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Response to the second 'review' of 'Functional specialization in the visual cortex?'


This reviewer did not obviously skip complete paragraphs as the first 'reviewer' did, and he wrote more. However, this review is still not a scientific review.

The response to (1) is based on irrelevant evidence from primate brains, the argument is not to the point, and it is full of misleading statements. Like the first reviewer, he ignores completely the dimensions that I explicitly gives in the first sentence of my criticism.

The response to (2) is the worst: The reviewer first misquotes my review as to distort its meaning, hence misinterprets it and brings irrelevant evidence. Then the text deteriorates, through sloppy thinking to plain demagogy.

The response to (3) is just a word game.

Like the first reviewer, this one ignores completely the question of reproducibility that I raised in the last paragraph but one of my review.

1) The authors ignore the higher level nature of the stimuli, i.e their conceptual emotional significance

[1] The underlying idea is serial processing:...

This is against the evidence from neuroanatomy, which shows that the flow of information in the other direction is of the same magnitude. This knowledge appears in any neuroanatomy textbook. The reviewer, like the authors of the paper, ignore this knowledge.

[2] The design of the experiment attempts to minimize the emotional or conceptual properties....

But far from enough. For example, in the coherent motion, the authors could use one of he pictures in either optical flow or biological motion, thus reducing the differences. They could also use in biological motion an object that has less conceptual content (e.g. a dog). It is obvious that the authors did not consider this question at all. Not using a video of a real person is useful in reducing the amount of information in the input, but as long as people can recognize anything in the input, this recognition cannot be ignore.

[3] whether they are additionally ..

This sentences are a subtle effort to get the user to believe that there are no conceptual effects, because in most of the cases the subjects will not be 'prompted to imagine...'. However, he ignores the dimensions of the stimuli that I gave in the first sentence of my criticism, and other similar dimensions, like how amusing it is. In addition, we haven't got a clue of what the subjects do unconsciously, and they may be 'prompted to imagine', but do it unconsciously.

[4] More accurately, to show all ..

The use of the term all here is misleading. Howard et al marked as 'differentially active' only voxels with differential activity over some threshold. They don't actually give the threshold they use, but they do mention the probability of false positive as 0.00005 (in a conditional sentence), so I assume that threshold for the discussion. That means that a voxel with a lower apparent differential activity, which gives a probability of false positive of, say, 0.1, is not marked as 'active'. However, of these voxels, only 1 in 10 is false positive, and the rest 9 of 10 are really positive, i.e. have a real differential activity, albeit lower (on average) than the differential activity of the marked voxels.

The authors don't give us any clue of how many voxels are at this level of apparent differential activity, i.e. how many voxels would give false positive at probability of 0.1. However, since the authors use a very stringent threshold, which leaves as marked only a small number of voxels, it is likely that there are many more voxels below the threshold but still above the relaxed threshold of 0.1, than there are above it. Since almost all of these voxels (9/10) are really positive (have real differential activity), and there are many more of them, the number of voxels with differential activity which are not marked outnumber the marked voxels. Thus the voxels that the authors present are likely to be only small part of the voxels with differential activity, and to represent only peaks of differential activity, rather than 'all the differences'.

Note that this analysis does not rely on the exact numbers, but on the fact that the number of marked voxels is relatively small, compare to the total number of voxels. It is not necessarily true in any case, but it is, by far, the most probable assumption, and a counter-evidence is needed before dismissing it. Instead, the reviewer tries to dismiss it simply by words.

[5] ... supported by a vast body of evidence from experimental work..

This 'vast body' does not tell us anything on the distribution of the peaks of differential activity in this territory (MT), nor does it tell us anything about specialization for specific kinds of movement. It is therefore irrelevant. Here the reviewer simply rely on the reader not to be familiar enough with the literature.

[6] It would be nothing but perverse to attribute ...

This is not to the point. The conclusions of Howard et al do not rely merely on activity in the MT ('this territory'), but on the different locations of peaks of differential activity in it. Thus the question is not if the activity in the MT is coming from higher or lower level, but what determine the location of peaks of differential activity in it. The reviewer did not bring any evidence about this point, and simply avoid discussing it.

[7] The smaller patch ..

It is not obvious to me how this discussion is relevant to the point I raised. It certainly does not give any reason why we can ignore high level effects.

I suspect the reviewer tries here to show how 'taking conceptual significance into account' leads to a dubious interpretation. However, in my criticism I did not say that the higher level effects have to be part of the interpretation, I said "These effects must be controlled in some way, ..".

[8] The doubts attach ..

This statement probably rely on the analysis in the previous paragraph, which are faulty (comments 4-6), and therefore it is wrong as well.

2) The authors assume that high differential activity is equivalent to functional significance.

[9] "the bulk of information in the brain is not coded in level of activity, but in the pattern"

This is a gross misquote. My original sentence is:
".. the bulk of the information in the brain is not coded in level of activity (how many neurons are active in a specific region), but in the pattern of activity (which neurons are active and when)."
My sentence was completely unambiguous. However, after the reviewer chopped away the clarifying brackets and the last two words, the result is ambiguous, because it can be interpreted as:
"the bulk of information in the brain is not coded in level of activity [of each neuron], but in the [temporal] pattern [of spikes of each neuron]"
and this is the way the reviewer is going to interpret in the following text (comments 10-12 below).

[10] ".. as it essentially implies all scanning experiments are worthless."

This presumably refer to the reviewer misinterpretation. The original statement cast doubt on the way these experiments are interpreted, not on the data itself.

[11] "However no evidence is cited to substantiated this criticism..."

The original sentence is obvious to anybody that knows anything about the brain, and it is hard to believe that a neuroscientist would ask for an evidence for it. The misinterpreted version of it is indeed doubtful (in my opinion, it is completely wrong). However, this is not relevant to my original sentence, or to the argument as a whole.

[12] There is some, very recent ...

These two sentences give a clear confirmation that the reviewer did the misinterpretation that I outlined in [9] above. Apart from this, they are irrelevant, as the question is about the importance of the rate of differential activity in voxels, each of which contain in the order of magnitude of million neurons, and single unit recording cannot tell us anything about this.

[13] The scanning evidence is also beginning to build a self-consistent picture,...

This statement is simply false, and neither Howard et al nor the reviewer could bring any support for it. In fact, howard et al could not even match their results to their own previous results, as they themselves admit. There is evidence for correlation between peak of activity and processing only for some special cases, and only in coarse grain, as was discussed in the response to the first reviewer.

[14 It seems more likely that scanning may give too exuberant a picture of activity,...

I am not sure what the reviewer says here, but it is clearly not opposite my criticism, which is: "differential neuronal activity does not entail functional significance". It is probably opposite his own misinterpretation, whatever that is.

[15] In his initial comments Harpaz writes .... This is a clear contradiction.

That is plain nonsense. Processing is a change in pattern, but that does not mean it cannot cause peaks of activity here and there.

[16] The other reasons given, (b) and (c) are completely incomprehensible to me...

The reviewer seems not to believe that any input can escape processing. That is simply sloppy thinking. There is no way to know in advance what stimuli are going to enter the visual system, so it cannot be designed perfectly to process all the input in a useful way. There will always be a large amount of noise, i.e. activity that is not process usefully. This 'noise' is even larger due to the fact the system discards part of the input most of the time (the part that it 'doesn't pay attantion' to).

the claim that (c), which says "completely irrelevant effects", is incomprehensible, cannot even be described as sloppy thinking. It is obvious that the reviewer did not want to admit that irrelevant effects are possible, but could not come up with any sensible argument why they are not possible.

[17] It is worth noting ...

This paragraph is plain demagogy of the worst kind. The reviewer intentionally mislead the reader to thinks that I put a 'complete ban' on coincidence between activity and functional significance. What I actually wrote is:

[18] I agree with the final ..

Again, the reviewer repeat the blame that I ignore the 'body of evidence', even though this body is irrelevant (5 and 8-12 above).

3. The authors regard localization as specialization.

[19] Very likely both factors are at play ...

This looks like a benign assertion, but it is in disagreement with the facts. We know that the input-output wiring of the cortex (including cortical neurons with axons that go outside the cortex) does cause different parts of it to be dedicated to different activities, so this factor is indeed very likely. As yet, nobody could work out how any of internal features that vary across the cortex can cause parts of it to specialize in anything, even though many people tried to, and there is no experimental evidence for it. Thus, at the moment, local structure and physiology of the cortex don't seem to determine which region of the cortex is dedicated to what activity.

[20] but Harpaz wants to...

That is not 'harpaz wants'. The word 'specialization' is almost universally used to refer to intrinsic property(ies) of the specialized entity, rather than to the effects of other entities on it. More relevantly, this is the way it is used in neuro- and cognitive-sciences.

[21] This might be a reasonable definition but it is not the one used in cortical physiology.

Using such a common word as 'specialization' in a different way in cortical physiology is misleading for both neuro- and cognitive-scientists, especially here, because it is the main 'take home message' of the paper. It is even more important in a journal like Current Biology, where most of the readers are not cortical physiologists.

I also have my doubts about the claim itself. My impression is that when Howard et al (and other cortical physiologists) say 'specialization', they do mean some physiological modifications, like the rest of the world does. This is supported by the fact that the reviewer fails to tell us what 'specialization' does mean in cortical physiology.

[22] the alternative "there is functional specialization for motion in the mid-temporal" is neutral in this respect.

But what does it mean? The reviewer did not tell us what is the meaning of 'specialization' in cortical physiology. We can interpret the reviewer as saying that it means something like "assigned to" or "dedicated to", but it is significant that the reviewer himself did not actually give any definition.