1. This study examined how visual feedback of arm movements affects grip force control when the visual feedback is rotated and conflicts with proprioceptive feedback. 2. The results showed that when visual feedback of arm movements conflicts with proprioceptive feedback, it can elicit independent changes in the temporal pattern of grip force control. 3. Specifically, the time to peak grip force was gradually scaled over the first 10 trials when exposed to conflicting visual feedback, suggesting vision influences grip force control even after object contact. However, this visual influence on grip force plateaued with repetitions, indicating somatosensory information gains prominence.

1. Contact Info: simone.toma@asu.edu, marco.santello@asu.edu
[1] Toma S., Sciutti A., Papaxanthis C. and Pozzo T. 2015. Journal of Neurophysiology, 113(6): 1885-95.
[2] Sciutti A., Demougeot L., Berret B., Toma S., Sandini G., Papaxanthis C. and Pozzo T. 2012. Journal of Neurophysiology. 107(12): 3433-45
[3] Johansson R. and Westling G. 1998. Experimental Brain Research, 71(1): 59-71
691.24
Visuomotor rotation to quantify the impact of vision on grip force control Neural Control of
Movement LaboratorySimone Toma, Marco Santello
School of Biological and Health Systems Engineering, Arizona State University
In visuomotor rotation contexts, vision elicits stable changes of arm kinematics, regardless of the actual dynamics¹ sensed
through proprioception. It has been proposed that during arm movement execution, visual feedback is favored when
conflicts between expected and actual proprioceptive and visual signals occur². In contrast, in object manipulation the
weight of visual feedback seems to be drastically reduced once the object has been grasped³, and therefore grip force
control mainly relies on somatosensory information. In light of this latter evidence, grip dynamics should be insensitive to
visual feedback of arm kinematics when this conflicts with somatosensory feedback. This would suggest the involvement
of a general control strategy that does not consider visual feedback of arm kinematics to infer grasp dynamics.
Visual feedback direction influences both arm kinematics and digit forces control
Discussion
Background Rationale
trials
TimetoPeak
GripForce
(%ofmvttime)
20
40
60
0 0
20
40
60
trials
TimeToPeak
GripForce
(%ofmvttime)
* original Time to peak Grip Force
contribution of somatosensory
contribution of vision
0
0.25
0.5
VisualWeight(𝛼)
DU
UD
Asymmetric effect of visual feedback on grip force control
trials
Time to peak grip force is asymmetrically modulated across-trials
In accordance with recent studies4
, our findings show that, in certain conditions of dynamic grasp, vision has a significant
impact on grip force control even after that object has been grasped.
Specifically, we have provided evidence that:
1. Conflicting visual feedback of the arm motions elicits modulation of grip force control. Indeed the influence of the
displayed kinematic of the arm, and maybe the associated sensory gating, also is generalized to hand thereby
influencing the temporal pattern of grip force control
ResultsMethods
Data Analysis
Protocol and Predictions
Sensory Contributions:
𝑇𝑡𝑜𝑃𝑘 𝑡𝑜𝑡 = 𝛼 ∙ 𝑇𝑡𝑜𝑃𝑘 𝑣𝑖𝑠 + (1-𝛼) ∙ 𝑇𝑡𝑜𝑃𝑘ℎ𝑎𝑝𝑡𝑖𝑐
Adaptation Rate (ΔAdpt):
𝑇𝑡𝑜𝑃𝑘 𝑢𝑢 − 𝑇𝑡𝑜𝑃𝑘 𝑢𝑑
𝑇𝑡𝑜𝑃𝑘 𝑢𝑢 − 𝑇𝑡𝑜𝑃𝑘 𝑑𝑑
·100
Adjusted Adaptation Rate:
Adj.ΔAdpt. = ΔAdpt 𝑔𝑟𝑖𝑝 - ΔAdpt𝑙𝑜𝑎𝑑
This study aims to quantify the effects of a rotated visual feedback of arm motion on fingertip force control by addressing
the following questions:
1. Can visual information, when in conflict with other sensory signals about arm movement direction, elicit independent
changes in grip force control?
2. If visual feedback or arm kinematics affected grip force modulation, how long would this influence last, given the
conflict between visually-perceived and actual arm kinematics?
3. As visual feedback of upward and downward arm movements are associated with two different task dynamics, will grip
force control be influenced by the displayed feedback in a arm movement direction-dependent fashion?
Half of mvt duration
Time to Peak Force
BASELINE
(NOCONFLICT)
UU
0 10.5
mvt time
GripForce
Time to Peak Force < 0.5 DD
0 10.5
mvt time
GripForce
Time to Peak Force > 0.5
CONFLICT
UD
0 10.5
mvt time
Time to Peak Force > 0.5
0 10.5
mvt time
GripForce
Time to Peak Force < 0.5DU
GripForce
LoadForce
% of mvt time
Time to Load Force Peak
% of mvt time
GripForce
Time to Grip Force Peak
Baseline (UU)
Time (s)
0 21
PositionVelocityGripForceLoadForce
Whole trial profiles
Movement related profiles
UD
20
-20
0
Adj.ΔAdpt.(%)
Later Peak
Earlier Peak
trials
20
-20
0
DU
3 trials binned
trials
Adj.ΔAdpt.(%)
20
0
-20
-10
10
DUUD
Adj.ΔAdpt.(%)
UD
TimetoPeak
Velocity
UU DDUD DU
0
Arm kinematic
Load Force
0.5
1
DD DU
0
0.5
1
UU UD
0
DD DU
*
0
0.5
1
0
UU UD
TimetoPeak
0.5
1
Grip Force
TimetoPeak
TimetoPeakTimetoPeak
[4] Sarlegna F., Baud-Bovy G. and Danion F. 2010. Journal of Neurophysiology, 104(2) 641-653
[5] Flanagan R. and Beltzner G. 2000. Nature, 3(7): 737-41
Main Variables
2. Fingertip force control was gradually scaled across the first 10 trials. This finding accords with previous studies
investigating the effect of conflicting visual information5
. Interestingly, grip control changes plateaued across
repetitions, suggesting gating processes of somatosensory information about the actual dynamic of the movement
3. The observed variations in the temporal pattern of grip force control is direction dependent. In fact, we observed
asymmetries in both the amount of absolute changes and in the relative modulation across trials when actual
movements were performed upward or downward
Set-up