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Machines Like Us

Delayed gratification – how the hippocampus helps us hold off

Tuesday, 22 October 2013
by Michael Valenzuela

Would you prefer a beer right now or a bottle of champagne next week? So begins an interesting new study published today in the journal PloS Biology.

Of course these kinds of choices feature throughout our lives, sometimes with profound ramifications. A conference fling or lasting long-term relationship? Just one more harmless bet, or your savings for a deposit?

How we consider small, short-term gains versus large long-term windfalls has long been of interest to psychologists and economists. In fact, these mental trade-offs are described in the neuroeconomic literature by the term “hyperbolic decay function."

It turns out that when rewards are in simple monetary form our choices trace a sigmoid curve (stretched out s-shape). That is, we have high chances of choosing the distant reward if it is large enough, but almost zero chances when we’re talking about small change.

Under these circumstances humans are predictably consistent – how we differ is whether our personalised curve is shifted left (biased towards long-term gains) or right (biased towards short-term gains).

In this field (and this paper) researchers use somewhat pejorative terms for these two styles of thinking: non-impulsive or impulsive.

Sooner or later?

Subjects were asked whether they’d prefer an immediate (“now”) or delayed reward (“in a month or year or in ten years") using real world examples from sport, culture and food.

A bowling session today was set against Premier League football tickets next year; a packet of chips pronto versus lobster in the Tour Montparnasse restaurant in ten years time (the researchers were French, after all).

Subjects did two versions of this forced-choice task. One was with the delayed scenario provided as text, so participants had to use comprehension and imagination to figure out if they wanted it. In the other, a simple monetary reward was used as the delayed choice option.

The first result was to show that imagined long term choices behave just like concrete monetary choices, however, not based on their dollar value but on how much the participants ‘like’ them.