Complex sentence: Before designing the cover, Yokoo listened to a tape of the concert, meditated, and thought about his reading of Raymond W. Bernard's 1969 book "The Hollow Earth"; critics thought he had been inspired instead by the psychedelic drugs popular at the time.
Split into simpler sentences: Before designing the cover, Yokoo listened to a preliminary tape of the concert, meditated, and reflected on his reading of Raymond W. Bernard's 1969 book "The Hollow Earth". Critics who eventually saw the album's packaging thought he had been inspired instead by the psychedelic drugs popular at the time.