Choice Reaction Time Task

The Choice Reaction Time (CRT) task is one of the most fundamental paradigms in cognitive psychology, measuring the speed at which a person can identify a stimulus and select the appropriate response from two alternatives. It is the canonical measure of processing speed and forms the cornerstone of Hick's Law (Hick, 1952; Hyman, 1953), which states that reaction time increases as a logarithmic function of the number of equally probable response alternatives.

In this implementation, a filled black square appears unpredictably on either the left or the right side of the screen. The participant presses the Left Arrow key for a left-side target and the Right Arrow key for a right-side target, as quickly and accurately as possible.

The task includes a variable preparatory foreperiod (500–2,500 ms, five uniform levels) between the fixation cross and the target, balanced across left and right trials. This prevents participants from timing the onset and pre-programming their response — a methodological requirement for clean RT distributions. Response deadline is 1,500 ms.

A short practice block (10 trials) with trial-by-trial accuracy feedback precedes the 40-trial main task. All participant-facing text is exposed as translatable parameters so the task can be administered in any language without opening the lab.js builder.