# Choice history biases in dyadic decision making

## TL;DR

This study shows that people's past decisions influence their current choices in shared tasks, and they treat their own and their partner's history differently.

## Contribution

The paper introduces a dual-participant approach to study choice history bias in shared decision-making.

## Key findings

- Participants show choice alternation after a partner's decision and repetition after their own.
- Similar effects are observed at 2-back with an additive repetition bias.
- Partner decisions are not ignored but treated differently from one's own.

## Abstract

How do we interact with our environment and make decisions about the world around us? Empirical research using psychophysical tasks has demonstrated that our perceptual decisions are influenced by past choices, a phenomenon known as the “choice history bias” effect. This decision-making process suggests that the brain adapts to environmental uncertainties based on history. However, single-subject experiment task design is prevalent across the work on choice history bias, thus limiting the implications of the empirical evidence to individual decisions. Here, we explore the choice history bias effect using a dual-participant approach, where dyads perform a shared perceptual decision-making task. We first propose two competing hypotheses: the participants equally weigh their own and their partner’s decision history, or the participants do not weigh equally their own and their partner’s decision history. We then use a statistical modeling approach to fit generalized linear models to the choice data in a series of steps and arrive at a model that best fits the observed data. Our results indicated that the own and partner’s trial history cannot be treated independently. The findings suggest an interaction of actor and decision at 1-back, leading to a choice alternation bias after a partner’s decision in contrast to a choice repetition bias after an own decision. A similar effect is observed at 2-back, in addition to an additive choice repetition bias of similar size. The effects of actor and decision at 2-back do not depend on the properties of the 1-back trial. Together, these findings support the idea that the participants do not ignore their partner’s decisions but treat these qualitatively differently from their own.

The online version contains supplementary material available at 10.1038/s41598-025-96182-5.