Several prominent theories have been developed to account for changes in cognition that occur with age, and most of these theories focus upon age-related impairments in domain-general cognitive processes, such as processing speed, cognitive resources, and inhibitory functions. However, a relatively new theory has been put forth to account for age-related changes that are specific to episodic memory. The pattern completion bias (PCB) in aging theory suggests that older adults are biased to generalize a novel but similar representation (i.e., pattern complete) as opposed to creating a distinct representation (i.e., pattern separate). It has yet to be tested whether domain-general theories of cognitive aging may account for, or alter, the PCB in aging. To this end, the current dissertation project consisted of three experiments, each manipulating the study phase of the mnemonic similarity task, to assess the contribution of cognitive slowing (Experiment 1), reductions in cognitive resources (Experiment 2), and reduced inhibitory function (Experiment 3) to the age-related PCB. Regardless of the manipulation at encoding, the test phase consisted of recognition judgments regarding whether the object was a repetition of a previously seen object, a rotated version of a previously seen object, or a novel object. Successful pattern separation was measured as the ability to correctly recognize that an object was rotated at test, as compared to the orientation presented at study. The results indicate that processing speed and inhibitory function are contributors to the PCB in aging. However, although attentional resources are critical for the formation of complex memories, there was limited evidence to support the hypothesis that attentional resources contribute to the pattern completion bias. The current set of experiments provide novel support for the notion that pattern separation processes are altered by a variety of domain-general processes that change with age. Therefore, the mnemonic similarity task, thought to specifically tax pattern separation, captures domain-general processes as well as pattern separation processes. Future research should modify the mnemonic similarity task to account for domain-general cognitive aging processes, as well as investigate the neural underpinnings of older adult improvements on the task when these accommodations are considered.