Research press release


Nature Communications

Behaviour: Understanding judgment bias in humans



今回、Alireza Soltaniたちは、行動実験とモデル化を組み合わせて、選択によって確率の異なる結果が得られる状況下での意思決定バイアスに関係する機構についての解明を進めた。この研究に参加した37人の大学生に、異なる結果(報酬)と関連づけられた最大4つの形状の組み合わせを示し、課題を遂行させた。参加者には、形状の組み合わせを次々と示して、報酬の異なる(赤と青の)2つの標的のいずれかを選ばせた。この実験で、参加者は、報酬を得る可能性を最大化するような選択を行い、120回の実験を通じて、それぞれの形状について報酬が得られる確率を学習していた。これに対して、それぞれの形状に対する報酬の可能性を参加者に推測させる実験では、参加者は、報酬を得られる確率が低い形状の方が高い価値を有すると評価した。これは、「基準値の無視」という既知の判断バイアスで、複数の手掛かりを同時に示されたヒトが、発生確率の低い結果に先行する手掛かりの予測力を過大評価する傾向のことだ。


The mechanisms underlying biases in decision making in humans are described in a new model published online in Nature Communications. This behavioural study highlights the strong links between reward-dependent learning, decision making and attention in human reasoning.

Humans usually combine multiple lines of evidence when making decisions, but are sometimes biased in their judgment about which choice or option is associated with most reward in any given situation. The neural mechanisms that accompany these decision making processes are not fully understood.

Alireza Soltani and colleagues combine behavioural experiments and modelling in order to understand the mechanisms involved in decision making bias when the outcomes of a given choice are associated with different probabilities. In the study, 37 undergraduate students completed a task in which combinations of up to four shapes were presented and associated with different outcomes (rewards). The participants were asked to choose between two targets (represented by the colours red or blue) for each shape combination, each target being associated with a high or low reward. The authors find that the participants made choices that maximized their likelihood of being rewarded and, over the course of 120 trials, learnt the probabilities of reward associated with each shape. However, when asked to guess the likelihood of a reward for each of the shapes, those shapes that rarely delivered rewards were assessed as more valuable by the participants. This is a previously recognized judgment bias known as ‘base-rate neglect’, whereby humans tend to attribute too much predictive power to cues preceding rare outcomes, when presented with multiple cues simultaneously.

In order to explain how this bias occurs, the authors construct a biophysically inspired neural model - incorporating reward-based learning, decision-making and attention processes - and show that the interaction of all of these processes takes place and is essential to explain these counterintuitive behavioural findings.

doi: 10.1038/ncomms11393

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