B. Alexandra Szerlip at The Believer:
Hypnopaedia aka Sleep Learning had been thrust upon the public in 1921, courtesy of a Science and Invention Magazine cover story. Echoing Poe, Hugo Gernsback informed his readers that sleep “is only another form of death,” but our subconscious “is always on the alert.” If we could “superimpose” learning on our sleeping senses, would it not be “an inestimable boon to humanity?” Would it not “lift the entire human race to a truly unimaginable extent?”
Gernsback proposed that talking machines, operating on the Poulsen Telegraphone Principle (magnetic recordings on steel wires) be installed in people’s bedrooms. The recordings library would be housed in a large central exchange; subscribers could place their orders by radiophone. Then, between midnight and 6 a.m., requests would be “flashed out,” over those same radiophones, onto reels, each with enough wire to last for an hour of continuous service. Eight reels would give the sleeper enough material for a whole nights’ work!
In other words, in 1921 he anticipated the first spoken word LPs (Caedmon Records, est. 1952), Books of Tape (est. 1975) and the first digitally downloaded audio books (mid-1990s).