Johnson, who died in 2013 at 88, is sometimes described as a sexologist or psychologist. In reality, she had been studying for a sociology degree when Masters took her on, but the demands of their work prevented her from completing her degree.
In Masters and Johnson's studies from 1957 until 1965, they recorded laboratory data on the anatomy and physiology of human sexual response based on direct observation of 382 women and 312 men aged between 18 and 89 in having sex or masturbating.
In the late 1990s Johnson opened the "Virginia Johnson Masters Learning Center", in Creve Coeur, Missouri, providing advice on overcoming sexual dysfunction.
They debunked Sigmund Freud's assertions about the difference between "vaginal orgasm" and "clitoral orgasm" (which he deemed "immature", proper only for pubescent girls).
In their findings, the physiological response was identical.
One of the most important contributions of their work was identifying the four stages of sexual response:
1. Excitement phase (initial arousal)
2. Plateau phase (at full arousal, but not yet at orgasm)
3. Orgasm
4. Resolution phase (after orgasm)
They showed that these occurred in both sexes.