[Valence series] 1. Introduction

Steven Byrnes4 Dec 2023 15:40 UTC

98 points

1.1 Summary & Table of Contents

This is the first of a series of five blog posts on valence. Here’s an overview of the whole series, and then we’ll jump right into the first post!

1.1.1 Summary & Table of Contents—for the whole Valence series

Let’s say a thought pops into your mind: “I could open the window right now”. Maybe you then immediately stand up and go open the window. Or maybe you don’t. (“Nah, I’ll keep it closed,” you might say to yourself.) I claim that there’s a final-common-pathway^[1] signal in your brain that cleaves those two possibilities: when this special signal is positive, then the current “thought” will stick around, and potentially lead to actions and/or direct-follow-up thoughts; and when this signal is negative, then the current “thought” will get thrown out, and your brain will go fishing (partly randomly) for a new thought to replace it. I call this final-common-pathway signal by the name “valence”. Thus, the “valence” of a “thought” is roughly the extent to which the thought feels demotivating / aversive (negative valence) versus motivating / appealing (positive valence).

I claim that valence plays an absolutely central role in the brain—I think it’s one of the most important ingredients in the brain’s Model-Based Reinforcement Learning system, which in turn is one of the most important algorithms in your brain.

Thus, unsurprisingly, I see valence as a shining light that illuminates many aspects of psychology and everyday mental life. This series explores that idea. Here’s the outline:

Post 1 (Introduction) will give some background on how I’m thinking about valence from the perspective of brain algorithms, including exactly what I’m talking about, and how it relates to the “wanting versus liking” dichotomy. (The thing I’m talking about is closer to “motivational valence” than “hedonic valence”, although neither term is great.)
Post 2 (Valence & Normativity) will talk about the intimate relationship between valence and the universe of desires, preferences, values, goals, etc.—i.e. the “normative” side of the “positive-versus-normative” dichotomy, or equivalently the “ought” side of Hume’s “is-versus-ought”. I’ll start with simple cases: for example, if the idea of doing a certain thing right now feels unappealing (negative valence), then we’re less likely to do it. Then I’ll move on to more interesting cases, including what it means to like or dislike a broad concept like “religion”, and ego-syntonic versus ego-dystonic desires, and a descriptive account of moral reasoning and value formation.
Post 3 (Valence & Beliefs) is the complement of Post 2, in that it covers the relationship between valence and the universe of beliefs, expectations, concepts, etc.—i.e. the “positive” side of the “positive-versus-normative” dichotomy, or equivalently the “is” side of “is-versus-ought”. The role of valence here is less foundational than it is on the normative side, but it’s still quite important. I’ll talk specifically about motivated reasoning, the halo effect (a.k.a. affect heuristic), and some related phenomena.
Post 4 (Valence & Liking / Admiring) argues that when my brain assigns a positive valence to a person I know, that corresponds to a familiar everyday phenomenon that I call “liking / admiring”. I argue that this has close ties to social status, mirroring, deference, self-esteem, self-concepts, and more. I also argue that there’s an “innate drive to be liked / admired” which is critically important in human affairs, and I speculate a bit on how it works in the brain.
Post 5 (‘Valence Disorders’ in Mental Health & Personality) notes that, given the central role of valence in brain algorithms, it follows that if something creates systematic impacts on valence, it should lead to a characteristic suite of major downstream effects on mental life. I’ll propose three specific hypotheses along these lines:
- (A) If the valence of every thought is shifted negative, that leads to a suite of symptoms strongly overlapping with depression;
- (B) If the valence of every thought is shifted positive, that leads to a suite of symptoms strongly overlapping with mania;
- (C) If the valence of every thought is “extremized”—very positive or very negative, but rarely in between—that leads to a suite of symptoms similar to narcissistic personality disorder.
Appendix A (Hedonic tone / (dis)pleasure / (dis)liking) has some more details about the hedonic tone (i.e., the “liking” side of the “wanting-versus-liking” dichotomy, in contrast to valence which is more about “wanting”). This appendix thus elaborates on the very brief discussion in §1.5.2 below. I suggest that “hedonic tone” is a different brain signal from “valence”, but centrally involved in the valence-calculation algorithm.
Valence and AI alignment deserves a post too, but actually I already wrote that one a while ago: see Plan for mediocre alignment of brain-like [model-based RL] AGI. Check it out if you’re interested. I won’t discuss AI further in this series, with some minor exceptions, including a section at the very end of the last post.

1.1.2 Summary & Table of Contents—for this first post in particular

This article introduces how I define and think about valence, in the context of high-level brain algorithms.

Section 1.2 argues that the brain does model-based reinforcement learning, and what I mean by that.
Section 1.3 talks more specifically about actor-critic reinforcement learning, and how “valence” is a control signal within that framework.
Section 1.4 relates valence to other terms like “aversion”, “incentive salience”, and “based versus cringe”.
Section 1.5 offers seven clarifications on common confusions, including the relation between valence and thoughts, and pleasure, and motivation, and other feelings, and imagination, and reinforcement learning in the brain more generally.
Section 1.6 is a brief conclusion.

1.2 Model-based reinforcement learning (RL)

The human brain has a model-based RL system that it uses for within-lifetime learning. I guess that previous sentence is somewhat controversial, but it really shouldn’t be:

The brain has a model—If I go to the toy store, I expect to be able to buy a ball.
The model is updated by self-supervised learning (i.e., predicting imminent sensory inputs and editing the model in response to prediction errors)—if I expect the ball to bounce, and then I see the ball hit the ground without bouncing, then next time I see that ball heading towards the ground, I won’t expect it to bounce.
The model informs decision-making—If I want a bouncy ball, I won’t buy that ball, instead I’ll buy a different ball.
There’s reinforcement learning—If I drop the ball on my foot just to see what will happen, and it really hurts, then I probably won’t do it again, and relatedly I will think of doing so as a bad idea.

…And that’s all I mean by “the brain has a model-based RL system”.

I emphatically do not mean that, if you just read a “model-based RL” paper on arxiv last week, then I think the brain works exactly like that paper you just read. On the contrary, “model-based RL” is a big tent comprising many different algorithms, once you get into details. And indeed, I don’t think “model-based RL as implemented in the brain” is exactly the same as any model-based RL algorithm on arxiv.

1.3 Actor-critic RL, and “valence”

Within the space of RL algorithms, a major subcategory is called “actor-critic RL”. I claim that the brain is of this type. A “critic” is basically any learning algorithm trained to assess whether something is a good idea or bad idea, based on the past history of RL rewards. In the context of the brain, for present purposes, I propose that we should think about it like this:

(Oversimplified in various ways; slightly more details here.)

Valence has implications for both the “inference algorithm” (what the brain should do right now) and the “learning algorithm” (how the brain should self-modify so as to be more effective in the future). In this series, I’m mainly interested in the inference algorithm. There, the main thing that valence does is:

If valence is very negative, the current “thought” tends to get thrown out, and the “Thought Generator” part of the brain goes rummaging around and (partly-randomly) picks a new different thought to replace it.
If the valence is very positive, the current “thought” tends to stay active and get stronger. Relatedly, if the thought involves an immediate plan to issue motor outputs, then those motor outputs are likely to actually get issued. And if the thought is one piece of a temporal sequence (e.g. you’re in the middle of singing a song), then that temporal sequence will tend to continue. And so on.

As I have discussed here, you can draw an analogy between valence in the human brain, and the final-common-pathway control signal for a run-and-tumble mechanism in a simple mobile organism like a bacterium. Specifically:

When valence is positive, it roughly means “whatever (metaphorical) path I’m on—including not only what I’m doing right now, but also the plans currently in my head for what to do later—is a good path! I should carry on with that!”. This is analogous to the “run” of run-and-tumble: the bacteria keeps going in whatever direction it is currently going.
When valence is negative, it roughly means “I should randomly generate a new activity / plan right now”. This is analogous to the “tumble” of run-and-tumble: the bacteria randomly picks a new direction to go.

In fact, I don’t think it’s just an analogy—my guess is that there’s literally an unbroken chain of descent from the valence signal in my brain all the way back to a run-and-tumble-like control signal in the proto-brain of my tiny worm-like ancestors 600 million years ago.

Alternatively, we can take an AI-centric perspective, in which case I think the exact role of “valence” in the brain’s RL algorithm is a kind of funny mixture of value function (a.k.a. “critic”) and reward function:

It’s a bit like a conventional RL reward function in the sense that it can be “ground-truth-y”—for example, the brain has innate circuitry that issues negative valence in response to pain-related signals, and positive valence in response to eating-when-hungry, and so on for various other “innate drives”.
It’s a bit like a conventional RL value function in the sense that it can be “forward-looking”—for example, “the idea of walking to go get candy” can be positive valence (a.k.a. motivating), not because the walk itself is immediately pleasant, but because I’m hungry and want to eventually eat the candy.

(I won’t go into details about how valence relates to specific reinforcement learning algorithms—see the appendix for more on that.)

Either way, hopefully it’s clear that “valence” is one of the most important ingredients in one of the most important algorithms in the brain.

1.4 Terms closely related to “valence”

If you say “the thought of X is appealing” or “motivating”, that’s more-or-less synonymous with saying that such a thought has positive valence. Such thoughts have a kind of magnetic pull on our brains. The psychology jargon term “appetitive” means something similar.

On the other side, if you say “the thought of X is aversive”, that’s mostly synonymous with saying that such a thought has negative valence, but has a further connotation that this thought also strongly induces physiological arousal (increased heart rate etc.). For example, suppose you’re doing a math problem, and you think to yourself “What if I subtract 3 from both sides? Nope, that won’t work.” There was a negative-valence thought in here—I can tell because you did not in fact follow through with the plan to subtract 3 from both sides, and instead went back to brainstorming other ways to simplify the equation. But you probably wouldn’t call that thought “aversive”. For example, it wasn’t particularly unpleasant (more about pleasantness in §1.5.2 below). It’s just a bad plan that you’re unmotivated to execute.

As mentioned above, when a negative-valence thought pops into our head, our brain tosses it out and goes fishing for a new thought to replace it—and in the longer term, our brain stops thinking those negative-valence thoughts in the first place. However, highly aversive thoughts—involving both negative valence and arousal—can seem to defy that rule, in that our brain sometimes seems to be trying to get rid of these thoughts, but failing—for example, consider anxious rumination, or pain. I’ll explain what’s going on there in a later post—hang on until §3.3.5. (The short version is: I claim that such thoughts persist because of “involuntary attention”, which is a separate brain mechanism unrelated to valence.)

“Incentive salience” is another psychology jargon term. As far as I can tell, “the cheese has incentive salience” is basically synonymous with “if you’re paying attention to the cheese, then that thought will evoke positive valence”.

There are loads of heavily “valenced” words that we use on a day-to-day basis—“good” & “bad”, “yay” & “boo”, “pro-” & “anti-”, “based” & “cringe”, etc. These words are used mainly to communicate about valence. Much more on this topic in the next two posts, where I will also argue that pretty much every word we use is at least slightly valenced (although some words, like “religion”, have different valences for different people).

1.5 Clarifications

1.5.1 “Valence” (as I’m using the term) is a property of a thought—not a situation, nor activity, nor course-of-action, etc.

For example, suppose I have “mixed feelings” about going to the gym. What does that mean? In all likelihood, it means:

If I think about going to the gym in a certain way—if I pay attention to certain aspects of it, if I think about it using certain analogies / frames-of-reference, etc.—then that thought is appealing (positive valence);
If I think about going to the gym in a different way, then that thought is unappealing (negative valence).

For example, maybe the first thought is something like “I will go to the gym, thus following through on my New Year’s Resolution” and the second thought is something like “I will go to the loud and cold and smelly gym”.

So the action of “going to the gym” does not have a well-defined valence. But each individual thought does have a well-defined valence.

1.5.2 Valence (as I’m using the term) is different from “hedonic valence” / pleasantness

For example, suppose you consider doing something unpleasant (e.g. walking upstairs and getting a sweater) to avoid something even worse (e.g. continuing to feel cold), and you find that thought motivating, and so you do it. By my definitions, that was clearly a positive-valence thought. But it’s associated with unpleasantness—walking upstairs to the drawer is not particularly pleasurable in and of itself. The thought is positive valence mainly because the expected consequences are part of the same thought too—as you walk up the stairs, the thought in your head is more like “I’m getting a sweater”, not just “I’m walking up the stairs”.

More generally: If I find the thought Θ appealing / motivating (positive valence), I claim there are basically two possibilities. First, as in the sweater example above, maybe Θ entails paying attention to an expectation of something desirable that will happen later. Second, maybe the thought Θ entails paying attention to something good that is happening right now—e.g., if I’m getting a back massage. Both of those are common reasons for a thought Θ to have positive valence. But only the latter would be described using words like “pleasurable”, or “positive hedonic tone”, etc.

I’ve already said much about how I think about valence. So you might be wondering: What about pleasure?

By and large, when people say “X is pleasurable”, we can safely infer:

X is associated with a stable (as opposed to transient) mental state;
When in state X, the thought of staying in state X is positive-valence;
When not in state X, the thought of getting back into state X is positive-valence.

So valence and pleasure are not totally unrelated, but they’re not the same either. In terms of neuroscience, they’re associated with different signals in different parts of the brain, and in terms of conscious experience, I think they’re associated with different interoceptive sensory inputs (and hence they “feel different”, subjectively). There’s more to say here—about both the algorithms and how they relate to neuroanatomy—but that’s out-of-scope of this series.

For a mainstream take, see Berridge & Kringelbach 2015; for my own more detailed opinions see Appendix A.

1.5.3 “We do things exactly when they’re positive-valence” should feel almost tautological

Try to think of a time when the thought of doing a certain (motor) activity felt purely negative-valence, but then you went ahead and did it anyway. Did you think of an example? If so, we are not on the same page—you are not using the term “valence” in the same way that I am.

Back when you decided to do that activity, there must have been something motivating you to do that—some aspect of it must have felt motivating, even if it was “the idea of getting it over with”, or “morbid curiosity”, or “something about the kind of person I want to be and the stories I want to be able to tell myself”, or “just to prove to myself that I can”, or “to get rid of such-and-such annoying feeling”, or “it’s hard to articulate”. If you actually did the thing, there must have been some source-of-motivation within you making it happen, or you wouldn’t have done it! That source-of-motivation, whatever it is, was enough to make the overall thought “positive valence”, at least the way I’m using the term.

(If you think the “valence” signal with the properties that I ascribe to it in §1.3 simply doesn’t exist, then OK sure, we can talk about that. Instead, here I am trying to avoid the situation where you latch onto some brain signal that doesn’t match the §1.3 spec, and say to yourself, “Steve meant to be talking about this signal, but he is confused about its properties!”.)

1.5.4 Valence is also part of the world model, and hence (confusingly) a valence can be either real or imagined

Imagine seeing a purple tree out the window. What would it look like? In order to answer that question, your brain temporarily represents imagined visual stimuli—stimuli matching a purple tree, which are quite different from the real visual stimuli hitting your retinas right now.

Next: Again, imagine seeing a purple tree out the window. What would you feel upon seeing it? In order to answer that question, your brain temporarily represents imagined feelings, one of which is an imagined valence. (Your brain can also represent imagined arousal, imagined pleasure, and so on.) Just as in the visual case, these imagined feelings can be quite different from the real feelings active at that same moment.

But I find that most people have no issue with the former thing (distinguishing real versus imagined visual stimuli), yet get very confused by the latter thing (distinguishing real versus imagined valence and other “feelings”).

Maybe it helps that real visual stimuli seem to be “out there in the world” whereas imagined visual stimuli are “in our head”, so it feels very intuitive to treat them differently. By contrast, real valence and imagined valence are both “in our head”, so it’s not so obvious how they’re two different things. Moreover, if you’re imagining a valence, then that valence is part of the “thought”, and thus it can impact the thought’s (real) valence!! Likewise, imagined arousal can contribute to real arousal, and so on. Or the same root cause can lead to both real arousal and imagined arousal. That dynamic makes it even more tempting to lump them together into a confused mush. But really, they’re different!

For example, if I imagine something and I say “Boy, in that situation, I would be so incredibly angry!”, then I would have bodily reactions consistent with being slightly angry, but not consistent with being “so incredibly angry”. My heart rate would probably be slightly elevated compared to normal, but not extremely elevated. My face would be slightly flush, but not extremely flush. My hands might be slightly clenched into fists, but not strongly clenched. Etc. Thus, whereas I am imagining being “so incredibly angry”, my actual state right now is one of merely mild anger. Thus, I can imagine “feelings” different from my internal state. And again, I think the same idea applies to valence and lots of other things.

To clarify, let’s add some extra detail to the diagram from above:

Same diagram as above, apart from the new green part. The Thought Generator contains a world-model built by self-supervised learning of sensory inputs. Valence serves as *both* a control signal (§1.3 above) *and* one of those sensory inputs.

The “Thought Generator” has a bunch of sensory inputs that are used for training a generative model by self-supervised learning (i.e., predicting imminent sensory inputs, then updating on prediction errors). Some of those sensory inputs are visual, so the model winds up “knowing” what visual inputs are expected in what circumstances. Some of those sensory inputs are auditory, so the model winds up “knowing” what auditory inputs are expected in what circumstances. And in exactly the same way, one of those sensory inputs is a copy of the valence signal, so the model winds up “knowing” what valence signal is expected in what circumstances.

And when we imagine things, that involves “querying” this learned model, and thus we can imagine feeling a valence in just the same way that we can imagine seeing sights and hearing sounds.

Thus, valence-as-a-sensory-input (green curvy arrow) is nothing special—just one of many things that gets incorporated into the learned model. By contrast, valence-the-control-signal (black arrow) has a special superpower—the power to throw out bad thoughts, and to keep and strengthen good thoughts (§1.3). In other words:

If you’re imagining X, and it involves a negative imagined valence, then maybe you imagine yourself not being motivated to pursue X.
If you’re imagining X, and the real valence of that thought is negative, then you stop imagining X in the first place and start thinking about something else instead.

See the difference? Here’s a diagram illustrating both:

Just like you can imagine a visual input (purple tree), you can likewise imagine a (interoceptive) valence input. And just as the imagined purple tree is unrelated to the light currently hitting your retina, likewise, the imagined valence can be different from the actual valence of the current thought. However, in the latter case, the imagined valence can *affect* the valence of the current thought, making this situation potentially even more confusing.

1.5.5 Valence is just one of many dimensions of conscious interoceptive experience

I already mentioned this in the previous section, but it’s worth emphasizing. At any given time, your brain (especially hypothalamus and brainstem) is keeping track of probably hundreds of innate parameters: What’s my blood pressure? Salt level? How dilated are my pupils? How fertile am I? How lonely^[2]? Am I geared up for a fight? Am I suppressing a laugh? How’s my immune system doing? On and on. And valence—an assessment of whether the current “thought” is better off kept versus discarded, all things considered (§1.3)—is one of those hundreds of innate parameters.

And I think that, as in the previous subsection, many or most of those innate parameters serve two roles:

First, they create various innate effects via lots of connections mainly within the brainstem and hypothalamus—e.g., the “I’m fertile” signal tends to increase sex drive, the “I’m hot” signal tends to initiate sweating, and the “valence” signal either throws out or strengthens thoughts (§1.3).
Second, they go up to our “Thought Generator” (a.k.a. world-model) and serve as interoceptive sensory inputs (as in the previous subsection), allowing us to “feel” what their current values are.

(Regrettably, the full catalog of interoceptive sensations is currently unknown to Science, and seems to have only a loose relationship to English-language emotion words, as I discuss here.)

So if you think a thought, it can bring forth positive or negative valence, and it can simultaneously bring forth a wide variety of other “feelings” that we might identify as anger, sorrow, regret, pleasure, pain, curiosity, and so on. There are systematic relationships between these things, just as there are systematic relationships between sights and sounds, but they are different axes of conscious experience.

1.5.6 Fine print: Throughout this series, I’m only talking about the brain’s “main” reinforcement learning system

I actually think there is more than one reinforcement learning (RL) system in the brain. But only one of them is the “main” RL system, and that’s the primary one I care about, and pretty much the only one that I ever write about, including in both this series and my previous series, and this is the RL system that is related to “valence”. I sometimes refer to this RL system as the “success-in-life” RL system, because it’s in charge of estimating whether something is a good or bad idea for the organism to do right now all things considered, including considerations of homeostasis, and sociality, and childrearing, and everything else that might be relevant to inclusive genetic fitness. (See discussion here.)

What are the other brain RL systems besides the “main” a.k.a. “success-in-life” one? My general answer is: these are narrowly-scoped RL systems that learn to perform very specific tasks with the help of a very specific reward signal.

One example, I believe, is related to motor control. I think the “main” RL system specifies what the motor system is supposed to be accomplishing at any particular time, but the gory details of how exactly to execute those movements, by precisely moving specific muscles at specific times, are delegated to one or more “narrow” RL systems. The “reward” for that narrow RL system would involve an assessment of whether it is accomplishing the current motion goals set out for it by the “main” RL system, along with (presumably) assessments of various metrics like motion smoothness, energy-efficiency, and so on.

So motor control is one example, and I think there are at least a couple more examples of “narrow” RL systems in the brain as well. I have a (brief and outdated) discussion in an old post here, and see also my more intuitive old discussion in Reward Is Not Enough.

1.5.7 I’m sweeping some complexity under the rug

As I keep mentioning, I think that the mechanism of §1.3, where negative-valence “thoughts” get discarded and positive-valence “thoughts” get kept and strengthened, is one of the most important mechanisms in the brain. So obviously, there has been a lot of evolutionary pressure over the last half-billion years to make this mechanism work really really well. That translates to a long list of clever tweaks and add-ons. I don’t understand them all myself, but from everything I’ve seen, the simplified high-level picture I’m presenting in this series is a great starting point—much more helpful than it is misleading. So those details generally need not concern us.

But here’s one detail that seems worth mentioning: I claim that “thoughts” are compositional, i.e. made of different pieces snapped together—for example, if you’re looking at an apple, your current “thought” involves semantic aspects (it’s an apple), and visual aspects (it’s red). If part of a “thought” seems good (it constitutes evidence that the thought merits positive valence) and another part seems bad (it constitutes evidence that the thought merits negative valence), then (I claim) there’s a mechanism by which your brain will attempt to throw out and replace the bad parts of the thought, while keeping the good parts. That’s generally only possible to a limited extent, because the different parts of a single thought are related—they constrain each other. But still, this dynamic is importantly involved in things like brainstorming (coming up in §3.3.3).

1.6 Conclusion

If you read the literature, “valence” refers to dozens of different things. But hopefully you now know what I personally am talking about when I say “valence” in this series. With that under our belt, the upcoming posts will discuss the manifold effects of valence on our mental lives.

Thanks to Tsvi Benson-Tilsen, Seth Herd, Aysja Johnson, Charlie Steiner, and Justis Mills for critical comments on earlier drafts.

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Definition for non-neuroscientists: “Final common pathway” is a term I like. Start with a typical example from the literature of someone using that term: “motor neurons [in the spinal cord]…are the final common pathway for transmitting neural information from a variety of sources to the skeletal muscles.” What that means is: There’s some signal going down the spine to the muscles, and that signal will completely control what the muscles will do. But upstream of that signal, there’s a lot going on! Lots of different systems in the brain are all contributing to that signal, and modulating it, in complicated ways.
By the same token, when I call valence a “final-common-pathway signal”, I’m saying that there’s one brain signal called “valence” (ignoring some fine print, see §1.5.7), and it’s a real signal, encoded by real neurons firing, and this signal has extraordinarily important impacts on the brain. But the fact that it’s just one signal does not imply that it’s calculated in a simple way by a single system. There’s a single point of departure of the signal, but that’s merely the last step of a complex calculation involving systems all over the brain.
^
Yes, at least in rodents, the hypothalamus seems to have an innate circuit that specifically tracks how many days it’s been since I felt the comforting touch of a friend or family member. See Liu et al. (2023).

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