What does reaction time measure?

Reaction time measures the time it takes to respond to a stimulus, which is precisely why option C is the correct choice. This measurement is fundamental in cognitive psychology as it reflects how quickly an individual can perceive a stimulus and initiate a response. It encompasses various cognitive processes, including sensory perception, decision-making, and motor execution.

While the speed of mental processing and the speed of physical movement are related to reaction time, they do not fully encapsulate the concept. Reaction time specifically quantifies the total time from the presentation of the stimulus to the initiation of the response, capturing both cognitive and motor components in that timeframe.

The accuracy of a response, although important in evaluating performance, does not measure time but rather focuses on correctness, adding another layer that distinguishes it from reaction time. Thus, the essence of reaction time lies in its measurement of the duration it takes for an individual to react to a given stimulus, making option C the most appropriate answer.