Aphasia, a common secondary result of ABI, is a multimodal language disorder in which the manipulation, comprehension and formulation of linguistic symbols and elements present as the prominent deficit in individuals affected (20–22). Though the primary deficit in aphasia is language, researchers have also identified concomitant impairments in working memory, self-regulation, attention, and executive function (23–25). Attentional skills are integrated in different stages of word production tasks including phonological encoding and lexical retrieval, and attentional skills required for these tasks can be affected in persons with aphasia (26, 27).

Types of aphasia can be broadly categorized into fluent and nonfluent aphasia; though metacognitive skills may be disrupted differently in each, lack of awareness may be present. Levelt et al. (28) proposed the perceptual loop hypothesis, stating that language output was monitored by one's comprehension of language. Therefore, if one does not comprehend errors, they would not be able to recognize and correct errors. The theory accounts for decreased metacognitive skills in those with fluent aphasia. Contrast, metacognitive awareness is postulated to be a conscious experience relying on both attention and executive function (29). Since these cognitive skills rely on the integrity and connections within the frontal cortex (17, 24), awareness in those with nonfluent aphasia may be affected. Evidence shows cognitive control and monitoring are important for word selection tasks and may be interrupted due to infarcts linked with aphasia (30). Moreover, performance on measures of awareness do correlate with severity of language impairment (6). Enhancing metacognitive skills is therefore likely to aid general cognitive functioning, subsequently bolstering linguistic performance.

Metacognitive Strategy Instruction (MSI) involves training individuals to increase self-awareness of their strengths and weaknesses, thereby increasing their independence in completing everyday tasks. When describing treatment protocols that promote self-awareness, (31) state that self awareness retraining, “promote(s) internalization of self-regulation strategies through self-instruction and self-monitoring as a practice option” (p. 1688). In theory, once one is aware of strengths and weakness, they will be able to allocate resources where necessary (be it language or underlying cognitive deficits), thus increasing overall functioning. Another avenue for metacognitive training is a focus of error awareness throughout strategy training. The focus of this type of metacognitive training is the ability to recognize errors throughout completion of a task (14, 32). Once one has a heightened sense of awareness, they will be able to self-correct errors during language output.

Metacognitive therapy is used with individuals with traumatic brain injury (TBI) to increase self-awareness, self-reliance, and overall independence (33, 34). In this population metacognitive strategies commonly consist of breaking down goals into manageable steps, learning to change behavior to reach desired goal, and carrying out the change in behavior (35). Kennedy et al. (35) completed a meta-analysis evaluating therapeutic interventions for problem-solving, planning, organization, and multi-tasking in persons with TBI. The therapy dosage varied with each study, but all resulted in positive outcomes within a week post-treatment in various cognitive tasks with a trend of positive maintenance and generalization outcomes. The authors concluded that utilizing MSI for persons with TBI increased overall problem-solving skills.

Recent literature has emerged regarding the use of metacognitive therapy with people with aphasia (18, 25, 36–38). When provided during rehabilitation of cognitive-linguistic skills, metacognitive therapies are intended to enhance self-awareness and promote greater cognitive understanding and control during IADLs. Targeted skill sets include: the ability to set goals, evaluate performance throughout a task in relation to goals, decide how to change behavior in order to meet goals, and how to apply behaviors to new strategies in order to reach the desired outcome (39).

The purpose of this systematic review is to identify the therapeutic effect of using metacognitive intervention for individuals with ABI, including persons with aphasia. There are four research objectives: (1) Describe and appraise the studies and the methodological quality of the studies reviewed (2) investigate whether metacognitive interventions result in positive outcomes (cognitive, language, social) for persons with ABI (3) determine whether there is a specific type of metacognitive intervention that is more widely utilized for individuals with ABI within the research literature (4) explore whether metacognitive intervention is or has the potential to be effective for persons with aphasia given extent and quality of the current literature.

Articles were selected from six electronic databases, including PubMed, Scopus, Linguistics and Language Behavior Abstracts (LLBA), American Speech Language and Hearing Association Journals (ASHA Journals), PsychInfo and ProQuest. An initial search of the databases was completed June 2018, with an updated search completed October 2019. Reference lists of identified studies were reviewed to identify studies that did not show up in the database search. Preferred Reporting Items for Systematic Reviews and Meta Analysis Guidelines [PRISMA, (40)] was employed. Keywords were: “metacognitive”; “online awareness” AND “treatment”; “intervention”; “rehabilitation” AND “aphasia”; “acquired brain injury”; “stroke”. Deduplication and screening were performed manually.

In order to identify research articles appropriate for this systematic review, parameters for inclusion and exclusion criteria were set and included: full-text, peer-reviewed journal article in English, describing a completed metacognitive behavioral treatment published; original data from the study had to be reported; participants of interest were adults, over the age of 18, with a history of ABI, including penetrating head injury traumatic brain injury (PHI TBI), closed-head injury traumatic brain injury (CHI TBI), hypoxia, CVA, tumor, anoxia, arterial venous malformation, encephalitis or aneurysm.

We included only manuscripts that used treatments specifically designed to increase aspects of metacognition in participants, such as error detection, self-awareness, online awareness and the ability to identify and carry out appropriate compensatory strategies during a given task. Studies that sought to identify metacogntive deficits but did not explicity treat metacognition either directly or indirectly, were excluded. In this case, the researchers were looking for treatments explicitly targeting metacognition. For example, a study that treated attention as a primary outcome but that included metacognition as a secondary outcome would be included [i.e., (18, 37)] whereas one that only identified individuals with a metagcognitive deficit during the treatment process but did not track change, would have been excluded. Other articles excluded from the systematic review include: non-behavioral treatment studies such as those that use medication; studies including participants with a diagnosis of a degenerative disease (i.e., dementia). Gray literature and non-experimental publications (i.e., reviews) were excluded.

Three reviewers, the first, second, and fourth authors, completed initial parsing of the initial 266 journal articles based on the appraisal of the title and abstract of each paper included in the search results. If reviewers were not able to determine the eligibility of the paper based solely on the title and abstract, the full text was reviewed individually by two separate reviewers. Any disagreements between reviewers were brought to consensus through discussion.

In order to identify the methodological quality of the studies included in the systematic review, the Physiotherapy Evidence Database Rating Scale-Plus (PEDro+) and the Single Case Experimental Design Scale-Plus (SCED+) were utilized (41). The PEDro was chosen due to its reliability in evaluating the quality of randomized control trials, including evaluation of the study's internal validity and adequacy in communicating interpretable statistical results (42). The SCED was chosen as a reliable quality measure of single subject research designs (43). The PEDro+ and SCED+ designs, as amended by Cherney et al. (41), were utilized in order to account for each study's treatment fidelity and treatment replicability in addition to the original quality measures.

Four reviewers, the authors of this manuscript, extracted data and completed the PEDro+ and SCED+ quality ratings. For reliability, each study was independently assessed by two reviewers. Upon reviewer disagreement of the rating score, further review of the article followed by discussion resulted in rater consensus.

The following data were systematically extracted from each article: year of publication, number of participants, age and gender of participants, type and severity of brain injury, time post onset of brain injury of each participant, concomitant diagnoses of the participants, whether the study utilized a control measure, design of the study, treatment type utilized in the study, duration of the intervention, and whether or not home practice was required as part of the study. The following outcome measures were obtained: cognitive, language, and rating scale outcome measures as well as any reports of the maintenance and/or generalization of the outcome skills. The clinical implications, study conclusions, study limitations and future research directions were also collected from each research article.

The database search produced 257 articles following manual removal of duplicates. Through reference scanning and citation tracking, nine additional articles were determined to fit the study criteria, resulting in a total of 266 studies. Two-hundred and twenty-seven articles were removed following title and abstract screening. The remaining 39 articles underwent full article review, and ten additional articles were excluded due to inappropriate sample population [e.g., (44, 45)], treatment methods that did not involve metacognitive aspects [e.g., (46–49)], lack of peer review [e.g., (50–52)], or reporting of upcoming studies [e.g., (53)]. Of the 28 remaining articles, five were designed for people with aphasia. See Figure 1 for the PRISMA flow diagram, illustrating study selection.

In all, 29 studies were found to fit the criteria for metacognitive intervention. Twenty-eight of the 29 studies reported positive outcome measures on at least one of the measures utilized.

Six studies were reviewed using the PEDro+ rating scale and 24 studies were reviewed with the SCED+ rating. Levine et al. (54) included both a randomized control trial as well as a single subject design, so each was rated by the appropriate scale. Point by point interrater reliability was calculated for raters using the PEDro+ and the SCED+ scales, the interrater reliability scores were 93.65% and 95.24%, respectively. In order to be considered of adequate quality, a study must receive credit for at least half of the items on the checklist (41).

The results of the PEDro+ rating scale for each study are shown in Table 1. The methodological quality of the studies ranged from weak to high quality studies with scores ranging between six and eleven (out of a maximum of 13) (41). Five out of six RCTs received high ratings in this sample. On the PEDro+ rating scale, studies often lacked concealed allocation, blinding of therapists, blinding of assessors, and description of treatment fidelity.

The results of the SCED+ rating scale for each study are shown in Table 2. Scores on the SCED+ ranged from three to 12 (out of a maximum of 12). Sixteen out of 24 single case series designs achieved a high rating on the SCED+. In the SCED+, methodological quality ratings tended to be negatively impacted due to lack of interrater reliability, independence of assessors, and description of treatment fidelity.

Aim 2: investigate whether metacognitive interventions result in positive outcomes (cognitive, language, social) for persons with ABI

Outcome scores were recorded in three areas: rating scale outcomes (Table 5), cognitive assessment outcome measures (Table 6) and language outcome measures (Table 7). Positive changes in treatment were defined by authors of each paper and reported accordingly in this review.

The studies included in the final analysis utilized various research designs, therapeutic strategies, and assessment measures, making comparison difficult, but collectively they have provided insight regarding the use of metacognitive intervention with the ABI population. All 29 metacognitive interventions resulted in positive or mixed outcomes on rating scale, cognitive or language assessments (21 mixed outcomes and eight positive outcomes across scales). Of the studies measuring rating scale outcomes, eight of 19 studies had positive results, nine of 19 had mixed results between assessments, and two of 19 resulted in no change. Seventeen out of 19 studies utilizing rating scales observed at least one positive trend at completion. Nineteen out of 20 studies utilizing cognitive outcome measures reported at least one positive trend in cognitive measures following treatment that included metacognition. Fourteen of the 21 studies reported positive outcomes on all measures used, five out of the 21 studies had mixed outcomes between assessments [i.e, clinically significant change on the TEA Map Search, but not on CPT-II; (37)], and two out of the 21 studies reported no change on any outcome measure (34, 55). Similarly, seven out of nine metacognitive interventions resulted in at least one positive language outcome amongst measures.

Positive characteristics of metacognitive treatment include the feasibility and functionality of the treatment program, where participants can apply treatment to their everyday life (25, 58, 59). The programs are also flexible, allowing each treatment to be tailored to an individual's needs (25, 33, 38).

Authors also reported caveats of treatment protocols, including that the treatment can be taxing on cognitive skills that may be interrupted due to brain injury. The reliance on cognitive skills that may have been impacted due to injury may inhibit treatment outcomes due to the inability of individuals to apply learned material, thus making metacognitive treatment difficult for some. Inadequate length of treatment was also deemed to have had a negative effect on treatment outcomes, with authors suggesting that more time in treatment may have a more positive impact on effectiveness and generalizability of the treatment (55, 60). Considering these factors, metacognitive treatment for persons with ABI does appear to be effective, where positive changes across participants were observed on at least one measure in 22 out of 29 of the studies.

Aim 3: determine whether there is a specific type of metacognitive intervention that is more widely utilized for individuals with ABI within the research literature

MSI, GMT, CO-OP and APT-II are the only metacognitive interventions that were utilized in more than one study, however, no one of these appears to have been used more widely than others. On the other hand, there are some techniques that are more commonly used within each treatment paradigm. Goal setting and providing feedback on errors emerged as important components within treatment paradigms. MSI was utilized across two studies for individuals with mild to severe ABI (39, 59). Each study included eight participants where Finch et al. (59) utilized metacognitive intervention for social communication and Copley et al. (39) utilized MSI to address receptive language skills. Finch et al. (59) obtained mixed rating scale outcome measures (positive PPIC and GAS, no change seen onLCQ) and Copley et al. (39) identified positive language outcome measures.

GMT was utilized in three studies for individuals with ABI (severity unreported), with a total of 54 participants. Positive outcome measures were observed on both rating scale measures and cognitive measures (16, 54, 56).

CO-OP was utilized in two studies included in this systematic review; three participants were diagnosed with mild to severe TBI (58) and one participant was diagnosed with a moderate to severe right hemisphere stroke (15). Both research teams identified positive rating scale outcome measures upon completion of treatment.

APT-III was used to treat reading comprehension in ten individuals with mild to moderate aphasia in two studies and in both explicit feedback on performance was provided following each treatment session (18, 37). Findings on cognitive and language outcome measures were mixed between participants within these studies on both the TEA and Maze reading tasks. Two studies utilized feedback groups on persons with mild to severe TBI through completion of iADLs.

Although there is an inherent difference between self-awareness retraining (MSI, GMT, CO-OP) and error awareness training (Verbal and Video Feedback), there are many similarities between the two. In MSI, CO-OP, and GMT, breaking down the steps to completion and review of a task are still the main tenants; each of these metacognitive treatment paradigms include a review of success of task completion and errors. The self-awareness treatments also encourage participants to self-generate strategies to ensure successful task completion in the future, which implies recognizing errors. In Verbal and Video Feedback groups, participants were asked to rate their performance prior to initiating a task as well as following task completion. This strategy promotes self-awareness of abilities in addition to highlighting error awareness throughout the task. There is a cross-over between these two approaches, though each focuses different skills.

Several different interventions were utilized among the studies examined in this systematic review. GMT was the most commonly utilized and had consistently positive outcome scores compared to the other interventions. It was utilized in only three studies but included a relatively large number of participants (n = 54). Three studies are not sufficient to deem it the most effective type of treatment, but there is strong evidence supporting its use.

Aim 4: Explore whether metacognitive intervention is or has the potential to be effective for persons with aphasia given extent and quality of the current literature.

Though ABI includes individuals with aphasia following a stroke, those with different etiologies may respond differently to treatment. Only five of the 29 studies, with a total of 15 participants, focused on metacognitive rehabilitation for people with aphasia (18, 25, 36–38). Fourteen of the individuals with aphasia presented with mild to moderate aphasia, and one presented with severe aphasia. Three of the five studies focused on a combination of cognitive and language outcome measures (18, 36, 36) and two of the studies focused on language outcomes only (25, 66). Of the 15 participants, nine participants demonstrated positive results on language measures in response to metacognitive treatment, incuding increased attention, expressive language, and oral reading skills. With over half of the participants demonstrating a positive response to metacognitive treatment, one could make a case for implementing these aspects into language treatments. More research needs to be done to determine the optimal candidate with aphasia for this type of treatment.

Table 8 provides characteristics and outcomes from the studies focused on aphasia.

Treatments of persons with aphasia focused on those diagnosed with nonfluent aphasia with a given severity ranging from mild to severe. The individual with severe aphasia did not show improvement on language measures, though more research should be completed to identify the optimal population for metacogntive treatment. No singular treatment protocol was used throughout studies; APT-III was the only treatment protocol used more than once in the studies included for analysis (18, 37).

Effectiveness of treatments varied across measures and participants within each study. Though some positive effects were observed by researchers, most treatments did not identify positive outcomes for every participant and/or on every measure used (including cognitive, language and rating scale outcome measures). Of the studies utilizing rating scale measures, three out of three participants demonstrated positive changes on quality of life and goal attainment measures (36). Of the studies utilizing cognitive measures in addition to language measures, six out of 13 participants demonstrated positive increases on the RBANS and subtests of the TEA (18, 36, 37). Nine out of the 15 participants demonstrated positive increases on the language scores as well (18, 25, 36–38).

In summary, the evidence shows that though metacognitive paradigms can be applied to language therapy for people with aphasia, the results are equivocal with only a little more than half of all participants benefitting overall. The varied outcomes can be explained by the heterogeneous samples of participants utilized between studies with vastly different designs, and only small sample sizes available for evaluation. Though the results demonstrate the viability of utilizing metacognitive treatment for people with aphasia, there is not yet enough evidence to conclude the benefits of such treatment in this population. See Supplementary Material D for further details on treatments utilized.

The cogntive deficits that commonly follow TBI make metacognitive training an obvious choice for this population. Researchers tend to think of those with aphasia as having language disorder distinct from cognitive deficits, making metacogitive training appear to have less relevance. In fact, the relatively stronger cognitive skills may make those with aphasia stronger candidates. If memory and attention are less impaired, it follows that there is a higher likelihood of effectively using those skills to self-monitor language production.

The most commonly utilitzed outcome measures for testing cognitive skills as related to metacognition include attention and cognitive flexibility. Attention and cognitive flexibility, facets of executive function, which are closely related to metacognition, should be tested pre and post treatment in addition to target language outcomes. The treatment itself should utilize the breakdown of goals as seen in GMT, CO-OP and MSI as goal breakdown was observed in seven of the studies reporting positive results. Further, in order to foster self-awareness, verbal and video feedback should be utilized in addition to self-rating scales. In each of the studies that this was done, the effect was positive (14, 32). Using what has worked for individuals with TBI provides aphasiologists with the foundation needed to identify whether there is a therapeutic effect of metacognitive treatment for people with aphasia.