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REVIEW 2 major objections 5 minor 3 references

Different factors determining Motor Execution and Motor Imagery performance in a serial reaction time task with intrinsic variability

T0 review · 2 major / 5 minor · reviewed 2026-08-11 · deepseek-v4-flash

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Pith's one-line read Motor imagery and motor execution in a probabilistic finger-tapping task are timed by distinct factors, with imagery reaction times improving across blocks and tracking the last unpredictable stimulus while execution reaction times do not.

desk verdict The context-tree SRTT in motor imagery is a useful new combination with open code and data, but the central claim that imagery duration is governed by distinct factors is undercut by an unmatched response structure between groups. read the letter →

arxiv 2412.05319 v1 pith:H63YV7ZA submitted 2024-12-03 q-bio.NC q-bio.QM

Patricia Silva de Camargo , Paulo Roberto Cabral-Passos , André Frazão Helene This is my paper · ORCID
classification q-bio.NCq-bio.QM
keywords motorimageryexecutionserialreactiontimetaskcontexttreeprobabilisticsequencelearningmentalpractice
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

This paper studies whether mentally rehearsing a finger-tapping sequence is timed by the same factors as actually performing it. In a serial reaction time task, two groups of ten participants heard 750 auditory cues generated by a probabilistic context tree with fixed and variable transitions; one group tapped the matching key with the right hand, the other imagined each tap and pressed a key with the left hand when the imagined movement finished. The imagery group's reaction times decreased across five blocks, whereas the execution group showed no block effect, and the two groups reacted differently to deterministic versus variable events and to the most recent variable event. The paper's central claim is that the duration of motor imagery, measured indirectly through reaction times, is influenced by distinct factors from those governing motor execution. If true, mental-practice and rehabilitation protocols should not assume imagined movements are paced by the same cues as real ones.

What carries the argument

The key machinery is the probabilistic context tree that generates the 750-item auditory sequence. The tree defines two fixed events, F1 (1 follows 3) and F2 (2 follows 1), each with 100% probability, and two variable events, V2 (2 follows 2, 26%) and V3 (3 follows 2, 74%), making some transitions predictable and others not. Reaction time to each event is the behavioral readout of how well the participant is tracking the tree, and in the Motor Imagery group the left-hand spacebar press converts the end of the imagined right-hand finger movement into a measurable reaction time. Comparing the four event types across blocks, and conditioning on the last variable event, is what exposes the different timing factors in the two groups.

What would settle it

Run the Motor Imagery group with the variable-event probabilities reversed (V2 at 74% and V3 at 26%) and include a control condition in which the Motor Execution group performs the real tap and then presses the left-hand key to end the trial; the predicted inversion of the V2-after-V2 and V3-after-V3 reaction-time pattern in imagery, or a shift in the execution pattern toward the imagery pattern in the control, would directly test whether the distinct-factors claim is real or an artifact of the response structure.

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Extended reading notes

Core claim

The central discovery is that in a task with an intrinsically variable stimulus sequence, motor imagery performance improves across blocks while motor execution performance does not show a block effect, and the two conditions produce different reaction-time profiles across deterministic (F1, F2) and probabilistic (V2, V3) events. In the imagery group, reaction times were shorter when a variable event repeated its own identity (V2 after V2, V3 after V3), a pattern not seen in execution; and the execution group's difference between F1 and F2 disappeared under imagery. The authors treat reaction time as an indirect measure of the duration of the imagined movement and interpret these contrasts as evidence that motor planning during imagery continuously incorporates the last variable event, so the factors timing imagery are different from those timing executed responses.

Load-bearing premise

The central claim rests on the assumption that the time from the auditory cue to the left-hand spacebar press in the imagery group truly measures how long the imagined right-hand finger movement took, rather than reflecting the different response structure or the time needed to decide to press the left hand.

Editorial extensions

If this is right

  • If imagery duration is governed by distinct factors, then mental-practice training must be designed around the probabilistic structure of events rather than merely repeating the movement at a fixed pace.
  • Imagery reaction times improved across blocks in this task, so mental rehearsal alone supports sequence learning even when the sequence contains unpredictable transitions.
  • The execution group's F1-versus-F2 contrast, absent in imagery, suggests anticipation of an upcoming variable event is tied to effector-specific motor preparation that does not operate when the movement is only imagined.
  • The imagery group's sensitivity to the last variable event shows predictive context is updated during imagery, allowing imagery-based protocols to probe predictive sequence learning without overt movement.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • A direct test of the paper's weakest assumption would be to give the Motor Execution group the same single-response structure, having participants actually perform the indicated right-hand tap and then press a left-hand button to end the trial; if the event-dependent pattern changes to resemble the imagery group's, the distinct-factors claim would instead reflect the response structure.
  • The 26%/74% probabilities attached to V2 and V3 are natural dials for a follow-up: if imagery reaction times follow the probabilities as they are varied, that would confirm that imagery tracks event likelihood; if not, the effect may be driven by event identity rather than probability.
  • The paper implies that in rehabilitation, imagined movements should be rehearsed in variable, context-dependent sequences rather than fixed rhythms, since imagery appears sensitive to probabilistic context but not to the same timing cues as execution.
  • One could extend the design to patient populations where sequence learning and motor imagery are both affected, using the context-tree task to separate predictive-timing deficits from execution deficits.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

2 major / 5 minor

Summary. This paper compares motor execution (ME) and motor imagery (MI) in a serial reaction time task with a probabilistic context-tree sequence of three auditory stimuli. Participants in the ME group (n=10) respond by pressing one of three right-hand keys, while participants in the MI group (n=10) imagine performing the corresponding finger movements and then signal completion with a single left-hand spacebar press. The authors report that MI reaction times decrease across blocks, that both groups are sensitive to event probabilities, and that a significant Group×Event interaction indicates that imagery duration is influenced by factors distinct from those influencing execution RT.

Significance. The study uses an elegant probabilistic sequence design and makes its code available, which is a strength. The statistical approach (rank-transformed mixed ANOVAs with Greenhouse-Geisser corrections) is appropriate for the within-subject comparisons. If the central claim were supported, it would have implications for motor imagery theory and motor emulation theory. However, the current design confounds group membership with response structure, and the small sample and multiple testing limit the strength of the conclusions.

major comments (2)
  1. [Methods 3b; Results §1 (Figs 3-4); Discussion] The central claim that 'the duration of the motor imagery ... are influenced by distinct factors than those of Motor Execution' rests on the significant Group×Event interaction (F3,54=7.172, p<0.01) and on the event-specific differences between groups shown in Figure 4. However, the two groups differ not only in the mental operation but also in response mode: ME participants select among three right-hand keys (1/2/3), whereas MI participants make a single fixed left-hand spacebar press after the imagined sequence. The MI RT therefore includes an extra stop-response component and lacks the three-alternative response-selection component present in ME RT. The observed interaction and group differences could thus reflect the absence of response-selection demands in MI rather than a genuine difference in the temporal organization of imagery and execution. The Discussion's characterization of RT as an 'indirect measure' does not rule out this alternative. To support the abstract's claim, the design needs a control condition that equates response structure—for example, an execution group that performs the three finger movements and then emits a separate stop response, or an imagery group that indicates the imagined finger with a keypress.
  2. [Methods §4; Results §1-2] The manuscript reports a large number of ANOVA tests (per-group event/block analyses, a mixed group×event analysis, and per-group event×last-variable-event analyses) without any correction for multiple comparisons across these tests. With n=10 per group and rank-transformed data, the power of these tests is limited, and the probability of false positives is inflated. No effect sizes are reported, making it difficult to gauge the magnitude of the significant effects. The authors should report effect sizes (e.g., partial eta-squared) for each ANOVA and either correct for the number of tests or explicitly frame the results as exploratory. The significant interaction that supports the central claim would be considerably more convincing if accompanied by an effect size and a sensitivity analysis.
minor comments (5)
  1. [Methods 3b] The text has a typo: 'spacebarkey' should be 'spacebar key.'
  2. [Figure 5 caption] The caption says 'depicted in Figure4' when it should refer to Figure 5.
  3. [Methods 3a] The familiarization phase is described only for the execution-style response; it is unclear whether MI participants practiced the left-hand spacebar response or imagined the finger movements during this phase. Please clarify the familiarization procedure for the MI group.
  4. [Results §1] The statement 'The mean reaction times for V2 and V3 decreased across the blocks' is not tied to specific statistical results; please indicate which post-hoc comparisons support this claim.
  5. [Discussion] The discussion of the lack of Block effect in the ME group attributes this to task simplicity, but no independent measure of task complexity is provided. This claim should be softened or supported.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the central claims are empirical inferences from reaction-time group comparisons, not derivations from fitted parameters or self-cited theorems.

full rationale

The paper's central assertion—that motor imagery duration, indirectly measured by reaction times, is influenced by distinct factors from motor execution—is supported by direct statistical comparisons of measured reaction times across groups, blocks, events, and last-variable-event conditions. The key results are a two-way mixed ANOVA interaction between Group and Event (Results 1) and significant Event×LastVariableEvent interactions within each group (Results 2). These are empirical outcomes, not consequences of a definition, a fitting procedure, or a prior theorem. The authors use reaction time as an operational measure of performance and of imagery duration; this is an interpretive assumption about construct validity, not a circular reduction of the conclusion to the input. The self-citations that appear (Helene and Xavier, 2006; Cabral-Passos et al., 2024) are used only for background motivation, such as the shared neural substrate of imagery and execution, and for describing the probabilistic sequence; they do not carry the load of the central difference claim. The context tree was previously tested in another study, but that fact is about stimulus construction, not about the conclusion that imagery and execution differ. There are no fitted parameters that are later renamed as predictions, no uniqueness theorem imported from the authors' prior work, and no ansatz smuggled in by citation. The potentially important limitation that the two groups use different response structures (three right-hand finger responses vs. one left-hand spacebar press) is a plausible threat to the validity of the Group×Event interaction, but it is a confound or construct-validity concern, not a circularity: the inference is not equivalent to its own inputs by construction. Therefore the paper is self-contained as an empirical study and receives a circularity score of 0.

Assumptions & free parameters 0 free parameters · 4 assumptions · 0 invented entities

No free parameters or invented entities. The principal unstated premises are the validity of the MI reaction-time measure and the comparability of the groups.

assumptions (4)
  • ad hoc to paper Reaction time in the Motor Imagery group, from stimulus offset to spacebar press, indexes the duration of the imagined finger-tapping.
    Central measurement assumption; the spacebar press is a secondary motor response that is not part of the imagined action (Methods, section 3b).
  • domain assumption The two participant groups are comparable for the group comparison despite differing KVIQ scores.
    KVIQ-10 visual and kinesthetic scores differ (26.1 vs 35.1, 25.8 vs 32.9) but no statistical test or matching is reported (Table 1).
  • domain assumption The context-tree generated sequence with stated probabilities is sufficiently learned within 750 trials.
    The sequence was used in prior work (Uscapi 2020; Cabral-Passos 2024) and is assumed to induce learning; no independent measure of sequence knowledge is reported.
  • standard math Rank-transformation and ANOVA assumptions are met after transformation.
    Normality and sphericity are checked and corrected; this is standard repeated-measures ANOVA practice.

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Cite this review

Pith. "Pith review of Different factors determining Motor Execution and Motor Imagery performance in a serial reaction time task with intrinsic variability." pith.science (2026). https://pith.science/paper/H63YV7ZA

@misc{pith2026241205319,
  author       = {Pith},
  title        = {Pith review of: Different factors determining Motor Execution and Motor Imagery performance in a serial reaction time task with intrinsic variability},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/H63YV7ZA}},
  note         = {Machine review of arXiv:2412.05319}
}
read the original abstract

Motor imagery corresponds to the mental practice of simulating visual and kinesthetic aspects of a given motor task. This practice shares a similar neural substrate and correlated temporal scale with motor execution. Besides that, it can lead to performance improvements in the actual execution of the imagined task. Therefore it is important to understand functional differences and equivalences between motor imagery and motor execution. To tackle that we employed a finger-tapping serial reaction time task in two groups of participants, a Motor Execution (n=10) and a Motor imagery (n=10). The sequence of stimuli defining the task had 750 items composed of three distinct auditory stimuli. Also, this sequence had some intrinsic variability making some of the next items unpredictable. Each auditory stimulus was mapped to a single right hand finger in the Motor Imagery group. The Motor imagery group indicated the end of the imagination with a single response using the left hand. The results show improvement in performance of the Motor Imagery group throughout the task and that the duration of the motor imagery, indirectly measured by reaction times, are influenced by distinct factors than those of Motor Execution.

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

3 extracted references · 3 canonical work pages

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    Schuster, C.,Hilfiker, R.,Amft,O.,Scheidhauer,A.,Andrews,B.,Butler,J.,andet.al.(2011).Bestpracticeformotorimagery:asystematicliteraturereviewonmotorimagerytrainingelementsinfivedifferentdisciplines.BMCMedicine9.doi:10.1186/1741-7015-9-75 Seabold,S.,andPerktold.J.(2010).Statsmodels:Econometricandstatisticalmodelingwithpython. Proceedingsof the 9th Python i...

    work page Pith review arXiv 2011

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Reviewed August 11, 2026 · model on record in the stance chip above.