Interaction between visual feedback of object motion and grip force modulation
To prevent objects from slipping, digit grip force is adjusted in synchrony to the load changes induced by hand motion.1,2 Due to unavoidable delays in detecting load force modulation by the fingertips, the timing of grip force adjustments need to be planned in an anticipatory fashion by predicting when load peak will occur. This prediction depends on sensorimotor memory (internal models) built through previously-experienced hand-object interactions. Vision appears to be critically important for estimating object dynamic before contact, whereas somatosensory signals are used for rapid grip correction after the object has been grasped. However, recent studies have shown that visual feedback of object kinematic play a role in predictive control of grip force even after contact.3 To better understand the relation between visual and non-visual feedback on grasp force control, we investigated whether non-veridical visual cues of object motion direction can elicit changes in the timing of grip force modulation. We addressed this question while leaving somatosensory signals associated with digit load forces intact. We asked participants to produce ballistic vertical object movements, while controlling the visual feedback of object displacement which was rotated with respect to the direction of actual hand motion (Fig. 1). We found that visual feedback influenced grip force modulation in a direction-dependent fashion. This suggests that, during manipulation, vision and somatosensory cues can be differentially weighted with respect to the visual context and predicted error.4
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- Flanagan J.R., Wing A.M. (1993). Modulation of grip force with load force during point-to-point arm movements. Experimental Brain Research.
- Kinoshita H., Backstrom L., Flanagan J.R., and Johansson R.S. (1997). Tangential torque effects on the control of grip forces when holding objects with precision grip. Journal of Neurophysiology.
- Sarlegna F.R., Baud-Bovy G., and Danion F. (2010). Delayed visual feedback affects both manual tracking and grip force control when transporting a handheld object. Journal of Neurophysiology.
- Toma S., Santello M. (2017). Poster: Visuomotor rotation to quantify the impact of vision on grip force control. Annual meeting of Society for Neuroscience.