Figure 2. Schematic representation of the decision-making process in the diffusion model for a task that involves deciding between upwards and downwards motion.

In the diffusion model, the decision-making process is represented as a noisy accumulation of evidence from a starting point towards one of two decision bounds. When a participant decides between upwards and downwards motion, the decision bounds correspond to “up” and “down” responses. In this representation, the overall motion in the stimulus is going upwards. Boundary separation represents the width between the two bounds and reflects how cautious an observer is. Wider decision boundaries reflect that more evidence is required before making a decision (i.e., more cautious responses). Drift-rate reflects the rate of evidence accumulation, which depends on both the individual’s sensitivity to a stimulus and the stimulus strength. Non-decision time is the time taken for sensory encoding processes prior to the decision-making process and response generation processes after a bound is reached. Manning et al. (2022a) showed that younger children accumulate evidence more gradually (i.e., have a lower drift-rate) and make decisions more cautiously (i.e., have wider decision bounds) than older children and adults, as well as taking longer for non-decision processes (i.e., longer non-decision time). Adapted from Manning et al. (2022b).