What makes some sentences more difficult to process, and why? Memory- and expectation-based theories both attempt to explain sentence processing difficulties, and decades of sentence processing literature have found evidence in support of both theories. This dissertation further investigates these theories of sentence processing by exploring processing of subject- and object-extracted relative clauses (SRCs and ORCs) in Modern Standard Arabic, and how expectations affect the resulting interpretation of low-frequency structures. We investigate this question through various experimental paradigms. We first tested memory- versus expectation-based theories using a self-paced reading task. Results showed longer reading times for ORCs, supporting expectation-based theories, with difficulty localized at the relative clause noun phrase. We also found that misinterpretations were more frequent for ORCs, suggesting possible misreading as SRCs or good-enough and noisy-channel processing. To investigate this phenomenon, we conducted a recall task where participants re-wrote sentences word-for-word. Errors showed both ORCs being re-written as SRCs and vice versa, supporting good-enough and noisy-channel processing theories. We then explicitly tested the possibility of misreading versus good-enough or noisy-channel processing through eye-tracking. Findings indicated that readers were not misreading ORCs, but instead accepting noisy SRC interpretations. Finally, we explored the impact of grammatical cues versus statistical expectations in a second eye-tracking experiment. Results showed that increasing grammatical cues in favor of a veridical ORC interpretation did not significantly affect noisy interpretations or processing behaviors, indicating that grammatical cues were insufficient to override statistical expectations in a good-enough or noisy-channel framework. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]