<H4>Psychedelic Rock</H4> Emerging in the mid-'60s, as British Invasion and folk-rock bands began expanding the sonic possibilities of their music. These groups confined themselves to the brief, concise verse-chorus-verse patterns of rock & roll, they moved toward more free-form, fluid song structures. Just as important, the groups began incorporating elements of Indian and Eastern music and free-form jazz to their sound, as well as experimenting with electronically altering instruments and voices within the studio.