Overview of the workflow.

(A) Planar view of the experimental setup. (B) Schematic diagram of the setup unit. The orthogonal optical data recorded by the motion cameras were sent to the host computer through the Lock unit. The main system used the orthogonal optical data to generate the grasping skeleton template we have created based on the position of the markers on the dorsal surface of the hand: IND (index finger), THU (thumb), WR1 (wrist, left side) and WR2 (wrist, right side). In turn, the position of the index finger and thumb markers was used in real time to activate the vibration motors through the Arduino UNO microcontroller. Arduino UNO was also responsible for triggering the start and stop VICON system capture during the experiment. (C) Characteristics of the devices used in the experiment.</p

Saccade amplitude values during pre- and post-grasping manual estimation phases.

(A) Scatter plots representing post-grasping phase saccades against pre-grasping phase saccades under the different horizontal size perturbation conditions: non-perturbation (black squares), shortening (blue circles) and lengthening (orange rhombuses). Reference diagonal is defined by the dashed line. (B) Difference between saccadic amplitude values inthe post- and pre- grasping phases for each size perturbation condition. Saccadic amplitude values are shown in degrees (deg). Error bars from the bar charts indicate pooled standard deviations. Asterisks indicate p-values less than 0.05.</p

Task design.

(A) Scheme of the experimental paradigm. (B) Tactile feedback implementation during the grasping phase. Tactile feedback was implemented through the coordinates of the index finger and thumb spherical markers. Once these markers were at a distance of ≤1cm from the screen, the vibration was activated. The graphs on the right show two examples illustrating the position of the markers (index finger and thumb) with respect to the screen position and the vibration threshold. Two conditions are exemplified: static position and moving position (grasping).</p

Grip aperture difference values between pre- and post-grasping phases clustered by 2 groups of bar sizes.

Grip aperture difference values between pre- and post-grasping phases clustered by 2 groups of bar sizes.</p

Relationship between grip aperture values and horizontal bar sizes.

(A) Grip aperture values in pre- and post-grasping phases for each horizontal bar size and horizontal perturbation conditions (non-perturbation, shortening, and lengthening). (B) Grip aperture difference values clustered into 2 groups of bar sizes (Cluster-1: sizes 1 to 5; Cluster-2: sizes 6 to 10). Each bar represents the different horizontal size perturbation conditions for each size cluster: non-perturbation (black), shortening (blue) and lengthening (orange). Values from bar charts are represented as pooled mean and error bars as pooled standard deviations. All values are presented in millimetres (mm). Bar sizes from 1 to 10 (in ascending order): 3.18, 3.56, 3.94, 4.32, 4.71, 5.09, 5.47, 5.85, 6.23, 6.62 deg.</p

Multiple regression analysis of the association between bar sizes and predictors (grip aperture and saccade amplitude).

Multiple regression analysis of the association between bar sizes and predictors (grip aperture and saccade amplitude).</p

Grip aperture values during pre- and post-grasping manual estimation phases.

(A) Scatter plot representing post-grasping phase perceptual responses against pre-grasping phase responses under the different horizontal size perturbation conditions: non-perturbation (black squares), shortening (blue circles) and lengthening (orange rhombuses). Reference diagonal is defined by the dashed line. (B) Difference between grip aperture values in the post- and pre- grasping phases for each size perturbation condition. Grip aperture values are shown in millimetres (mm). Error bars from the bar charts indicate pooled standard deviations. Asterisks indicate p-values less than 0.05.</p