The purpose of the current study was to better understand performance variability in sentence comprehension in people with aphasia, compared to a control group of adults. People with aphasia often have difficulty understanding sentences that are complex in structure and meaning. Comprehension difficulty is variable, which may confound the clinical assessment of a person's true comprehension abilities. Evidence to date suggests that the observed variability in people with aphasia results from memory and attention limitations, although the nature of relevant individual differences is not clear. In four experiments, pupillometric and behavioral measures were combined to closely examine performance variability in sentence comprehension as a function of memory and attention limitations. Specific aims were (a) to characterize sentence processing and comprehension variability (Experiment 1) and (b) to understand the influence of active memory maintenance and immediate recall (Experiment 2), delayed memory retrieval and recall (Experiment 3), and sustained attention control (Experiment 4) on sentence comprehension variability. Overall, results point to the importance of active immediate storage in sentence comprehension and its associations with sustained attention and delayed memory retrieval. The results of the study will shed light on the nature of post-stroke aphasia and provide an important step to enhance validity of` sentence comprehension assessment in people with aphasia. [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.]