Dissociating habit and recollection: evidence from Parkinson's disease, amnesia and focal lesion patients.

We investigated the role played by the striatum and the medial temporal lobes (MTL) in memory performance by testing patients with Parkinson's disease (PD) and amnesia with Hay and Jacoby's habit-learning task [Journal of Experimental Psychology: Learning, Memory and Cognition 22 (1996) 1323]. Using equations from Jacoby's process-dissociation procedure [Journal of Memory and Language 30 (1991) 513], we were able to separate out the contribution of habit (automatic memory) and recollection (intentional memory) to performance within a single probability-learning paradigm. Amnesics showed the expected dissociation of impaired recollection and intact habit, highlighting the important role of the MTL in recollective processing. Mild PD patients did not perform differently than matched controls for habit or recollection, however, moderate PD patients were impaired in their ability to rely on habit and in their ability to recollect specific information. The performance of focal lesion patients further supported the interpretation that PD patients have a significant deficit in automatic, habit-learning due to striatal dysfunction while their deficit in recollection may arise from impoverished frontal lobe contributions.