If I understand correctly, you're suggesting that animals could react to stimuli
that we would consider painful by following the same behaviours that they
would if they felt pain, not because they feel pain but because they have been
programmed to follow those behaviours in response to those stimuli?
I find this unlikely. The set of stimulus-response behaviours necessary to
avoid every possible danger that might arise in an animal's environment would
be immense. It seems much more economical to "program" behavious that avoid any
painful stimulus (e.g. by setting some "pain threshold" and programming the
animal to avoid anything that causes a sensation of pain above that
threshold). This is particularly so for insects that have a limited number of
neurons in which to store their stimulus-specific programs.
>by following the same behaviours that they would if they felt pain
This is taking the claim I made too far. My point was that reacting to noxious stimuli does not a priori require the conscious experience of pain (which includes a suffering component). When it comes to analyzing sets of possible behaviors, that provides more evidence with which to decide between nociception and pain. I do think that most "animals" (excluding insects) probably experience pain due to, as you said, the varieties of possible behaviors being too large to be merely reflex based. But it's not obvious to me that this holds for insects.
>this leaves open the question of how noxious stimuli (thanks) lead to avoidance behaviours, if they are not unpleasant.
It triggers networks that are designed to cause avoidance behaviors, for example the withdraw reflex[1]. Reflex networks do not require any conscious experience of the stimuli that triggers the specific action.
>why most animals but not insects? What is different about insects?
The size of the set of possible unique behaviors, complexity of brain, existence of higher order brain processes.
They would have to experience some negative stimulus to avoid it. Disagreement with the term pain does not remove the resume that learned avoidance requires detection of a negative stimulus.
Further, while we separate negative stimulus into say thirst and pain, the fact you can torture people with either means the difference is ethically more semantic than meaningful.
There is a distinction in biology between sensory perception of noxious stimuli (nociception) and the experience of suffering in response to noxious stimuli. The distinction is in higher order brain processing. An organism does not need to experience suffering to react to noxious stimuli: https://en.wikipedia.org/wiki/Withdrawal_reflex
Withdraw reflex also doesn't preclude learning. We see learning in all sorts of reflex arcs that get over-triggered and thus become downregulated. So the fact that the fly "learned" to be more sensitive to noxious stimuli does not rule out a reflex mechanism at play in its behavior.
Down regulated withdrawal reflex is the opposite of avoidance behavior. It’s effectively increasing an organism’s tolerance for putting it’s limb in fire.
So, no what you’re describing does not mean learning to avoid stimulus. Learned avoidance behavior really requires a negative perception not just a neutral reflexive one.
I'm not sure why you're giving my comments such an obtuse reading. My example was to show how learning can happen in a reflex network, thus undermining your claim that learning indicates conscious experience.
The issue here is regarding the capabilities of a reflex network. I have established that learning can happen in such networks, as shown by common examples. You have not established that learning avoidance behaviors requires conscious networks.
Because you don’t seem to understand the difference between learning avoidance and reducing sensitivity. (If you notice my first comment I specifically referred to learned avoidance not simply any kind of learning.)
Reflexive behavior is a predefined response to a stimulus over some predefined limit and thus on it’s own it’s reactive not predictive. In a purely neutral context there is no reason to increase the response based on the external stimulus.
Avoidance requires the ability to predict before a negative response occurs. Without the negative association there is no impetus to increase avoidance.
Aka, don’t put your hand in fire is inherently different than how quickly you remove your hand from fire.
PS: Reducing sensitivity with exposure is a rather different thing as it helps deal with edge cases. At a meta level, strong constant uncontrollable spasms is extremely unlikely to be an ideal response to a given stimulus.
I see the distinction you're going for, but ultimately it doesn't work.
>Avoidance requires the ability to predict before a negative response occurs
The article discusses the mechanism by which the "avoidance behavior" they describe is learned. It mentions that the downregulation of inhibitory neurons causes heightened sensitivity to stimuli. But downregulation of inhibitory neurons is the same species of process involved in desensitizaion of reflex arcs, i.e. make a certain set of neurons require a higher threshold for activation. Your assumption that "avoidance behavior" requires something beyond reflex activation doesn't follow.
And lets be clear, all learning is predictive. A reflex being upregulated or downregulated is a mechanism of prediction by which an organism's response is modified to more closely correlate with the environment. What you seem to be going for when you use prediction is an organism's mental model of the environment that is detailed enough to associate certain states with negative valence, and behavior planning to avoid entering into such states. In organisms with that level of processing, I agree that an experience of pain is required. But it doesn't follow that any behavior that can be described as predictive requires such mental models.
I think you are making an arbitrary distinction between levels of response.
“more closely correlate with the environment” that’s leaning.
A tree that grows to light will physically reflect information in learned about the environment. It’s encoded in it’s physical form rather than neurons, but it’s still encoding information. In that case lack of sunlight is clearly not what we would associate as pain and I would not say it has ethical implications, but it is a negative stimulus from a tree’s perspective.
Anyway, avoidance is assumed to already happen as a separate system. “it’s already been shown in lots of different invertebrate animals that they can sense and avoid dangerous stimuli that we perceive as painful.“ Fruit fly’s have 250,000 neurons they can encode quite a bit to their mental model. This is simply changing the thresholds before learning occurs, or updating the system that updates their mental model.
As to the encoding, I think physical damage as a negative stimulus is kind of obvious.
>I think you are making an arbitrary distinction between levels of response.
I don't think the distinction between behavior carried out by reflex networks and behavior carried out by planning involving mental models is arbitrary. We have no reason to think reflex networks involve experience whereas we do have reason to think behavior involving mental models does. So it seems like this distinction is the critical distinction in terms of determining if some organism experiences pain.
>Anyway, avoidance is assumed to already happen as a separate system.
You're projecting more onto the term "avoidance" than is warranted, and you haven't defended your reading of the term. I take something like the withdraw reflex as an example of an avoidance behavior. Clearly you don't, but since your argument rests on your different understanding of the term, and your assumption that the authors of the article intend your reading of the term, its the key disagreement and deserves more attention.
Continuing the quote from the article you started "...In non-humans, we call this sense ‘nociception’, the sense that detects potentially harmful stimuli like heat, cold, or physical injury". So it doesn't seem like the authors are intending to reference predictive behavior, but simply protective behavior in response to noxious sensory perceptions, what you called reactive behavior.
Learned avoidance is in the literature ex: “A Drosophila larva essentially lives to eat. If one odour is repeatedly paired with a sugar substrate, and another is not, it will start to preferentially approach the first odour. If the pairing is with a quinine or high salt substrate, it will start to avoid the odour.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3427554/#!po=27...
Which is why I am saying learn avoidance behavior is simply not the topic of this research.
PS: That also includes some examples of complex behaviors.
I find this unlikely. The set of stimulus-response behaviours necessary to avoid every possible danger that might arise in an animal's environment would be immense. It seems much more economical to "program" behavious that avoid any painful stimulus (e.g. by setting some "pain threshold" and programming the animal to avoid anything that causes a sensation of pain above that threshold). This is particularly so for insects that have a limited number of neurons in which to store their stimulus-specific programs.