Full context:   Study of the unconscious mind, a part of the psyche outside the individual's awareness but that is believed to influence conscious thought and behavior, was a hallmark of early psychology. In one of the first psychology experiments conducted in the United States, C.S. Peirce and Joseph Jastrow found in 1884 that research subjects could choose the minutely heavier of two weights even if consciously uncertain of the difference. Freud popularized the concept of the unconscious mind, particularly when he referred to an uncensored intrusion of unconscious thought into one's speech (a Freudian slip) or to his efforts to interpret dreams. His 1901 book The Psychopathology of Everyday Life catalogs hundreds of everyday events that Freud explains in terms of unconscious influence. Pierre Janet advanced the idea of a subconscious mind, which could contain autonomous mental elements unavailable to the direct scrutiny of the subject.