sexual-response cycle
a conceptualization of a four-stage cycle of sexual response exhibited by both men and women, differing only in aspects determined by male or female anatomy. The stages include the arousal (or excitement) phase, which lasts several minutes to hours (see sexual arousal); the plateau phase, lasting 30 seconds to 3 minutes, marked by penile erection in men and vaginal lubrication in women; the orgasmic phase, lasting 15 seconds and marked by ejaculation in men and orgasm in women; and the resolution phase, lasting 15 minutes to 1 day (see refractory phase). This conceptualization was introduced by U.S. sex researchers William H. Masters (1915–2001) and Virginia E. Johnson (1925–2013) in 1966, but it has subsequently been criticized, particularly in the way that it equates the male and female pattern.