What Does "Signalling" Mean?

For example, a bird performing an impressive mating display signals that it is healthy and has good genes.

But we already have a term for signalling desirable properties about yourself: virtue signalling!

I don't understand the objection.

Virtue signalling is a subset of signalling. Specifically, it is signalling of moral virtues.

Therefore, a bird signalling health and good genes is not virtue signalling (but it is signalling in general). Because health and good genes are usually not considered to be moral virtues.

In some of these cases, mere assertion goes a long way. [...] In other cases, mere assertion doesn't work.

I'll charitably assume that he meant both cases to be types of signalling.

I think Scott got this right, but you misunderstood it.

X is a signal of Y if seeing X makes Y more likely. In some cases, mere assertions do that, in some cases, they don't.

For example, saying "I read Less Wrong" is a signal of reading Less Wrong, because people who read Less Wrong are more likely to say that they read Less Wrong. However, saying "I am not a criminal" is not a signal of not being a criminal, because criminals also say it a lot.

It's not about what the words mean, it's about what they correlate with. Sometimes the act of speaking the words correlates with their literal meaning (not lying, or lying rarely). Sometimes the act of speaking the words has almost zero correlation with their literal meaning (lying almost always).

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I agree with your third objection, that Less Wrong uses signalling in the narrower sense (about agent), because that is how Robin Hanson typically uses it, and most of us were probably introduced to the concept by him.

(I am not sure whether Robin never used signalling in the wider sense, or he did but we just didn't notice.)

Oddly enough, the Signaling tag is currently awaiting a merge between the description you quoted, and a description imported from the old wiki, which links to and quotes the Scott Alexander post you referenced. (You can see both in the edit history; it looks a bit weird because there's a revision written in the context of the tagging system before we imported stuff, which was written in isolation, but presented as though it were a diff relative to the imported, older wiki page.)

Signaling theory as a term in economics or game theory usually refers to the analysis of situations where an agent takes an action that transmits information that some other agent (or rather, the "principal") does not have, and which influences the principal's behavior. The agent is also often called the sender and the principal the receiver of the signal.

Often, this is information about the agent, but sometimes it is information about something else, so we can generally just say it is information about "the state of the world" or "the state of nature". Usually, signaling theory is concerned with situations in which the information cannot be transmitted by "mere assertion" (or "cheap talk", see below) but only by a costly action, and the cost of transmitting information about certain states of the world has to be different from transmitting information about other states of the world in certain ways; e.g. in Spence's job-market signaling model, low-ability workers must have a higher cost of attaining education than high-ability workers, otherwise low-ability workers would also do it and the signal is worthless. (Note that in these models, the agent moves first and the principal second, but still the principal offers a contract based on the received information. If the principal moves first and offers a contract to the informed agent, we are in contract theory. Signaling theory and contract theory together are sometimes referred to as "information economics", "economics of asymmetric information", or sometimes the "theory of incentives".)

Situations in which there are no such costly signals are usually called "cheap talk" models. Of course, if there is no conflict of interest, the informed party can always just transfer the information (and there would also be no need for costly signals then). But suppose there is a conflict of interest between the informed sender and the uninformed receiver. Then which kind of information is transmittable? The seminal paper is by Crawford and Sobel. They show that, basically, very fine-grained information transmission does not work when there is a conflict of interest.

Finally, if a sender can send costless credible signals but can strategically choose which ones, we are in the domain of "Bayesian persuasion" models.

(If you can send signals that are costless and there is no conflict of interest, then we are maybe back in basic statistical theory if the signals are noisy, but I guess there is no room for an economic analysis.)

Perhaps there should be a place illustrating the differences between LW terms and academic terms of the same name -- besides this there's also game theory [LW(p) · GW(p)] and I feel like I've seen others as well (though I can't remember what they were).

Signaling is behavior whose main purpose is to demonstrate to others that you possess some desirable trait. For example, a bird performing an impressive mating display signals that it is healthy and has good genes.

This is a hopelessly narrow definition and should be changed. An agent can signal anything about itself, including undesirable traits such as "I'm not edible" or "I'm batshit crazy violent, don't mess with me". So lets first lose the clause "desirable".

And signals can be costly to the sender but not necessarily. The cost (or more precisely, lower cost to honest signallers and higher cost to pretenders) makes a signal more trustworthy in the cases where the sender may have a motive to cheat. In biology, low cost signalling is still signalling. Mothers' signals to offspring tend to be pretty low cost for example. The offspring trust their mothers anyway and are incentivized to respond as intended; they have not much to gain from distrusting the mother. Babies' signals to mothers may be costlier in cases when the mother is likely to abandon some offspring based on their fitness. E.g. possibly human babies pack on so much fat and look so plump so as to signal their high fitness to moms (human mothers are known to selectively abandon infants, unlike chimp mothers, whose infants are not so plump). The lower fitness infants are incentivized to look like they had high fitness, so mothers use a hard-to-fake trait such as fat content to assess fitness.

"I'm batshit crazy violent" obviously has a cost because being violent exposes you to aggression by the ones you attack, but I don't think it involves the competition element like is present in the previous example. Consider a Northern lapwing singlehandedly attacking a hawk many times bigger than itself: she's not intending to actually fight the hawk, she's signalling to the hawk that she's absolutely crazy and will fight to the death; that, of course, would be uncomfortable and painful to the hawk, so the hawk pretty reliably leaves, when it sees the lapwing coming. (Although sometimes lapwings are still killed by hawks). The signalling behavior here is approaching fast in a menacing manner, but lapwings are not competing with each other and the hawk is not trying to assess which lapwing is most violent; this signal is risky (costly) but it's not subject to runaway competition and not therefore likely to accelerate into depressingly wasteful levels. It can still be perhaps modelled as a handicap signal like the plump infant example, because the costliness of the behavior is a feature not a bug: the hawk can trust the lapwing's signal because a lapwing who's not really willing to risk a fight would not dare to approach a hawk.

The alarm signals to one's flock ("there's a predator in the grass") were already mentioned as not signalling anything about the sender; alarm signals are also costly if they attract the predator to the signaller, but here the cost is a bug that cannot be avoided, it's not a feature of the signal. (Of course, one may combine alarm signals with status signalling, e.g. in some birds the ones who sound most alarms are the most dominant and respected birds in the group because alarm calling is dangerous and only the fittest birds can afford to do it a lot.)

In conclusion, signalling as used in ecology or economy is so much more diverse than in the quoted definition, I don't see why it should be so narrow in the Wiki. The narrow meaning may be captured by some other term, such as "fitness signals", "signals of high quality", or suchlike.

eg, birds warning each other that there is a snake in the grass

Wait, this is not the example in the Wikipedia page, which is actually "When an alert bird deliberately gives a warning call to a stalking predator and the predator gives up the hunt, the sound is a signal."

I found this page which gives a good definition of signaling:

Signalling theory (ST) tackles a fundamental problem of communication: how can an agent, the receiver, establish whether another agent, the signaller, is telling or otherwise conveying the truth about a state of affairs or event which the signaller might have an interest to misrepresent? And, conversely, how can the signaller persuade the receiver that he is telling the truth, whether he is telling it or not? This two-pronged question potentially arises every time the interests between signallers and receivers diverge or collide and there is asymmetric information, namely the signaller is in a better position to know the truth than the receiver is. ST, which is only a little more than 30 years old, has now become a branch of game theory. In economics it was introduced by Michael Spence in 1973. In biology it took off not so much when Amotz Zahavi first introduced the idea in 1975, but since, in 1990, Alan Grafen proved formally that ‘honest’ signals can be an evolutionarily stable strategy.

Typical situations that signalling theory covers have two key features:

• there is some action the receiver can do which benefits a signaller, whether or not he has the quality k, for instance marry him, but
• this action benefits the receiver if and only if the signaller truly has k, and otherwise hurts her — for instance, marry an unfaithful man.

So in the alarm example, the quality k is whether the bird has really detected the predator, and the "action" is for the predator to give up the hunt. Later in the Wikipedia article, it says "For example, if foraging birds are safer when they give a warning call, cheats could give false alarms at random, just in case a predator is nearby."

But we already have a term for signalling desirable properties about yourself: virtue signalling!

That's not what "virtue signalling" means.

Communication under adversarial conditions? i.e. you expect noise with an incentive to ape signal.

But a bird warning other birds that there is a snake in the grass does reveal a fact about the bird: that it is a good bird who will risk its life for the other birds, and therefore is helpful for the other birds to keep around, perhaps even with bribes.

If 'virtue signaling' has the wrong connotations, maybe 'Hansonian signaling'?

But the alarm call is a fact about the signaller - it conveys the fact that it is aware of the predator. For a bird to give the alarm call without being aware of a predator, it would have to do it a lot more often, wasting precious time and energy. Dishonest signal is more expensive than honest signal because a bird that sounded the alarm because it noticed a predator can minimize the alarm time and get back to whatever it was doing as soon as the predator is gone.

It does not follow for me, say "yelling" is a type of "talking" this we all agree.

but when I say "I am yelling" I am giving more/different information than just "I am talking"

sure mere "assertion" is a type of "signalling"

but for me when we use "signalling" I infered that we are doing things differently than "asserting"

is this what you mean?