May 31 2016

Postdictive Illusion of Choice

fmri brainDo we truly have free will? This is a vexing question, and as with the question of consciousness, there are complementary philosophical and neuroscientific approaches. Philosophy gives thoughtful possible answers given what we know, but neuroscience advances what we know.

As I have discussed many times before, the totality of neuroscientific evidence strongly supports the conclusion that consciousness is a phenomenon of brain function. Dualist philosophies, those that posit that consciousness is anything other than or in addition to brain function, are simply trumped by the scientific evidence.

Free will, however, is a thornier question and more entangled with the philosophy. There are those who maintain that free will is entirely an illusion, because our brains are machines so they must follow physical laws which determine their behavior, hence our behavior, therefore no true free will. While I do not think this can reasonably be refuted, some think the real question is whether or not we make choices. If we do, whether or not those choices are free from physics, then perhaps that can be considered a form of free will.

Putting aside the philosophical question here, the neuroscientific question is this – to what extent do we make conscious choices vs subconscious choices?

In other words, when you make a decision, such as what to wear on a particular day, to what extent is that a conscious decision where you are weighing variables of which you are explicitly aware, and to what extent is that choice made by subconscious algorithms with you more automatically following that choice?

There is evidence that, at least to some extent, some of the decisions we make are made subconsciously, before we are even aware that we made a decision. There is at least preliminary evidence showing that some decisions are made in the brain (indicated by lighting up on fMRI) before the person is aware of the choice. And yet, when asked people will almost always indicate a conscious reason for the choice. They invent a justification for a choice they never consciously made, and they believe that was the true reason for their non-decision.

This is most dramatically demonstrated in the split-brain experiments. Briefly, if the major connection between the two hemispheres is severed, they cannot fully communicate. If you then show the right half of the brain an image and then ask the subject to choose an item with their left hand (the hand controlled by the right hemisphere) they will choose the image they just saw. If you then ask the left hemisphere why they did that (the left hemisphere doesn’t know) it will invent a justification – “I chose the bottle of water because I was thirsty,” when in fact their other hemisphere had just seen a picture of a bottle of water.

There is another neuroscientific phenomenon going on here as well, the extrapolation of reality briefly into the future. Imagine catching a baseball thrown quickly at you. There is an unavoidable delay in the time it takes for neurons to conduct signals, a few hundred milliseconds. In that time the baseball would whack you in the head. So how do you catch it? Well, neuroscientists have found that our brains extrapolate into the future to compensate for the delay in processing time. We see and feel things slightly before they actually happen in order to compensate for the processing delay.

This creates the illusion that we are perceiving now as it happens in real time, but we do not. As is often the case, this system works fine most of the time, but can be stressed to create perceptual illusions.

Recently neuroscientists asked how this phenomenon, projecting into the future, might influence the illusion of choice. Perhaps we not only project our perceptions into the future, but our decision-making as well. They conducted an experiment in which subjects were shown five what dots on a computer screen. After a warning a random dot would turn red. The subjects had to decide which of the dots was going to turn red, and then indicate if they guessed correctly. On some trials the time between the warning and the dot turning red was too short for the subject to make a decision, and they were told to indicate that they did not have enough time to choose.

When the subjects were given enough time to choose, they reported choosing the correct dot 20% of the time, which is in line with chance and demonstrates that they are honestly reporting their choices. However, when the interval between the warning and the dot turning red was decreased, sometimes they did not have enough time to choose. During those trials, subjects reported an overall 30% accuracy.

What the researchers think is going on is that for some trials (when the delay was in the sweet spot) the subjects perceived the dot turning red then chose that dot but had the illusion that they had made the decision beforehand. The researchers call this a postdictive illusion of choice.

They go on to speculate about whether or not this is a feature or a bug of the brain. Perhaps our brains are wired to give the illusion of choice, even when that choice is made after the fact, in order to enhance our motivation through belief in our own power. Even more interesting, perhaps some mental illnesses could involve an exaggeration of this feature. Delusional people might believe that they intended for something to happen before it happened, when in reality the intention came after the reality.


Given what we know about how our brains function, the notion of a postdictive illusion of choice makes sense. Our brains generally construct a narrative of reality in a very active process that involves perceptual attention, filtering, and selection, significant processing that weaves the various sensory streams together with our knowledge, expectations, and internal dialogue, and adding a generous helping of pure confabulation to fill in any missing pieces and make everything internally consistent. We already know that there is a temporal dimension to this construction. It is certainly plausible and consistent with existing evidence that the illusion of choice, even when that choice comes after events, can be part of that constructive process.

It also seems from this and other experiments that the question of whether or not choices are conscious or unconscious is not black or white. They are a combination, depending on events. There are certainly times when we consciously deliberate our choices, even while we may not be entirely aware of all the subconscious influences. Other choices, however, may be more automatic and involve little to no conscious choice.

Regardless of how much a choice is conscious or unconscious, we seem to be wired to have the illusion that our choices are conscious, even to the point of thinking we made a choice before we could have made it.

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