Lexical access is the process in which basic components of meaning in language, the lexical entries (words) are activated. This activation is based on the organization and representational structure of the lexical entries. Semantic features of words, which are the prominent semantic characteristics of a word concept, provide important information because they mediate semantic access to words. An experiment was conducted to examine the importance of semantic feature distinctiveness and feature frequency in accessing the lexical representations of young and older adults in an off-line task using features of animals. The McRae, Cree, Seidenberg, and McNorgan (2005) feature norm corpus is the basis for the selection of stimuli for the current research project. Semantic features were utilized to explore the structure of the lexicon. Stimuli varied in feature distinctiveness based on the study by McRae, et al. (2005) in 3 broad stimulus groups: Distinctive (D), Low Frequency Non-Distinctive (LFND), and Non-Distinctive High Frequency (NDHF). Participants were asked to list all of the concepts that came to mind for a given feature in an untimed task. Distinctiveness was examined between stimulus groups for the number of concepts and variety of first concepts given to the presented feature. It was found that fewer concepts were given and there was less variety in first concepts given for the distinctive features and the most concepts and greater variety of first concepts were given for the high-frequency non-distinctive features. Distinctiveness appears to vary along a continuum, supporting theories of lexical access based on activation and competition between concept words. Additionally, participant age groups were compared for the number of concepts given and the variety of first concepts given. The older adult group produced more concepts and more variety of first concepts than the younger group, in all three feature categories. These results indicate that greater (lifetime) language experience of the participants in the older group was reflected in their performance. A continued interest in semantic features is important to our understanding of the influence of features on the retrieval of semantic concepts and the changes in those retrieval processes over the lifespan. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]