Influence of Visual and Haptic Feedback on the Detection of Threshold Forces in a Surgical Grasping Task

Feedback from sensory modalities is crucial for the precise grasping of tissues during minimally invasive robotic surgery. The aims of the study are to determine the influence of visual and haptic feedback on the detection of threshold forces and to evaluate the applicability of the sensory integration model to a surgical grasping task. A sensorized surgical grasper and a fingertip haptic force feedback device were used. Three types of stimuli were presented (i.e. visual-alone, haptic-alone, and bimodal visual and haptic stimuli). Threshold forces of 100 mN and 87.5 mN were detected for visual and haptic feedback, respectively. When bimodal feedback was provided, the participants detected a threshold force of 75 mN. The threshold force for the bimodal condition was 28.6% lower than the visual-alone feedback and 15.4% lower than the haptic-alone feedback stimuli. Our bimodal condition results showed that there was a 13.1% difference between the experimental result and the predicted value from the sensory integration model. The threshold force discrimination was strongly influenced by the haptic force feedback. It is likely that the tissue stiffness can be more intuitively perceived through the direct force stimulation of the fingertip than just by visual observation alone. Cues like small deformations or changes in the grasping angles of the surgical tool are more difficult to interpret visually as compared to the haptic modality.