Dear authors

Your manuscript has now been reviewed by one of the previous reviewers. Rather than spending further time on waiting or recruiting a further reviewer, I decided to go ahead now. The reviewer's comments merit another revision to address questions about the statistical sensitivity.

Your manuscript is close to receiving in-principle acceptance but please be aware that Stage 2 acceptance is contingent on sufficient reliability being observed. While RRs are never rejected based on their main results, but they can be rejected if prospectively defined quality checks or positive controls fail to such an extent that the research question can’t be answered. You may formally achieve this by setting the reliability test as a positive control at Stage 1 and passing it a condition at Stage 2.

It could be useful to require a Bayes Factor Design Analysis to establish the probability of observing results in favour of H1 vs H0 (see e.g. https://link.springer.com/article/10.3758/s13423-017-1230-y). BFDAs are very useful for establishing the futility or otherwise of a Bayesian design.

Best wishes
Sam

Dear authors

First, let me apologise for the delay in getting back to you. With the December closure and summer in southern hemisphere, this time of year is usually particularly slow.

We have now had comments on your manuscript from two expert reviewers. As you can see, both reviewers were a bit confused by the fact that there have been several rounds of triage to meet RR criteria, which is partly independent from the scientific review. I will discuss this with the PCI:RR management to see if this can be clarified more in future submissions.

Either way, you see detailed and constructive comments from the reviewers that should be addressed before we can recommend in-principle acceptance of Stage 1 and data collection can commence. One reviewer raises a good point about the use of thumbs when typing with a smartphone. Thumbs were probably the primary mode for older pre-smartphone devices. However, when using modern touchscreen devices this may not be that common. Just checking how I type on my own phone, I realised that I use the index finger, and I usually rely a lot on the swype functionality rather than tapping individual letters. Of course, that's just me and this does not invalidate your research question - but I agree with the reviewer that this deserves more thought. It would probably be worth screening for participants who use the thumb of their dominant hand to type? Or alternatively the reviewer also makes suggestions.

The reviewer also has concerns about the prediction of a null result. I realise that your use of Bayes Factors will address this to some extent. However, the reviewer is correct that the sample size may be insufficient. Please consider and report the likelihood of obtaining conclusive results with your minimal and maximal sample size. I also agree with the reviewer that it would be important to support this null prediction with a positive control or outcome-neutral sanity check (e.g. the reliability test the reviewer proposes).

If you choose to submit a revision, please include a version with changes tracked/highlighted as this will expedite the review. Also please include a detailed response letter addressing each comment.

Best regards
Sam Schwarzkopf

Dear authors

I am very sorry but I'm afraid I still need to ask you to make some further changes and/or clarify a few parts. I know this must be tedious but it is important that we have the manuscript ready for reviewers who will likely be unfamiliar with the processes and guidelines of PCI:RR. If you can address all these points quickly I expect we can invite external reviewers. At this stage I would also suggest not having tracked changes but simply refer to where the changes are in your response letter - it would be ideal to have a clean version of the manuscript for reviewers (or alternatively upload a clean and a tracked version - but the main weblink will need to be to the clean version that we will send to reviewers).

Direct link to the manuscript

Thanks for updating the link. However, this now points to the overall project rather than the latest version of the manuscript. This is better than before but I'm willing to bet it will still be confusing for many reviewers. Please use the direct link to the manuscript. For the present version this would be:
https://osf.io/57w2s/?view_only=ecc03e1a965b4d70bd1f7883fc14f709

However, for a further revision it will be yet another address of course.

Design table

Thanks for the modifications. Condensing the text there certainly helped with clarity (and it will be even clearer once tracked changes have all been accepted). However, there now seems to be an error in your interpretation of Hypothesis 2 - unless I'm getting very confused. Hypothesis 2 compares LI_typing_corrected between left- and right-handers, using an indep. sample t-test. In the Interpretation column, you interpret a null effect (no difference between left- and right-handers) as evidence that the lateralisation is unrelated to the medium - but isn't the exact opposite the case? If there is no difference between left- and right-handers for typing even though you'd expect to find this for handwriting, that would indicate that lateralisation does depend on the medium?

Moreover, in this context I wonder if you shouldn't be testing the interaction contrast here - that is, whether the Right-Lefthander_handwriting is greater than Right-Lefthander_typing. However, this is probably something to debate with your reviewers from this field.

I must concede that I find the whole concept generally quite confusing (e.g. talking about the absence of evidence for a reduction in the left/right laterality between left and right handers...). I suspect Doppler ultrasound and handedness experts will be familiar with this but I wouldn't necessarily count on that - however, I'll also let reviewers be the judge of that.

General changes required

You should have also received a generic list of required changes to the manuscript. As far as I can tell some of these have not yet been incorporated:

1) Data must be available to readers after recommendation, either in the text or through an open data repository such as Zenodo (free), Dryad (pay) or some other institutional repository. Data must be reusable, thus metadata or accompanying text must carefully describe the data;
Please add a data availability statement.

2) Details on quantitative analyses (e.g., data treatment and statistical scripts in R, bioinformatic pipeline scripts, etc.) and details concerning simulations (scripts, code) must be available to readers in the text, as appendices, or through an open data repository, such as Zenodo, Dryad or some other institutional repository. The scripts or code must be carefully described so that they can be reused;
Include this also in your availability statement.

3) Details on experimental procedures must be available to readers in the text or as appendices;
As for as I can tell this is all fine, so there shouldn't be anything to add - reviewers may of course have further questions about the methods though.

4) Authors must have no financial conflict of interest relating to the article. The article must contain a "Conflict of interest disclosure" paragraph before the reference section containing this sentence: "The authors of this article declare that they have no financial conflict of interest with the content of this article.";
Please include the COI disclosure before the reference section.

5) This disclosure has to be completed by a sentence indicating that some of the authors are PCI recommenders: “X is a recommender at PCI Registered Reports.”
Please include if this applies to you (since you submitted your manuscript anonymously I cannot ascertain if it does).

Best regards,
Sam Schwarzkopf

Dear authors

Thanks for your resubmission. I believe this is almost ready for being sent out to peer review. However, there are still a few things to fix and consider before that:

1. Design table

I appreciate that you kept in the table due to the requirements for authors. (My apologies for this oversight; I'm familiar enough with the recommender guidelines but not the author guidelines it seems!). I personally prefer flowcharts for this purpose and for relatively straightforward designs I don't think this adds very much, but obviously you should follow the requirements. However, the table as it stands in the current version seems to contain errors:

• Under Hypothesis 1 Analysis Plan and Rationale, you still mention a prior scaled with r=0.2 instead of the new r=0.707.
• Under Hypothesis 2 Question, Hypothesis and Analysis Plan, the table still mentions handwriting and typing as separate t-tests, even though you removed the former.
  
  
• In your response letter you said you changed the orientation of the table (which I agree would be a good idea) but it is still the same.
  
  
• Obviously you could also keep this orientation, but then I'd definitely suggest further condensing the text (and this seems wise to me in either case):
  
  The sentences in the table make sense as part of the manuscript text but to make the table easily digestible you could simplify this much more. Is it necessary to say "We will perform a Bayesian samples t-test..." or would it suffice to say "Bayesian dependent samples t-test..."? Similarly, I don't think we need statements like "This choice is justified because...".
  
  Or under Hypothesis the phrasing "There will be an absence of difference..." sounds like a bit of a double (or even triple?) negative. I appreciate that Bayesian tests for the null lend themselves to this sort of awkwardness. But in the interest of clarity you could simply say "There is no difference..." or even more directly "Cerebral laterality during handwriting is not different from writing with a smartphone" (the fact that your outcome measure is the linguistic component after motion correction is established in the methods and so I don't think this even needs to be mentioned here).
  
  Obviously, these last few points are mere suggestions. You can write your manuscript however you like but I believe it is advisable to make it clearer for reviewers/readers.

2. Link to your preregistered manuscript

Please ensure that the link in the system points to the latest version of the manuscript (ideally one with the last round of tracked changes). The current link points to the original version of the manuscript. It took me some time of clicking through to find the latest version. I am fairly familiar with using the OSF platform but I am sure many reviewers won't be. It also wouldn't be obvious to anyone coming in at this stage that this isn't the final version.

3. Bayes Factor criterion

I appreciate that you have updated the prior definition for your Hypothesis 1 test. The justification makes sense and all this is fine as it is. However, please note that a criterion of BF10=3 and 1/3 is insufficient for the evidence threshold set by many RR-friendly journals. Of course there are still many RR-friendly journals that do not have a strict minimum and you could still submit there when the Stage 2 manuscript is accepted (and in fact you don't need to submit to any journal). If you do want to meet those stricter thresholds, you probably need to rethink the sample sizes.

Best regards
Sam Schwarzkopf

Dear authors

Thank you for your Stage 1 submission. You propose an interesting study and I am curious to see the results. However, we regularly triage manuscripts before sending them out to reviewers to ensure RR criteria are met from the outset. You have done a commendable job in preparing your manuscript, but there are nevertheless a few points I'd suggest addressing before review by experts in your field:

1. Statistical approach / Power analysis

You propose to use a default Bayes Factor with a Cauchy prior scaled with r=0.2 for Hypothesis 1. This hypothesis is set to confirm the null. By using a small scaling factor you are concentrating probability density for the alternative hypothesis near small values and this may very well make sense for what you are testing here - but it also limits your ability to actually confirm the null. It is important to ensure sufficient sensitivity to reliably detect hypothesised effects - or the lack thereof.

Using the original Rouder implementation of the Bayesian t-test with your minimum sample size of 32 your BF10 would be 0.4891 even for a perfect null effect (d=0). Even with your maximum sample size of 48 it is still 0.4332, nowhere near your criterion of 1/6 of confirming the null. While this calculation may be different in whatever implementation of Bayesian inference you're using (e.g. my understanding is that JASP has undergone some changes since Rouder's paper was published), this is the kind of information that is required to ensure adequate power.

If experiment is not sensitive enough to obtain conclusive results, you either need to adjust the prior or increase your planned sample sizes.

2. Hypothesis 2

This hypothesis strikes me as a "main effect" of handedness. This should be a 1-df test that ignores the writing mode. Rather than two independent t-tests you effectively only need one for the sum (or average) of handwriting and typing. However, since you are interested in whether or not left-handers show weaker lateralisation than right-handers, isn't the crucial contrast here an interaction? Specifically you want to test whether the difference between left- and right-handers is weaker for typing than handwriting, and you hypothesise that this is a null effect. If this is incorrect, please clarify.

3. Exclusion criteria

Please provide more detail/information about how exclusions/rejections of participants will work.How will you detemine "Inadequate ultrasound penetration of the skull"? A similar question applies to the second criterion about noisy data: what determines whether epochs are "accepted"?

4. Hypothesis table

This is perhaps a matter of taste. Certainly any journal you may eventually submit this to will probably want to copyedit this in any case. However, I found that table very difficult to digest. A lot of text is awkwardly squeezed into narrow columns. Words are broken across lines. Generally it is very hard to understand. I realise that such tables are often used in RR manuscripts but I would reduce the amount of text here considerably. Move most of the prose into the manuscript itself (where it should be read) and keep this to the essentials and/or abbreviated statements. Instead of a table, it might perhaps in fact be better to have a box diagram outlining the various possible outcomes? This will make it a lot easier for reaers (and reviewers!) to understand. [Note added by Managing Board: please keep the design table in the manuscript as it is a required component, but abbreviate it as much as possible to improve readability. The idea of adding a box diagram or flowchart is a good idea]

5. Quantifying handedness with the pegboard

You have a thorough design for quantifying participants' handedness. However, the way you calculate the handedness index from the pegboard task is different from the other two measures (Edinburgh Handedness Inventory and the Hand Preference task), and even of the opposite sign. This is definitely a matter of taste, but for clarity I wonder if you could consider changing how the pegboard index is calculated to make it directly comparable to the other two tasks (at least by changing the sign so (LH-RH)+(LH+RH)). This would make it easier for readers to understand and might also reduce potential for confusions and errors for experimenters. But as I said, this is just a suggestion.