This is a technique which became popular in the early 20th century, though it did exist before. In fact, the stream of consciousness is an attempt to convey exactly what is going on in a character's mind – conscious and unconscious thoughts, feelings and impressions – without any sense of the author's presence. Some early 18th-century novelists anticipated the technique with the epistolary novel, which was written in the form of letters between characters so that, again, an obvious "author" wasn't needed. One reason why stream of consciousness became so popular in the 20th century was that, as the findings of psychiatrists like Sigmund Freud became widely known, writers and artists became more interested in exploring and describing the subconscious mind. In fact the term was originally coined by the psychologist Wiliam James in 1890.
Famous exponents of this technique include James Joyce and Virginia Woolf, both of whom describe the rambling or disconnected thoughts and feelings of their characters just as they occur; in Joyce's "Portrait of the Artist as a Young Man," for instance, the language is limited and childish as the protagonists early years are portrayed, and increases in complexity as he grows up.
Famous exponents of this technique include James Joyce and Virginia Woolf, both of whom describe the rambling or disconnected thoughts and feelings of their characters just as they occur; in Joyce's "Portrait of the Artist as a Young Man," for instance, the language is limited and childish as the protagonists early years are portrayed, and increases in complexity as he grows up.