Kinematic Strategies for Upper Arm–Forearm Coordination in Three Dimensions
Bibliographic record
Abstract
This study addressed the question of how the three-dimensional (3-D) control strategy for the upper arm depends on what the forearm is doing. Subjects were instructed to point a laser-attached in line with the upper arm-toward various visual targets, such that two-dimensional (2-D) pointing directions of the upper arm were held constant across different tasks. For each such task, subjects maintained one of several static upper arm-forearm configurations, i. e., each with a set elbow angle and forearm orientation. Upper arm, forearm, and eye orientations were measured with the use of 3-D search coils. The results confirmed that Donders' law (a behavioral restriction of 3-D orientation vectors to a 2-D "surface") does not hold across all pointing tasks, i.e., for a given pointing target, upper arm torsion varied widely. However, for any one static elbow configuration, torsional variance was considerably reduced and was independent of previous arm position, resulting in a thin, Donders-like surface of orientation vectors. More importantly, the shape of this surface (which describes upper arm torsion as a function of its 2-D pointing direction) depended on both elbow angle and forearm orientation. For pointing with the arm fully extended or with the elbow flexed in the horizontal plane, a Listing's-law-like strategy was observed, minimizing shoulder rotations to and from center at the cost of position-dependent tilts in the forearm. In contrast, when the arm was bent in the vertical plane, the surface of best fit showed a Fick-like twist that increased continuously as a function of static elbow flexion, thereby reducing position-dependent tilts of the forearm with respect to gravity. In each case, the torsional variance from these surfaces remained constant, suggesting that Donders' law was obeyed equally well for each task condition. Further experiments established that these kinematic rules were independent of gaze direction and eye orientation, suggesting that Donders' law of the arm does not coordinate with Listing's law for the eye. These results revive the idea that Donders' law is an important governing principle for the control of arm movements but also suggest that its various forms may only be limited manifestations of a more general set of context-dependent kinematic rules. We propose that these rules are implemented by neural velocity commands arising as a function of initial arm orientation and desired pointing direction, calculated such that the torsional orientation of the upper arm is implicitly coordinated with desired forearm posture.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".