The direction after-effect is a global motion phenomenon

Prior experience influences visual perception. For example, extended viewing of a moving stimulus results in the misperception of a subsequent stimulus's motion direction—the direction after-effect (DAE). There has been an ongoing debate regarding the locus of the neural mechanisms underlying the DAE. We know the mechanisms are cortical, but there is uncertainty about where in the visual cortex they are located—at relatively early local motion processing stages, or at later global motion stages. We used a unikinetic plaid as an adapting stimulus, then measured the DAE experienced with a drifting random dot test stimulus. A unikinetic plaid comprises a static grating superimposed on a drifting grating of a different orientation. Observers cannot see the true motion direction of the moving component; instead they see pattern motion running parallel to the static component. The pattern motion of unikinetic plaids is encoded at the global processing level—specifically, in cortical areas MT and MST—and the local motion component is encoded earlier. We measured the direction after-effect as a function of the plaid's local and pattern motion directions. The DAE was induced by the plaid's pattern motion, but not by its component motion. This points to the neural mechanisms underlying the DAE being located at the global motion processing level, and no earlier than area MT.

from one experiment…). Also, the writing (especially in terms of connecting the present study with the literature) and some analyses needs to be improved. Below I list the major and minor issues to be addressed by the authors.
Major issues: 1. drifting speed of the component as a confound: The authors were careful in controlling the component drifting speed in the unikinetic condition to produce the same perceived pattern speed across different adaptor directions. But that means the component drifting speed varied across adaptor directions, which was an obvious confound. One way to address the issue is to rerun the unikinetic condition with constant component drifting speed so that the pattern speed varied across adaptor directions. If the results were similar with the original unikinetic condition, then the main driving factor should be the "perceived pattern direction of the adaptor". But if the results were different, it may require further investigation.
2. a loosely-connected Discussion: The author may consider focusing the Discussion on discussing the present study and the results, especially the limitations of the experiments. Currently, some of the Discussion (especially the first and second paragraphs) sounds like repeating some parts of the Introduction in reviewing previous findings, with no connection to the present study. For example, the authors may want to suggest how readers can reconcile the apparently contradictory conclusions drawn in the present study and that in Curran et al. (2006). Also, the definition for "global" and "local" may need further clarification, as, currently, "global" only refers to the "pattern direction from a plaid", without addressing other "global" characteristics such as cross-location integration, large receptive field size, etc. Lastly, the authors may want to include two relevant studies from Tony Movshons lab to enrich the discussion/intro (Majaj, Carandini, and Movshon, 2007, which shows that motion integration in MT could be locationspecific; and Tailby, Majaj, and Movshon, 2010, which may be related to the authors' discussion on interocular transfer of DAE).
3. inadequate analysis and interpretation on the results: First, there seems to be a significant difference in DAE in between baseline and unikinetic at 67.5 degrees (i.e., the rightmost bar in each of the two figures). The author should report the test of difference and provide potential explanation if the difference is significant (which, I suppose, is the case, by eyeballing the graphs). Second, if this difference is indeed significant, they authors may want to comment on the overall trend of the DAE, especially in the baseline condition, because it was not consistent with those in the literature, in which DAE typically peaks at 45 degrees (e.g., Schrater and Simoncelli, 1998).
4. How about bikinetic plaids? If DAE is driven by the "global-motion" detectors, a bikinetic plaid with, say, upward and leftward drifting components with identical speed should signal a 45-degree top-left global motion direction. If an observer adapts to this bikinetic pattern, there should be significant DAE on a test stimulus presented at the upward (0-degree) direction. In fact, I have a paper recently accepted by the Journal of Vision, addressing a very similar question asked by the authors in the present study, but I used a different approach: a multiple-aperture stimulus (Amano et al., 2009, JoV) with multiple global directions embedded in the adaptor (Lee and Lu, 2014, AP&P). In one of the experiments, I used bikinetic plaid as both the adaptor and test stimulus, but I did not find a stronger DAE when compared to a single-grating case (for both adaptor and test). Although the general conclusion of my paper is in line with that of the present study (that DAE relies on global-level adaptation, especially when tested with a global-level stimulus), I believe this bikinetic plaid condition would be interesting to explore, and should be discussed by the authors, given that they used plaid as their main stimulus.
Minor issues -Page 10: for the unikinetic condition, why was the moving component drifted at 45 degrees only in the 0-degree case? If I understand this correctly, a unikinetic plaid with a vertical static orientation and an upward drifting component should still be perceived as moving upward. The author would need to justify why they used a different tilt for the static orientation for the 0degree, unikinetic case, or rerun this case with the above-described setup, so that the 0-degree case in the unikinetic condition could be more fairly compared with the other adaptor directions.
-What was the speed of the test RDK? This is an important piece of information because DAE is speed-tuned, and this is somewhat related to the Major issue number 1 above.
-Some details about the procedure need to be added, e.g., exact number of trials in each block, number of blocks completed by each observer, and the order of presentation of the adaptor directions.
-There were both clockwise and counter-clockwise (relative to vertical) directions for the nonvertical adaptors, but it was not described how these adaptor directions were presented. I suppose they were alternated or at least randomized across different blocks, but this needs to be clarified.
-I assume the authors took the estimated PSE as DAE magnitude. But this was not explicitly mentioned in method or results. Please add it back. -The doi link at the bottom of the manuscript does not work for me.

Recommendation?
Major revision is needed (please make suggestions in comments)

Comments to the Author(s) Please see attached file (Appendix A).
Decision letter (RSOS-181271.R0)

27-Sep-2018
Dear Dr Curran: Manuscript ID RSOS-181271 entitled "The direction aftereffect is a global motion phenomenon" which you submitted to Royal Society Open Science, has been reviewed. The comments from reviewers are included at the bottom of this letter.
In view of the criticisms of the reviewers, the manuscript has been rejected in its current form. However, a new manuscript may be submitted which takes into consideration these comments. This new manuscript should include additional data as requested by reviewers 2 and 3.
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We look forward to receiving your resubmission. Comments to the Author: Expert reviewers have read your manuscript and raised some important points that will require more data collection. For example reviewer 3 highlights the need for testing naive subjects and reviewer 2 suggests rerunning the unikinetic experiment. Both have suggestions for improving the readability/accessibility of the manuscript. Please provide a point by point reply to the reviewers.
Reviewers' Comments to Author: Reviewer: 1 Comments to the Author(s) The manuscript investigates the level in the visual system that the direction aftereffect (DAE) occurs. The two levels investigated are the local (V1) and the global (V5) motion levels. These two levels are teased apart by comparing the DAE tuning functions produced by a unikinetic plaid and a sinewave grating. The perceived direction of a unikinetic plaid is in the direction of the static grating and its perception has been linked to V5 and above. The logic of the study was that if the DAE is driven by the local-motion cells, then the tuning function for the unikinetic plaid should be relative to the local-motion direction (the direction of the moving grating) whereas if it is driven by global-motion cells it should be relative to the plaid direction (parallel to the static grating). Results clearly indicate that the plaid direction drives the DAE, and hence supports a global-motion locus to the DAE. This is an elegant study that nicely addresses the question of what level in the motion system drives the DAE. The manuscript is well written and clear and I have no concerns with it.

Reviewer: 2
Comments to the Author(s) The authors used drifting gratings and unikinetic plaids to assess whether DAE comes from the local or global level of motion processing, and their findings support the global-level side. The experiment was carefully conducted, but there seems to be a possible confound that needs to be handled before the authors could draw such conclusion. Along this line, the authors may want to present more data in order to draw a more convincing conclusion (currently, there are only data from one experiment…). Also, the writing (especially in terms of connecting the present study with the literature) and some analyses needs to be improved. Below I list the major and minor issues to be addressed by the authors.
Major issues: 1. drifting speed of the component as a confound: The authors were careful in controlling the component drifting speed in the unikinetic condition to produce the same perceived pattern speed across different adaptor directions. But that means the component drifting speed varied across adaptor directions, which was an obvious confound. One way to address the issue is to rerun the unikinetic condition with constant component drifting speed so that the pattern speed varied across adaptor directions. If the results were similar with the original unikinetic condition, then the main driving factor should be the "perceived pattern direction of the adaptor". But if the results were different, it may require further investigation.
2. a loosely-connected Discussion: The author may consider focusing the Discussion on discussing the present study and the results, especially the limitations of the experiments.
Currently, some of the Discussion (especially the first and second paragraphs) sounds like repeating some parts of the Introduction in reviewing previous findings, with no connection to the present study. For example, the authors may want to suggest how readers can reconcile the apparently contradictory conclusions drawn in the present study and that in Curran et al. (2006). Also, the definition for "global" and "local" may need further clarification, as, currently, "global" only refers to the "pattern direction from a plaid", without addressing other "global" characteristics such as cross-location integration, large receptive field size, etc. Lastly, the authors may want to include two relevant studies from Tony Movshons lab to enrich the discussion/intro (Majaj, Carandini, and Movshon, 2007, which shows that motion integration in MT could be locationspecific; and Tailby, Majaj, and Movshon, 2010, which may be related to the authors' discussion on interocular transfer of DAE).
3. inadequate analysis and interpretation on the results: First, there seems to be a significant difference in DAE in between baseline and unikinetic at 67.5 degrees (i.e., the rightmost bar in each of the two figures). The author should report the test of difference and provide potential explanation if the difference is significant (which, I suppose, is the case, by eyeballing the graphs). Second, if this difference is indeed significant, they authors may want to comment on the overall trend of the DAE, especially in the baseline condition, because it was not consistent with those in the literature, in which DAE typically peaks at 45 degrees (e.g., Schrater and Simoncelli, 1998).
4. How about bikinetic plaids? If DAE is driven by the "global-motion" detectors, a bikinetic plaid with, say, upward and leftward drifting components with identical speed should signal a 45-degree top-left global motion direction. If an observer adapts to this bikinetic pattern, there should be significant DAE on a test stimulus presented at the upward (0-degree) direction. In fact, I have a paper recently accepted by the Journal of Vision, addressing a very similar question asked by the authors in the present study, but I used a different approach: a multiple-aperture stimulus (Amano et al., 2009, JoV) with multiple global directions embedded in the adaptor (Lee and Lu, 2014, AP&P). In one of the experiments, I used bikinetic plaid as both the adaptor and test stimulus, but I did not find a stronger DAE when compared to a single-grating case (for both adaptor and test). Although the general conclusion of my paper is in line with that of the present study (that DAE relies on global-level adaptation, especially when tested with a global-level stimulus), I believe this bikinetic plaid condition would be interesting to explore, and should be discussed by the authors, given that they used plaid as their main stimulus.
Minor issues -Page 10: for the unikinetic condition, why was the moving component drifted at 45 degrees only in the 0-degree case? If I understand this correctly, a unikinetic plaid with a vertical static orientation and an upward drifting component should still be perceived as moving upward. The author would need to justify why they used a different tilt for the static orientation for the 0degree, unikinetic case, or rerun this case with the above-described setup, so that the 0-degree case in the unikinetic condition could be more fairly compared with the other adaptor directions.
-What was the speed of the test RDK? This is an important piece of information because DAE is speed-tuned, and this is somewhat related to the Major issue number 1 above.
-Some details about the procedure need to be added, e.g., exact number of trials in each block, number of blocks completed by each observer, and the order of presentation of the adaptor directions.
-There were both clockwise and counter-clockwise (relative to vertical) directions for the nonvertical adaptors, but it was not described how these adaptor directions were presented. I suppose they were alternated or at least randomized across different blocks, but this needs to be clarified.

Recommendation? Accept as is
Comments to the Author(s) I think the topic addressed by the manuscript is an interesting one, the experiments were well designed and conducted and the results make a worthwhile contribution to the field.

Are the interpretations and conclusions justified by the results? Yes
Is the language acceptable? Yes

Recommendation?
Accept as is

Comments to the Author(s)
The manuscript looks much better and the issues I raised have been adequately addressed.
Just one minor but general point about the tone: the authors seem quite confident in various parts in the manuscript that their results have definitively settled the debate (e.g., in Discussion, second paragraph, "this points squarely to the DAE being driven by global motion adaptation"). But apparently there are still some loose ends, e.g., as the authors acknowledged in discussing Curran et al.'s (2006) results. However, this may be more of an issue about writing style, and I don't have a very strong view on it. I'll leave this to the editor.

20-Feb-2019
Dear Dr Curran, I am pleased to inform you that your manuscript entitled "The direction aftereffect is a global motion phenomenon" is now accepted for publication in Royal Society Open Science.
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On behalf of the Editors of Royal Society Open Science, we look forward to your continued contributions to the Journal. Comments to the Author(s) The manuscript looks much better and the issues I raised have been adequately addressed.
Just one minor but general point about the tone: the authors seem quite confident in various parts in the manuscript that their results have definitively settled the debate (e.g., in Discussion, second paragraph, "this points squarely to the DAE being driven by global motion adaptation"). But apparently there are still some loose ends, e.g., as the authors acknowledged in discussing Curran et al.'s (2006) results. However, this may be more of an issue about writing style, and I don't have a very strong view on it. I'll leave this to the editor.

Reviewer: 1
Comments to the Author(s) I think the topic addressed by the manuscript is an interesting one, the experiments were well designed and conducted and the results make a worthwhile contribution to the field. Follow Royal Society Publishing on Twitter: @RSocPublishing Follow Royal Society Publishing on Facebook: https://www.facebook.com/RoyalSocietyPublishing.FanPage/ Read Royal Society Publishing's blog: https://blogs.royalsociety.org/publishing/