Science of Chess: Subliminal Chess in the Expert Mind?

One of the big ideas - maybe THE big idea - in the cognitive science literature about chess is something called template theory. This refers to the idea that chess players build up a library of chess-position "chunks" over time, which allows them to quickly identify familiar patterns over the board and respond to them. The more chunks you have in your library, the better you may be at rapidly evaluating a position and finding the best move...at least, so goes the theory. Below is a potential template I'm guessing you may have some familiarity with, for example.

The Greek Gift is a chunk a lot of beginner and intermediate players acquire early in their training.

There is a fair bit of evidence for template theory by now, which has motivated chess improvers and coaches (both real and digital) to emphasize tactics training: Drill those tactics, and you'll assemble your own library of chess chunks! With a healthy collection of templates, you too may be able to immediately spot key configurations during play and make the right moves with ease! Obviously it's not as simple as that, but nonetheless when I'm not playing too many Blitz games, I do my share of puzzles too in the hopes that I can take advantage of this formula.

I can't decide whether spending 5 full 24-hour days on chess puzzles is a point of pride or not.

Besides a better rating, what else does the accumulation of templates do to your chess playing? As ever, I'm not so interested in talking about how one might get better at chess. Instead, I'm much more interested in how acquired expertise changes perception and cognition. Expert players who presumably have stored lots of chess patterns in their long-term memory (or LTM) have a bunch of advantages over weaker players that I've described in previous Science of Chess posts. They tend to be better able to remember chess positions accurately and can reconstruct them from memory (De Groot et al., 1996), for example. They also seem able to correctly perceive where pieces are on the board without needing to move their eyes very much,an ability that suggests a greaterperceptual span than novices(Reingold et al., 2001). Stored templates almost certainly contribute to successful blindfold chess, too: The more you can reference long-term memory to keep a position in mind, the less likely it is that the bottleneck of your short-term memory (or STM) limits your ability to calculate, etc.

Presently, I want to introduce you to another interesting by-product of having lots of chess knowledge stored in templates, patterns, or "chunks" if you prefer: Making chess judgments without awareness. Besides the various ways experts outpace novices that I described above, it turns out that experts also seem capable of making meaningful judgments about chess positions without being conscious that they are doing so. But what does this mean and how would we ever measure such a thing? The answer to both of those questions lies in understanding a cognitive science phenomenon called priming.

What is Visual Priming?

To understand what priming is, there are a few facts you need about how your mind and your brain process visual information. The first fact may be one you have some intuitions for: It's possible to show you an image so quickly that you don't really see it. To be just a little technical, we can use a technique called visual masking to get this done. Masking works by showing you one image for a very short amount of time (maybe 16ms or so) and then immediately showing you a second image, usually visual noise of some sort. Even though both patterns were visible, that second picture effectively cancels your experience of seeing the first one. This means that though your retina might have had that pattern of light land on it for a moment, your mind never gave you awareness of it. You can see a schematic view of how masked stimuli are deployed in an experimental setting, in this case, including both a pre-stimulus mask and a post-stimulus mask.

Presenting images of static or clutter before and after a target image (here, the word "radio") can make the target image invisible to an observer. This is called visual masking. MattF, CC0, via Wikimedia Commons

The second fact I need to give you is the more counter-intuitive one: An image you weren't aware of seeing can still affect your behavior. I'll give you my favorite example of this, which I think is so much cooler than so-called subliminal advertising - the phenomenon of blindsight. Blindsight refers to a circumstance in which individuals with extensive damage to their visual cortex (critically, NOT their retina!) are blind, but nonetheless prove able to avoid obstacles while walking, point towards visual targets, and in some cases identify letters, all without a subjective experience of seeing anything. I've put a link to a short video of a patient with blindsight in the references in case you want to see what this is like.

A still frame from the video linked in the references in which a patient with blindsight can walk down this cluttered path without any experience of seeing. This is one example of how visual information can affect your behavior without conscious awareness.

A blindsight patient's ability to step around an obstacle they can't see is a remarkable example of how visual information can end up being used by your nervous system without reaching visual awareness. The phenomenon works by virtue of some visual information getting to a part of the brain that can use that data to guide where your feet go next. That part of the brain doesn't provide any kind of conscious awareness of the information, however! The primary visual cortex (at the posterior end of the occipital lobe, labeled V1 in the figure below) appears to be crucial for providing you with a subjective experience of what you are seeing. In cortically blind patients with blindsight, this is the part of the visual cortex that is extensively damaged. The result is that the patient takes the right step around a dropped object, (supported by intact retinae and functioning areas outside of V1) but still doesn't see that it's there.

Patients with blindsight lack the neural pathway at right that leads to conscious visual experience in area V1. They retain the pathway at right that delivers visual information to other sites that can guide motor behavior and other processes, leading to "seeing without seeing."

Together, these two facts are what we need to understand how visual priming works. In priming experiments, the idea is to (1) use visual masking as a tool for showing people images they don't "see" and then (2) see if the information in those images was used by the mind and the brain.

A priming example

Imagine this situation, for example: I'm going to show you some pictures of objects that are either red or green. Your job is just to look at each picture and tell me the color you see by pushing one button or the other. Easy, right? The tricky part is that I am secretly going to show you a masked image right before each picture you'll actually see. That masked image might be congruent, meaning it is the same color as the one that will be visible, or it might be incongruent, having the opposite color. It turns out that even though you won't see the masked images, you'll be a little faster to push the right button when the masked image is congruent than when it is incongruent. Like our blindsight patient, an image you never saw has the potential to change the way that you respond.

A diagram of how visual priming is intended to work: The red prime images on the left may be presented too quickly for someone to see, but the fact that the prime would be called "Red" makes the "Red" response to the first target image a little quicker (top row) than if the prime doesn't match the target (bottom row).

With that in mind, let's return to our chess experts with lots of stored templates in their LTM and our chess novices who are stuck using their STM and working memory more heavily. Kiesel et al. (2009) decided to see if the differing libraries of templates these two types of players stored meant that expert players could effectively play chess without awareness. That is, could they evaluate chess positions that they weren't really seeing? To test this idea, they used a priming design very much like the red/green experiment I described above, only they had to make the task a little harder.

Can you prime chess players with checking attacks?

Specifically, instead of asking players to make a basic judgment about something like object color, they asked their participants to do a check-detection task on a 3x3 mini chessboard. Each board had a Black King and a White piece that was either attacking the King (Check condition) or not (Non-check condition). Players would get to see this target image for 250ms (a quarter of a second) and were asked to report if the Black King was in check or not. By itself, this is already a fairly tough task given just how quickly these images are being shown! Nonetheless, players tended to be good at this part of the task.

A check-detection example on a mini-board from Reingold & Sheridan (2023): Is the White King in check from either of these two pieces?

But now the tricky part again: Before each visible mini-board, a masked mini-board was presented for just 20ms, sandwiched between two 70ms pictures of visual static. (see the figure below) This masked board couldn't be seen by the participants, but it was either congruent or incongruent with the 250ms image that they could see. Half of the time, the Black King's status was the same in the masked image and the target image. The rest of the time, it would be different. The question is: Does unseen visual information about check/noncheck affect judgments about boards you can see? If so, that suggests that the masked board is not only being delivered to parts of the visual system, but that the information on the board is being used to make a judgment about a checking attack.

Figure 1 from Kiesel et al., (2009). Mini-boards that either match or don't match target images according to the presence of checks serve as masked primes. Can players detect the checks in those boards quickly enough to affect their speed with the target images?

The interesting result here is two-fold. First, those masked images do turn out to affect how quickly players responded to the visible images - congruent masked images led to faster responses to the visible target images. Second, however, this effect depended on players' expertise. Only experts showed a clear affect of priming, while novices were not affected significantly by the masked images. You can see the actual response times in the table below, where I've highlighted the numbers you need to see these two features of the data.

In the table above, the yellow boxes show you the time it took experts (left box) and novices (right box) to detect checks in target images after non-matching and matching primes. That small difference in the response time of the experts in those two conditions means "unseen" boards were being understood without awareness.

You may feel a little skeptical about this result given how small the difference in response time is between the congruent and incongruent conditions: We're talking about an effect of ~10ms on average, after all. There are two things I have to say about this. First, the size of the response time difference isn't what we're really interested in here. Instead, the presence of that significant difference is taken as evidence that the masked image was indeed interpreted as a "check" or a "non-check" - else there should be no effect on the response to the target image at all. Now for the grain of salt: These kinds of small effect sizes are very much the kind of thing that my lab (and my colleagues' research groups) tend to look at more critically these days. Thereplication crisis in psychology made a lot of us start thinking more carefully about best research practices including how we determine our sample sizes, how we plan to analyze our data, and how precisely we measure the effects we hope to draw conclusions from. There are things in the Methods section that I like to see (the direct test of the interaction between participant group and priming, for example) but other things that make me worry (only 12 expert players!). This is all to say that while this is an intriguing result that's consistent with other research about expert play vs. novice play, this is also one of those things I'd love to see replicated and extended.

Still, to the extent that this result holds up, what this suggests is that chess experts' library of templates and patterns may make it possible for them to get information about checks, attacks, and captures from images that they are unaware of. Another way to put this is to say that useful information about chess positions is measured automatically by expert players and influences their behavior even if they aren't conscious of the data. While a poor patzer like me usually resorts to carefully working my way through a checklist of things to look for over-the-board, expert players' vast experience gives them the capability of playing chess even when they aren't conscious that they're doing so.This has implications for how various cognitive processes, including distinct kinds of memory, may be recruited in players of different strength.

The CHREST model from Smith et al. (2009) includes interactions between various kinds of memory during chess play - experts likely rely on these different kinds of memory in ways novices can't.

There are a lot of interesting questions that follow from this result, too. Just how much information does an expert get from a masked image like the ones used here? Sure, subliminally "seeing" check on a 3x3 mini-board is cool and all, but what could a player get from a full board that was masked? Also, while templates are useful for a lot of things, they also have their pitfalls: The Einstellung Effect refers to errors players make when relying too heavily on stored chunks and patterns. Are there circumstances where a prime could be detrimental to accurate board judgment? Finally, how do effects like these develop as a player gains more experience?

Conclusion

As always, I hope that this discussion highlights some interesting things about how our brains and our minds play chess. For me, this study is a great example of how techniques from visual cognition can reveal things about expert play that aren't easy to observe from what happens during a game. Thanks as always for reading, and look for more Science of Chess soon.

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References

1. de Groot, A. D., Gobet, F., & Jongman, R. W. (1996). Perception and memory in chess: Studies in the heuristics of the professional eye. Van Gorcum & Co.
2. Kiesel, A., Kunde, W., Pohl, C., Berner, M. P., & Hoffmann, J. (2009). Playing chess unconsciously. Journal of experimental psychology. Learning, memory, and cognition, 35(1), 292–298. https://doi.org/10.1037/a0014499
3. Reingold, E.M.. & Sheridan, H. (2023) Chess expertise reflects domain-specific perceptual processing: Evidence from eye movements. Journal of Expertise, 6(1), 5-22.
4. Reingold, E. M., Charness, N., Pomplun, M., & Stampe, D. M. (2001b). Visual span in expert chess players: evidence from eye movements. Psychological science, 12(1), 48–55. https://doi.org/10.1111/1467-9280.00309
5. Smith, Ll., Gobet, F., & Lane, P. C. R. (2009). Checking chess checks with chunks: A model of simple check detection. Proceedings of the Ninth International Conference on Cognitive Modeling.
6. Blindsight video: https://www.youtube.com/watch?v=GwGmWqX0MnM