It's become fashionable for the right-brain/left-brain separation to be boiled down to the kind of thing that lets one take an online test to decide whether or not they're more creative or more practical. Left unsaid in this kind of talk is that there is interaction between left and right, and that using one's creative faculty has practical applications:abstraction allowed man to prepare for the hunt and elude predators who were physically superior to him, and the practical, logical mind is necessary to bring any massive creative endeavor to fruition (filmmakers, for instance, only get to let their imaginations soar after navigating hurdles involving everything from financing to pre-production headaches).
Some thinkers and writers, as disparate as Bruno Snell, Julian Jaynes, and Colin Wilson himself, believed that Man may have previously lived in a more integrated, "animal" state, and that this separation of the minds inside the brain was a sort of schism that led to man's psychic dyspepsia manifested in movements as disparate as Romanticism and Existentialism.
In "Access to Inner Worlds" Colin Wilson takes the anecdotes and "automatic writing" poetry of a man he meets during a retreat (the eponymous Brad Absetz) as the starting point for linking bicameralism to his lifelong obsession with what he called "Faculty X." This "X" was a cornerstone of his philosophy of "Positive Existentialism" (which no doubt strikes some existentialists as a contradiction in terms).
Mr. Wilson lays out his case in the book that we, as humans, possess the ability to use both the left and right "worlds" of our mind to create a third world whose existence is at once as miraculous and yet obvious as "perspective drawing" must have seemed to people who'd perceived art as something done on a two-dimensional plane before that moment when some artist blew their minds open for good.
According to Mr. Wilson peak performance of the mind does not require peak experience, which can many times be destructive. Hard drugs and brushes with death may allow one to experience a sort of focused perception (opium, contra what many claim, gives users a sense of euphoric "clarity," not the muddled high we associate with depressants or most strains of marijuana), but putting a needle in one's arm or a revolver to one's head (a la Graham Greene) is a strategy with diminishing returns. Wilson argues that access to this World 3 can be summoned nearly at-will, through retraining of the mind and recognition of some basic facts that should have been self-evident, had we as humans not ceded so much control to the robot (see "Beyond the Robot," a solid biography of Colin Wilson, for more on this subject).
Based on one's own disposition and beliefs, Colin Wilson and his book may strike you as everything from the vague hucksterism of a charlatan to providing a kind of hidden code for unlocking your higher potential as a sentient being. For me, what I can extract from such a book in a utilitarian sense is irrelevant, because Wilson is always such a congenial and knowledgeable guide through whatever subject he explicates that it's impossible to not find oneself infected by the man's enthusiasm, his joy at learning and sharing that learning.
He's a bit of a manic autodidact, which probably explains why his stint as one of the good people during his feting as an "Angry Young Man" was short lived, since the cognoscenti like their enthusiasms restrained. Colin Wilson was a writer capable of mentioning Marcel Proust, Adolf Hitler, and the Buddha in one paragraph and having it all somehow tie together. His genius was in the joy he never abandoned and always championed, even though post-war Continental philosophy was predicated for the most part on giving primacy to the hopeless, to the pointless, as some ultimate expression of genius.
Highest recommendation from me, but again mileage may vary.