Your Brain, The Fortune-Teller

Your Brain, The Fortune-Teller

Today's post is by Lara Ehrenhofer, a Ph.D. student in the Linguistics Department at University of Maryland, College Park. Take it away, Lara!

It’s Friday night and you’re sitting at a bar with a good friend, winding down after a long week. Your fingers curl around a cold beer, and you take in the scene: men in suits hurriedly make a few last phone calls; customers shout out their requests to the bartender, who mixes cocktails amid the clattering of the kitchen; some drunk dudes are hollering at each other; and then your friend starts telling a story. You can’t quite hear, but you nod, and your friend continues... 

                    “… just slammed the [CRASH] and left!”

You put on your alarmed/infinitely sympathetic face, and the story continues. Question, though: What was that word you missed?
            Was it horse?
            Was it eaten?
            Was it… door?
Of course it was “door.” But how did you know that, if you didn’t hear the word at all?

Sometimes the information your senses perceive is incomplete, but your trusty brain will come to the rescue and fill in the gaps. It can do that because, all along, it’s been predicting what will come next.

How so? Every time you encounter a word, neurons in your brain fire. Every time you encounter a word that you didn’t expect, they fire differently. Here, give it a try:

He spread the warm bread with socks.

That “wait, whoa!” effect is based on a subconscious process of prediction. A ton of information goes into that. You know what kind of word will come up: the sentence structure of English won’t allow a verb like sang to appear there, it has to be a noun. The word also has to have the property of being spreadable: you wouldn’t predict, say, a fried egg. And it’s got to be the bread-compatible kind of spreading, because you’d also get the “wait, whoa!” effect if the last word was rumours.

Considering everything that goes into prediction, it’s all the more surprising that it happens so fast: you can measure the “wait, whoa!” effect just 400 milliseconds after you read socks, about the speed of a blink. It has to be that fast to be useful, otherwise you’ll have encountered the next word before your prediction is ready. Remember, those 400 milliseconds also include the time it took for the visual information about the letters in the word socks to get transmitted, for you to recognise the word, activate the concept behind it, match it against the word you predicted, and set the neuronal alarm bells going. Impressed much?

Psycholinguists are studying what goes into prediction. For instance, how do we use specific parts of the sentence context? Brain responses show that the sentence He scored a touchdown in a great game of… predicts football more strongly than She made coffee and realised she didn’t have a clean… predicts cup (or was it spoon?). It’s not exactly clear what makes sentences more or less predictive. But it’s probably a combination of the statistics of the language input you’ve encountered during your entire lifetime (touchdown tends to occur with football; coffee with both cup and spoon), and world knowledge (you know that the rules of football reward touchdowns, even if that word also co-occurs with vocabulary from other sports).

Linguistic prediction reflects a general capacity of human cognition: the ability to actively predict sensory input before it really occurs. That helps us make sense of our surroundings far more efficiently.

Next time you’re stuck at a noisy bar, take a minute to appreciate your brain’s ability to tell the future – well, about a blink’s worth of it!

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Worldview