A SHORT COURSE IN BEHAVIORAL ECONOMICS

Edge Master Class 2008
Richard Thaler, Sendhil Mullainathan, Daniel Kahneman
Sonoma, CA, July 25-27, 2008

AN EDGE SPECIAL PROJECT

INTRODUCTION
CLASS ONECLASS TWOCLASS THREECLASS FOURCLASS FIVECLASS SIX
PHOTO GALLERY
THE REALITY CLUB


On "Two Big Things Happening In Psychology Today": A Talk By Daniel Kahneman

W. Daniel Hillis, Daniel Kahneman, Nathan Myhrvold, Richard Thaler, Daniel Kahneman, Nathan Myhrvold, Daniel Kahneman, Nathan Myhrvold, Daniel Kahneman Nathan Myhrvold


W. DANIEL HILLIS

I have one more minor observation.

Dick Thaler assumed that we already understood and accepted the standard models economic discussion making. When you think about it, it is very flattering—he assumed that we had internalized the standard models to such a degree that we needed to be talked out of them.


DANIEL KAHNEMAN

Quick reply to Nathan on priming—I believe that the comparison of priming with the curiosities of visual illusions sells it short.
   

A) The priming studies provide a mechanism that explains the major "heuristics and biases" effects.        

1) Anchoring effects are (mostly) caused by the fact that when I ask you if the tallest redwood is more than 800 feet tall I have primed you to think of very tall trees, and the sample of trees you recover from memory is biased upward—compare to what would have happened if I had asked if the tallest redwood is more than 80 feet tall. What you think about redwoods is affected by mention of the number. (true even if the anchor is known to be random).        

2) Other heuristics come to be used because activating a cognitive goal actually activates a whole cluster of goals. You ask whether something is true, and that activates judgments of whether it makes sense in context, whether it is metaphorically true, etc. You ask whether someone will be a good President and an enormous amount or irrelevant garbage questions get answered automatically. This is how you can get judgments of similarity being used as proxies for judgments of probability.    

B) Priming effects tell us generally that we don't have much access to what goes on in our minds. They make some common ideas sound silly—like "voters who are concerned about the economy prefer Obama". The kind of associative coherence in which everything primes everything else within a bundle of reactions is a better model than this. Associative and intuitive coherence is different from logical coherence.

C) Priming effects may provide one of the mechanisms by which culture works. Some cultures provide the equivalent of constant reminders of money. Other cultures remind you that there are eyes looking at you. Some make you think in terms of 'we', others in terms of "I"—and those are just examples that I mentioned in that one random hour.


NATHAN MYHRVOLD

One reply to Danny Kahneman's reply about optical illusions and priming... After reading your response, I still wonder if the optical illusion analogy isn't quite apt. I say "wonder" because I don't really know and it would require more thinking—and probably some experiments—to really tell. The mechanism of priming that Danny gives in his reply is that the brain unconsciously retrieves (a computer scientist would say "pre-fetches") a context based on environmental cues. This context then indelibly colors the next thought. Even if you are told that the data (such as tree height) is known to be random. This seems entirely plausible, and I accept it (but I have to ask, is there direct evidence of this, or is it a surmise?). But isn't this very closely analogous to what happens in optical illusions? In that case the brain also automatically processes the scene in light of visual context and it reaches a conclusion. It is entirely subconscious and works even if you are told that you are looking at an optical illusion. This seems to me to be almost exactly analogous to priming.

Here is a classic example:

I can tell you the punch line up front, but it won't change the results. The lines are all the same length—but no matter how much you know that, you still see them as different lengths. The arrowheads on the end of the horizontal lines subconsciously change our estimate of the length of the lines. They are like giving a number when talking about tall redwoods.

There are many optical illusion sites—but for quick reference here is a very nice one that has LOTS of quite different effects—http://www.michaelbach.de/ot/

Of course any analogy is only that—an analogy—and it will break down somewhere. Priming is not identical to optical illusions, but both seem to be due to unconscious processing by the brain, which is highly context dependent. I've read that there are multiple kinds of priming—conceptual and perceptual—and this may not apply to all of them (but I bet it does). I think what Danny doesn't like about this analogy is not how closely it applies, but rather the inference that priming might only be as important as optical illusions—i.e. as "just" an optical illusion. That is a fair comment, since that was partly what I intended. But not as a condemnation of priming—what I wrote is that "I wonder" how close the analogy is. Now I could be foolish for confessing this, but I will admit it: I wonder how important priming is to everyday life, or, in keeping with our theme, to economic life? Rather than wonder indirectly I'll put this as a question to Danny—how important is priming to everyday life, or economic life? How could that be measured?

The processing that goes on in optical illusions exists because it often gives the right answer—often enough that it is very useful. In particular many of the seeming paradoxes in optical illusions arise because the visual system is trying to solve what we know mathematically to be an ill-posed problem that has no unique solution. One example is inverting a 2D picture into a 3D shape. The simple classic is a Necker cube.


This is a perfectly good 2D picture, but we cannot help trying to force into being a 3D object. The 3D reconstruction problem is ill posed—there are two very different solutions, each of which is feasible. So, when you look at it you alternately see one then the other—you can feel it pop in, or pop out. Without a unique solution your brain flips between the possible solutions. If we had a bit more context it would lock in one interpretation and keep it there. To create this class of optical illusion you must carefully balance two different visual interpretations so closely that they compete.

Similarly, the experiments under which priming shows up are also highly artificial contexts—that is not a criticism because to make a controlled experiment you need this. Part of that is asking people questions about things that they don't know—to which there is no solution.

If you asked a park ranger from Redwood National Park, I don't think he'd be influenced by priming up front—because he gives tours to tourists all the time quoting the world's tallest redwood (by the way, it is a tree named Hyperion that is 379.1 feet tall).

My guess is that the largest priming effect is going to occur when you have somebody who either has no clue about the real answer, or who is grasping for a poorly remembered solution, or sitting on the fence between two compelling solutions. That is the case where context sensitivity would seem to be most important.

A lot of life is spent sitting on the fence trying to decide between multiple solutions or courses of action (purchase decisions, for example), and a lot of life is about things that we don't have a clue about or only dimly grasp. So priming could be quite important even if it is restricted to that case. Or maybe it isn't restricted, and we are all at sea in a storm of contextual metaphors.

Anyway to sum up here are my questions:

1. Is priming strongest when your the answer is indeterminate (i.e. subject doesn't know, or is struggling to get the answer, or to choose between answers)?

2. Or, does priming influence people even on topics where they feel that they know the answer?

3. How important is priming? Is there a way to measure this? Is it a curiosity that occurs in some corner cases (which is how I would characterize optical illusions)?

Finally, I will admit to wondering about more thing, which I am sure you've all be thinking also : why on earth am I arguing with the guy who won the Nobel prize in this area?

Nathan


RICHARD THALER

Nathan, lots of good questions here, except the last one. Being with you for 36 hours was enough to not be surprised that you are still pushing the debate! Danny is really the right one to have this debate with but I am not sure your questions have good answers. For example, we have no idea what percentage of the time we are fooled by optical illusions. Presumably the answer is a small number, but how would we know?

Let me respond briefly to two of your points regarding my stuff.

First, I agree that unit pricing was a bust, though interestingly, in an experiment done by Jay Russo, when prices were listed in order of unit prices, this had a big effect on behavior. However, I am not excited about that result because we don't know whether it leads to a good outcome if the products are not of homogeneous quality. For example, I pointed out in an old paper (1985) that the price of dish washing liquid per dish washed was inversely related to the price per ounce. So the "most expensive" brands were actually the best values, at least as evaluated by Consumer Reports.

This is an example of the mapping problem Sendhil and I talked about. If consumers don't know how to map their purchase into utility, then markets can break down. Some firms will make money selling diluted dish washing liquid to consumers who use the wrong heuristic for buying (price per ounce). But they won't make huge amounts of money because it costs more to bottle and distribute diluted product, so competition itself does not solve the problem. Nor does Consumer Reports if most people don't read it. (They re-did the study a few years later and got the same result.) My idea of electronic, machine-readable disclosure will not solve these problems completely either, because not everyone will go on-line, but it would make markets more efficient.

The most interesting question is whether it is necessary for the government to mandate the disclosure. Before I address that let's clarify one point. It may not be necessary that the government be the body that decides what the template is for disclosure.

For example, the travel web sites might determine what the disclosure template would be for hotels and airlines. The only problem with this is if the airlines and hotels capture the travel web sites. However, there can be no debate about whether it is necessary for the government to require that the disclosure be made at all.

Consider the case of mortgages. Let's stipulate that some borrowers took out loans that they did not understand, and that mortgage brokers, especially those marketing to the sub-prime sector, were profiting exactly by not disclosing clearly some of the features of the loan. If I am making money precisely because I do not disclose everything, then I cannot be expected to start disclosing voluntarily. (Suppose the guys who play Three-card Monte on the street had to reveal all their tricks. Who would play?)


DANIEL KAHNEMAN

I have no problems with Nathan's discussion of illusions and the Necker cube—both appear in early chapters in what I have been writing. Indeed, illusions have something in common with priming effects and with most of mental life: the processes that determine them are not represented in consciousness. As Nathan suspected, my objection to the comparison of priming to illusions related to their importance. Illusions do not play a very important role in the modern study of perception, whereas priming is, I believe, critical to understanding how the mind works.

Anchoring effects work on everybody—including professionals, such as judges in actual courtroom cases, who get demonstrably anchored on numbers that have little more content than random numbers. Anchoring also works quite well in negotiations, where getting your number in first gives an advantage (this is experimental, but confirmed by negotiations experts as a phenomenon observable in significant negotiations).

True, anchoring effects are largest in areas in which there is little experience. If you know how tall the tallest redwood is you won't show an anchoring effect. But not everyone knows everything—although there may be one or two exceptions… Anchoring is not a laboratory curiosity. Nor are framing effects, which are best explained as effects of priming—different frames evoke different associations in memory and different emotions.

I cannot resist quoting a paragraph from a discussion of anchoring:

German judges were shown detailed files on a rape case, then told that someone with no expertise in the law—a freshman computer-science student—had recommended a prison sentence for the rapist. One group of judges saw that the amateur had suggested 12 months in prison; a second group read that he had suggested 34 months. Most of the judges were firmly convinced that the opinion of the computer-science student could not influence their own sentencing decision, but they were wrong. When the judges were asked how long a term they would assign in their own courtroom, those who had seen the amateur advice of a 12-month term recommended 28 months in prison; the judges who had seen the 34-month suggestion concluded that 36 months was appropriate.

These effects are large and robust—Nathan, they work on you too!


NATHAN MYHRVOLD

Well, I am going to sound like I was primed by the recent X files movie, but Danny, I want to believe!

Nevertheless it is not easy to believe it. Despite your having primed me, I'm just not getting it. So while I believe you that it does work on me, in this particular instance it seems to be failing me. So I have a couple more questions.

Perhaps practicing on me will help your book :-), but don't feel compelled to answer if you don't have the time. Indeed one reply you give would be "wait for the book".

My natural inclination is to go in two directions with this:

1. There must be a catch—meaning something which winds up lessening the importance of priming from what you seem to be saying. Here is a list (I will try to be brief) of objections that come to mind.

a. The effect occurs, but it is proportional to ignorance, or indecision, or making your mind up when you don't have enough information (indeterminate or ill posed problem). So it is a very real effect, but only occurs a portion of the time. And in that portion, we don't know what to do anyway (see coin flip argument below).

b. In particular, the kind of question one asks on a questionnaire tends to be something where the person must either grasp at an answer, or make up a hypothetical—or otherwise are particularly prone to the effect. So this might be much stronger in precisely the cases studied in the experiments. Is it known whether people act this way "for real"? For example, one branch of experimental economists holds that doing experiments with real money (which may itself be priming!) makes things more real than hypothetical questions. Have those experiments been done with priming? I can't help but point out here that your colonoscopy experiment was real—to the extreme! Have similarly real world tests been done here?

c. Other influences may drown out priming in cases of interest. The German judges were asked about a sentence—they weren't presiding over an actual trial where they had heard weeks of testimony and had both prosecution and defense repeatedly try to prime them. Would the freshman opinion count as much after all that context?

d. It may last only a short time, in which case the next priming comes in and overwrites it.

2. Or, I believe. But now explain how to reconcile our intuitive view of life with the strange reality you propose. The naive reaction to taking you seriously is the storm tossed sea of metaphors—can we really be reality? Could unconscious suggestion send us lurching between extremes all the time without our being aware of it? Perhaps, but it deserves explanation. How could it be so hidden? Why aren't we all switching political parties, wives, cars, and other decisions randomly based on some damn number we hear, or points we plot on graph paper? How can we go thorough life so gullible? Most aspects of life do not seem like a totally random walk—yet that is what you seem to be leading us. The incredible constancy and directionality of some aspects of life is hard to reconcile with the notion that we are almost whimsically influenced by cheap metaphors.

I think it would help the uptake of this idea if you gave people some sense that one can reconcile priming with our life experience. Otherwise it becomes easier to reject the whole thing. Here are some attempted reconciliations I have thought of:

a. Dick asked whether we know how often optical illusions come into play in real life. I would argue that the neural processing behind optical illusions happens almost constantly. What is rare is that it produces a paradoxical answer. So, the answer to Dick's question depends on whether you mean "tendency to recognize faces" which occurs constantly, or the "picture that might be an old lady's face, or a young woman's torso" (another classic illusion) which occurs only rarely. So, perhaps priming is just as constant as the processing behind illusions, but its impact is usually small. You won't like this because it seems to de-emphasize priming, but there is a pro-priming way to think of this.

b. Similarly one could make a case that lots of subtle things—like the example of culture you mentioned—could be due to priming. Yet culture, while pervasive at a large scale does not utterly dominate individual life. Indeed most people would agree that there is such a thing as culture, while at the same time arguing that they are their own man (or woman), exercising free will. One could argue that priming is not only responsible for culture, but like culture it is simultaneous palpable in some ways and diffuse in others, subject to ex post facto denial.

c. If indeed priming works best when we don't otherwise know, or have enough information, then it could be a substitute for a coin toss. If you are asked a hypothetical question, or are sitting on the fence on a decision, then what does it matter whether it is a priming effect, or a cosmic ray that pushes you over one way versus another? Instead of tossing the coin the brain takes whatever random thing it was told recently and turns up the gain on that noise to get an answer.

d. The sum of sufficiently many random vectors is arbitrarily close to zero. So, maybe we are totally influenced—slaves to the cheap metaphors of life's contextual poetry. But if there are enough of those influences in enough directions, then overall they tend to balance out. Culture would be a good example of a systematic bias, but many other things would wash out. So maybe German judges just go by the last thing they heard, but there are plenty of integers so overall it would wash out over time.

e. Perhaps it is getting caught that is rare. It is very unusual for German judges to get caught in the act of cribbing their jurisprudence from freshman CS majors. Instead we have plenty of ex post facto rationalization, and lots of other window dressing to explain how we act. So perhaps that is the strange part.

f. In fact life is a random walk in most ways and we just don't see it. I don't believe this, but out of completeness thought I would add it.

Finally, I have one additional question. Have you considered "Bayesian priming"?

Suppose that I am an Econ, not a human, and I am a very good Bayesian. Before making a judgment I recall my priors—the prior distribution has a very strong sway on what I do. Let's assume my prior distribution is accurate. But although I aspire to Econ-hood, I am only human. So if we assume my prior distribution is faulty—for example if the last thing I heard influenced my prior distribution, then I could use a good procedure (Bayes' theorem) and get a bad answer.

The question here would be this—if you do numerical priming experiments (guess tallest redwood after hearing a random number), then one might be able to calculate what people's prior distribution was, and how it changed on hearing the priming number.

The answer might be that people are non-Bayesian, or that they can't do the prior. But it seems like there would be some merit in figuring out what effect the priming number is. If you said the tree was 1 million miles high, or 1 inch high, I bet it would be less priming effect. I would guess that the maximum effect occurs once you are in a zone of plausibility (i.e. has a probability consistent with your naive prior), and that the priming number tends to cause you to update the prior distribution in a systematic way.

Nathan


DANIEL KAHNEMAN

Let me postulate a few things:    

1. I know my date of birth. Priming will not change my mind about it.    

2. I do not believe there is anything anyone could do within the law to make me vote for a Republican this November.

So yes, of course there are limits to priming effects and to all forms of influence. My point was not that priming could make a person do anything at all. It was that priming has much more influence than people think it could have. Furthermore, people are generally not aware of having been influenced.

Let me respond to your points in your previous message above.

1a. Not correct. The German judges were not completely malleable. They would not have assigned the same sentence to jaywalking. But under the influence of a prime they added an average of 8 months to the sentence.

1b. Yes, similar world test have been done here. Priming has been shown to have a marked influence on the behavior of people in an ultimatum game with real money. I don't know why this should be surprising. People's behavior in games is affected by sniffing oxytocin, which tends to make them more tolerant of exploitation. Oxytocin does not change their nature completely, but it biases their behavior in predictable ways, just as priming does. Much of priming research has been done with real behavior as a dependent variable. Recall the story of the eyes affecting behavior at the "honesty box" (repeated in Monday's NYT). The "artificial questionnaire/no incentive" gambit does not work here.

1c. The power of anchoring effects is such that if a freshman opinion had been the only number proposed as a sentence, it would very likely have an effect. An anchoring effect occurs whenever you recruit arguments to make sense of something that sounds like a solution to your problem.

1d. Two responses to this. First, decisions and judgments are made at a particular time and in a particular context. What priming effects demonstrate is that random features of the context can have a surprisingly large effect on decisions and judgment. The second response is that some priming-like effects are not short-lived. A defendant's physical attractiveness is a long-term prime that has significant effects. And a culture can provide very frequent reminders of the importance of money, or of the importance of community.

2. As I said above, let us stipulate that no one can make me vote Republican. I did not say that behavior is infinitely malleable, only that it is much, much more malleable than people know. So the fact that people stay with wives and political parties is not a challenge to what I said. But there was a lot of luck and a lot of random priming in the choice of the wife, if not of the party. There is a classic study in which male subjects encountered an attractive woman on a swaying bridge in Vancouver, or just off the bridge. They were much more likely to be smitten if the encounter was on the bridge—they did not know exactly why they had been excited. This is one of many ways in which behavior is moved by forces of which we are not aware.

2a. It really depends on what you mean by "small". I think that 8 months is not small, and many significant anchoring effects with real money are quite large in absolute terms. The effects are not huge—they are within the range of what people would consider unsurprising behavior for themselves. But I may be giving too much ground here: in the post-hypnotic suggestion case, people find themselves doing pretty bizarre things and are not subjectively very surprised. They find a reason for what they observe themselves doing. However, we know that even hypnotic suggestion has bounded effects. Repeating myself, I don't know how to use large or small—I do know that the effects are larger than most people think—otherwise the research would not be interesting and we would not be having this exchange.

2b. See above—who claimed that random priming effects utterly dominate individual life? You insist that the effect of priming is either overwhelming or negligible, but of course it is neither.

2c.d. Tell that to the felon who got sentenced. And there is really no reason to expect priming effects to cancel out. Yet again, you respond to a claim that has not been made, that we are totally influenced by context.

2e. This is coming close to what I believe.

2f. This is much stronger than I believe. Life is not a random walk, but there is more randomness than we see.

In response to your final question, the experiments you suggest have been done. Totally ridiculous numbers will not work, but you can be quite extreme and still get large priming effects. Dan McFadden (Econ Nobel Laureate) and I reported on a study in which one group of subjects made free estimates of a set of quantities, or answered hypothetical open-ended questions about contributions to various causes. Other subjects were anchored by a dichotomous question (the redwood example was from that study). The anchors were set either at the 5th or at the 95th percentile of the distribution of free responses. We could measure the anchoring effect as the proportion of the distance between the anchors that was spanned by the responses of the anchored groups. The results of such studies produce a robust estimate: about 50%. I have called this measure the anchoring index.

Nathan, priming and anchoring do not dominate your life—but they affect your choices and judgments more than you can tell by introspection. You can see your face in the mirror but not the brain behind it, and you can see some of what goes on in your mind, but most of it is hidden.

Best,

Danny


NATHAN MYHRVOLD

Danny complains that I am objecting to something he never said. I suppose that may be technically true, but what it tells me is that I must have done a poor job of explaining why I was bringing these points up in the first place. My apologies, let me try again.

Priming as Danny presents it is quite a strange phenomenon:

• omnipresent—happening all the time, all around you.

• impossible to guard against.    

• equally hard to detect—in yourself anyway, but also in others (unless you have a control group and can do the statistics, as one does in an experiment).

• very important to understanding human perception.

• also very important in terms of real world impact on thinking and decisions, with large real-world consequences.

I'm pretty sure Danny said each of these, one way or another. Or maybe I was just primed to draw these conclusions myself, but I think they are accurate.

If find that set of characteristics to be fascinating. However, they are also strange, and perhaps a bit alarming if you really take them seriously. It very naturally begs a set of other questions.

That is really the point—the explanation of priming (and particularly those factors above) begs some important questions. When Danny says that I am responding to claims he didn't make, I think he is misunderstands this point. I think that that the claims Danny did make beg the questions I was responding to.

If somebody told me "the sun is green", there are two natural reactions I would have. The first would be to be skeptical and discount the assertion, thinking it is either false, exaggerated or occurs in very weird conditions. The second is to accept it provisionally and say "ok, if the sun is green, help me understand and accept that by explaining further how this could it be that I've lived my whole life thinking the opposite". Even if I want to believe, if I get no answer to this second approach, then I surely will be driven back to skepticism. But hey, maybe that's just me.

When explaining something this strange, it is very helpful to provide preemptive rebuttals to the first line of skeptical theories. That way, even before the first few objections arise you can swat them down. It is perhaps even more important to provide the perspective on "how could it be that I've spent my whole life thinking the opposite". I didn't get either one from the discussion at the Master Class. Of course that may just be me being really dense. The brevity of the discussion is clearly a factor. Danny's forthcoming book probably handles this all brilliantly and I should just shut up and wait for it. But I'm impatient so I sought to clarify them in this response and counter response format.

My previous response cataloged a bunch of possible reactions to priming in each direction. The first was a list of ways of possible objections to discount the effect. The second was a set of possible ways to reconcile the phenomenon of priming with a naive intuitive notion of perception.

Frankly, approach this hasn't been all that successful, so I'll stop. Some of Danny's responses are spot on in providing the extra insight that I am looking for—they either rebut a skeptical point, or they explain that. Mostly however, I seem to have phrased things badly so Danny's responses seem aimed at trying to debate a recalcitrant heathen.

Incidentally, the sun is indeed green! But not usually—it is only green during a rare and very brief phenomenon called the "green flash". The rarity and brevity are why we don't think of it that way.

Nathan


DANIEL KAHNEMAN

Let's look at the second question first. There have been hundreds of experiments (thousands?) on the phenomena of priming and anchoring (these days often viewed as a species of priming). A common feature of these experiments is that the participants uniformly do not know what is going on (the few who do become aware are normally removed from the sample) and strenuously deny that the manipulation to which they were exposed (typically, the presentation of some obviously irrelevant stimulus) had any effect on their behavior. This highly robust observation does not explain why people can live their whole life without awareness of these phenomena, but it demonstrates the possibility (indeed, the likelihood) that if there is such a general effect we would not be aware of it. It is in the nature of unconscious effects that we are not conscious of them, and it also a universal and fully justified initial response to doubt their existence, generality and significance. I don't know anyone who was not initially skeptical, including myself. It is the sheer mass of results that I find compelling.

To deal with the first question, let me suggest an interpretation that makes the phenomena less weird. We are all aware that our behavior and our thoughts and feelings are highly context-dependent: none of us is quite the same person at home and in the office, in bed or in the subway. We are used to the context-dependency of our behavior and we have stories that make sense of it—social pressure, norms etc. What we are learning from the priming-anchoring effects is that context-dependency is mediated in part by multiple subtle cues of which we are not necessarily aware. The effect of pictures of eyes on contributions to the honesty box illustrates this. People were barely aware of this contextual cue and had no idea it had a large effect on their behavior—they were responding pretty much as if they were under observation. The example shows that it does not take actual fear of social sanctions to make us behave in a manner that would be appropriate in a truly social context. I believe that if you consider the factors that govern our adjustments to the contexts of our lives, the suggestive effects of primes and anchors should become less mysterious.

The novelty of the recent priming literature is in something that I called "Associative coherence" or "the poetry of priming". The characteristic of our responses to stimuli (I believe I used the word VOMIT as an example) is that they are coherent—the entire associative machinery (including the autonomic and skeletal responses that the machinery controls) seems to be reset for a new context. We are more alert, we are prepared to recognize stimuli that are predictable (in a Bayesian sense) in the new context, we are ready to escape etc. This coherent response makes a great deal of sense in an evolutionary context. The fact that some associations appear bizarrely symbolic (e.g., to notions of distance or reminders of money) makes sense in the context of theories of "embodied cognition", which trace some of the concepts people have to early experiences, e.g., of social and physical distance or of the difference between situations in which money and exchange are or are not relevant).

Finally, let's look at the importance of the phenomena. Perhaps wrongly, I read Nathan as proposing that the effects are either extremely powerful or negligible, and my response was that they are somewhere in the middle. I find it helpful to think of behavior as a choice of values along multiple continua (e.g., of friendliness, wariness, effort, driving speed, etc.). At any one time each of these features of our behavior and mental state can be represented as an equilibrium, which is influenced by multiple forces, some of which are internal (habits, intentions, stored knowledge) others drawn from the context. We are not specifically aware of all these forces (any more than we are fully aware of what determines our choice of speed on a winding road), but they are at work, and priming is one of the ways this comes about.

Nathan, thanks for the skepticism. I learned both from the questions and from the answers. In this context, 'recalcitrant heathen' is not pejorative—it refers to someone who says "you will have to do more to convince me", which is a pretty good description of our exchange.


NATHAN MYHRVOLD

Well, with this I think we can declare our commentary finished! Danny and I seem to be largely in agreement.

But I can't resist one final point. The strangeness of priming is much worse than simply that we are not aware of it—we also don't seem to find its traces afterward.

Psychology is full of unconscious phenomena. So, for example, I can accept that my eyes may dart around and the pupils contract or dilate, betraying my interest in things. That by itself is strange, but easy to reconcile with intuition because you'd never know it without careful observation (with video cameras or the like). Last year Danny told us of the "peak plus end" rule that says people tend to remember the peak and the last bit of an experience (such as pain). This is fascinating stuff, which ultimately is easy to accept because it is explicitly about what we don't remember.

However, in the case of priming, the unconscious phenomenon leaves an indelible mark on our lives. It's not just about something transitory—it is about lasting decisions, like what we pay for communal tea, or what sentences are given in a court of law. I think that this makes it doubly weird. If indeed we were so open to influence, then wouldn't we see that influence in the records of our deeds? Pupil dilation by German judges is one thing—the sentences they give quite another. If in fact there is a meaningful priming influence on such things, why don't we see life as a random walk? If a judge hired for his or her professional competence at administering justice responds to arbitrary priming, then shouldn't that show up in the judicial record? Wouldn't a statistical analysis show it?

That is why it is not enough (for me, anyway) to say it is a robust empirical fact that experimental subjects are unaware of priming. Yes, that is the first step! It makes me believe! But now tell me why don't we find their record of actual decisions to have that influence? If we were all tugged in different directions by factors beyond our control, then wouldn't evidence of that be recorded? If we are tossed about on a stormy sea of metaphors, why don't we notice, even after the fact?

There are many examples where economists and statisticians have indeed used statistics do show cumulative effects of all sorts of influences that may be unconscious—like correlation of height with income. The more one says that priming is important, the more I would expect it to come out in the statistics—probably as variance after known systematic effects were removed. Priming is so dependent on ephemeral context that it would seem that it would appear as the noise rather than then the signal.

Several of the points in my email were attempting to reconcile this aspect—that our lives seem ordered in retrospect. So, if the effect was small compared to other sources of variance, then you wouldn't see it—it would be hidden by other variability. Or perhaps priming is the primary source of variance. Or maybe priming falls within the same range as other forms of variance so it goes unnoticed. Or... at this stage it is time to stop before I reprise the whole discussion all over again. I think I have some idea of what Danny's answer would be here and I look forward to the fuller explanation in his book.

Nathan


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