Relationship Between the P300 and Sequence Knowledge in a Changing Environment

The P300 amplitude has been linked to the processing of uncertain events. Studies have assumed that knowledge extracted from sequences of events corresponds to event probability. The relationship between the P300 and event uncertainty has been studied using the model-based analysis, in which the subjective expectancy of event probability is modeled and examined by using a quantity called “surprise.” However, other types of sequence knowledge exist, such as event transition probabilities, which comprises both event repetitions and event alterations. Whether the state of the environment affects the encoded sequence knowledge is not fully understood, and the type of sequence knowledge, event probability or event transition probability, that is encoded in the brain in a changing environment remains unknown. We determined whether fluctuations in the P300 are better explained by surprise based on a model of event probability or by surprise based on a model of event transition probability. Participants completed a two-choice response task in which a binary sequence was generated from a hidden Markov model. Reaction times indicated that behavior changed depending on the event transitions. The model-based analysis revealed that trial-by-trial P300 was better explained by surprise based on a model of event transition probability. Our results suggest that humans use the sequence knowledge of event transitions in a changing environment.