AUTHOR'S REPLY: Thanks to both reviewers for their helpful comments. I have put my replies below in square brackets following each comment.
REVIEW 1 Suggestions for minor changes:
- typo: "stimuli delived"
- When stating that the 2D layout "remained a matter for speculation" it might be useful to add a reference or two, particularly to any ideas which made sense at the time but were then contradicted by the subsequent data.
[the obvious one would be Braitenberg & Braitenberg (c.1979) - I left this out and didn't go into more detail for reasons of brevity. I still prefer not to do this but can do it if you really think the article needs it.]
- Saying "This model predicted a layout of orientation preference that was subsequently confirmed" is quite strong. Perhaps something like "This model predicted general features of the layout of orientation preference that were subsequently confirmed" would be more appropriate.
[I have made that change]
- I think Maldonado et al (1997) showed that "orientation preferences remain well defined right in to the pinwheel center" before Ohki (2006). What Maldonado didn't show was that the map structure was preserved right in to the pinwheel.
[I have changed this to read "well defined, and spatially ordered, right in to ..." ]
- The Fig 5 caption should explicitly mention that black represents one eye, white the other. [I have added that]
- In the "Other Properties" section the following paper might be worth mentioning:
Lu HD, Roe AW. Fnctional Organization of Color Domains in V1 and V2 of Macaque Monkey Revealed by Optical Imaging. Cereb Cortex. 2007
[I have added this reference but to the 'Comparative Studies' section where it seems to belong]
- Given that the conclusions of Swindale et al (2000) have been questioned, I think it would be appropriate to soften "are arranged in ways that optimise coverage" to "may be arranged...", or similar.
[I have altered the wording to 'there is evidence that ...'. (I might add that this section was put in at the suggestion of another reviewer)]
- Introductory paragraph: o Towards the end of the introductory paragraph, “… these quantities can be assigned to neurons in primary visual cortex on the basis …”, gives the impression that visual maps only occur in V1. Tere is a section later for retinotopic maps outside primary visual cortex, but perhaps the presence of maps beyond V1 could be mentioned here.
[I have added the following sentence: "These are not the only quantities that may be mapped: in principle any well-characterised receptive field property is a candidate for mapping in any of the visual areas."]
- Section 2 (Quantification of retinotopic maps): o In the last two sentences of this section: the functional significance of variations and anisotropies in the retinotopic map is unclear. It might be worth mentioning here that the functional significance of maps in general is unclear (other than potentially minimizing wiring length).
[this is mentioned in a later section - it is a good point, but there is presumably still some functional reason why the retinotopic map in area 18 would be severely anisotropic - you would have to point to some kind of functional difference in addition to wirelength, to explain it.]
- Section 3 (Retinotopic maps outside of Primary Visual cortex): o It may be worth mentioning that there are critical periods for the development of the different maps. [my understanding is that, apart from ocular dominance, distinct critical periods have not been well established for other properties. I mention critical period in the ocular dominance section - this can be linked to the topic which I gather will be written about by Nigel Daw (I think wiki will do this automatically)]
o “…these gradients are believed to help establish a rough degree of retinotopic order which is then refined by mechanisms that depend on hebbian synaptic plasticity and neural activity.” In most instances, the exact mechanisms that relate activity to fine tuning connectivity in the maps remain not entirely clear (and a matter of intense research). While the “hebbian plasticity” hypothesis is a compelling one in general, we find that this is not rigorously established yet. We suggest simply stating that the maps are refined by mechanisms that depend on neural activity. If the author wants to mention that this is dependent on hebbian plasticity, then he could state this as a potential mechanism.
[this may be true - my feeling is that the qualification "are believed" is adequate inasmuch as most people assume it to be true - and there is a lot of circumstantial evidence for it even if it has not been rigorously established - my view at any rate; if it had been rigorously established I would have left out the "are believed" part]
- Section 4 (Orientation maps) o In other sections, the author discusses the development of retinotopic maps and ocular dominance columns. It might be worth briefly discussing how orientation maps develop as well.
[again - my understanding is that we don't know much about that, although I know of remarkable new data from Mark Hubener that may tell us more in the near future - perthaps I can update the article when this gets published?]
o “This constancy across layers is refered to as columnar organization…”. Although not necessarily in the context of visual maps, many of the pioneering ideas about columns were put forward by Mountcastle, who could well be cited when defining “columns”.
[there is a link there to an article on columnar organization - which is planned to be written by Mountcastle]
- Section 6 (Other properties represented in visual maps) o It’s not clear what the conclusion of this section is.
[I suppose there isn't really meant to be one]
- Section 7 (Theoretical approaches): o “… Continuity specifies that neighbouring points in the cortex should be mapped, as far as possible, to neighbouring…”. Replace as far as possible by “to the extent possible”.
[this seems purely stylistic. I prefer 'as far as possible' because it avoids repeating 'to'.]
- Section 8 (Comparative studies) o This section is less clearly written than the previous ones.
[this may be the result of keeping it short]
o “…While the organization of corresponding visual areas in cat and ferret appears similar there are differences between maps in these species and those found in primate V1. Notably, maps of direction preference seem to be absent in primate V1 but are present in both areas 17 and 18 of cats and ferrets.” I always took this as evidence that vision can work quite well without these maps. I am not sure that this is the general conclusion from these observations. If so, then maybe it is worth emphasizing that function could be dissociated from maps (and perhaps maps are present due to other constraints such as wiring).
[direction preference gets mapped in primates in MT, so it doesn't affect the argument about the functional role of maps; I mention the issues about wiring being the main reason for maps in the following section: "a reasonable consensus exists that a major function of visual maps, and probably brain maps in general, is to minimise the connection lengths of axons and dendrites"; I am trying to be brief, but I could enlarge a bit on the issues about the functional role or roles of maps if you want.]
- Section 9 (Significance of visual maps): o “the structural details of individual maps and their relation to others”. The meaning of this sentence is unclear. Is the author referring to variations among individuals within the same species?
[I have changed this to read "the structural details of individual maps and their geometrical relationships with others in the same cortical area" - I hope it is clearer now.]
- We have edited few typos directly. [thanks]
Ana Calabrese & Gabriel Kreiman