Hegarty and Halliwell identify the Beatles, the Beach Boys, the Doors, the Pretty Things, the Zombies, the Byrds, the Grateful Dead and Pink Floyd "not merely as precursors of prog but as essential developments of progressiveness in its early days". The Doors' hit "Touch Me", from their fourth album "The Soft Parade", has been declared as an early example of progressive rock music. According to musicologist Walter Everett, the Beatles' "experimental timbres, rhythms, tonal structures, and poetic texts" on their albums "Rubber Soul" (1965) and "Revolver" (1966) "encouraged a legion of young bands that were to create progressive rock in the early 1970s". Dylan's poetry, the Mothers of Invention's album "Freak Out!" (1966) and the Beatles' "Sgt. Pepper's Lonely Hearts Club Band" (1967) were all important in progressive rock's development. The productions of Phil Spector were key influences, as they introduced the possibility of using the recording studio to create music that otherwise could never be achieved. The same is said for the Beach Boys' "Pet Sounds" (1966), which Brian Wilson intended as an answer to "Rubber Soul" and which in turn influenced the Beatles when they made "Sgt. Pepper".