natselrox wrote:This is bloody not going anywhere. Perception of depth is a needed for the concept of height. Locomotor experiences being necessary for the fear of heights is totally dependent on the perception of depth. So we have three entangled systems here. And we are trying to gauge the relative importance of external signals in a proper co-ordination of the three, right?

Nobody is arguing that depth perception isn't necessary for a concept (and thus, fear) of heights. I was just pointing out that the difference between crawling and pre-crawling infants (fear vs no fear) is not dependent on depth perception at all, since pre-crawling infants with adequate depth perception continue to show no fear when held above heights. Even in the study you presented above it's clear that the pre-crawling infants had depth perception, otherwise why would their heart rate change? If the two surfaces, without depth perception, appeared to be at the same level, then why would this evoke a physiological response?

natselrox wrote:So let's go back to the drawing board, shall we?

I have to take out my pen and paper.

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So let's say our stick man has arrived at this point and the question is whether he takes the step forward or not? The avoidance of taking the step and any other associated physiological response (heart beat, adrenaline blah blah) is called fear of height. Am I correct up to this point?

Mean photoshop skills! Did you work on Avatar?

But yes, you're correct enough for our purposes. (Technically, the avoidance and other physiological responses would be measures of fear, not fear itself. But this is a pedantic niggle, they are practically interchangeable).

natselrox wrote:

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So if he does not take the step forward, that means he understands that surface B is deeper than surface A and there is a difference 'h' between the two.

Now the physiological response that follows is dependent on the relative value of 'h' (the relation may not be linear). Now what the articles you quoted are saying is that the integration between these two systems is dependent on the locomotor experiences of the individual within a critical time period. This is obvious. It wouldn't make sense if you are afraid of heights but you are stationary at a position. So the integration of the depth perceptive device with the height-avoidance device is dependent on the locomotory status of the individual.

From your article:

“artificial” experience locomoting in a walker generates evidence of wariness of heights

See the point? Locomotion just enforces or maybe even establishes the connection. And it does not matter if the locomotion is 'artificial'. Seems like a clever evolutionary solution to me.

But that does not give any inference as to whether there is any significant environmental contribution in linking the two.

I hope I'm clear now.

That is an extreme interpretation to take... But let's say you're right, and that this innate "fear of heights" (controlled by the part of the brain called the "Fear Acquisition Device") relies on a critical time period in which the individual must learn depth perception and have locomotive experience. Now, as a rough but probably mostly correct approximation, let's say 99% of all people meet the requirements for this critical period and thus, under this interpretation, must develop a fear of heights. As such, we should find that 100% of those people tested (as infants or adults, if we accept the limited ability of neural plasticity like you argue) should refuse to walk/crawl out onto the plexiglass.

This is false though, at least some of the babies do crawl out onto them. This is why the measure of "fear" in the visual cliff experiment is not the dichotomous "yes|no" of whether they did or not, it's measured according to latency. That is, some subjects do crawl out onto the glass and the measure is how long it takes them to do so. This is clearly inconsistent with the innate perspective you are arguing for.

I recommend you look up Chomsky's concept of the "Language Acquisition Device" as you are systematically making the exact same mistakes with fear as he made with language. History is doomed to repeat itself, it seems. As a spoiler, scientists view his suggestion as utterly ridiculous now.

Mr.Samsa wrote:

natselrox wrote:This is bloody not going anywhere. Perception of depth is a needed for the concept of height. Locomotor experiences being necessary for the fear of heights is totally dependent on the perception of depth. So we have three entangled systems here. And we are trying to gauge the relative importance of external signals in a proper co-ordination of the three, right?

Nobody is arguing that depth perception isn't necessary for a concept (and thus, fear) of heights. I was just pointing out that the difference between crawling and pre-crawling infants (fear vs no fear) is not dependent on depth perception at all, since pre-crawling infants with adequate depth perception continue to show no fear when held above heights. Even in the study you presented above it's clear that the pre-crawling infants had depth perception, otherwise why would their heart rate change? If the two surfaces, without depth perception, appeared to be at the same level, then why would this evoke a physiological response?

This goes on to show that pre-crawling infants without any locomotor experiences do have a depth perception and they produce a physiological response when exposed to an awkward height but they are not properly connecting the two. This is further strengthened by the fact that pre-crawling infants, when in an artificial locomotor, develop this connection earlier. So, fear of heights and perception of depth are connected only after a significant amount of locomotor experience. A stationary quadriplegic baby who is afraid of heights is a bad idea.

natselrox wrote:So let's go back to the drawing board, shall we?

I have to take out my pen and paper.

Untitled.jpg

So let's say our stick man has arrived at this point and the question is whether he takes the step forward or not? The avoidance of taking the step and any other associated physiological response (heart beat, adrenaline blah blah) is called fear of height. Am I correct up to this point?

Mean photoshop skills! Did you work on Avatar?

But yes, you're correct enough for our purposes. (Technically, the avoidance and other physiological responses would be measures of fear, not fear itself. But this is a pedantic niggle, they are practically interchangeable).

You should see my Monalisa. It's better than Vinci's.

That is an extreme interpretation to take... But let's say you're right, and that this innate "fear of heights" (controlled by the part of the brain called the "Fear Acquisition Device") relies on a critical time period in which the individual must learn depth perception and have locomotive experience. Now, as a rough but probably mostly correct approximation, let's say 99% of all people meet the requirements for this critical period and thus, under this interpretation, must develop a fear of heights. As such, we should find that 100% of those people tested (as infants or adults, if we accept the limited ability of neural plasticity like you argue) should refuse to walk/crawl out onto the plexiglass.

Now, we're talking.

This is false though, at least some of the babies do crawl out onto them. This is why the measure of "fear" in the visual cliff experiment is not the dichotomous "yes|no" of whether they did or not, it's measured according to latency. That is, some subjects do crawl out onto the glass and the measure is how long it takes them to do so. This is clearly inconsistent with the innate perspective you are arguing for.

Oh no no no no!!! I'm not at all arguing for an innate perspective. The epigenetic landscape through which most genes move to ultimately express themselves is largely dependent on the environment.

I was arguing for the extreme position just because you seemed to be coming from the other extreme. Each and every step in the development of this complex behaviour has an environmental component.

First, take the 'depth perception device'. Clearly, a cat grown in an environment of vertical stripes or with one eye patched would lack the binocular vision necessary for depth perception. And there is indeed a variability among population of humans regarding how they perceive depth. Squints are not as adept in it as normal people and so on. So this is hugely dependent on environment.

Next, the 'fear controlling device'. Now I didn't specifically mention this, you twisted mind! But if we are to agree upon the universality of the fear-response (sympathetic/adrenaline surge etc.) on facing a variety of stimuli, we can agree upon such a device and its role in each of the fears/phobias. Now this is also hugely dependent on the environment. Not every one has the similar sympathetic activity. Sympathetic neurons are specifically dependent on the NGF for their correct growth. The role of NTs are also dependent on them. But knockout mice have shown that the brain/genome somehow compensates for what would be a terrible loss. I am just mentioning these to show how complicated the growth of a single subsystem of the brain is and how inter-related environment and genes are in this process. So it is natural that a variation exists in the population.

And as for limited plasticity, I was just trying to show how absurd the infinite plasticity idea of behaviourists is, given the universality of most human traits.

I recommend you look up Chomsky's concept of the "Language Acquisition Device" as you are systematically making the exact same mistakes with fear as he made with language. History is doomed to repeat itself, it seems. As a spoiler, scientists view his suggestion as utterly ridiculous now.

There is a difference between Chomsky and me though. I do not like to generalise from trivial data. I am doing in this thread for the purpose of an argument but in general, I am more interested in observing the empirical data.

Oh and one more thing, I'm obviously smarter than Chomsky. Chomsky! I take that as an insult, mate!

natselrox wrote:
Oh no no no no!!! I'm not at all arguing for an innate perspective. The epigenetic landscape through which most genes move to ultimately express themselves is largely dependent on the environment.

I was arguing for the extreme position just because you seemed to be coming from the other extreme. Each and every step in the development of this complex behaviour has an environmental component.

I thought this part of the discussion was about your claim that fear was an innate response? I wasn't intending to come across as an extreme position to counter this, I was just trying to point out that this claim is unequivocally false - not only is there no evidence to support it, but it's flatly contradicted by all the data we have on the subject.

Now, if your claim was that the fear response and the development of depth perception etc relies on a complicated interaction between environmental events and genes, then yes, this is undeniably true and I have no argument with that. But obviously, saying that there are genetic/biological events that are necessary for a fear of heights to take place is a completely different claim from saying that fear of heights is innate; i.e. the former is sensible and true, the latter is ridiculous and disproved.

natselrox wrote:First, take the 'depth perception device'. Clearly, a cat grown in an environment of vertical stripes or with one eye patched would lack the binocular vision necessary for depth perception. And there is indeed a variability among population of humans regarding how they perceive depth. Squints are not as adept in it as normal people and so on. So this is hugely dependent on environment.

The development of those neural pathways is largely dependent on environment, no arguments there..

natselrox wrote:Next, the 'fear controlling device'. Now I didn't specifically mention this, you twisted mind!

It was a subtle comparison with what you were arguing and Chomsky's LAD

natselrox wrote:But if we are to agree upon the universality of the fear-response (sympathetic/adrenaline surge etc.) on facing a variety of stimuli, we can agree upon such a device and its role in each of the fears/phobias.

Well it depends what the fear or stimulus is. Different phobias produce different physiological effects, mostly it can be measured by something like an adrenaline surge (essentially the body preparing for fight or flight) but this will only occur in situations where the best strategy is to prepare the body in this way. Possums, for example, have a fear response which results in lowered heart rate and respiration, followed by complete stillness ("playing dead"). So such a response is far from universal, but in the majority of cases this response is generally the best reaction to a fear stimulus. (And I don't suppose you'd appreciate me pointing out that you can condition someone with a fear of snakes to respond to the sight of a snake with a lowered heart rate and suppression of the sympathetic system?...)

natselrox wrote:Now this is also hugely dependent on the environment. Not every one has the similar sympathetic activity. Sympathetic neurons are specifically dependent on the NGF for their correct growth. The role of NTs are also dependent on them. But knockout mice have shown that the brain/genome somehow compensates for what would be a terrible loss. I am just mentioning these to show how complicated the growth of a single subsystem of the brain is and how inter-related environment and genes are in this process. So it is natural that a variation exists in the population.

No disagreements there.

natselrox wrote:And as for limited plasticity, I was just trying to show how absurd the infinite plasticity idea of behaviourists is, given the universality of most human traits.

I only claim what the available data suggests (but seriously I can't think of any behaviorist that would argue for an infinite plasticity perspective). And universality of human traits? I'd be interested in hearing about them... Behaviorally, we don't have many of those. Biologically I imagine there are quite a few though.

natselrox wrote:

I recommend you look up Chomsky's concept of the "Language Acquisition Device" as you are systematically making the exact same mistakes with fear as he made with language. History is doomed to repeat itself, it seems. As a spoiler, scientists view his suggestion as utterly ridiculous now.

There is a difference between Chomsky and me though. I do not like to generalise from trivial data. I am doing in this thread for the purpose of an argument but in general, I am more interested in observing the empirical data.

Oh and one more thing, I'm obviously smarter than Chomsky. Chomsky! I take that as an insult, mate!

Fair point, you are infinitely smarter than Chomsky. Your argument above just stank of Chomsky-like reasoning though; that is, the claim that even though something requires a massive amount of learning, there must be a biological system to control it as it's too complex to come about by chance learning.

"Most of your ancestors used to hang around in mountains. Some of them weren't afraid of heights, some were. Those who were reproduced more and hence fear of height is a common trait in humans."

natselrox wrote:"Most of your ancestors used to hang around in mountains. Some of them weren't afraid of heights, some were. Those who were reproduced more and hence fear of height is a common trait in humans."

Is that a quote from Pinker?

Mr.Samsa wrote:

natselrox wrote:"Most of your ancestors used to hang around in mountains. Some of them weren't afraid of heights, some were. Those who were reproduced more and hence fear of height is a common trait in humans."

Is that a quote from Pinker?

Haha!! How simple life would be if it were true! You scientists are so mean!

natselrox wrote:Haha!! How simple life would be if it were true! You scientists are so mean!

We can't help it, meanness was a trait found in populations of our scientist ancestors - those who were mean went on to reproduce, and those who weren't slowly died out.

Brilliant!

A thought that's been bugging me for the last seven days:

There is this term called Neural Darwinism. It says that that synaptic activity is required for synaptic stability. Inactive synapses lose the struggle for survival. So it seems that during the development of the human brain, synapses compete with each other within the environmental framework provided within the cranium. The amount of negative sculpting that goes on via apoptosis and pruning of connections is huge (some of the neural systems studied so far produce 40-100% excess neurons which are culled in a rather short period of time).

My question is, does natural selection rely on a sort of 'natural selection' to develop the brain? And can it afford the huge plasticity (not necessarily provided by the extrinsic environment) that it implies?

natselrox wrote:Brilliant!

natselrox wrote:A thought that's been bugging me for the last seven days:

There is this term called Neural Darwinism. It says that that synaptic activity is required for synaptic stability. Inactive synapses lose the struggle for survival. So it seems that during the development of the human brain, synapses compete with each other within the environmental framework provided within the cranium. The amount of negative sculpting that goes on via apoptosis and pruning of connections is huge (some of the neural systems studied so far produce 40-100% excess neurons which are culled in a rather short period of time).

My question is, does natural selection rely on a sort of 'natural selection' to develop the brain? And can it afford the huge plasticity (not necessarily provided by the extrinsic environment) that it implies?

There is some debate over whether Edelman's ideas are correct or not (I think he had some nuttier ideas which sullied his more valid ones), but essentially yes the culling and strengthening of the neural networks in the brain is a selection process analogous to natural selection - the successful ones are strengthened and the maladaptive ones are culled (determined by the consequences of each neural network). Processes like Long Term Potentiation and In-Vitro Reinforcement (more detail here) are examples of this. This process is obviously the result of some evolutionary influences as that's how we came about, everything can be traced ultimately back to evolution in this sense - our body is formed by selective processes and the brain is part of the body, so it's no exception to this.

I'm not sure what you mean by "extrinsic environment"? As for whether the brain can "afford" the huge plasticity, I think the better question is whether it can afford NOT to have such plasticity. We can argue over how much of behavior is innate and how much is environmental, but at the end of the day most animals are thrust into the world with only a few simple tools to help them survive and very little to help them understand. They don't know what associations are important and which are not, what sounds to pay attention to or what visual cues signal what etc, so the best approach is to simply treat everything as important and form associations with all of them. Rather quickly though, all these associations become unnecessary and basic rules about how to organise information are formed, and so massive amounts of neurons can be culled in favour of a more organised approach.

But this is straying a bit out of my comfort zone. I know a little bit about the brain, but there are far more knowledgeable people on the forum who know much more than me.