Examination of Kinect’s Torso PCA Model for Planar Activities Assessment after Stroke

Compensatory movement after stroke occurred when inter-joint coordination between arm and forearm for the purpose of arm transport becomes limited due to the weaknesses of the upper limb after stroke. This limitation causes an inefficiency of hand movement to perform the activity of daily living (ADL). Previous work has shown the possibility of using Kinect to assess torso compensation in typical assessment of upper limb movement in a stroke-simulated setting using a Torso Principal Component Analysis (PCA) Model. This research extends the study into evaluating Torso PCA Model in terms of orientation angles of the torso in three dimensional when performing planar activities namely circle tracing and point-topoint tracing. The orientation angles were compared to the outcome of the measurement from a standard motion capture system and Kinect’s intrinsic chest orientation angles. Based on the statistical results, Torso PCA model is concurrently valid with the clinically accepted measures of torso orientation and can be used further to analyze torso compensation in stroke patients.

Functional magnetic resonance adaptation reveals the involvement of the dorsomedial stream in hand orientation for grasping

Reach-to-grasp actions require coordination of different segments of the upper limbs. Previous studies have examined the neural substrates of arm transport and hand grip components of such actions; however, a third component has been largely neglected: the orientation of the wrist and hand appropriately for the object. Here we used functional magnetic resonance imaging adaptation (fMRA) to investigate human brain areas involved in processing hand orientation during grasping movements. Participants used the dominant right hand to grasp a rod with the four fingers opposing the thumb or to reach and touch the rod with the knuckles without visual feedback. In a control condition, participants passively viewed the rod. Trials in a slow event-related design consisted of two sequential stimuli in which the rod orientation changed (requiring a change in wrist posture while grasping but not reaching or looking) or remained the same. We found reduced activation, that is, adaptation, in superior parieto-occipital cortex (SPOC) when the object was repeatedly grasped with the same orientation. In contrast, there was no adaptation when reaching or looking at an object in the same orientation, suggesting that hand orientation, rather than object orientation, was the critical factor. These results agree with recent neurophysiological research showing that a parieto-occipital area of macaque (V6A) is modulated by hand orientation during reach-to-grasp movements. We suggest that the human dorsomedial stream, like that in the macaque, plays a key role in processing hand orientation in reach-to-grasp movements.

Optimal Force Distribution for Payload Positioning Using a Planar Dual-Arm Robot

This paper presents a parameter optimization technique for deciding the force distribution on a payload being transported along a predetermined trajectory using two planar manipulator arms. The methodology begins by transforming the singular dynamics of two-arm transport to an ordinary set of differential equations and then proceeds to obtain a relation between the torques exerted by each arm. This relation is then used in a quadratic torque cost which is subsequently minimized to yield an optimal torque distribution. Significant savings in energy were found to occur when the arms were allowed to interact by transmission of forces through the payload. Even more significant are the savings found over one-arm transport of payloads where the arm torques are fixed by the prescribed trajectory.