Conversation so far:
What is progressiveness?
Elements contributing to the progressive label include: lyrics were more poetic, technology was harnessed for new sounds, music approached the condition of art, and the studio became the focus of musical activity
What is psychedelia?
Psychedelic music (sometimes called psychedelia is a wide range of popular music styles and genres influenced by 1960s psychedelia, a subculture of people who used psychedelic drugs
How did the Beatles contribute to progressiveness?
The Beatles' experimental timbres, rhythms, tonal structures, and poetic texts on Rubber Soul and Revolver encouraged a legion of young bands that were to create progressive rock“.

Question: What instrument did the Beatles spark a musical craze for?
Self-contained rewrite: What instrument did the Beatles spark a musical craze for?