Memory systems research has established the importance of two distinct types of memory systems in the brain: explicit and implicit. While a robust literature exists on individual differences in the explicit domain (Chapter 3), research on individual differences in implicit learning remains relatively limited. The key question guiding the investigation into individual differences described in this dissertation lies in the arguably natural assumption that certain individuals are more equipped to learn particular skills, such as in sports or music, that are supported by implicit learning mechanisms. Historically, researchers have assumed that individual differences in implicit learning are relatively small or nonexistent due its reliance on evolutionarily older neural mechanisms and its incidental or "automatic" nature. Such an automatic process should not be able to translate into individual advantages or weaknesses in implicit learning. However, the body of research investigating "automaticity" in implicit learning has proved inconclusive in many ways.

Furthermore, researchers who study the types of real-world skill learning that implicit learning is thought to support have argued in favor of individual differences. In particular, consideration of the nature of skill expertise has led some to argue that innate talent does play an important role in skill learning. This suggests that implicit learning, as a key component of skill learning, may vary across individuals in a similar way to constructs with a much deeper history of individual differences research, such as fluid intelligence or working memory capacity. In other words, particular individuals may simply be more gifted when it comes to skill learning, a notion that likely seems logical or even obvious to most.

In my own research using an implicit sequence learning task, I have found that altering participants' mental state (e.g., depleting mental resources, inducing a particular motivational state) can impact the expression of implicit knowledge, providing a firmer argument against the notion of "automaticity" in implicit learning (Chapter 2). In addition, other researchers have begun to investigate the relationship between individual differences in working memory capacity and individual differences in implicit learning (Chapter 3). Together, these studies led me to ask the question: is implicit learning ability a reliable trait measure that differs across individuals? Surprisingly, the results from the four experiments at the core of this dissertation (Chapter 4) suggest that the answer is a resounding no. Evidence from both correlational and factor analyses indicated that sequence-specific learning ability is not a stable individual trait. This finding adds significantly to the discussion of the nature of skilled expertise by implying that the basic implicit learning mechanism underlying skill learning is a universally shared process---all individuals have an equal capacity to learn.