Consciousness is a late arrival on the evolutionary scene. Sophisticated unconscious perceptual and cognitive functions preceded its emergence by a considerable margin.
Reber, A.R. (1993). Implicit learning and tacit knowledge: An essay on the cognitive unconscious
Perception Without Awareness of What Is Perceived, Learning Without Awareness of What Is Learned
By John F. Kihlstrom
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The turning point came in the early 1980s, with a new round of demonstrations of subliminal perception by Marcel (1980, 1983a, 1983b) and Kunst-Wilson and Zajonc (1980). Marcel�s experiments employed a semantic-priming paradigm in which the prime was masked. When the prime and the target were semantically related, priming was observed on lexical decisions concerning the targets, even though the subjects did not detect the prime itself. Kunst-Wilson and Zajonc (1980) employed an adaptation of the mere exposure paradigm with extremely brief tachistoscopic exposures of the stimuli, which in this case were nonsense polygons. Subjects showed an enhanced preference for stimuli which had been repeatedly exposed, even though they had not detected the exposures themselves. In short order, both results were replicated by other investigators: Marcel�s by Fowler and her colleagues (Fowler, Wolford, Slade, & Tassinary, 1981) and Balota (1983); those of Kunst-Wilson and Zajonc by Seamon and his colleagues (Seamon, Brody, & Kauff, 1983; Seamon, Marsh, & Brody, 1984) and many others (for a review, see Bornstein, 1989). By presenting evidence that meaning (denotative in the case of Marcel, connotative in the sense of Kunst-Wilson and Zajonc) could be processed subliminally, these experiments moved beyond the pioneering study of Pierce and Jastrow (1885), which involved only the discrimination of stimulus qualities such as brightness and weight, and seemed to fulfil the promise of the New Look.
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Another variant on the unconscious acquisition of knowledge is provided by studies of implicit learning (Reber, 1967), in which subjects appear to learn from experience without being aware of what they have learned, or even of the fact that they have learned anything at all.
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