In one of Freud's earliest metapsycholog ical papers, "A Project for a Scientific Psychology", he proposed that the infant needed a capacity for defense to protect its vulnerable psyche against the continuous bombardment of internal and external stimuli (Beebe, 1975; Pribram, 1962). Although Freud retained this idea throughout his life, as he did a number of other hypotheses from the "Project", he developed two alternative formulations of it. In one he hypothesized that the protective shield served to reduce the quantity of excitation while at the same time sampling the stimulation to detect its nature and direction (Freud, 1961). In the other, he posited that the shield acted as a threshold barrier such that stimuli penetrated the psyche only when of sufficient quantity (Beebe, 1975); it is this view which has received most attention and elaboration. It is significant, however, that in both formulations Freud perceived no psychological or theoretical consequence in whether the external stimuli emanated from animate or inanimate objects.