MANUAL DISCRIMINATION OF COMPLIANCE USING ACTIVE PINCH GRASP - THE ROLES OF FORCE AND WORK CUES

In these experiments, two plates were grasped between the thumb and th e index finger and squeezed together along a linear track. The force r esisting the squeeze, produced by an electromechanical system under co mputer control, was programmed to be either constant (in the case of t he force discrimination experiments) or linearly increasing (in the ca se of the compliance discrimination experiments) over the squeezing di splacement. After completing a set of basic psychophysical experiments on compliance resolution (Experiment 1), we performed further experim ents to investigate whether work and/or terminal-force cues played a r ole in compliance discrimination. In Experiment 2, compliance and forc e discrimination experiments were conducted with a roving-displacement paradigm to dissociate work cues (and terminal-force cues for the com pliance experiments) from compliance and force cues, respectively. The effect of trial-by-trial feedback on response strategy was also inves tigated. In Experiment 3, compliance discrimination experiments were c onducted with work cues totally eliminated and terminal-force cues gre atly reduced. Our results suggest that people tend to use mechanical w ork and force cues for compliance discrimination. When work and termin al-force cues were dissociated from compliance cues, compliance resolu tion was poor (22%) relative to force and length resolution. When work cues were totally eliminated, performance could be predicted from ter minal-force cues. A parsimonious description of all data from the comp liance experiments is that subjects discriminated compliance on the ba sis of terminal force.