Objective: Implicit memory, defined as the recollection of knowledge unconsciously, automatically, and without being aware of it, is different than explicit memory, in which knowledge is recollected consciously, while being aware of it. In the present study, the implicit memory performance of patients with mild cognitive impairment (MCI) and Alzheimer’s type dementia (ATD) (different stages) were compared to healthy controls.

Method: The study included 19 MCI patients and 23 ATD patients (11 mild-moderate and 12  severe stage ATD). Control subjects were matched to the patient groups according to age, gender, education, and hand preference. DSM-IV and NINCDS-ADRA diagnostic criteria were used for clinical assessment.

Results: The 4 × 3 ANOVA revealed a significant main effect of the level of processing, and group and level of processing interaction effect was also significant.  Group main effect was not significant.

Conclusion: MCI and ATD groups performed similarly on the implicit memory task. Implicit memory performance was intact in patients with MCI and ATD; however, implicit memory performance of the patient groups differed according to the level of processing manipulation. For that reason, implicit memory tasks should be used for clinical diagnosis in ATD.