comments:
Basically, to answer the primary question, telepathy, "psionics", etc. generally. At the beginning of the 20th century it was not totally out of reason to think maybe there was something there. Reasonable, intelligent people were open-minded about the possibility of ESP plus John W. Campbell who was powerful in the world of science fiction was obsessed with it: Campbell was a true believer. So you end up with this entire era of science fiction in which every single novel includes some plotline in which secret powers of the human brain are unlocked. On works that ended up being accurate, I think it is kind of surprising how few scifi writers predicted basically smart phones. I find it surprising because all you have to do is extrapolate the trend of technology getting smaller and apply it to digital computers and take to its logical extreme, people walking around with powerful computers in their pocket. But anyway who got it right? Well, whoever made the props for 2001: A Space Odyssey basically made a fake iPad in 1968. Stanislaw Lem wrote “But if as a result of gradual merging of computing machines and memory banks there emerge national, continental, and later even planetary computer network, which is a realistic direction of development, the whole system, constituted by humans and these networks, may take up a dynamic trajectory, quite divergent from the civilizational hopes” in 1957 (https://www.amazon.com/Dialogues-Stanislaw-Lem/dp/0262542935) but in a speculative essay not in a story. i believe, he also predicted virtual reality calling it "phantomatics" in slightly later work.