Research ArticleNEUROSCIENCE

Touch as an auxiliary proprioceptive cue for movement control

See allHide authors and affiliations

Science Advances  05 Jun 2019:
Vol. 5, no. 6, eaaw3121
DOI: 10.1126/sciadv.aaw3121
  • Fig. 1 Experimental setup and protocol.

    (A) The experimental setup, including the textured circular plate, the load cell, and the motion tracking system. In each trial, the servomotor placed under the plate (not visible in the picture) set the orientation of the plate. (B) Blindfolded participants were asked to slide their finger over the ridged plate along a straight direction away from their body. We assumed that extracutaneous proprioceptive cues provided an accurate measurement of motion direction (solid arrow). Instead, the cutaneous feedback produced an illusory sensation of bending toward a direction perpendicular to the ridges, in accordance with previous literature (dashed arrow). This eventually led to an adjustment of the motion trajectory toward the direction indicated by the dotted arrow. (C) Example of trajectories with different ridges. Data are from a single participant. (D) Plate orientations ranged from −60° to 60°. Photo credit: Matteo Bianchi, University of Pisa.

  • Fig. 2 Results of the experiments 1 and 2.

    (A) Experiment 1: The motion angle of the hand trajectory with respect to body midline regressed against the orientation of the textured plate. Positive y values are for a leftward deviation from the midline, whereas negative values are for a rightward deviation. In accordance with our predictions, there is a negative relationship (negative slope) between the error and the plate orientation. Data and linear fit are from a representative participant. (B) The slope of the linear relationship for 10 participants with group estimate and SD (LMM estimates). (C and D) Experiment 2: Conditions with and without glove are represented as orange and azure lines/bars, respectively. *P < 0.05, ***P < 0.001.

  • Fig. 3 Stimuli and results in experiment 3.

    (A) The virtual disk had the same size and position as the real plate. The visual target was arranged on the arc of an ideal circumference with a radius of 5 cm on the plate in one of the following angular positions: −15°, 0°, and 15°. The white arrow and labels were not visible during the experiment. Visual stimuli were displayed by means of an HMD. (B) The position error of the hand trajectory with respect to body midline. The color code is for the different target position, with light, medium, and dark purple corresponding to −15°, 0°, and 15°, respectively. Plate orientation is with respect to the position of the target. Data are from a representative participant. (C) The slope of the linear relationship for eight participants with group estimate and SD (LMM estimates). ***P < 0.001.

  • Fig. 4 The Kalman filter model.

    On the basis of the estimate of the current state and the motor command, a forward model predicts the following state of the limb. This internal estimate is compared to the sensory measurement, generating an error term. In our task, the sensory measurement is equal to the Bayesian integration of the proprioceptive and the tactile cues. This error term, weighted by a gain factor (the Kalman gain), is used to update the estimate of the system and eventually corrects the motor command.

  • Fig. 5 Simulated data from the Kalman filter model.

    (A) The simulated trajectory. (B) Simulation of experiment 2. The tactile weight, wT was set to 0.15 and 0.05 to simulate the with- and the without-glove condition, respectively (with wP = 1 − wT). We used the same color code as for experiment 2; with- and without-glove conditions were represented in orange and azure, respectively. (C) Simulation of experiment 3. The color code is for the different target position, with light, medium, and dark purple corresponding to −15°, 0°, and 15°, respectively.

  • Table 1 Parameters of the observer model.

    For the sake of readability, the subscript indicating the discrete time interval (e.g.,X^t) was omitted in the table.

    θActual motion angle
    θ^Measured motion angle
    uMotor command
    X^State estimate
    X^Forward model of the motor command
    KKalman gain

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/6/eaaw3121/DC1

    Hand displacement: LMM fit and raw data

    Power analysis

    Motion velocity and normal force

    Fig. S1. Convention for the angles of the hand trajectory in experiments 1 to 3.

    Fig. S2. Experiment 1: The angular deviation of the hand trajectory as a function of the orientation of the grating in participants P01 to P10.

    Fig. S3. Experiment 1B (lubricated surface): The angular deviation of the hand trajectory as a function of the orientation of the grating in participants P01 to P04.

    Fig. S4. Experiment 2: The angular deviation of the hand trajectory as a function of the orientation of the grating in participants P01 to P11.

    Fig. S5. Experiment 3: The angular deviation of the hand trajectory as a function of the orientation of the grating in participants P01 to P08.

    Fig. S6. If participants were following the ridges, then the absolute error would have been larger for ±30° stimuli and smaller for ±60°, which was the opposite of what we found.

    Fig. S7. Velocity and force profile in a representative participant.

    Fig. S8. The distribution of peak velocity across trials and participants in experiment 1.

    Fig. S9. The distribution of peak velocity across trials and participants in experiment 2 (with-glove/without-glove experiment).

    Fig. S10. The distribution of peak velocity across trials and participants in experiment 3 (virtual target experiment).

  • Supplementary Materials

    This PDF file includes:

    • Hand displacement: LMM fit and raw data
    • Power analysis
    • Motion velocity and normal force
    • Fig. S1. Convention for the angles of the hand trajectory in experiments 1 to 3.
    • Fig. S2. Experiment 1: The angular deviation of the hand trajectory as a function of the orientation of the grating in participants P01 to P10.
    • Fig. S3. Experiment 1B (lubricated surface): The angular deviation of the hand trajectory as a function of the orientation of the grating in participants P01 to P04.
    • Fig. S4. Experiment 2: The angular deviation of the hand trajectory as a function of the orientation of the grating in participants P01 to P11.
    • Fig. S5. Experiment 3: The angular deviation of the hand trajectory as a function of the orientation of the grating in participants P01 to P08.
    • Fig. S6. If participants were following the ridges, then the absolute error would have been larger for ±30° stimuli and smaller for ±60°, which was the opposite of what we found.
    • Fig. S7. Velocity and force profile in a representative participant.
    • Fig. S8. The distribution of peak velocity across trials and participants in experiment 1.
    • Fig. S9. The distribution of peak velocity across trials and participants in experiment 2 (with-glove/without-glove experiment).
    • Fig. S10. The distribution of peak velocity across trials and participants in experiment 3 (virtual target experiment).

    Download PDF

    Files in this Data Supplement:

Stay Connected to Science Advances

Navigate This Article