Reader Comments
Post a new comment on this article
Post Your Discussion Comment
Please follow our guidelines for comments and review our competing interests policy. Comments that do not conform to our guidelines will be promptly removed and the user account disabled. The following must be avoided:
- Remarks that could be interpreted as allegations of misconduct
- Unsupported assertions or statements
- Inflammatory or insulting language
Thank You!
Thank you for taking the time to flag this posting; we review flagged postings on a regular basis.
closeReferee Comments: Referee 2
Posted by PLOS_ONE_Group on 02 Jul 2007 at 13:41 GMT
Reviewer 2's Review
“The paper by Hemond et. al investigates the contra-lateral bias of visual responses to object images at different levels of the visual hierarchy. They demonstrate that there is a general reduction in the bias as one ascends the hierarchical level- however, they report that even in high order object and face areas one can still find a significant measure of contra-lateral bias.
The paper is generally solid and the experiments conducted appropriately and provide clear results. My main suggestions for improvement concern the discussion part.
A. Some contradiction with a prior study of ipsi-lateral representations- the data of the authors appears somewhat at odds with the work of Tootell on the ipsi-lateral representation of early retinotopic areas- which appear to suggest some ipsi-lateral input at least for V2. Since the authors emphasize the lack of ipsi-lateral contributions they should discuss the possible sources of their difference.
B. The contra-lateral bias is by necessity found for off-foveal stimuli. To understand the significance of this ocntra-lateral bias in high order object areas, it is critical to understand how rapidly the activation declines as the stimuli are moved off-center. If the authors have relevant information this should be highly valuable. Even if they don't, they should consider the possible implication of a strong foveal bias to the interpretation of their results. For example, the potential of partial volume effects with near bye retinotopic cortex should be considered.
C. A particularly interesting finding is the category specific difference they find between face and object bias in LO. The authors should discuss possible implications- could it mean that faces and objects receive different retinotopic inputs? Is it, again, related to a different foveal bias for these stimuli?”
N.B. These are the general comments made by the reviewer when reviewing this paper in light of which the manuscript was revised. Specific points addressed during revision of the paper are not shown.
RE: Referee Comments: Referee 2
Hans1 replied to PLOS_ONE_Group on 18 Jul 2007 at 07:59 GMT
These interesting suggestions were addressed as follows prior to publication:
A) The ipsi-lateral activation in the work of Tootell et al. (1998, PNAS) is only seen for stimuli that come close to the vertical meridian, and even then only in a small foveal sub-region of V1/ V2. Tootell reported weak but widespread de-activations for other stimuli (further from the vertical meridian). Given that our stimulus area does not map easily onto the stimuli of Tootell et al. (at the horizontal meridian being further from the vertical meridian than in the Tootell study, but not in the upper/lower field) and given that we did not perform a retinotopic mapping to differentiate between sub-regions of V1/V2 (no eccentricity mapping), we can only speculate about the relationship between the two studies. Most importantly, there is no reason to speak of a contradiction. In the published paper we restrict our conclusion about the presence/absence of ipsilateral responses to our stimulation protocol (see e.g. 4th sentence of the Abstract).
B) The importance of a foveal bias for the interpretation of our findings with non-foveal stimuli is discussed in the published paper on p. 5.
Partial volume effects should be less of a problem in our study compared to many other fMRI work because of the relatively high resolution of scanning. Furthermore, that hypothesis is contradicted by the results of an analysis focusing on the "center voxel" of the FFA (p. 3 in the published paper).
C) In the published paper, this finding is highlighted on p. 5.