Limitations
aphasia, chronic aphasia
There are several important limitations that require discussion. First, we focused on naming as the primary outcome measure. Some authors have criticized the use of naming outcomes in aphasia therapy research based on the view that the ability to name objects does not reflect the multifaceted nature of human communication (e.g., Second, although we aimed to recruit a representative sample of persons with chronic aphasia, those most severely affected were excluded as they were unlikely to be able to participate fully in the therapy tasks. Along a similar vein, it is possible that the participants who entered the study were relatively motivated (i.e., searching for resources) and/or had a social network in place that supported them in pursuing therapy. Both aspects may have introduced an inherent sampling bias. In addition, the number of items trained in each therapy session varied depending on performance, which unavoidably may correlate with severity of aphasia symptoms. Notwithstanding, despite these challenges, our sample represented the heterogeneous nature of this population as well as reasonably possible.Third, as the POLAR trial was not designed to examine the efficacy of aphasia therapy, we cannot definitively conclude that the average improvement in naming performance pre- to posttherapy was a result of the therapy tasks administered here. While it is highly unlikely to observe the positive changes reported under Aim 1 by chance, it is certainly possible that factors other than the therapy tasks may have influenced these changes. For instance, engaging with the clinicians and other study participants outside of the treatment room may have forced participants to hone their functional communication skills more than they would have outside of the trial. Nonetheless, the therapy tasks were selected based on efficacy established in prior research, and these particular tasks were intended to induce language gains robust enough to enable examination of prognostic factors. Thus, we explicitly assume that the language gains observed here are the result of the therapy participants underwent.Last, our examination of prognostic factors is by no means exhaustive. The factors investigated here were chosen as they have frequently been implicated as potentially important for understanding therapy response in aphasia, but prior literature is ripe with mixed and, sometimes, contrasting findings. In an effort to elucidate the relationships between these factors and treated recovery, we therefore asked questions that have been asked before, but in a much larger sample. Future research should focus on other sources of variability, such as lesion location, genetic factors, specific language domains, and the interactions between these variables. As the field moves toward personalized medicine, it will be critical to disseminate how multiple different variables independently and in tandem may inform clinical decision making with the clients' interests at the forefront.