P-p-p-poker face, p-p-poker face (mum mum mum mah)

I was reading the current issue of Ante Up magazine, and came across an interesting column by psychologist Stephen Bloomfield. He discusses the results of a study that I had not heard about elsewhere. It's available online here (in fact, it seems to have been published only online, not in a traditional peer-reviewed scientific journal).

Here's the formal citation: Schlicht EJ, Shimojo S, Camerer CF, Battaglia P, Nakayama K (2010) Human Wagering Behavior Depends on Opponents' Faces. PLoS ONE 5(7): e11663. doi:10.1371/journal.pone.0011663

The gist of it is this: They took a bunch of volunteers and made them play lots of simplified Texas Hold'em hands against an imaginary opponent. The subjects' only decision in each case was to call a raise to 5000 chips, or fold and lose the 100-chip blind they had posted. The only information they had available on which to make the decision each time was (1) their own hole cards, and (2) an image of the face of the opponent.

There were actually 100 different artificial opponents, i.e., 100 different synthetic faces, each of which could be presented in a neutral variant, a trustworthy variant (relaxed, smiling, friendly), or an untrustworthy variant (scowling, hostile). The central research question was whether the subjects would tend to alter their betting patterns based on which type of face they were looking at, when their hole cards were held at a constant absolute value.

The answer: Yes. But only in one direction. The trustworthy facial variant triggered more folds than the neutral one, but the untrustworthy facial variant did not cause more calls than the neutral one. Most of the shift in betting patterns occurred, as might be expected, where there was not much difference in expected value between calling and folding. In other words, a trustworthy face tended to tip the decision toward a fold only where it was already a close, difficult choice to make.

The increased influence of trustworthiness on reaction time (Figure 3B) and correct decisions (Figure 4B) around the optimal decision boundary suggests that people are using face information most for medium-value hands. This could be explained by optimal data fusion [33]–[35], which states that the more uncertainty people have about the value of their hand, the more they should weigh face information when making a betting decision. Since participants in our experiment were novices (12 of 14 play less than 10 hours/year), they may have a more reliable estimate of high-value hands since those tend to be more salient/memorable (e.g., face cards, aces, pairs, etc.) than medium- and low-value hands. Indeed, participants in our study took significantly longer to react to hands in the optimal fold region (Figure 3B), and also made significantly more mistakes for medium- and low-value hands (Figure 4B), supporting this notion.

It is also interesting that all of the changes in wagering decisions were observed against trustworthy opponents, while untrustworthy opponents did not yield any significant results. This asymmetry is even more fascinating given that people's perception of trustworthiness is more sensitive to changes between untrustworthy and neutral faces, than between neutral and trustworthy faces [27]. One possible explanation stems from the assumption that people use a random opponent decision criterion in this task, unless there is information that an opponent is betting with non-random hands. In this respect, neutral and untrustworthy faces are functionally the same: neutral faces do not provide information about an opponent's style, while untrustworthy faces may suggest that opponents are betting with poor hands. However, if participants are already assuming opponents bet randomly, they cannot decrease their criterion any further. In agreement with this proposal, Figure 5B shows that the inflection point for the neutral (Green) and untrustworthy (Red) curves is very close to the optimal decision boundary for a random opponent. However, trustworthy faces may provide information that the opponent has a high-value hand, leading to the observed shift towards more conservative wagering behavior.

(Incidentally, I think the fact that these subjects were not proficient players puts significant limits on the generalizability of the results. Even if they hadn't specified this, you could infer it. Inexperienced players tend to want to play every hand; they're reluctant to throw anything away, which explains the increased reaction time and increased frequency of mistakes with poor starting hands. What an expert would muck instantly (bluffing not being an option), the amateurs tend to want to play. Given that the researchers set the opponent's raise size at a rather ridiculous 50 big blinds, good players would immediately start with the assumption that their best strategy will be to reject all but the strongest starting hands.)

The authors' bottom-line conclusion:

Interestingly, contrary to the popular belief that the optimal poker face is neutral in appearance, the face that invokes the most betting mistakes by our subjects is has attributes that are correlated with trustworthiness. This suggests that poker players who bluff frequently may actually benefit from appearing trustworthy, since the natural tendency seems to be inferring that a trustworthy-looking player bluffs less.

I suppose there's some truth to that, but it seems to give opponents little or no credit for being able to learn. (There was no opportunity to learn and therefore adjust strategy in this study, because each trial involved a different opponent.) Frequent bluffers get sniffed out even by inexperienced opponents. After some period of time of frequent raising, everybody is going to be thinking, "He can't have a real hand every time." No facial expression is going to change that reaction. At best it might delay it a bit. And what about the player who isn't bluffing, who wants to induce calls from weak hands held by weak opponents? The information from this piece of research doesn't seem to offer any assistance there. I suppose you could try adopting the trustworthy face when you're bluffing and not when you want a call, but again, any opponent with two neurons connected inside his skull will figure out that obvious ruse before too long.

Still, I found it interesting that there is at least a modicum of empirical evidence to support Mike Caro's frequently repeated maxim that being friendly and open, chatty, relaxed, fun-loving will win you extra calls compared to the guy making the same bets with the same hands, but who is silent, scary-looking, deadly serious, intimidating, or insulting. Caro's reasoning has to do not so much with the issue of trustworthiness, but just the fact that recreational players don't mind losing money to people they like and who they know will not criticize or embarrass them for making a bad call, so they're more willing to make what they know is a likely futile or "keeping you honest" or mere curiosity call.