21 research outputs found
Evaluation of the Leap Motion Controller during the performance of visually-guided upper limb movements
<div><p>Kinematic analysis of upper limb reaching provides insight into the central nervous system control of movements. Until recently, kinematic examination of motor control has been limited to studies conducted in traditional research laboratories because motion capture equipment used for data collection is not easily portable and expensive. A recently developed markerless system, the Leap Motion Controller (LMC), is a portable and inexpensive tracking device that allows recording of 3D hand and finger position. The main goal of this study was to assess the concurrent reliability and validity of the LMC as compared to the Optotrak, a criterion-standard motion capture system, for measures of temporal accuracy and peak velocity during the performance of upper limb, visually-guided movements. In experiment 1, 14 participants executed aiming movements to visual targets presented on a computer monitor. Bland-Altman analysis was conducted to assess the validity and limits of agreement for measures of temporal accuracy (movement time, duration of deceleration interval), peak velocity, and spatial accuracy (endpoint accuracy). In addition, a one-sample t-test was used to test the hypothesis that the error difference between measures obtained from Optotrak and LMC is zero. In experiment 2, 15 participants performed a Fitts’ type aiming task in order to assess whether the LMC is capable of assessing a well-known speed-accuracy trade-off relationship. Experiment 3 assessed the temporal coordination pattern during the performance of a sequence consisting of a reaching, grasping, and placement task in 15 participants. Results from the t-test showed that the error difference in temporal measures was significantly different from zero. Based on the results from the 3 experiments, the average temporal error in movement time was 40±44 ms, and the error in peak velocity was 0.024±0.103 m/s. The limits of agreement between the LMC and Optotrak for spatial accuracy measures ranged between 2–5 cm. Although the LMC system is a low-cost, highly portable system, which could facilitate collection of kinematic data outside of the traditional laboratory settings, the temporal and spatial errors may limit the use of the device in some settings.</p></div
Grand average obtained from the 15 participants.
<p>(A) movement time, (B) duration of the deceleration interval, (C) peak velocity. Error bars show standard error of the mean.</p
Three typical trials showing reach velocity data obtained along the primary direction of movement (i.e., depth axis) from the Optotrak and LMC.
<p>(A) Raw and filtered velocity data from the LMC trials that were accepted for analysis. (B) Comparison of the Optotrak and LMC velocity data obtained on concurrent trials.</p
The average difference between the Optotrak and LMC, and the associated standard deviation for each outcome measure plotted for participants 1–14.
<p>(A) movement time, (B) duration of the acceleration interval, (C) duration of the deceleration interval, (D) peak velocity, (E) endpoint accuracy along the azimuth. Each filled circle represents the mean±standard deviation. The unfilled diamond symbol represent the grand average and the corresponding standard deviation.</p
Picture illustrating the experimental set up.
<p>The IREDs were placed on the participant’s index finger (intermediate phalanx) and the radial aspect of the wrist. At the initiation of each trial participants were holding the tip of the needle with their index finger and thumb while the other fingers were extended. When movement was initiated, the index finger was extended and the other fingers flexed slightly.</p
Picture illustrating the experimental set-up used in experiment 3.
<p>Picture illustrating the experimental set-up used in experiment 3.</p
Average sampling rate obtained with the LMC, and the number of usable trials (≤ 40 ms of missing data) obtained from the LMC and Optotrak.
<p>Average sampling rate obtained with the LMC, and the number of usable trials (≤ 40 ms of missing data) obtained from the LMC and Optotrak.</p
Grand average obtained from the 15 participants for each outcome measure.
<p>(A) movement duration for reach-to-bead and reach-to-needle, (B) PV-bead and PV-needle, (C) duration of the grasp and placement tasks. Error bars show standard error of the mean.</p
Bland-Altman plots for kinematic outcome measures.
<p>Difference (Δ Optotrak–LMC) in (A) movement time, (B) duration of the acceleration interval, (C) duration of the deceleration interval, (D) peak velocity, (E) endpoint accuracy along azimuth.</p
The average difference between measures obtained from the Optotrak and LMC systems, and the associated standard deviation plotted for each of the 15 participants.
<p>(A) reach-to-bead duration, (B) reach-to-needle duration, (C) grasp time, (D) placement time, (E) PV-reach-to-bead, (F) PV-reach-to-needle. The unfilled diamond symbol represents the grand average and the corresponding standard deviation.</p