Implicit learning is the learning of complex information in an incidental manner, without awareness of what has been learned. According to Frensch and Rünger (2003) the general definition of implicit learning is still subject to some controversy, although the topic has had some significant developments since the 1960s. Implicit learning may require a certain minimal amount of attention and may depend on attentional and working memory mechanisms. The result of implicit learning is implicit knowledge in the form of abstract (but possibly instantiated) representations rather than verbatim or aggregate representations, and scholars have drawn similarities between implicit learning and implicit memory.