'Happy ending effect' can bias future decisions, say scientists

https://www.eurekalert.org/pub_releases/2020-10/uoc-ee101320.php

News Release 19-Oct-2020
University of Cambridge

        Our brains can't always reliably evaluate experiences that unfold over time
    We tend to give disproportionate weight to the later part of an experience
    This can lead to bad decisions when choosing whether to repeat an experience

Humans are hard-wired to prefer experiences that end well, and the influence of previous experience declines the longer ago it happened. This means we can't always trust that choices we make based on previous experience will serve our best interests in the future.

New research, published today in The Journal of Neuroscience, has revealed that two different parts of the brain are activated, and compete with each other, when we make decisions based on past experience. They can cause us to overvalue experiences that end well despite starting badly, and undervalue experiences that end badly despite starting well - even if both are equally valuable overall.


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The further back in time an experience was, even if still quite recent, the less weight it carries in making the next decision. The researchers call it the 'happy ending effect': we tend to make decisions based on previous experiences that ended well, irrespective of how good the experiences were overall.

In the study, twenty-seven healthy male volunteers were asked to choose which of two pots of coins, viewed on-screen one at a time, had the greatest total value. They watched as coins of varying sizes - representing their value - fell from the pots in quick succession, while a brain scanner revealed what was happening in their brain using functional magnetic resonance imaging (fMRI). The task was repeated several times with different sequences of coins.

The volunteers systematically chose the wrong pot when the coins decreased in size towards the end of the sequence. This reveals that the brain was imposing a penalty on the whole sequence, irrespective of its total value, when the ending was not good. The effect varied from person to person, but only a few were able to ignore it entirely and make a completely rational decision.

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