Introduction

How the human brain processes stimuli, events, and how it does orchestrate different functions have long intrigued scholars. However, it is worth noting that a considerable number of these inquiries were left unexplored during the two-decade ban on psychology studies in Hungary. The pioneer of providing knowledge on physiology for psychologists was György Ádám. He was convinced that psychologists have a solid background in the most important subjects, including anatomy, physiology, genetics as well as several fields of medicine such as, pediatrics, psychiatry, neurology. Clinical studies of the language domain gave rise a multidisciplinary field where aphasia became one of the study fields of linguists, psychologists, and neurologists.

Traditionally, researchers in the field of neuropsychology and linguistics have focused on language deficits as the primary symptom of aphasia following a stroke. It is now evident that individuals diagnosed with aphasia do not only experience language impairments but also cognitive deficits (Purdy 2002; Murray 2012). Investigating the interactions between language and cognitive functions is crucial because cognitive impairments may worsen communication difficulties and slow down the rehabilitation process. Despite their significant influence on each other, the role of executive functions has not been extensively studied in the existing aphasia literature (Murray 2017a, b). Therefore, the present study investigates cognitive functions like working memory updating, selective attention, cognitive flexibility and inhibition in individuals diagnosed with different types of aphasia and their relationship to language functions.

Aphasia

Due to its variable manifestations, the study of aphasia is complex and, therefore, can be conceptualized in various ways. Generally, aphasia is regarded as an acquired communication disorder following brain damage and causes impairment in language modalities (Chapey 2008). According to the multidimensional view, multiple forms of aphasia exist, all of which correspond to a distinct underlying lesion site that exhibits individual characteristics (Goetz 2007). A broadly accepted distinction is made between fluent (Wernicke’s, conduction, transcortical sensory and anomic) and non-fluent (Broca’s, global, transcortical motor) subtypes of aphasia. Fluent aphasia means that the individual can converse with spontaneous speech using meaningful filler phrases and without pausing for prolonged periods of time. Non-fluent aphasia means that the individuals tend to have a reduced rate of speech. Furthermore, it also refers to individuals who are completely nonverbal (Pléh and Lukács 2014). The main characteristics of aphasia subtypes are presented in Table 1.

Table 1 Main characteristics of the different aphasia types
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The aphasia assessment process requires not only the use of aphasia batteries, but also the use of neuropsychological and cognitive assessments (Goodglass et al. 2001). This information is fundamental in understanding language and communication difficulties. As noted by Byng and colleagues (1990, p. 67), a comprehensive, specific, and detailed assessment is necessary to provide high-quality treatments for individuals with aphasia, as it indicates which aspects of language performance are most suitable for treatment. Therefore, the assessment process is crucial in planning the most appropriate treatment for individuals with aphasia as it can help expedite the recovery process or, if planned incorrectly, delay it.

The study involved participants with various types of aphasia, including Wernicke’s, conduction, anomic and global, highlighted in Table 1. Wernicke’s aphasia is a type of fluent aphasia and located in the left hemisphere of the brain, typically in the posterior part of the superior temporal gyrus and is crucial for language comprehension and speech production (Papathanasiou et al. 2011 p. 42). It is characterized by impaired reading and auditory comprehension. Although verbal output is normal or increased, the speech of individuals with Wernicke’s aphasia is usually meaningless (paraphasia). Additionally, neologisms are often present (Pléh and Lukács 2014).

Conduction aphasia is a fluent type of aphasia and is characterized by impaired repetition of words and sentences and fluent speech but is less abundant than in Wernicke’s aphasia (Damasio 1998). The primary lesion area associated with conduction aphasia is the arcuate fasciculus which connects Broca’s and Wernicke’s area, damage to this pathway disrupts the ability to transmit information between the two areas. In addition to the arcuate fasciculus, the following areas can also be affected such as the superior temporal gyrus and the angular gyrus. These regions play a crucial role in different aspects of language processing and damage to these regions can result in challenges with accurately repeating and producing spoken language, even when comprehension abilities remain intact (Papathanasiou et al. 2011). Conduction aphasia is associated with intact comprehension, and it can be “Wernicke’s-like” as the speech of sufferers is fluent and characterized by paraphasia, albeit limited. Furthermore, it may also resemble Broca’s aphasia due to excellent articulation (Goetz 2007). Conduction aphasics may comprehend the general meaning of spoken language but have difficulty repeating it. They also experience moderate impairments in reading, writing, and naming (Squire 2009).

Anomic aphasia, also known as amnesic aphasia or nominal aphasia (Goetz 2007), is the mildest form of aphasia. It refers to the difficulty in recalling a word (Squire 2009), making word retrieval extremely challenging (Damasio 1998). The lesion areas associated with anomic aphasia can vary depending on the underlying cause. However, common areas of damage or dysfunction angular gyrus and middle temporal gyrus. Thus, anomic aphasia is considered to have little or no localization value (Papathanasiou et al. 2011). Although their speech is generally fluent, they may experience pauses due to word retrieval deficiencies. Despite being able to engage in spontaneous conversation, their speech can may lack substance. The grammar of individuals with anomic aphasia is generally intact (Chapey 2008). Their ability to read and write may be entirely normal (Goetz 2007). Additionally, the comprehension of spoken language and repetition abilities of these patients are normal.

Global aphasia is the most severe type of aphasia (Squire 2009). The primary lesion area in global aphasia is typically a large portion of the perisylvian area, which is in the dominant hemisphere of the brain, usually the left hemisphere. This area includes structures such as the Broca’s area, Wernicke’s area, and the arcuate fasciculus, which are crucial for language production and comprehension. (Papathanasiou et al. 2011, p. 43). It is predominantly characterized by the impaired comprehension and expression of language. It is often regarded as a combination of Wernicke’s and Broca’s aphasia. Individuals with global aphasia have little or no understanding in all modalities. Their communication is severely impaired as they can only produce a few utterances (Chapey 2008).

Cognitive control and aphasia

The study of cognitive control in patients with brain injury dates to the earliest studies in human neuroscience. Before explaining the concept of cognitive control, it is important to note that in academic literature, the terms ‘executive function’ and ‘cognitive control’ are frequently used interchangeably. According to Miyake et al. (2000), executive functions (EFs) are a collection of higher-order cognitive abilities that are essential for goal-directed behavior and regulating cognitive processes. They proposed a model comprising three distinct components of executive functions: updating, inhibiting and shifting. Updating refers to the ability to actively manipulate and monitor information in working memory (WM), while inhibition involves the capacity to suppress prepotent responses, interfering stimuli or relevant information. Shifting, on the other hand, pertains to the ability to flexibly switch between mental sets or tasks. Miyake and colleagues argued that these components represent core processes underlying executive control and can be measured separately. Their model has influenced further research in the field and helped understand the complex nature of EFs (Miyake et al. 2000). The modern conceptualization of cognitive control is influenced by clinical observations and most scientists agree that specific regions of the brain specialize in particular cognitive functions (Egner 2017, p. 514). According to the most popular concept, cognitive control functions refer to processes that direct, configure, and/or modulate the performance in different cognitive domains (Hart 2015). According to Kim et al. (2018), higher level cognitive abilities result from the concerted action of a multifunctional cognitive system. Cognitive functions are activated when a person participates in complex tasks that require planning, monitoring, and organizing via adapting to the current situation, and subsequent changes. Core cognitive control functions include processes like selective attention, working memory, inhibition, and cognitive flexibility (Diamond 2013). Selective attention refers to the ability to focus on a specific stimulus or task while filtering our other irrelevant or distracting information (Goldstein 2021). Cognitive flexibility, also referred as “shifting”, refers to our ability to switch between diverse mental frameworks, tasks, or strategies (Diamond 2013). In the context of aphasia, cognitive control plays a crucial role in language production and comprehension. In language production, PWA often struggle with finding the right words, forming grammatically correct sentences, and organizing their thoughts. Cognitive control helps in overcoming these difficulties by regulating attention, inhibiting relevant information, and selecting appropriate words and sentence structures. In language comprehension, cognitive control helps in focusing attention on relevant linguistic cues, inhibiting distractions, and integrating information from various sources to comprehend language (Egner 2017).

In the field of aphasia research, an increasing body of evidence suggests that people with aphasia (PWA) commonly experience cognitive impairments in their executive functions (Purdy 2002; Marinelli et al. 2017; Murray 2012, 2017a; Ramsey et al. 2017; Szöllősi et al. 2015; Schumacher et al. 2019). It is postulated that there is a correlation between non-linguistic cognitive skills and language capabilities in aphasic individuals due to the shared neural circuits involved. These deficits can greatly influence the traits and consequences of their language abilities (Murray 2012; Villard & Kiran 2016). However, previous research has mainly focused on memory in aphasia (Murray 2017b), with limited attention given to the significance of executive function abilities. In case of studies investigating EFs, it has been observed that PWA are capable to recruit extra cognitive resources if the task demands increase and are able to control the automatic responses with high accuracy, albeit more slowly due to impaired information processing. As a result, it is assumed that slowness may influence the information processing of aphasic patients (Szöllősi and Marton 2016, p. 182). In the case of naming, Biegler et al. (2008) observed that naming is a very difficult task for most of the aphasics due to the impaired inhibition processes. In addition, problems associated with naming seem to be connected to an impaired semantic blocking as well due to the impairment of inhibition processes (Biegler et al. 2008). Other studies investigating executive functions in PWA revealed impaired working memory, cognitive flexibility, and inhibition (Murray 2012; Vallila-Rohter & Kiran 2013; Lee and Pyun 2014). Marinelli et al. (2017) investigated the link between language deficit and cognitive impairment in a sample of 184 individuals diagnosed with aphasia. The study found that PWA experienced more pronounced language deficits, which were subsequently associated with more severe cognitive impairment (Marinelli et al. 2017).

In conclusion, it is important to assess cognitive functions in aphasia for a comprehensive evaluation and treatment planning. Obtaining an individual’s cognitive profile is useful for diagnosing aphasia and predicting potential recovery because cognitive abilities play a crucial role in language processing and communication (Schumacher et al. 2020; Lacey et al. 2017; Dignam et al. 2017; Mirman et al. 2015).

Working memory deficit and aphasia

WM is defined as a system of limited capacity, responsible for holding and manipulating information while undertaking cognitive tasks (Baddeley 2003). The connection between working memory and cognitive control in aphasia has been a topic of considerable interest in neuropsychological research. Neuroanatomical data provide evidence of the coexistence of WM and language impairment in aphasia (Wright and Shisler 2005; Tompkins et al. 1994; Murray et al. 2001; Gabrieli et al. 1988). Studies examining verbal and spatial WM assume the left hemisphere’s role in this coexistence (Baldo & Dronkers 2006). The role of WM in language comprehension, problem-solving, reasoning, and decision-making has been widely acknowledged (Novais-Santos et al. 2007). Consequently, PWA may experience difficulties in language comprehension and in other cognitive control functions due to impairments in their working memory capacity (WMC). WM is essential for cognitive control processes to function effectively. For example, difficulties in attentional control, response inhibition, task switching and monitoring. Attentional deficit can comprise the ability to allocate cognitive resources efficiently, resulting in reduced comprehension and slower retrieval of linguistic information (Murray 2012). This can be particularly evident in complex sentence structures, where individual with aphasia may struggle with maintaining the necessary attentional resources to process and comprehend the entire sentence. The deficit in attentional control may be related to WM limitation, as maintaining task-relevant information in mind is crucial for selective attention (Barde et al. 2010). Furthermore, individuals with aphasia frequently show deficits in response inhibition, manifested by difficulties suppressing prepotent or automatic responses (Szöllősi & Marton 2016). This deficit has also been linked to WM limitations. WMC plays a crucial role in inhibitory control, as it requires the active maintenance and manipulation of task-relevant information while inhibiting automatic responses (Wright and Shisler 2005). Thus, WM impairments in aphasia may contribute to deficits in response inhibition. Task- switching is another cognitive control process that is often impaired in PWA. Task switching involves the ability to flexibly shift attention and adjust cognitive strategies in response to changing task demands (Squire 2009). Research has shown that WMC is closely related to task switching abilities, as it requires the ability to maintain and manipulate multiple task sets in mind (Draheim et al. 2016). Therefore, WM deficits in aphasia may lead to difficulties in task switching and cognitive flexibility. Monitoring is another cognitive control process that has been found to be impaired in individuals with aphasia Monitoring involves the continual evaluation and updating of ongoing performance, detecting errors, and adjusting behavior accordingly (Botvinick et al. 2004). WM plays a critical role in monitoring by maintaining task goals and relevant information in mind while continuously comparing it to ongoing performance (Redick 2014). Consequently, PWA may show deficits in monitoring due to WM limitations. It is important to note that the specific cognitive control processes that are affected by working memory impairments may vary across individuals with aphasia, depending on the specific lesion location and the extent of brain damage. Moreover, the treatment of EFs, including updates and conflict resolutions in relation to working memory, should be considered essential, as these components have a pivotal role in several language processes. Zakariás and colleagues showed in their study that executive function training of aphasics has had a positive impact, although individual differences found might affect how the training effect develops (Zakariás et al. 2018).

Research aim

The primary objective of this study was to examine the correlation between impairments in language modalities and cognitive functions. To achieve these aims, we employed a range of neuropsychological tests to identify deficits in executive functions and further investigate these deficits in language modalities. Additionally, our study aimed to explore the effects of these impairments on performance in fluency and naming tasks.

Hypotheses

  1. 1.

    We proposed that the impairment of cognitive functions would negatively affect naming in aphasics, resulting in slower performance, increased reaction time and decreased accuracy. This study investigated these negative effects through various neuropsychological (TMT, FAB, WAIS-IV, ROCF, TOH) and linguistic batteries (WAB, TROG, TOKEN, BNT). Furthermore, the predictable value of these batteries was also tested. We assumed that the longer the reaction time required to finish the task, the more mistakes were made. For this reason, a special attention was paid to the Boston Naming Test, and its relationship to the potential impaired executive functions (inhibitory control, WM) assumed to lead to longer reaction times and/or decreased accuracy. A further key question was how the spared intactness of the working memory may influence the use of semantic and phonemic cues to help in recall in BNT. Our assumption was that the recall of a word cannot be aided by semantic or phonemic cues if it is not stored in the working memory.

  2. 2.

    Furthermore, this study compared the performance in the word fluency task included in the western aphasia battery (WAB) with naming in the Boston naming test (BNT) to investigate their potential relationship. It is known that the aphasics’ performance in word fluency tasks may show dissociation with naming, here measured by using BNT. We expected if an individual performed poorly or successfully in the word fluency task, they might not perform similarly in naming. Moreover, we examined potential deficits in inhibitory control, WM, and cognitive flexibility as measured by these tasks.

  3. 3.

    This study also aimed to examine the potential correlation between individual naming difficulties and locations of brain damage. It is worth noting that an individual's mental lexicon comprises neutrally activated patterns involving different brain regions. Proper nouns are stored in the temporal lobe, common nouns in the inferior temporal cortex and verbs in Broca’s area. Thus, we compared naming impairment across different types of aphasia, while considering the location of the participants’ lesions. We expected that participants with similar CT results (middle cerebral artery stroke), but different types of aphasia would exhibit varying degrees of naming impairment, ranging from very severe to mild.

Methodology

Participants

The study involved five native Hungarian speakers diagnosed with aphasia, comprising two males and three females aged between 60 and 70 years. The aphasia group consisted of individuals with different types of post-stroke aphasia (global, conduction, Wernicke's and anomic) after their first or second stroke. The control group comprised five neurologically healthy individuals, matched to the aphasia group in terms of age and sex. Individuals with aphasia were recruited from Szent Donát Kórház Egészségügyi és Szolgáltató Kft. (St. Donát Hospital, Várpalota), and the study was approved by the hospital. All participants provided written informed consent. The description of the sample of individuals with aphasia can be found in Table 2.

Table 2 Characteristics of the sample of individuals with aphasia
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The first participant (P01) was a 60-year-old female with global aphasia. She was hospitalized following an ischemic stroke due to the occlusion of the left middle cerebral artery (MCA) in 1998. In January 2019, she suffered a second stroke and was admitted for rehabilitation after developing symptoms of upper limb paralysis on her right side and severe mixed aphasia. A head CT scan showed a 32-mm-deep hypodensity on the left side in line with the inferior horn of the lateral ventricle affecting the cortex. It revealed multiple small hypodense nodules in both hemispheres in the periventricular white matter and in the vicinity of the semioval center. The lumen diameter of the common carotid artery was normal. A few pinhead-size calcified plaques could be seen proximally in the left internal carotid artery (ICA). Chronic microvascular lesions in both hemispheres were visible. The latest brain CT scan identified fresh Ischemia in the brain supplied by the left middle cerebral artery (MCA).

The second participant (P02) was a 69-year-old female suffering from global aphasia. A CT scan showed subacute ischemic lesions in the left hemisphere supplied by the middle cerebral artery. She was admitted for rehabilitation immediately after having suffered a stroke. Following admission, her symptoms had improved significantly. Although her right arm was paralyzed and she suffered from mild paresis on her right side, these symptoms did not deteriorate. Given that a CT scan showed occlusion of the left middle cerebral artery and 70% stenosis in the left ICA, multiple nodular ischemic lesions were observed.

The third participant (P03) was a 70-year-old female with conduction aphasia following a second stroke. She suffered her first stroke in 2013 and the second in 2018. A CT scan identified previous ischemic lesions and an occlusion of the left MCA. Since she was admitted within the time frame for thrombolytic therapy, systemic thrombolysis was performed, thereby improving her symptoms. After this therapy, another CT scan measured the dimensions of the fresh ischemic lesion in the temporoparietal region to be 84 × 40 mm. The latest brain CT scan revealed a large region of frontal-parietal temporal hypodensity affecting the cortex.

The fourth participant (P04) was a 64-year-old male with Wernicke’s aphasia following his first stroke. According to his medical record, he suffered from hypertension. The CT scan showed that the lumen diameter of the common carotid artery was normal. Additionally, it showed hyperdense thrombosis in the left MCA with a good degree of collateral circulation. Before his rehabilitation, he was treated with NOACs (Novel Oral Anticoagulants). Although the motor function in his speech was intact at the time of his admission he was, severe sensory aphasia was present.

The fifth participant (P05) was a 70-year-old male with anomic aphasia. According to his medical record, he is a known sufferer of hypertension, hyperlipidaemia, obesity, and vascular dementia. He was admitted for rehabilitation due to deteriorating hemiparesis and aphasia. A stent was implanted in his right ICA, and he was regularly treated in the neurology department. No CT scans were available.

Procedures

The present study included both linguistic and neuropsychological assessments which were conducted at St. Donát Hospital in Várpalota. The hospital provided the patients, a quiet and private room for the assessments, a speech therapist, and psychologists. The assessments were conducted individually over multiple occasions due to their length. The linguistics tests were carried out by the speech therapist in the presence of the authors of this study, while the neuropsychological tests were carried out by psychologists only.

Neuropsychological tests

The present study examined the accuracy, speed, and efficiency of participants in neuropsychological tests designed to assess cognitive flexibility. We employed several tests, such as the trail making test, Frontal assessment battery, wechsler adult intelligence scale, Rey-Osterrieth complex figure test, and the game called Tower of Hanoi. These tests are specifically designed to evaluate cognitive flexibility and problem-solving abilities directed toward achieving goals. The reason for adding nonverbal tasks was to minimize the impact of language impairments on participants’ performance. The assessment commenced only after the participants demonstrated a clear understanding of the task.

The trail making test (TMT) consists of two parts. In part A, the participants must draw a line connecting consecutive numbers, while in part B, they must join numbers and letters in an alternating progressive sequence (McMorris 2016). TMT was used to measure visual attention, task switching, working memory and cognitive flexibility.

The frontal assessment battery (FAB) is a short screening test that assesses executive functions by investigating damage in the frontal lobe. In this study, only some parts of the FAB were used, that is, motor programming and sensitivity to interference, which measure inhibitory control and interference (Dubois et al. 2000). In the motor programming task, the Luria fist-edge-palm motor series was applied. P02-Global and P05-Wernicke’s performed these tasks with their left hand due to existing medical conditions. Additionally, the tapping exercise, in which patients were required to tap twice on a table if they heard a single tap, measured their sensitivity to interference. Firstly, a sequence of 1–1–1 was heard and the participant responded or should have responded appropriately. Secondly, the subject was asked to tap once on the table if they heard two taps, in this case the sequence was 2–2–2. Finally, the last sequence heard was 1–1–2–1–2–2–2–1–1–2 (Cunha et al. 2010).

The fourth edition (WAIS-IV) of the Wechsler adult intelligence scale (WAIS) was employed. This test consists of a complex comprehensive set of tasks and support the evaluation of cognitive functions by assessing verbal, visual-perceptual and auditory working memories (Drozdick et al. 2013). The present study measured block design and coding. In terms of the block design, the ability of participants to analyze and synthesize an abstract design as well as reproduce that design using colored plastic blocks was measured, which required spatial visualization, visual motor conditioning, analyzes, and simultaneous processing. The second task, that is, coding, measured their nonverbal short-term memory and visual-motor dexterity.

The Rey-Osterrieth complex figure (ROCF) is a valuable tool for assessing cognitive impairment, particularly in people with aphasia (Lezak et al. 2012). We assessed a range of cognitive functions, including visuospatial skills, visual memory, and executive function. It involves copying and recalling a complex geometric figure. (Kirkwood et al. 2001). The copying phase primarily evaluates visuospatial skills, perceptual organization, and motor planning. After a delay of 3 min, we asked the participants to draw the figure from memory. The recall phase assesses visual memory, organizational strategies and planning, monitoring, and inhibitory control.

Finally, we used the game Tower of Hanoi (TOH) to examine goal-directed planning behavior. In this task, the participants must put the blocks on top of each other ensuring that larger disks are not placed on top of smaller ones. Completion of this task depends on whether the tower is accurately constructed according to this rule. How efficient the individual will depend on the number of moves required to finish the task (Purdy 2002). It may cause difficulties for the participants with aphasia to complete the TOH task because of their deficit in cognitive flexibility or impaired working memory, that is, they might struggle to solve two tasks simultaneously. The Tower of Hanoi is also widely used to investigate complex problem solving, e.g., Prescott et al. used this game in their research involving ten aphasics and their results demonstrate that 30% of the participants could not complete the task. In addition, those who were able to manage the task required more moves and time than the healthy control group (Prescott et al. 1987).

Language tests

In this study, we assessed language and cognitive functions implementing linguistic batteries such as the Western aphasia battery (WAB), the standardized Hungarian version of the Test for reception of grammar (TROG), the Boston naming test (BNT), and the Token test (TOKEN). We used WAB to measure the severity of impairment in aphasia. The principal objective of applying these batteries in this study was to investigate cognitive control functions in terms of comprehension and naming. We employed TOKEN and TROG to examine comprehension. Furthermore, we used BNT to evaluate naming. Naming, matching tasks, sentence completion as well as question-and answer tasks are typical methods to assess convergent thinking in neurolinguistics.

Primarily, WAB serves as an assessment tool for identifying the type of aphasia and language abilities in individuals with aphasia. While it does not specifically target executive functions, some aspects of executive functions may be indirectly assessed during the evaluation process. For instance, attention, working memory, problem solving, inhibition and cognitive flexibility. We used four main parts to examine these cognitive functions such as spontaneous speech, comprehension, repetition, and naming. In the spontaneous speech component, the participants are asked to answer simple questions, including picture descriptions. The comprehension tasks consist of yes/no questions, auditory word recognition and sequential commands. The examiner asks the participants to only answer ‘yes’ or ‘no’ to 20 questions. In the auditory word recognition task, the participants must identify real as well as drawn objects, forms, letters, numbers, colors, items of furniture and body parts. The sequential commands part includes 11 commands from simple to complex ones. In the third main part of the WAB, the examiner asks the participants to repeat the words and sentences they hear, which includes 15 sentences of various degrees of difficulty. We examined participants’ short-term memory in the repetition task. The last section, that is, naming, consists of word fluency, sentence completion and responsive speech tasks. In the word fluency task, the participants had to name as many animals as possible in one minute.

In our study we measured the deficits in auditory comprehension at the sentence level using the TOKEN test. The following cognitive functions collectively contributed to an individual’s ability to perform well on the test: working memory, cognitive flexibility, inhibition, problem solving, attention control, planning and organization. The test consisted of 20 figures, 10 large and 10 small. The figures had two shapes (square and circle) and in different colors (red, green, yellow, white and black). The participants had to follow the instructions using the correct figures, six blocks and 36 commands. They had to concentrate on several factors at the same time. The last section contained the most complex commands which could not be repeated.

We employed TROG to measure the participants’ comprehension of grammatical structures. Several EFs were assessed, including working memory, inhibition, cognitive flexibility, attention, problem-solving, planning and organization. In this test, we asked the participants to choose one of four pictures that represented the verbal command. We added TROG to the current study to collect further information about what grammatical structures are intact and which sections are impaired in individuals with aphasia, for instance, nouns, verbs, adjectives, etc. Furthermore, this test can also serve as a basis for assessing comprehension, especially when the participants are unable to take the TOKEN test. In this case, TROG is essential in terms of preparing the therapy as information is gathered about the state of everyone’s level of comprehension. This is an extremely significant stage when planning the therapy as it provides the therapist with the necessary data or informs the clinician about the linguistic strengths and weaknesses of the individuals.

Furthermore, we added BNT to evaluate naming. Naming is our ability to refer to an object, person, place, concept, or idea using its proper noun (Chapey 2008). While it primarily assesses language and semantic memory, it also involves certain EFs for example inhibition, working memory, cognitive flexibility, attention, planning and organization. The participants, whose accuracy and reaction times were measured, had to access their internal dictionary to be able to name a word. They were presented with 60 pictures and their task was to name the object they see.

Results

It is important to note that all the findings presented in this study are derived from the comparison conducted between the aphasia and the matched control groups. The order of analysis follows the same pattern for all the assessment tools, starting with the control group and continuing with the aphasia group.

Effects of impaired EFs on performance, resulting in increased reaction time and decreased accuracy in neuropsychological and language tests

Neuropsychological test results

Control group

The results of the control group are similar in all the neuropsychological assessments. We expected that the control group's scores would be considerably higher than those of the aphasia group, given that all participants in the control group were healthy individuals with no discernible cognitive impairments. Consequently, they were able to comprehend the instructions proficiently and successfully complete the assigned tasks within the allocated time frame. We measured reaction time in TMT, and ROCF. In TMT, the control participants completed part A between 30 and 40 s and part B between 90 and 120 s. In ROCF, they did the task under 60 s. We compared the aphasia groups’ reaction time with the matched controls.

Aphasia group

In the aphasia group, we expected that impaired EFs would result in longer reaction time and decreased accuracy. We measured several EFs through these batteries to examine deficits and further investigate these deficits in the language tests.

Table 3 illustrates the test results in the aphasia group, highlighting the successfully completed parts. All participants experienced some level of difficulty comprehending and completing the tasks. Furthermore, the frustration and reluctance observed in some participants may be the cause of their poor performance for example in P05 with anomic aphasia. Our results indicate that the severity of impairments varied among the participants, with some showing mild deficits (P04 with Wernicke’s aphasia), moderate (P05 with anomic aphasia) and others demonstrating more significant difficulties (P01 and P02 with global and P03 with conduction aphasia) based on their performance. Participant with Wernicke’s aphasia performed most successfully within the group; however, his reaction time was greatly slower compared to the control group. In part A in TMT, P04 performed the task in 2 min, whereas the controls managed it between 30 and 40 s. In part B in TMT, P04 performed the task in 6 min, while the controls between 90 and 120 s. Other participants with aphasia were stopped when they were unable to solve the tasks over 4–10 min. Overall, our findings suggest that the participants in the aphasia group exhibited slower task completion times and decreased accuracy compared to the control group, suggesting some level of impairments in various cognitive skills which were necessary to solve the tasks successfully. For example, inhibitory control, working memory, task switching, visual attention, visual memory, motor programming and planning.

Table 3 Neuropsychological test results in the aphasia group
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Language test results

Results of the WAB test

The aim of utilizing the WAB was to evaluate the severity of language impairment in individuals with aphasia. More specifically, our attention was directed toward the word fluency task, which measured the number of animals that participants were able to name within a minute.

Control

Table 4 presents the results of the world fluency task within the control group. The control participants were able to name 15–24 animals in one minute.

Table 4 Language test results of the control group
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Aphasia

The participants involved in this study had varying levels of WAB scores, ranging from 8.19 to 73.16, suggesting a diverse range of aphasia severity (0–25 very severe; 26–50 severe; 51–75 moderate; above 76 mild). The findings are presented in Table 5. Furthermore, we used the WAB to examine language deficits and certain aspect of EFs. Completing these tasks involved EFs such as cognitive flexibility, planning and organization and inhibition. Our primary focus, using the WAB, was on the word fluency task. Participants P01 with global aphasia and P03 with conduction aphasia performed notably poorly in comparison to the rest of the aphasia group, suggesting a potential impairment in working memory, inhibition, and cognitive flexibility. Furthermore, we compared the word fluency results with the control group, highlighting the impairment in fluency in the aphasia group. As controls were able to name 15–24 animals in one minute, while PWA were able to name 1–11 animals in one minute, highlighting the difference between a healthy brain and the impacts of stroke on individuals.

Table 5 Language test results of the aphasia group
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Results of the TROG and TOKEN tests

The TROG test was employed to investigate comprehension and intact grammatical structures in PWA. It was especially useful when PWA were poorly performed in the TOKEN test, then we measured their comprehension based on their TROG results. Table 6 shows the grammatical structures examined in TROG. In this study we evaluated the number of completed blocks. The test contained twenty blocks (from A to T), each block consisting of four commands. We accepted a block as completed if the participants successfully solved all the four commands in the given block. The assessment ended if participants failed to solve three consecutive blocks. The TOKEN test included 36 commands; we measured the number of correct answers (0–8 very severe; 9–16 severe; 17–24 moderate; 25–29 mild; above 30 no impairment).

Table 6 Parts of the TROG test
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Control

The control group demonstrated exceptional performance in both the TROG and TOKEN tests, achieving high scores (90–100%), presented in Table 4. Notably, in the TROG, participants made errors in the N, R and T blocks, which contained more complex instructions. A similar pattern emerged in the TOKEN test, where errors were mainly observed in the final section, which contained more complex instructions. However, it is important to note that the frequency of errors remained insignificant.

Aphasia

The TROG test revealed both grammatical weaknesses and strengths in PWA. Participants with Wernicke’s aphasia and anomic aphasia could solve 5 blocks, presented in Table 5. We observed weaknesses during blocks C, D, E, F, G H, I, J within the group, see Table 6 for identifying the blocks. However, most participants managed to solve blocks A, B, C, D, and E. Results of P01, P02 and P03 indicate severe impairment in comprehension. Solving the test involved several EFs such as working memory, inhibition, attention, problem solving, planning and organization. The poor performance of aphasic patients may indicate impairment in these EFs. As they struggled to retain information while completing the tasks and often asked repetition of instructions. However, repeating the instructions did not improve their performance. In the TOKEN test we observed difficulties in complex commands as they caused confusion, leading to complete the tasks unsuccessfully This suggests potential severe impairment in comprehension in participants P01, P02, P03 and P05. Impaired inhibitory control may be responsible for this. Completing the tasks required simultaneous execution and proper inhibition, such as, selecting the correct form, size, and color all at once. Furthermore, these results may also indicate impairments in comprehension and working memory as repeating the commands did not help. On the other hand, P04 with Wernicke’s aphasia showed mild impairment in comprehension by achieving 25 scores out of 36. In comparison to the control group, individuals with PWA exhibited slower performance and achieved lower scores. For instance, the average number of blocks completed by the aphasia group in the TROG was 3.2, while the control group completed 19.2 blocks on average. Similarly, the average score for the aphasia group in the TOKEN test was 13.8, compared to 35 for the control group.

Results of the Boston naming test

In BNT we presented 60 pictures. We evaluated the correct number of answers and measured reaction time. Only answers provided by the participants or with the aid of semantic cues were accepted, while those resulting from phonemic cues were disregarded. However, we compared the number of correct answers using semantic and phonemic cues to determine which was more effective.

Increased reaction time and decreased accuracy in BNT

Our assumed was that the longer the reaction time required to finish the task, the more mistakes were made. As a result, we compared the number of correct answers in BNT and reaction time in the aphasia group.

Control

The control group generally performed well in the BNT (see Fig. 1), with scores ranging from 45 to 56 out of a maximum 60. Most participants’ reaction time was similar between 200 and 316 s (see Fig. 2), except, participant C04 who managed to solve the test in 134,98 s. We used their results to see how the reaction time changes after having a stroke. Our results showed no correlation between increased reaction time and decreased accuracy within the control group.

Fig. 1
figure 1

Number of correct answers in the Boston naming test

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Fig. 2
figure 2

Participants’ reaction time in seconds in the Boston naming test

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Aphasia

As it can be well seen on Fig. 1, the number of correct answers given by the aphasic patients varied significantly (from 0 to 40). The participants P01 with global and P03 conduction aphasia performed extremely poorly in the test. While P04 with Wernicke’s aphasia performed the most successfully, meaning 40 scores out of 60, suggesting mild impairment in naming. For P01 and P03 took the longest to finish the test, P01 managed in 1954, 4 s and P03 in 1925,41 s (see Fig. 2), suggesting very severe impairment in naming. As we expected, the longer the reaction time was, the more mistakes were made within the aphasia group. All participants with aphasia showed slower performance compared to the matched controls, suggesting a general slowness in performance.

Comparing the efficiency of semantic and phonemic cues in BNT

The reason for comparing semantic and phonemic cues in the BNT was to investigate the impact of WM on these. Our assumption was that the recall of a word could not be aided by semantic or phonemic cues if it was not stored in the WM.

Control

According to the results presented in Fig. 3, it appears that the control group found phonemic cues to be more helpful than semantic cues. With the assistance of phonemic cues, most participants were able to recall the word. However, some words, such as sphinx, pelican, and seahorse, were unfamiliar to them due to a lack of prior knowledge.

Fig. 3
figure 3

Comparing semantic cue and phonemic cue in the Boston naming test

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Aphasia

The numbers of cases when semantic and phonemic cues helped to recall a word in the aphasia groups are illustrated in Fig. 3. We observed that the semantic cues were the less effective ones. P01 with global and P03 with conduction aphasia scored zero in using semantic cues. On the other hand, phonemic cues proved to be more useful in the word retrieval process. P02 provided a considerably high number of correct answers (28) because of the phonemic cues, suggesting that although the words were familiar to P02, she was unable to retrieve them. By examining the semantic and phonemic cues of P01 and P03, it was demonstrated that the words were not found in their working memory because of two possible explanations; firstly, the words were not in their internal dictionaries or, if they were, they found it difficult to recall them.

Comparing word fluency and BNT

Our assumption was that we would find dissociation between word fluency and naming. We expected that if a participant performed poorly or successfully in the word fluency, they might not perform similarly in naming. Our results presented in Fig. 4 support our assumption.

Fig. 4
figure 4

Comparing word fluency (WAB) and BNT

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Control

In the control group, all participants except for participant C02 performed better in the word fluency task than in the naming task, ranging from 95–120%. There is dissociation in C01 and C02 performance. C02 performed better in the naming task 87%, whereas she reached 75% in the fluency task. While, C01 performed exceptionally in the fluency task, achieving115%, and reaching 75% in the naming test. On the other hand, C04 and C05 performed similarly in both tasks 90–95%.

Aphasia

Participants with aphasia yielded different outcomes, showing dissociation between the two tasks. For example, P01 and P02 with global aphasia performed better in the word fluency than in the naming task. P01 reached 20% in the fluency task and zero in the naming task. P02 achieved 55% in the fluency task and 28% in the naming task. While P04 and P05 performed better in naming than in word fluency. P04 achieved 5% in the fluency and 67% in the naming. P05 was unable to solve fluency task but reached 52% in the naming test. P03 was the only with similar performance in both tasks, reaching no points at all. Our observations suggest that different outcomes may occur within the same aphasia type. Specifically, in P01 and P02 with global aphasia, the varying results may be due to the number of strokes. It is worth noting that P01 had her second stroke at the time of assessment, while P02 had her first stroke, which may have had a negative impact on performance. Further research is necessary to investigate the difference between the two participants with global aphasia.

Comparison of the results between the aphasia group and the control group showed that participants in the aphasia group performed worse in both tasks than the matched controls, as expected. It is possible that individuals with PWA may have poorer performance due to impairments in executive functions such as inhibitory control, working memory, and cognitive flexibility resulting from their stroke. These executive functions are crucial for successful task completion. According to the results, it appears that individuals with PWA may encounter challenges with inhibitory control and working memory. This is indicated by their difficulty in suppressing irrelevant words and retaining and recalling relevant ones.

The correlation between lesion site and naming impairment

Our aim was to explore the correlation between individual naming difficulties and the location of brain damage. We assumed that participants with similar CT results (MCA stroke) would demonstrate varying degrees of naming impairment, ranging from very severe to mild. Table 2 presents the participants’ CT results. Among the three participants who experienced MCA stroke, P01 and P02 demonstrated global aphasia, whereas P04 exhibited Wernicke’s aphasia. The MCA is responsible for supplying blood to parts of the frontal, temporal and parietal lobes of the brain. Research has shown that damage to these areas is associated with naming difficulties in PWA (Breining et al. 2022). The results of participants P01, P02 and P04 in the BNT (see Fig. 1) varied, confirming our assumption. P01 with global aphasia scored zero on the BNT, while participants P02 and P04 performed better. P02 reached 17 scores and P04 reached 40 scores out of 60. Our findings indicate that P01 had very severe impairment in naming, P02 had severe and P04 had mild impairment in naming. The results suggest that individuals with similar lesion locations may experience varying levels of naming impairment rather depending on the type of aphasia. Additional research is needed with lager sample size to investigate naming deficits in different types of aphasia with similar lesion locations, which would lead to more valid conclusions.

Discussion

The purpose of this study was to examine the potential of EFs impairment in PWA using neuropsychological tests, with a particular focus on identifying any EF deficits in language tests. The results of the neuropsychological tests indicated that the aphasia group exhibited varying degrees of impairment (severe impairment in P01, P02 with global and P03 with conduction; moderate in P05 with anomic; mild in P04 with Wernicke’s aphasia). Successful completion of the tests necessitated the use of several EFs, including WM, cognitive flexibility, attention, task switching, planning, and organization. Comparing the results of the neuropsychological tests with the language tests revealed that P01, P03, and P05 performed similarly, whereas P02 and P04 demonstrated some differences. In case of participants P01 with global aphasia and P03 with conduction aphasia, we observed similarly poor performance in the language tests, with all the language tests indicating very severe and/or severe language deficits. Furthermore, we also observed similar performance in participant P05 with anomic aphasia, however, his results suggested moderate impairment in language functions. On the other hand, the results of participants P02 and P04 in terms of their neuropsychological and language tests were different. In case of P04 with Wernicke’s aphasia, his performance in the TOKEN, BNT, and TROG tests showed different level of impairment compared to the WAB. We observed mild impairment in completing the TOKEN, TROG and BNT tests, whereas result of the WAB suggested severe language impairment. In case of P02 with global aphasia, we observed that her WAB results indicated moderate impairment, whereas all the other language tests and neuropsychological test indicated severe impairment. This indicates the importance of assessing cognitive functions in addition to the WAB, as therapy should not be based solely on observations from the WAB. As demonstrated in the case of P02 and P04, it is now evident that the WAB does not always correlate with results from other tests. It is important to note that conducting these assessments can be time-consuming, taking approximately 3–4 h, due to the participants' slowness. However, based on our observations, it is necessary to perform all these assessments to obtain a comprehensive understanding of the participants' cognitive and language profile as it has been suggested previously by Byng et al. (1990) and Murray (2017a, b).

Based on the language test results, we observed that individuals with aphasia experienced challenges in information processing, which could impact their ability to recall and manipulate information. Furthermore, the results of the TOKEN and TROG tests suggest that individuals with aphasia may experience difficulties with complex tasks, which could be related to deficits in working memory and attention. In other words, it was found that participants in the aphasia group experienced more difficulty processing and comprehending longer sentences due to attentional demands. This finding is consistent with previous research conducted by Murray (2012).

Furthermore, special attention was paid to the Boston Naming Test (BNT) to investigate its correlation with potential impairments in executive functions (EFs). We assumed that deficits in inhibitory control and working memory would lead to longer reaction times and decreased accuracy. The results obtained from the aphasia group provided support for our hypothesis, as longer reaction times were found to be associated with a higher number of errors. To exemplify this, it is worth noting that participants P01 with global aphasia and P03 with conduction aphasia scored zero on the test, despite taking the longest time (over 1900s) in the group. Furthermore, the BNT was utilized to assess the efficacy of phonemic and semantic cues. The results indicate that the use of phonemic cues was more effective in both the control and aphasia groups. Nevertheless, it is important to emphasize that our primary focus was on the aphasia group. This study acknowledges that the validation of its results may be limited due to the small sample size of only 5 participants in the aphasia group. It is suggested that future studies could benefit from replicating this study with a larger sample size to determine if the same observations are found.

Furthermore, a comparison was made between word fluency and naming tasks. We assumed that poor or successful performance in the word fluency task may not correspond to similar performance in naming. The results supported this hypothesis, as participants with aphasia showed a dissociation between word fluency and naming tasks. Specifically, some participants (P01, P02) performed better in the word fluency task, while others (P04 and P05) performed better in the naming task. It is worth noting that only one participant, P03, demonstrated similar performance in both tasks, although her performance could not be evaluated as she scored zero in both tasks. Additionally, there was an interesting difference between the performance of the two global aphasics. P01 with global aphasia reached 20% in the fluency task, while in the naming task she scored zero. Conversely, P02, also with global aphasia, reached 55% in fluency and 28% in naming. It may be worth considering the examination of individual differences between global aphasics in a larger sample size.

Finally, the aim of our study was to investigate the correlation between individual naming difficulties and the location of brain damage. In this study, we compared three participants with different types of aphasia and similar lesion locations. It was observed that participants with MCA stroke (P01, P02, and P04) exhibited varying degrees of naming impairment, ranging from very severe to mild. The results of the BNT support this observation, as they suggest very severe impairment in P01 with global aphasia, severe impairment in P02 with global aphasia, and mild impairment in P04 with Wernicke's aphasia. This suggests that the type of aphasia has a potential greater impact on naming impairment than the location of the lesion. Nevertheless, given the limited sample size, further research is necessary to validate this hypothesis.

Conclusions for future biology

In conclusion, this study offers valuable insights into the potential impairment of executive functions in individuals with aphasia. The multiple case study emphasizes the significance of detailed performance analysis beyond aphasia typology for both researchers and practitioners. The purpose of assessing the cognitive profiles is to prepare the most appropriate therapy for participants. This approach is like György Ádám's approach, which was introduced in the psychology curriculum in the 1970s. Ádám's approach aimed to combine detailed investigations with a holistic view of human performance (Ádám, 1980).