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Amitai Shenhav Headshot

A Race Toward the Mental Finish Line

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Imagine that each time you have to make a choice there are two imaginary lines drawn, one to your left and the other to your right, both equally spaced from where you start out. A team of law clerks rushes to either side of you and begins searching your memory for evidence that favors the option on their side. As they do this you notice that you are being physically pulled in each direction. The more evidence each side generates, the stronger their pull, the more you find yourself moving left and then right again. Overall you notice that the team on your left is generating more pull than their counterpart, and eventually this leads them to pull you all the way past the imaginary line on their side: your threshold for choosing to go with the option supported by Team Left. Maybe it was the sandwich over the salad, the khakis over the jeans, answering 'true' rather than 'false,' or taking the job in Seattle over the one in Boston.

We are learning that the process I just described can be applied to most decisions we make, from the mundane (e.g., are more of these dots moving in one direction or another?) to the significant (e.g., which option is in my long-term best interest?). We aren't sure yet how right these models get it, but -- to invoke the statistician George Box who said, "all models are wrong, but some are useful" -- it is the case that they have proven extremely useful. They have helped psychologists understand the intricacies of choice, and allowed neuroscientists to better map out the neural circuits that contribute to the process. More generally, though, the properties of these models can also tell us a lot about our lay experience of decision making.

For instance, one of the most basic decision phenomena captured by these models is that greater confidence in our choice comes at a cost: time. Think about that finish line I described earlier. You can move it closer to you, and you are guaranteed to cross it sooner. But then you're relying on whichever team happens to have collected more evidence early on. You know that some of the evidence each team generates is crap (or noise, as we prefer to call it) so your earlier choice comes at a higher risk of being wrong. You can avoid this problem by setting your decision threshold much further out to either side. When you reach that threshold you will have more evidence at your back (or side I suppose), and will therefore be more confident it was the correct choice. But it is guaranteed to take longer to get there. In psychology this is referred to as the "speed-accuracy tradeoff," a term that appropriately implies that there are costs and benefits to any given decision threshold.

You might also opt for an intermediate option. Rather than setting both finish lines further out, maybe you set them at a reasonable distance but start the race closer to one than the other. There are plenty of reasons you might want to do this intentionally. Say, for instance, your friends have been urging you to try the salads at this particular cafe. It would be a good idea in that situation to err on the side of buying the salad but allow yourself to get a sandwich instead if an appropriate (but greater) amount of evidence is collected to support doing so (e.g., the sandwich special today looks particularly enticing). But you might also make this kind of adjustment to your decision process completely unintentionally, for instance if you have a bias (rational or otherwise) toward a certain color, away from a certain kind of person, or in favor of a certain political viewpoint. The important thing is that the same rules would apply, whether or not you meant for this to be the case. You would require a greater amount of evidence to be generated, a greater amount of time and effort, to act against that bias. In this way biases can become not only the rational choice (assuming you prefer not to exert too much effort) but also the self-sustaining choice (assuming you start future decisions closer and closer to your biased finish line).

And therein lies the rub. The relatively simple model I described of a choice process that can unfold under a second speaks volumes about how seemingly irrational actions (and perhaps judgments) can result from an entirely rational process. Researchers have yet to work out how much of our everyday decision-making is governed by changes in threshold (finish line) or where one starts out relative to those thresholds (bias) but, to the extent these are a factor in how our decisions play out, these models make transparent the trade-off that will always exist between how quickly you crossed the finish line and how far you traveled to get there.