Role of force cues in the haptic estimations of a virtual length.

This study investigated whether and how the force cues play a role in the haptic perception of length. We assumed that the introduction of a dynamic disruption during haptic exploration generated by a haptic display would lead to a systematic bias in the estimation of a virtual length. Two types of "opposition" disruption ("elastic" and "viscous") were proposed in Experiments 1 and 2, and two types of "traction" disruption ("fluid" and "full") in Experiments 3 and 4. In all experiments, blindfolded adults were asked to compare two lengths of virtual rods explored with the right index. Results revealed an underestimation of the length with elastic and viscous opposition disruptions and an overestimation of this length with fluid and full-traction disruptions. No systematic bias in the estimation was observed in the "control" sessions in which the active exploration of the segment was "normal" (i.e. not disrupted). These results suggest that the forces produced during exploratory movements are used as a relevant cue in the haptic length estimation.