Uncovering the Sequential Structure of Thought

Multi-voxel pattern recognition techniques combined with Hidden Markov models can be used to discover the mental states that people go through in performing a task. The combined method identifies both the mental states and how their durations vary with experimental conditions. The paper applies this method to a task where participants solve novel mathematical problems. It identifies four states in the solution of these problems: Encoding, Planning, Solving, and Respond. The duration of the planning state varies on a trial-to-trial basis with novelty of the problem. The duration of solution stage similarly varies with the amount of computation needed to produce a solution once a plan is devised. The response stage similarly varies with the complexity of the answer produced. Thus, we were able to decompose the overall problem solving time into estimates of its components and interpret what participants are doing on individual problem-solving trials.