Practicing Rotated Characters Sharpens the Brain’s Abstract Motor Code

When we learn a new physical skill, whether it is signing our name, playing a chord, or swinging a racket, the brain somehow manages to hold onto what matters about the movement while ignoring the countless incidental details of how it happens to be executed. Cognitive scientists have long documented this kind of abstraction in vision and language, where the mind extracts invariant structure from wildly variable inputs. But whether the motor system builds genuinely abstract representations, and whether those abstractions actually cause improvements in performance, has remained an open and contested question. A new study published in Nature Human Behaviour by Zekun Sun, Zhiran Xie and Samuel D. McDougle of Yale University now provides some of the strongest causal evidence yet that the motor system deploys abstractions from the very earliest stages of skill acquisition.

The researchers designed an elegant paradigm to probe this question: participants learned novel movement patterns by precisely copying unfamiliar handwritten characters on a computer. The task sounds simple, but it demands fine-grained trajectory control, because performance was scored using Procrustes analysis, a statistical method from shape analysis that measures how closely two trajectories match after allowing for translation, scaling and rotation. This metric captures trajectory-level precision in a way that is sensitive to the shape of the path drawn rather than to crude measures like speed or endpoint accuracy. By quantifying the geometric similarity between a participant’s drawn trajectory and the template character, the experimenters could track, trial by trial, how precisely a novel motor pattern had been learned.

The critical manipulation came next. Instead of simply practicing each character over and over in its canonical orientation, one group of participants was trained on markedly rotated versions of the same characters, at rotations such as 90, 180 and 270 degrees. These rotations recruit substantially different low-level movements: the joint angles of the arm and wrist differ dramatically depending on whether a character is drawn upright or upside down, as the authors verified with planar inverse-kinematic models of both a mouse-based and a trackpad-based effector. Crucially, however, the rotated versions preserve the abstract movement trajectory, the invariant sequential structure of the path itself. If learning depends only on rehearsing specific muscle commands, rotated training should confer little benefit. If the motor system instead extracts abstract trajectory representations, rotated training should transfer to the canonical form.

Across eleven experiments, the rotated-training participants showed robust improvements that were comparable to what participants gained from repetitive practice on the canonical characters themselves. In the primary experiment, the majority of individual motor patterns, 39 out of 45, or 87 percent, showed a positive training effect, and the improvement was consistent across participants rather than driven by a handful of outliers or easily learned items. A sliding-window analysis of the trajectories revealed that abstraction training selectively improved accuracy at specific segments of each pattern, indicating that the benefit was not a vague global warm-up but a targeted refinement of the movement’s structure.

Perhaps the most striking aspect of the effect is how thoroughly motoric it proved to be. The improvement did not require a visual template of the target character, did not depend on sustained trajectory feedback, and persisted even in participants with aphantasia, the inability to form conscious visual mental images. In the aphantasic sample of 88 participants, the pattern of improvement across the learning block closely mirrored that of neurotypical participants, providing further evidence that conscious visual imagery is not the engine of the effect. This dissociation matters because an obvious alternative explanation is that rotated training simply sharpens a visual representation of the character’s shape. The data argue instead that something specific to the movement system is being trained.

The experiments also ruled out a second family of explanations rooted in general practice. Merely moving the hand during training, without the relevant abstract structure, was not sufficient, and the benefit could not be attributed to low-level similarity between the joint configurations used during rotated and canonical drawing. The kinematic modeling showed that the cosine similarity between canonical and rotated joint-angle trajectories did not predict how much an individual character improved, with correlations near zero for both the mouse and trackpad models. In other words, characters whose rotated versions happened to demand similar postures to the original did not benefit more, which is exactly what one would expect if the learned quantity is the abstract trajectory rather than the posture.

One of the most revealing findings concerns the sequential structure of movement. When participants were trained by tracking the rotated trajectory forward, the benefit was larger than when they tracked it backward, and this forward-over-backward advantage held for the majority of individual patterns. The motor abstraction, it appears, is not a static spatial shape but an ordered sequence, sensitive to the direction in which the trajectory unfolds. Related analyses showed that rotation training preserved pattern-specific temporal dynamics: the relative time spent traversing each segment of a character remained coherent across rotated training trials, far more so than across trials involving unrelated patterns. Interestingly, though, individual differences in this temporal coherence did not predict the magnitude of learning, suggesting that while temporal structure accompanies the abstraction, it is not the primary driver of the improvement.

The abstraction even transferred across effectors: training benefits carried over from one hand to the other, echoing classic work on motor equivalence in handwriting, in which the same written output can be produced by different limbs. This effector independence aligns the new results with a broader literature suggesting that action representations in the brain can be coded at a level detached from any particular effector, including evidence from people born without hands who nonetheless show intact action systems. It also resonates with recent neural findings that the primate frontal cortex represents action symbols and that human motor cortex encodes complex handwriting through a sequence of stable neural states, a neural architecture well suited to storing abstract trajectory programs.

Theoretically, the study breathes new life into an old idea. Schema theory of motor learning, proposed by Richard Schmidt in 1975, held that learners abstract a generalized motor program from variable practice, and subsequent work showed that variable practice can enhance generalized program learning. Yet the claims of effector independence underlying that tradition were famously challenged, and variable practice effects have been debated for decades, with related approaches such as differential learning producing mixed evidence in meta-analyses. By isolating a manipulation, rotation, that changes low-level movements while preserving abstract structure, and by demonstrating transfer that matches direct practice, the Yale team provides a cleaner causal test than much of the earlier work, and one that survives controls for visual familiarity, imagery, feedback and general motor activity.

The implications reach beyond the laboratory. If abstractions are deployed in the earliest stages of skill acquisition, then training regimens that deliberately vary the surface form of a movement, its orientation, effector or context, may accelerate learning of the underlying structure rather than merely building tolerance to variability. The finding that the effect is sensitive to sequential order suggests that rehabilitation and athletic training should attend to the temporal organization of practice, not just its spatial content. And the demonstration that aphantasic individuals benefit fully underscores that motor learning need not piggyback on visual imagination at all. All data, materials and code from the study are openly available through the Open Science Framework, allowing other researchers to scrutinize and extend a result that reframes the motor system as an abstraction engine in its own right, quietly distilling the essence of every movement we make.

Subject of Research: Causal role of motor abstractions in human skill learning using a rotated handwriting-copying paradigm

Article Title: Motor abstraction training generalizes to the refinement of specific movement patterns

Article References: Sun, Z., Xie, Z., & McDougle, S. D. (2026). Motor abstraction training generalizes to the refinement of specific movement patterns. Nature Human Behaviour. https://doi.org/10.1038/s41562-026-02597-z

Image Credits: AI Generated

DOI: 10.1038/s41562-026-02597-z

Keywords: motor learning, motor abstraction, handwriting paradigm, Procrustes analysis, skill acquisition, generalized motor program, effector independence, aphantasia, trajectory representation, variable practice, Nature Human Behaviour, Yale University