Acid rock is a form of psychedelic rock, which is characterized by long instrumental solos, few (if any) lyrics, and musical improvisation. Tom Wolfe describes the LSD-influenced music ofthe Jimi Hendrix Experience, Pink Floyd, the Doors, Iron Butterfly, Big Brother & the Holding Company, Cream, Jefferson Airplane, Ultimate Spinach, Blue Cheer, Quicksilver Messenger Service, the Great Society, Deep Purple and the Grateful Dead as "acid rock" in his book about Ken Kesey and the Acid Tests, The Electric Kool-Aid Acid Test.