Analysis of Three-Dimensional Circular Tracking Movements Based on Temporo-Spatial Parameters in Polar Coordinates
Round 1
Reviewer 1 Report
General comments
The manuscript: ‘Analysis of three-dimensional circular tracking movements based on temporo-spatial parameters in Polar coordinate’ is interesting and could fit well in the special issue Movement Biomechanics and Motor Control. However it still needs to be amended in several aspects. In particular the objective should be made clearer and some considerations about the meaning of this study in relation to general knowledge and to possible clinical applications should be made. Secondly the experimental protocol should be more clearly described (see specific comments below). Third, there are several repetition of concepts, and for this reason the paper looks verbose, too long, and not easy to read. Please try to reduce the whole length of the manuscript and be more synthetical. Twelve figures and 4 complicated tables are really too much. The authors are encouraged to avoid unnecessary details and limit their data presentation to what is really informative and interesting to the reader. All details could be reported as additional material and made available to the readers on demand…The English language as well should be improved.
Specific comments
Line 85. …the subject perceived a virtual stick…but the subject is really handling a stick or what else device? How the movement of the subjects’ hand was detected?
Line 106…ΔR is defined as the absolute value of the radial position difference between the target and the tracer from the origin…is it function of time? was the average difference measured and used as an error parameter? Why the absolute value and not just the difference of the radial positions? What was the acquisition frequency (how many datapoints in a full revolution)?
Line 108… Δω…same questions as above.
Line 168. …M and SD…M stands for average? Is this the average of the absolute difference? Is it computed on a single trial.. over a single subject.. over all the subjects…Please specify before using it.
Line 171 …this sentence and all sentences like this in the following should be shortened, in fact the figures they are referring to are almost self explaining. Just keep the final consideration (ex.: figure…shows a comparison between….; the result is that ΔR significantly increases….)
Line 285 …during 2D tracking movements… In which plane? How oriented?
Line 288 …The high correlation on the ROT(0) is from the high correlation against X error in Cartesian coordinate and…this sentence is very obscure!!
…all along the text (and also in the title), please correct: Polar coordinates….Cartesian coordinates…(they are plural!)
Line 302 … errors in Cartesian coordinate provided us to confirm only the accuracy…this sentence as well is unclear…
Line 311 … characteristics were sensitive than ΔR, which…something is missing!
Line 319 … Intermittent FB…??? Probably FB stands for Feedback? And FF stands for Feedforward?...please specify
Line 321 … in 2D space… here and in several other locations along the texts, it should be made clear that moving in a single plane does not mean that we are moving in a 2D space. Space is always 3D. We just focus on the 2D coordinates of the movement. Furthermore, as suggested above, the orientation of the plane where the movement occurs should be specified.
Figure 2 … looking at these figures one wonder about where is the starting point? can the tracking wise be represented also here, over the circles? That could help understanding the exercise…
Legends, in general are too long. Please limit the legends to the description of the figures. The methodologic aspects and the numeric results should be explained in the text.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
The paper describes the results of an experiment where subjects had to track a moving target on a circular trajectory. The peculiarity of the experiment is the setup (a 3D virtual reality scenario) and the analysis of the effect of different target planes and velocities on kinematic performance. Even if the idea is interesting there are several issues to be addressed:
1) the differences in planes frontal and sagittal could be due to biomechanical constraints and not to motor control mechanisms. In the literature this is not clear because no clear studies have been conducted to understand the completely different biomechanics used in the two planes. In this case the authors should prove this point.
2) there are many indicators that have been used to analyse tracking movements and that take into account also spatial factors or more kinematic features (tracking error, longitudinal error, figural error, jerk ratio…). Authors should go deeper in the analysis to understand better the mechanism
3) why it is needed a 3D system for the target if then we don’t know about the hand posture? A 3D system is good if the movements and posture of the subjects can be controlled and measured. This was the main choice of the other experiments in literature using 2D target. So if the authors wants to add value to the old experiments with 2D targets they need still to control all the other variables related to posture and different biomechanical constraints.
Minor:
1) English should be drastically improved to make the paper easy to be read.
2) Authors speak about “motor control parameters”. Who defined kinematic features as motor control parameters? Are there any paper that argue this?
3) What about the weight of the controller and its effect on the results?
4) In the data analysis section the unit measures of the indicators should be defined
5) What about the effect of different antropometric parameters on the results? For example different arm-length among participants
6) In the result section authors say: “ For the circular tracking movement on both the frontal and sagittal planes, the trajectory variability tended to increase as the target speed increased. Also, there is more variability on the sagittal plane, compared to the frontal plane, at each target speed..” Variability in terms of what? How it is computed?
7) Few lines in the discussion about the possible mechanisms involved and the difference between feedback and feedforward control. Because this is the key interpretation of the results the authors should provide a really detailed explanation
8) Figure 2-3-4-5 should be collapsed in only one figure so the reader can properly see the differences in the conditions
9) Figure 9-10-11 do not provide any additional information respect to the text and can be removed.
10) Tables 2-3-4 are redundant and could be placed in supplementary material
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
The paper quantitatively evaluated motor control characteristics for circular tracking movement in 3D space. The temporo-spatial relationship in 3D space between the circular tracking movements and the target motion for various speeds and two different rotation axes (depth) were analyzed. Overall the paper was well written and presented. Here are some minor concerns:
It is not clear how the 16 participants were recruited. What were the inclusion/exclusion criteria? Why only male subjects? It is not clear whether the orders for the 4 trials, speeds and planes were randomized or not. If not randomized, then the learning effect should be discussed on the results. Maybe I missed it but it seem to me that the study showed that the three circular movement parameters varied among different target moving speed and depth, however, there was a lack of external validation of those three parameters with "golden standard" on the movement of target and the motor control. This is important and should be clearly described in the article. The significance of the work should be better phrased. It is not clear in the current paper the significant contributions of the work been done.Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
General comments
The manuscript has been considerably improved. There is still a minor point to amend:
Line 80. …The subjects used a tracer…No. If I understand correctly the subject used a physical controller (joystick or what else? please specify) to move a tracer in the 3D VR space. The tracer was visualized as a yellow ball, and the aim was to track the target, visualized as a red ball, moving circularly in the clockwise direction.
Author Response
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Author Response File: Author Response.pdf
Reviewer 2 Report
Response 1: The authors should states that biomechanical constraints have not been taken into account. They need to emphasize it in the discussion and introduction and male less stronger the conclusion about motor control mechanisms that are not supported by the results (they could be only biomechanical constraints)Response 2: OK
Response 3: arm posture of the kinematic chain is still not taken into account and can influence the results. The authors should prove this point or the results are less significant.
Response 4: a further improvement of English language is needed.
Response 5: OK
Response 6: The authors should state that the current results could be influenced by the weight and not only say that in future will be taken into account
Response 7: OK
Response 8: OK
Response 9: OK
Response 10: The authors explain the mechanisms. For completeness they should include something about strategies. Some suggestion:
van de Kamp C, Gawthrop PJ, Gollee H, Loram ID (2013) Refractoriness in Sustained Visuo-Manual Control: Is the Refractory Duration Intrinsic or Does It Depend on External System Properties? PLoS Comput Biol 9(1): e1002843.
Stabilization strategies for unstable dynamics P Morasso, M Casadio, D De Santis, T Nomura, F Rea… - Journal of Electromyography and Kinesiology, 2014Response 11: OK
Response 12: OK
Response 13: OK
Author Response
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Author Response File: Author Response.pdf
