The inclusion of reversed tape sounds on "Rain" (specifically, a portion of Lennon's vocal part) marked the first pop release to use this technique, although the Beatles had first used it, in some of the tape loops and the overdubbed guitar solo, on "Tomorrow Never Knows". The backwards (or backmasked) guitar solo on "I'm Only Sleeping" was similarly unprecedented in pop music, musique concrète, as well as standard contemporary rock and pop. In Rodriguez's view, the influence of Indian music permeates the album. Aside from the sounds and vocal styling used on much of the recording, this influence is evident in the limited chord changes in some of the songs, suggesting an Indian-style drone. According to cultural historian Simon Philo, "Revolver" contained " most sustained deployment of Indian instruments, musical form and even religious philosophy" heard in popular music up to that time.