Two-choice decisions race noisy evidence to a boundary

Correct: B — Noisy accumulation of evidence over time until a decision boundary is crossed

Ratcliff (1978) modelled simple two-choice tasks as a noisy diffusion process: evidence accumulates from a starting point at a drift rate determined by stimulus quality, and a decision is committed once the integrator hits one of two response boundaries. The framework simultaneously fits mean response times, full RT distributions for correct and error trials, and accuracy. It separates psychologically meaningful parameters: drift rate (perceptual or cognitive efficiency), boundary separation (speed–accuracy tradeoff), starting point (response bias), and non-decision time. Drift-diffusion models now dominate the analysis of perceptual, lexical, and value-based decisions, linking behaviour to neural recordings of accumulator-like activity in parietal and prefrontal cortex.