Developing Cognitive Control Training for Aphasia: Insights from Treatment Theory and Enablement Theory

Abstract

It remains challenging to optimize treatment for individuals with aphasia. One of the reasons is that the language processing deficits associated with aphasia have various underlying linguistic and nonlinguistic causes. The utility of cognitive training focusing on attention and working memory has been investigated in aphasia treatment. However, a related cognitive function, namely, cognitive control remains underexplored. This article leverages treatment and enablement theories to evaluate current cognitive treatments and guide the development of new treatments focused on cognitive control in aphasia. We provide the theoretical and empirical rationale for exploring the clinical significance of cognitive control in aphasia rehabilitation and discuss how treatment and enablement theories may be used to develop a systematic cognitive training approach. We conclude with future directions for cognitive control research that can advance more personalized aphasia rehabilitation.

2. Introduction

Approximately 795,000 people in the United States suffer a stroke each year¹. One-third of these experience aphasia², a language and communication disorder that significantly affects quality of life³, independence⁴, and social participation⁵. Aphasia rehabilitation is challenging because of the multi-faceted nature of the deficits. Deficits can stem from impairments to not just language but also cognitive control, attention, or working memory. Without precisely specifying the underlying causes of deficits, clinicians cannot make informed decisions about whether linguistic treatment (e.g., targeting semantics) and/or cognitive training (e.g., targeting attention) would be most beneficial for a given person.

Here, we apply treatment and enablement theories to different domains of cognitive training in aphasia treatment research. Treatment theories help us define the active ingredients of treatment and identify which specific actions clinicians must perform to effect desired outcomes. This specificity enhances the systematic evaluation and comparison of treatments, fostering the development of more effective, tailored, and evidence-based interventions⁶. Enablement theories, on the other hand, guide us in predicting the broader effects of a treatment (e.g., to what extent training attention can benefit language production or comprehension in persons with aphasia (PWA) and for whom such training would be most useful). Below, we first provide an overview of the current literature on cognitive interventions in aphasia and evaluate them within the framework of treatment and enablement theories. Next, we discuss the rationale for incorporating cognitive control in the pool of treatment targets. Finally, we present a blueprint for developing a new treatment approach targeting this function in PWA and conclude with broader implications for aphasia rehabilitation.

3. Does Cognitive Training Enhance Language Performance in Individuals with Aphasia?

Neurorehabilitation for aphasia involves improving language and communication skills by restoring specific functions (e.g., naming) or using alternative communication methods (e.g., gestures, printed words). There is large individual variability in how PWA respond to training⁷. This could be because aphasia impairments may stem from language deficits but also attention, cognitive control, and other executive deficits⁸. The question arises: Can cognitive training improve language and communication functions in aphasia? If so, which specific cognitive abilities should be trained and for whom would this training be most suitable?

Cognitive abilities like attention, working memory, and cognitive control play significant roles in language processing and are often impaired in PWA^8–12. Although related, they constitute different constructs. Clearly defining these cognitive functions is crucial to avoid ambiguity in the literature and ensure replicability. This is especially important in intervention research, where precise definitions enable more targeted treatments. Attention is an umbrella term encompassing arousal, focusing, and orienting and acts as a selection mechanism for prioritizing cognitive resources^13,10,14. Working memory involves the temporary storage and active manipulation of information^15,16. Cognitive (or executive) control orchestrates and adapts thoughts and actions to achieve goals and may involve planning, inhibiting irrelevant information, task-switching, and monitoring^17–19. A key aspect of cognitive control, particularly relevant to language processing yet distinct from attention and working memory, is the ability to detect and resolve conflicts between mental representations²⁰. This component is the focus of our article, and we expand upon it in section 5 and beyond. Below, we first review attention and working memory training because it constitutes the bulk of cognitive training research in aphasia. This prior work helps assess feasibility and identify challenges in applying cognitive training with PWA.

Emerging evidence suggests that attention and working memory training can improve language-related tasks in aphasia (for reviews see^21–23). For example, Attention Process Training–a multicomponent program that targets various types of attention—led to improved reading in three out of six PWA, in addition to enhancing their performance on attention assessments²⁴ (see also^25,26). In another study, language training combined with attention training benefited naming in three PWA, whereas language training without the attention component benefited two individuals²⁷ (see also²⁸). Working memory training showed beneficial effects on working memory as well as on sentence comprehension in two out of three participants in²⁹ (cf. replication study in²³). Naming combined with working memory training improved performance on the Western Aphasia Battery-Revised³⁰ and the Boston Naming Test³¹ more than naming or working memory training alone in³². Together, these studies provide initial evidence that attention or working memory training, either alone or combined with language treatment, might be a promising avenue for improving language skills in PWA.

The above studies also highlight potential challenges in implementing cognitive training for PWA, particularly related to aphasia severity. Those with severe aphasia may struggle with following task instructions, processing different presentation modalities (e.g., auditory, visual, or multimodal), or completing the tasks at all. For example, Attention Process Training²⁶ includes tasks with increasing difficulty, including repeating words in alphabetical order or performing addition and subtraction amid background noise. Individuals with severe aphasia may struggle with these tasks as they require residual language and cognitive functioning. Similarly, standard cognitive control tasks that may be used for training or assessment (like Stroop, where participants identify the ink color of a word while ignoring its meanings) require reading, which can be impaired in PWA. Thus, researchers and clinicians may need to adapt these tasks to match an individual’s specific abilities and aphasia severity. For instance, we have previously used an auditory version of the Stroop task—instead of the standard version—as it eliminates the need for reading while still targeting the intended cognitive function³³. Others have adapted working memory tasks. For example, The Modified Listening Span³⁴, which combines sentence-to-picture matching with word recall, can be modified to include short, simple sentences and high-frequency monosyllabic words, with recall changed to word-to-picture matching.

Demonstrating that a novel treatment approach is feasible in a given population and leads to measurable improvements is a useful first step in rehabilitation research. However, to make treatment more efficacious and targeted, we need to understand which specific actions done by clinicians affect which targeted mental processes. Furthermore, we need to understand how those targeted mental processes contribute to real-life functions such as engaging in conversation with friends. This can be accomplished by clearly articulating a treatment theory and an enablement theory, which we turn to next.

4. Treatment Theory and Enablement Theory

To facilitate effective and replicable treatment, it is important to use precise and consistent vocabulary and articulate the theoretical links between specific treatment ingredients and targets. This can be achieved using treatment theory, or more precisely the Rehabilitation Treatment Specification System (RTSS), developed by an interdisciplinary team of clinician-scientists. The RTSS outlines three fundamental variables of treatment theory: targets, ingredients, and mechanisms of action³⁵. Targets are measurable aspects of function or behavior expected to improve directly with treatment. Ingredients refer to the actions performed by clinicians. We can differentiate between active and inactive ingredients based on whether they induce clinical change in the target. Finally, mechanisms of action are the theoretically grounded hypotheses explaining how active ingredients affect the targets. Clearly defining these treatment variables is critical for a more rigorous understanding of how specific therapeutic actions lead to desired outcomes^35,36.

In aphasia rehabilitation, efforts are underway to integrate the RTSS and promote evidence-based interventions^37–41. Boyle et al.³⁷ recently described commonly used treatments within the RTSS framework. For instance, in Semantic Feature Analysis⁴², patients describe the semantic features associated with a pictured noun (active ingredient) that enhances lexical retrieval (target) by spreading activation between words and their semantic features (mechanism of action). In Structural Priming^43,44, clinicians provide specific syntactic structures prior to requesting a patient response (active ingredient), which can facilitate access to a particular syntactic structure (target) by increasing their use through implicit learning (mechanism of action).

While treatment theory provides effective tools for changing a specific mental process (e.g., lexical retrieval), enablement theory helps us understand the broader functional consequences of those changes^45,46. Specifically, enablement theory asks how improvements in one variable (e.g., function) in the International Classification of Functioning, Disability, and Health⁴⁷ impact higher-order functions, like activity and participation. It also asks how different levels within these higher-order functions are interconnected, for example, what communicative and social skills are required to enhance engagement in conversations.

How might treatment and enablement theories be applied to evaluate the attention and working memory training studies described above? Per treatment theory, the targets in these studies were increased attention scores and improved working memory span, respectively. The active ingredients were not clearly defined, however. For example, Attention Process Training included diverse activities, such as listening for different target sounds presented at various speeds, matching digital and analogue clock faces, or performing mental math calculations (see²⁴ and²⁶ for more examples). Similarly, the attention treatment in²⁷ included performing multiple non-verbal tasks such as finding a target picture with specified colors among distractor pictures and categorizing faces based on some properties while inhibiting others. It is not clear which specific ingredients within these activities are active and what mechanism of action links those ingredients to the treatment target.

In the working memory training study²⁹, an N-back task was employed with increasing difficulty. Target letters appeared at different N-back positions (N-1, N-2, or N-3), and distractor letters, known as lures, were included. These lures matched the target letter but were presented at non-target positions. It was hypothesized that trials with lures would induce conflict and engage cognitive control, unlike trials without lures. However, an open question remains whether the hypothesized active ingredient was the use of lures (cf. without lures; see also³²), or whether the key factor was the adaptive nature of the task. Additionally, it is not clear if the primary goal was to train working memory or cognitive control since the N-back task with lures could engage both functions.

Turning now to enablement theory, the broader functional goals of the above training studies were to improve skills like reading, naming, and sentence comprehension. Accomplishing these goals requires: (1) specifying the precise connections between the targeted mental process and the higher-order functions (e.g., how exactly would increasing attention benefit sentence comprehension?); (2) addressing individual variability in the extent to which different PWA use the mental process for the function in question (e.g., do all neurotypical adults or PWA need attention for sentence comprehension, or does attention preferentially benefit some individuals, such as those with poorer syntactic processing, more than others?); and (3) addressing the impact of contextual information (e.g., is increased attention required only for the comprehension of certain types of sentences, like syntactically complex or ambiguous ones, or is it equally engaged across all sentence types?). The reviewed studies on attention and working memory have primarily focused on (1) and (3) but less so on (2). For example, Lee et al.²⁴ proposed that attentional processes are essential for reading, and that inefficient allocation of these resources can negatively impact comprehension of paragraphs. Zakarias et al.²⁹ hypothesized that working memory supports the processing of complex sentences by maintaining linguistic information over short periods, facilitating the reanalysis of ambiguous interpretations. The relationships between these mental processes are well-described, with clear hypotheses supporting the expected effects (i.e., on longer paragraphs and ambiguous sentences, rather than isolated and unambiguous sentences). What is less clear is whether these relationships hold in all individuals or whether there are individual differences. For example, Caplan et al.⁴⁸ found that better working memory abilities were broadly associated with better sentence comprehension performance in a sample of sixty-one PWA. However, this pattern did not apply to all individuals. There were some double dissociations such that normal sentence comprehension was observed alongside poor working memory and vice versa⁴⁸. This suggests that different factors may contribute to successful sentence comprehension in different individuals, with some people relying more heavily on working memory and others on alternative cognitive functions. To make treatments more personalized, and thus effective, any such individual differences should be addressed through enablement modeling.

Together, current studies on attention and working memory training for aphasia provide important initial evidence that training these cognitive processes can be beneficial to language in PWA. However, further work is needed to specify and test hypotheses about the active ingredients and mechanisms of action that drive treatment effects. Additionally, enablement modeling is necessary for enhancing efficacy, replicability, and scalability across diverse clinical settings⁶.

5. Cognitive Control as a Potential Treatment Target

Cognitive control is linked to but distinct from attention and working memory because of its unique role in detecting and resolving conflicts between mental representations. Many PWA have cognitive control impairments^49–51 that may be the cause of some linguistic deficits⁵². For example, Kuzmina and Weeks⁵¹ found that both fluent and non-fluent PWA exhibit deficits in verbal cognitive control (measured with Stroop), with non-fluent cases additionally showing deficits in non-verbal cognitive control (measured with Flanker, where participants report the direction of a middle arrow while ignoring adjacent arrows). Further, correlation analyses demonstrated a link between non-verbal cognitive control and language comprehension across all PWA, while verbal cognitive control correlated with word retrieval. These findings underscore the impact of cognitive control deficits on language processing across different aphasia types. Other evidence of the link between cognitive control and language comes from neuroimaging studies, suggesting that the two functions rely on overlapping brain regions. Specifically, the left ventrolateral prefrontal cortex is activated during both language comprehension tasks involving conflicting sentences and cognitive control tasks such as Stroop^53,54, suggesting its role in domain-general conflict resolution. This brain area is also often damaged in stroke patients, leading to difficulties in resolving conflict in the context of language processing or other tasks^55–58.

Conflict can occur at different linguistic levels within a given population, whether neurotypical or PWA. For example, at the word level, two different meanings of a homophone can compete with one another (e.g., understanding “bank” as referring to the subordinate meaning “riverbank”, not the dominant meaning “financial institution”⁵⁹). At the sentence level, conflict can arise when there are alternative interpretations. For instance, in the sentence “Put the apple on the napkin onto the plate,” listeners initially interpret “on the napkin” as the destination of the apple (i.e., the apple should be placed onto the napkin). However, when the phrase “onto the plate” is introduced, the interpretation must be revised: the apple that is currently on the napkin should be moved onto the plate⁵³. Another example is when the syntactic structure of a sentence contradicts our knowledge of the world (semantics). For instance, in the sentence “The cop was handcuffed by the robber,” semantics suggests that the cop handcuffed the robber (a more likely scenario), whereas syntax indicates the opposite (i.e., the robber handcuffed the cop)⁶⁰. Cognitive control helps resolve such conflicts.

In addition to the evidence reviewed above for correlational and co-localizational links between cognitive control and language processing, there is also evidence that the former can causally affect the latter. For example, cognitive control training improves processing of ambiguous sentences in neurotypical individuals^61–63. Hussey et al.⁶¹ showed that N-back training with lures (engaging cognitive control) resulted in faster reading of syntactically ambiguous sentences compared to training that did not involve cognitive control, suggesting that enhanced cognitive control facilitates linguistic processing when conflict resolution demands are high.

Converging evidence that cognitive control is causally involved in language processing also comes from conflict adaptation studies^60,64. For example, Thothathiri et al.⁶⁰ recorded reaction times and eye movements while neurotypical individuals performed interleaved Stroop and sentence-to-picture matching tasks. Sentences were semantically plausible (“The patient was treated by the doctor”) or implausible (“The doctor was treated by the patient”), creating conflict between syntax and semantics. On the implausible sentence trials, participants responded faster and looked more often at correct pictures when cognitive control was upregulated (i.e., when previous Stroop trials were incongruent versus congruent), suggesting that individuals adapted to conflict. These results indicate that cognitive control can help listeners arrive at the correct interpretation of sentences with conflicting cues and that conflict adaptation can lead to a measurable improvement in behavior that stems from moment-by-moment modulations in cognitive control⁶⁰. Although this study focused on how cognitive control helps resolve conflicts between syntax and semantics during language comprehension, such effects may extend to other areas of language processing (e.g., lexical retrieval of homonymous words).

Recently, Krason et al.³³ applied the design of⁶⁰ to PWA. The effects varied between participants, with one of four PWA showing conflict adaptation in the form of faster performance and more looks at correct pictures when cognitive control was upregulated after incongruent versus congruent Stroop³³. This provides preliminary evidence that cognitive control training may be more effective for some PWA than others.

How can treatment and enablement theories be applied to improve the nascent cognitive control training research? The study by Hussey et al.⁶¹ with neurotypical adults is a good example where treatment and enablement theories are applied, implicitly if not explicitly. The target (cognitive control) is enhanced by a specific treatment ingredient (encountering N-back trials with lures) that triggers and strengthens cognitive control due to the presence of conflict (mechanism of action). The effects of training cognitive control have specific enablement consequences with the effects being most beneficial for comprehending syntactically ambiguous sentences (that contain conflict) rather than all sentences. Krason et al.³³ extended this work by demonstrating individual variability in training response with PWA. This raises new questions that could lead to refinement of both the treatment and the enablement theory in this domain. On the treatment theory end, findings of individual variability amongst PWA raise questions about who can upregulate cognitive control. Krason and colleagues suggested that those with mildly (rather than severely) impaired cognitive control abilities may be able to upregulate cognitive control because they have sufficient reserves for upregulation. However, this hypothesis needs to be tested in future studies. The authors also suggested that damage to the Multiple Demand Network–which includes the dorsolateral prefrontal cortex and is associated with domain–general cognitive control⁶⁵–may help predict who benefits from cognitive control interventions. Specifically, individuals with a relatively spared Multiple Demand Network may be better candidates for such training. While lesion location alone may not determine who benefits most (see e.g., case studies in³³), it could still be an important factor for assessing the feasibility of cognitive control training in specific PWA. Thus, assessing cognitive control abilities in PWA with Multiple Demand Network or other left prefrontal cortex damage could be useful for identifying responders early on, which could inform individualized treatment strategies.

With respect to enablement, it is possible that upregulating cognitive control (when possible) will benefit some individuals more than others. For example, Thothathiri et al.⁵² suggested that PWA who compute both a syntactic and a semantic interpretation may benefit from cognitive control upregulation for resolving conflict between those interpretations. In contrast, PWA who rely almost exclusively on semantic cues might not. They provided initial evidence that PWA can differ in their pathways to sentence interpretation but the downstream consequences for cognitive control training response remain to be investigated.

To summarize, considerable evidence using different behavioral and neuroimaging paradigms supports a role for cognitive control in sentence comprehension (e.g.,²⁰). There are articulable treatment and enablement theories in this domain along with demonstration of cognitive control training effects for sentence comprehension in neurotypical adults^61–63. Emerging evidence suggests that it might be fruitful to explore cognitive control training in aphasia^33,52. Although the extant cognitive control studies with PWA have typically used small-sample, multiple-case designs, the participants were well-characterized and tested multiple times. This approach allows for a large number of observations per participant per condition, enhances the sensitivity of the experimental design while remaining feasible for PWA, and produces statistically robust individual-level effects (see also e.g.,⁶⁶ for similar statistical approaches). Future studies with larger samples could test hypotheses about when and for whom cognitive control training could be most beneficial. Below, we draw on treatment and enablement theories to provide a blueprint for developing an effective cognitive control treatment approach for aphasia.

6. Blueprint for Developing Effective Cognitive Control Treatments

As with attention and working memory training approaches in aphasia, treatment theory can inform the development of cognitive control training interventions for aphasia. As mentioned earlier, the RTSS requires specifying which measurable targets are directly treated and which ingredients affect them, allowing for clearer outcome predictions. Let’s take³³ as an example, with cognitive control as the treatment target. Specifically, training could target the skill of selecting a goal-relevant representation in the context of competing activated representations (e.g., correctly selecting between the responses “green” and “blue” for the word “green” written in blue, or between two competing interpretations of sentences like “The cop was handcuffed by the robber”). The mechanism of action involves the upregulation of cognitive control prior to the task of interest, which can be achieved using an active ingredient that triggers cognitive control. According to Krason et al.³³, one possible active ingredient to use is a Stroop trial containing conflict, which can upregulate cognitive control (mechanism of action), and can have effects on the target (selection under competition or conflict). Here, the effects are measured by showing a difference in performance between when sentence comprehension is preceded by an incongruent Stroop (triggers the mechanism of action) versus a congruent Stroop (control condition, which does not trigger the mechanism of action). Other designs could use different tasks that engage cognitive control to assess treatment effects. However, demonstrating the upregulation of a general cognitive control mechanism first requires showing effects across multiple types of conflict. Figure 1 (left panel) summarizes how treatment theory can be applied in this context.

Figure 1.

A schematic representation of the development of cognitive control training for aphasia in accordance with treatment (left) and enablement (right) theories.

Note: The thick arrows represent a potential pathway for developing the new treatment. The dotted arrows represent possible connections between different functions. Each dotted arrow has a particular “weight,” reflecting its relative importance or contribution. For simplicity, the weights are not assigned and dotted arrows are shown as unidirectional, though some could be bidirectional. For other potential active ingredients, see section “Blueprint for Developing Effective Cognitive Control Treatments.”

Within this emerging training framework, several questions remain about other possible ingredients that might contribute to successful training. For instance, can nonlinguistic cognitive control tasks function as active ingredients? Can the interleaved presentation of cognitive and linguistic tasks lead to cognitive control depletion rather than upregulation, thereby reducing treatment benefit in some patients (see, e.g.,⁶⁷ for cognitive control depletion in children with weak cognitive control abilities)? Additionally, how long will the upregulation of cognitive control last? Will it be a temporary, trial-by-trial activation, or will it have a long-lasting effect? If it is the former, the active ingredients would include exposure to a single cognitive trial with conflict before a sentence trial with conflict (as seen in³³). However, if the activation is sustained rather than temporary, participants could engage in multiple cognitive control trials with conflict before sentence comprehension. Thus, if it turns out that cognitive control upregulation is better thought of as a learned skill and we observe long-lasting training effects, that would lead to refinement of the treatment theory to include other possible active ingredients (e.g., sustained practice with cognitive control tasks) and mechanisms of action (e.g., long-term learning). Different ingredients should be tested (and ruled out if needed) during the early stages of proof-of-concept treatment studies involving cognitive control, before moving to feasibility studies³⁶.

Assuming that engagement in a prior cognitive control task upregulates cognitive control as predicted by the treatment theory in Figure 1 (left panel), we could ask about the downstream consequences for language and communication (i.e., a patient’s overall rehabilitation goals or distal aims). For example, if a PWA becomes better at resolving conflicts in comprehension after cognitive control training, are they also more likely to engage in a conversation, order food in a restaurant without support from others, or play cards with friends? In other words, would cognitive control upregulation show improvements in higher-order functions, or would it only enhance the processing of isolated sentences with conflict? Figure 1 (right panel) provides an example of how enablement theory can help model the relationships between lower and higher-order functions in the context of cognitive control training. Per psycholinguistic theories, comprehension involves (at least) semantic processing, syntactic processing, and working memory. Cognitive control is an additional component that can help resolve conflict between alternative interpretations, when such conflict is present. Additionally, cognitive control can assist in turn-taking, which requires the ability to inhibit impulses and await one’s turn. Together, improvements in comprehension and turn-taking can enhance conversation with friends. Critically, however, the magnitude of these improvements will vary depending on individual differences in the ability and need to engage cognitive control resources. Armed with an articulated enablement theory like the above, future studies can test hypotheses about how cognitive control training influences PWA’s engagement and participation in specific daily activities.

Clearly distinguishing predictions at each level of functioning (Figure 1 right panel) is important to better understand why a given treatment may work for some patients but not for others^45,46. For example, if a participant fails to show improvements in comprehension after cognitive control training, we should consider whether the failure occurred at the level of treatment (e.g., cognitive control could not be upregulated) or at the level of enablement (e.g., sentence processing in a participant did not generate conflicting interpretations). In the former case, we would expect null treatment effects on any cognitive control task (not just sentence processing) while in the latter case, we would expect positive treatment effects in non-sentence-processing tasks that involve cognitive control. Determining which of these possibilities led to a null effect in a given PWA is important for identifying the subsequent steps. Failure at the treatment level (i.e., did not upregulate cognitive control) might entail exploration of increased dosage or change in the treatment ingredients. In contrast, failure at the enablement level (i.e., upregulated cognitive control but did not improve sentence comprehension) would involve exploration of how to strengthen sentence processing first via the other skills involved (Figure 1: Impairment [Body Structure & Function]), which can be supported subsequently by cognitive control.

To summarize, treatment theory and enablement theory both play important roles in developing a new treatment approach, though they contribute differently. Their interplay is key to the full cycle of treatment development and application⁴⁵.

7. Conclusions and Future Directions

Cognitive functions like attention, working memory, and cognitive control are part-and-parcel of using language in different contexts. Deficits in these functions can give rise to language and communication impairments such as those seen in aphasia. Research has recently started to investigate attention and working memory training in the context of aphasia treatment, but cognitive control training is relatively underexplored. In this article, we have advocated for using treatment and enablement theories to more systematically develop hypotheses and study designs for exploring cognitive training in aphasia. To optimize patient outcomes, researchers and clinicians must ensure that a newly developed training is: (i) grounded in a treatment theory with well-formulated hypotheses that link active ingredients to intended targets via specific mechanisms of action^6,35,36; and (ii) explicated further using enablement theories on how treated targets will impact broader functions in different individuals^45,46.

We conclude with three broader points about rehabilitation science in aphasia and provide suggestions for future directions. First, results in the field are often reported using group analyses, sometimes based on historic aphasia classifications (e.g., Wernicke’s, Broca’s), whose utility is debated⁶⁸. Going forward, we believe that developing and applying treatment and enablement theories that spell out the mechanisms of action and links between functions will necessarily lead the field in the direction of personalized medicine and individual subjects analyses. Cognitive control might be amenable to upregulation in some individuals and not others and further, such upregulation might improve sentence comprehension only in those individuals experiencing conflict between competing interpretations during online processing (relevant discussions in^33,52). Due to variability in how individuals process language, different mental processes and their interactions may be more or less effective for different people. Further, factors such as aphasia severity and lesion location may impact the development, delivery, timing, and/or efficacy of cognitive assessments and training. Severity may influence stimulus selection for cognitive control training tasks and, in extreme cases, determine whether an individual has the capacity to improve their cognitive control. Regarding lesion location, it remains to be seen whether it will be a better predictor than a patient’s behavioral profile. Any such variability is unlikely to be captured by traditional aphasia classifications. While it is quite possible that language processing in neurotypical individuals or PWA can be classified into specific categories, precisely what those categories are will need to be determined by psycholinguistic experimentation along with clearly articulated treatment and enablement theories. Until those categories become evident, we believe the field should complement group-based analyses with analyses focused on individual participants.

Second, it could be beneficial for clinical research and assessment to move beyond standardized tests that collect only behavioral accuracy. Many aphasia researchers have already employed multimodal approaches to inform treatment. For example, Geranmayeh et al.⁶⁹ combined fMRI with behavioral accuracy to investigate how the cognitive control network supports recovery, informing treatment targets. Moreover, language processing is a temporal process and online measures such as eye-tracking and neurophysiological signals can be useful in distinguishing processing differences that may not be obvious in overt behavioral performance (see, e.g.,⁵² for eye-tracking differences between PWA showing similar outward sentence comprehension behavior). More broadly, this multimodal approach can help researchers and clinicians refine treatments for improved outcomes by clarifying the mechanisms of action underlying a specific function. This is crucial because mechanisms of action are often difficult to measure in contrast to targets and ingredients that are observable.

Third, assessments using mobile apps and wearable devices can provide more accurate and real-time feedback (e.g.,⁷⁰). Communication most often happens face-to-face and requires integrating different kinds of information, resolving conflicts between cues, retaining information in working memory, planning responses, inhibiting certain reactions, etc. Testing in controlled settings may therefore not capture the necessary processes involved in everyday communication and impairments therein^71,72. Because cognitive control is inherently important for maintaining goal-directed behavior in the presence of distractions, cognitive control training approaches would especially benefit from innovations that capture real-time processing embedded in real-life contexts. Overall, combining individual-patient-level analyses, personalized treatments grounded in precisely articulated mechanisms, and the expansion of contexts in which language is assessed are necessary first steps before conducting large-scale group-level treatment studies. This, in our opinion, might require a shift in mindset when designing new studies and evaluating research in the field.

List of abbreviations:

PWA

People with Aphasia

RTSS

Rehabilitation Treatment Specification System