Abstract

The processes of acquiring new information and store that information is critical to the daily functioning of humans and in many ways help define us as sentient beings. Although quite a bit has been learned about the mechanisms and neural regions responsible for learning and memory, additional research is necessary to fully understand the components of these processes and their implications on human behavior. The first two experiments of this dissertation focused on performance of Parkinson's Disease (PD) patients on implicit learning tasks. Implicit learning, or learning without awareness, has been found to involve the basal ganglia, an area of the brain that is impaired in PD patients. In Experiment 1, we examined how this impairment affects performance on a rule-based task, the Artificial Grammar Learning Task, and found that PD patients are not impaired on this task. This supports emerging evidence that the role of the basal ganglia in implicit learning has less to do with the implicit aspect per se, and more with the particular task demands of some implicit tasks. There has been converging evidence from animal studies, imaging research, and neuropsychological research suggesting that the feedback-based learning aspect of some implicit tasks is responsible for the basal ganglia involvement. In Experiment 2, we tested PD patients on the Concurrent Discrimination Task, a task in which participants gradually acquire knowledge of object discriminations across trials with feedback. PD patients displayed the ability to learn the discriminations, but successful learning appeared to be dependent on explicit memory; patients who only relied on implicit processes were unable to acquire learning in this task. Controls were able to learn the discrimination task with or without the help of explicit processes. In Experiment 3, we turned our focus to explicit memory processes. We tested PD patients on the list method Directed Forgetting Task. This task has been used extensively to study how forgetting older information that has become irrelevant improves future learning. Our findings indicate that PD patients are less efficient at this process of forgetting, and as a result are less capable of new learning.