Effectiveness of an object moving depending on its orientation in the environment: a kinematic analysis of motor planning and execution

Background. Grasping objects with the hand is one of the most common movements in everyday life. It requires training involving the cognitive processes of goal selection and motor planning.

Aim. To investigate the effect of object rotation on motor planning using an experiment where participants moved abstract objects that sometimes required rotation, and movement was assessed using a kinematic analysis system. We hypothesized that reaction times and movements would be longer for tasks with rotation.

Materials and methods. Sixteen subjects participated in the study (11 females and 5 males), mean age – 23.375 ± 2.277 years. Participants were required to perform a task of moving 4 abstract objects onto corresponding platforms with their right hand, while periodically rotating the object by 90°, 180°, or 270°. The motion tracking system monitored the movement of trackers located on the subject’s right thumb and index finger, on the subject’s right wrist, and on the object and the subject’s special glasses.

Results. To assess the effect of object rotation on motor planning, the data were grouped according to the angle of rotation. A one-factor analysis of variance with repeated measures was used. The results showed statistically significant differences:

• total movement time as a function of turning angle: F(3.45) = 5.014, p = 0.004;
• time to reach the grasping target: F(3.45) = 61.79, p = 0.001;
• object motion time: F(3.45) = 14.641, p = 0.001;
• time to reach maximum capture aperture: F(3.45) = 8.559, p = 0.001.

Conclusion. Overall, our results support the hypothesis that object rotation during movement affects both the preparation and execution of the movement itself. The planning and executing the movement with the object rotated 180° was easier and faster than with 90° and 270° rotations. The testing allows distinguishing the stages of planning and preparation of the movement from the execution of the movement itself. Using this approach in patients with central nervous system lesions helps to assess and monitor the state of motor function, which is important for monitoring the recovery process.