Resolution of Virtual Grating Orientation With 2-DOF and 3-DOF Force Feedback Systems

Abstract

The present study describes experiments comparing human observers’ ability to resolve the orientation of grating stimuli presented on a 3-DOF haptic interface (PHANToM) and a 2-DOF haptic interface (Immersion IE2000 joystick). Although the force renderings for the two devices are of necessity quite distinct, both yield surprisingly credible percepts of surface texture. Accordingly, resolution for sinusoidal gratings (3-DOF device) and “square-wave” gratings (2-DOF device) was measured as the minimum spatial period required to determine which of two grating orientations had been presented. For the 3-DOF device, this ability was tested for a range of grating amplitudes. For the 2-DOF device, a range of damping constants was employed. Pilot results showed better performance for the 2-DOF device, most likely attributable to the sharp delineation of “edges” for the gratings presented, as compared to the “edgeless” sinusoidal gratings presented on the 3-DOF device. In addition, observers reported a number of interesting perceptual phenomena when stimuli were close to threshold.