I looked into this briefly: I suspect he means the one 1950s study that tried to see if people could remember facts they heard over audio while asleep? I found a snippet here. This doesn’t surprise me, I’ve heard sounds in sleep, and woken up from dreams to them, while remembering that in my dream, my mind had not recognised the sound for what it was, but woven them into a story. For e.g., my alarm beeps became the alarm on my car, and then reasons for why my car alarm would go off were formed in response. I can imagine that’s not useful when learning to associate new words to native language ones. On the other hand, I also have woken up from dreams where I speak much better German than I do as a student of the language in waking life - remembering in-dream all the words and grammar that I’ve learned effortlessly, which I have trouble accessing quickly in a conversation.
I’m certain the brain - as IMO basically the wetware interface between spirit and body - can do way more than it appears to in the every day, and that’s why I wouldn’t rule out learning from audio during sleep, since you can hear it, and the brain can process it, who knows what it does with it or if that can be taken advantage of? It’ll take more than two people back in 1950 to figure it out though.
However, this is an example using only one kind of learning, that relies on the left brain language centers, while dreaming is very right brained. So I find it equally unsurprising that other studies have the results that the subconscious can be manipulated during sleep, including learning and making new associations. For example, a study in 2012:
Then a 2012 study by a US group reported that participants were more likely to correctly play a melody in a musical video game (similar to Guitar Hero) if the tune had been previously played to them during the slow-wave stage of a 90-minute nap. The authors suggested that learning can occur subconsciously during sleep.
From this article:
Which goes on to discuss the idea that sleep enhances learning. The application for magicians is clear: by performing learning tasks timed around the sleep schedule we can accelerate our efforts, particularly where we are seeking to affect the subconscious - such as, learning to communicate more clearly with spirits… and then doing so.
In conclusion: doing a ritual with the conscious mind right before sleep and then sleeping with a audio is a very interesting line of experimentation, adding in an open energy portal right by your third eye - and I would expect to see something pretty exciting.