Final answer:
William Masters and Virginia Johnson were the first to conduct direct studies of human sexual responses, observing physiological changes during sexual activities to understand the sexual response cycle.
Step-by-step explanation:
The first to conduct a direct study of human sexual responses were William Masters and Virginia Johnson. Their influential research departed from the prior work of Alfred Kinsey, who collected data through surveys and interviews. Masters and Johnson, on the other hand, directly observed nearly 700 participants engaging in sexual activities and recorded physiological data related to sexual arousal such as blood pressure, respiration rate, vaginal lubrication, and penile tumescence. Through this direct observation, they were able to make substantial contributions to our understanding of the sexual response cycle.