The modality principle states that narration rather than on-screen text supports best learners in their understanding of information. Many of the modality studies involve content that is irrelevant to the participants. A few studies in the engineering domain have shown that development of self-efficacy affects students' belief in their ability to perform and is a motivator to learn more. The purposes of this study were: 1) to determine whether students, while learning abstract and complex technical content in an authentic setting, prefer narration only or text and narration, and 2) to investigate possible relationships between student's self-efficacy and performance. The hypothesis was that giving students the option of selecting to expose text explanations in a complex lesson would enhance self-efficacy and performance. This study stands out from the existing literature because the content was relevant to the participants and the study was conducted in an authentic setting. This quasi-experimental study, an asynchronous tutorial on control systems for a nuclear engineering three-credit course involving seventy-four undergraduate students, quantitatively assessed the choices students made with narration and text, examined their navigation patterns, and investigated whether their perceived self-efficacy in their ability changed by the end of the lesson. The results of this study showed that with this complex content and very capable learner population, there was no evidence that violating the modality principle, adversely affected student performance. In addition, the results showed that, when given the option, the majority of students chose to view the optional text throughout the online tutorial. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]