A clinical psychologist investigated whether adults diagnosed with developmental prosopagnosia (face blindness) are less accurate at identifying emotions from partial facial expressions compared to a control group of adults without the condition.

The researcher recruited 25 adults with prosopagnosia and 25 age-matched control participants. All participants completed a computerized emotion-recognition task in a quiet, distraction-free laboratory cubicle under strictly controlled conditions, where image exposure duration, screen brightness, and viewing distance were held constant.

Which of the following best describes the experimental method used in this study?