implicit. Explanatory models Traditional approaches to AGL claim that the stored knowledge obtained during the learning phase is abstract. Other approaches argue that this stored knowledge is concrete and consists of exemplars of strings encountered during the learning phase or "chunks" of these exemplars. In any case, it is assumed that the information stored in memory is retrieved in the test phase and is used to aid decisions about letter strings. Three main approaches attempt to explain the AGL phenomena: Abstract Approach: According to this traditional approach, participants acquire an abstract representation of the artificial grammar rule in the learning stage. That abstract structure helps them to decide if the new string presented during the test phase is grammatical or randomly constructed. Concrete knowledge approach: This approach proposes that during the learning stage participants learn specific examples of strings and store them in their memory. During the testing stage, participants do not sort the new strings according to an abstract rule; instead they will sort them according to their similarity to the examples stored in memory from the learning stage. There are multiple opinions concerning how concrete the learned knowledge really is. Brooks & Vokey argue that all of the knowledge stored in memory is represented as concrete examples of the full examples studied during the learning stage. The strings are sorted during the testing stage according to a full representation of the string examples from the learning stage. On the other hand, Perruchet & Pacteau claimed that the knowledge of the strings from the learning stage is stored in the form of "memory chunks" where 2 - 3 letters are learned as a sequence along with knowledge about their permitted location in the full string. Dual Factor approach: Dual process learning model, combines the approaches described above. This approach proposes that a person will rely on concrete knowledge when they can. When they cannot rely on concrete knowledge (for example on a transfer of learning task), the person will use abstract knowledge of the rules. Research with amnesia patients suggests the "Dual Factor approach" may be the most accurate model. A series of experiments with amnesiac patients support the idea that AGL involves both abstract concepts and concrete exemplars. Amnesiacs were able to classify stimuli as "grammatical" vs. "randomly constructed" just as well as participants in the control group. While able to successfully complete the task, amnesiacs were not