Excessive Flexibility? Recurrent Neural Networks Can Accommodate Individual Differences in Reinforcement Learning Through In-Context Adaptation.

Cognitive and computational modeling has been used as a method to understand the processes underlying behavior in humans and other animals. A common approach in this field involves the use of theoretically constructed cognitive models, such as reinforcement learning models. However, human and animal decision-making often deviates from the predictions of these theoretical models. To capture characteristics that these cognitive models fail to account for, recurrent neural networks (RNNs) have been increasingly used to model choice behavior involving reinforcement learning. RNNs can capture how choice probabilities change depending on past experience. In this work, we demonstrate that RNNs can improve future choice predictions by capturing individual differences on the basis of past behavior, even when a single model is fit across the entire population. We refer to this capacity as the individual difference tracking (IDT) property. While the IDT property might be useful for prediction, it may introduce excessive flexibility when RNNs are used as benchmarks for predictive accuracy. We investigate the nature of the IDT property through simulation studies and examine how it affects the interpretation of predictive accuracy when RNNs are used as benchmarks for cognitive models. We also present examples using real-world data. Through these analyses, we discuss practical considerations and limitations in using RNNs as benchmarks for cognitive models. Supplementary Information: The online version contains supplementary material available at 10.1007/s42113-025-00254-8.