Cognition, 5 (1977) 333-361 OElsevier Sequoia S.A., Lausanne - Printed in the Netherlands 2 Implicit learning: An analysis of the form and structure of a body of tacit knowledge* ARTHUR S. REBER and SELMA LEWIS Brooklyn College of CUNY zyxwvutsrqponmlkjihgfed Abstract Subjects learned implicitly the underlying structure of’ an artificial language bl’ memorizing a set of representative exemplars from the language. The form and structure of their resulting knowledge of the language was eval- uated and analqazed over a four day period bll several procedures.. (a) solving anagrams from the language, tbl determining the well-formedness of novel letter strings, and (c) providing detailed introspective reports. Several impor- tant implications about implicit acquisition of a novel complex s.)ystem emerged. First, the memorial representation of a structured system is acquir- ed through the dual operations of a differentiation-like process based upon relational invariances and a configurational process based upon overall struc- ture. Second, the form of tacit knowledge is an abstract representation of the intrinsic structure of the stimulus field. Third, while the ability to make explicit what is known implicitl? ! increases with performance levels, the conscious apprehension of structure always lags behind what is known unconsciousl?: The term “implicit learning” was coined several years back (Reber, 1967) to characterize the manner in which subjects came to apprehend the under- lying structure of a complex stimulus environment. At that time it was argued that there were two aspects of implicit apprehension that clearly differentiated it from various other, more explicit, acquisition processes. First, that it was a process which took place quite naturally and simply in any subject who devoted sufficient attention to a structured stimulus environment. Second, that it was manifested in the absence of conscious operations such as hypothesis testing about the nature of the stimuli and explicit strategies for learning. *Our thanks to Chris Hether for collection and initial analysis of the data and to an anonymous reviewer for a cogent and thoughtful review. The research was supported in part by Grant MH 20239- 01 from NIMIl. Reprint requests should be sent to Arthur S. Reber, Department of Psychology, Brooklyn College of CUNY, Brooklyn, N.Y., 11210.