The curmudgeon in the corner is thinking that merely addressing the brain as plural is just another way of sneaking in the modular theory of cognition into the discussion through the backdoor. There are different parts of the brain that are "responsible" for different functions. As Tallis points out in several places, this is little more than an extension of the long-discredited phrenology of the 19th century. The sardonic side of me is wondering why Sloterdijk hasn't brought this into his curiosity cabinet of obscure topics to discuss.
If we simply assume for the moment and for the sake of argument that Gebser was discussing an actual phenomenon within the magic structure of consciousness, and given that he discussed this in relation to the efficient mode of that consciousness, then we would be justified in thinking that this capability, if not actual ability, wouid still be present today. I believe that it is for a whole variety of reasons. What is more, it would be part of all our repertoires, albeit most likely buried under tons of misapprehensions, misunderstandings, and downright intimidation and peer pressure. Not everyone is as comfortable in his weirdness as @johnnydavis54; and as for me, I don't care what you call me as long as you don't call me late for dinner.
It is known that Australian Aboriginal peoples share their Dreamscape, I believe they call it. It is known that Maoris teach their children to dream communally. There is a fair body of scientific evidence, largely discredited (for obvious reasons) that was done by J.B. Rhine at Duke University's parapsychological lab, among others, which have been disbanded or outsourced in the meantime. Even more recently some research was done by Stanley Krippner and associates at the Maimonides Medical Center in New York. The biggest shortcoming of most research is -- surprise, surprise -- replicability. Still ... I do know that Stanford Research Institute received millions of dollars in both private and governmental grants to research telepathy, especially remote viewing, though the Navy was extremely interested in developing telepathic channels to communicate with their submarines since they could thereby avoid enemy communication interceptors and decryptors. Go figure. Somebody thinks it's real, that's for sure.
A number of folks I know and am familiar with are still looking into it, such as Russel Targ (who also had a TED talk on this subject pulled ... the New Orthodoxers are no less virulent than the Inquisitorial predecessors whom they replaced), but also IONS, which I mentioned in another post, is still exploring these avenues and aspects of consciousness, so that's another -- I feel -- reliable source to check out.
Of course, all of this comes back down to the main side discussion that has come out of the Sloterdijk reading: just how do we see, understand, comprehend, imagine the phenomenon of consciousness and how does it relate to how we see, understand, comprehend, imagine ourselves as human beings. This is why I'm so torn with Sloterdijk, because there are times ... such as in Excursion 1 ... when I think he's not a new orthodoxer and then he turns around with a statement like multiple brains that puts him right back in that camp. This was, I will remind us all, one of Precht's primary criticisms (the article I translated before our reading started): you can't really nail him down.
Personally, I have no problem with telepathy, ESP, remote viewing, telekinesis, psychic investigators helping law enforcement with difficult cases, or any other paranormal phenomena. They exist, we know they exist, therefore they are worthy of precise, clearly focused, rigorous investigation. In those instances in which traditional or commonly accepted "scientifc" methods are inappropriate or inadequate, we need to be thinking about developing new methods that are so.