTs and the JNDs do not depend on the presence or absence of an additional task. Surprisingly, the JNDs are not affected by the used knob diameters, as one would expect, whereas the DTs clearly do.