Short-term Memory Assessment in Patients With Poststroke Aphasia
Condition: Aphasia, Acquired; Short-Term Memory Impairment
MeSH terms: Aphasia
Study type: Interventional

Summary: 
      Background and aim

      There is a growing awareness that people with aphasia (language problems) after a stroke
      often have difficulties with their short-term memory (STM). As a result, the explanation
      underlying aphasia has recently been seen as a language processing disorder, where multiple
      cognitive processes interact. To evaluate the cognitive processes underlying aphasia, there
      is a need for reliable and valid assessment tools. However, the quality of tests usually used
      to assess STM problems in aphasia patients is questioned because they are not specifically
      designed to be used in aphasia patients. This raises some concern, as impairments of STM can
      be predictive for the recovery and rehabilitation of aphasia patients. As an important
      exception, a recent study has developed a new English evaluation tool (i.e., The Temple
      Assessment of Language and (Verbal) Short-term Memory in Aphasia; TALSA) that examines
      language and STM aspects specifically developed for persons with aphasia.

      However, the existence of a Dutch evaluation tool specifically designed to assess language
      and STM problems in people with aphasia after a stroke is lacking. Therefore, the aim of the
      current study is to develop a Dutch clinical version of the TALSA battery that may lead to
      better diagnosis and treatment of STM problems in persons with aphasia. The development of
      the test focuses on its clinical feasibility (e.g. test duration, difficulty of the items and
      response modality). Pilot testing of the Dutch STM assessment instrument in the clinical and
      healthy population is very important to adapt the test where necessary. In addition, the
      quality of the test should also be carefully evaluated.

      Method

      The first step towards the development of a Dutch STM assessment instrument is the careful
      selection of the most crucial subtests of the original TALSA battery. Not all subtests will
      be selected due to the long testing time of the TALSA battery, and as mentioned earlier, the
      Dutch STM assessment tool focuses on clinical feasibility of the test.

      The second step is pilot testing the Dutch STM assessment instrument in persons with aphasia
      and healthy persons. Persons with aphasia will be recruited at the Stroke unit of Ghent
      University Hospital. All eligible patients will be asked to provide written informed consent
      to participate in this study. Three tests will be administered, namely the Oxford Cognitive
      Screen, the Token Test and the Dutch STM assessment tool. It is important that these tests
      are taken on the same day or on two consecutive days, depending on the circumstances (e.g.
      fatigue). The Token Test and Oxford Cognitive Screen provide a picture of the patient's
      cognitive profile. Throughout the process of pilot testing, the Dutch STM assessment tool
      will be adapted and improved where necessary. In order to verify or adjust the difficulty of
      the items, it is crucial that the STM assessment instrument is also tested on a small number
      of healthy control subjects (recruited via social media platforms).
    

Detailed description: 
      1. Introduction

           1.1. Background

           The literature has witnessed a steady increase in the number of studies investigating
           the role of short-term memory (STM) and working memory (WM) impairments in aphasia
           patients, which clearly shows that aphasia patients have impairments in verbal STM and
           WM. Throughout the years, views on the nature of aphasia have changed from the loss of
           linguistic representations (e.g., semantic and phonological representations) into
           impairments in the processing (i.e., access and retrieval) of language representations.
           Therefore, the emphasis of research has been refined in identifying the component
           operations of language processing, such as the mechanisms behind the access and
           retrieval of words or the temporal course of language processing. These operations rely
           on other cognitive functions, such as the STM.

           Psycholinguistic models describe the role of the STM in language as the maintenance of
           activation of linguistic representations over the time course of processing words.
           Particularly, the interactive activation model takes levels of linguistic
           representations (e.g., semantic, lexical and phonological) and its connections into
           account. Specifically, according to this influential model, word retrieval is mediated
           by interactive spreading activation that activates the target word and semantically or
           phonologically related words. Two important concepts (i.e., connection strength and
           decay rate) play an important role in spreading and maintaining activation over time in
           the semantic-lexical-phonological network. In aphasia, the impairments are thought to
           occur through deficits in linguistic representations, and moreover, through deficits in
           connection weight and decay rate (i.e., processing impairment). Errors occur if
           connection strength is weak (activation spreads too slowly) or if the decay rate is too
           rapid (representations are activated but decay too fast). Therefore, the interactive
           activation model can explain different patterns of word retrieval errors (i.e.,
           semantical or phonological) in aphasia.

           In order to examine the role of the STM in language processing, there is an excessive
           need for reliable assessment tools. However, the psychometric properties of tests
           commonly used to assess STM problems in individuals with aphasia have been called into
           question. A common issue across these tests is that small standardized samples are used,
           which lead to validity and reliability problems of normative data. This raises some
           concerns since there is growing awareness that impairments in STM functions may be
           predictive of certain aspects of language function, recovery and rehabilitation in
           aphasia patients. Therefore, it is of crucial importance that STM assessment tools are
           reliable and valid in order to replicate, compare and further examine these findings.

           A recent study developed a new English assessment tool (i.e., The Temple Assessment of
           Language and (Verbal) Short-term Memory in Aphasia; TALSA) that evaluates language and
           verbal STM/WM abilities in individuals with poststroke aphasia in an interactive
           activation framework. In other words, to evaluate the nature of aphasia as a processing
           disorder. The TALSA battery is unique compared to other tests (e.g. Psycholinguistic
           assessments of language processing in aphasia (PALPA)) since it takes into account
           features related to temporal aspects of language processing and effects of memory load
           on production and comprehension of language. Therefore, the TALSA battery is a specific
           diagnostic assessment tool and is sensitive to language impairments at all levels of
           severity, including mild aphasia. The complete TALSA battery consists of three parts
           among which the last part involves verbal STM tasks. Note that the authors of the TALSA
           battery are still working on a clinical version that is not published yet.

           1.2. Rationale of the study

           To our knowledge, the existence of a Dutch assessment tool that examines verbal STM in
           individuals with poststroke aphasia is lacking. In other words, a Dutch STM test
           specifically developed for people with phatic disorders is not available. However,
           assessing non-linguistic influences in aphasia patients, such as the role of STM on
           language components, is of crucial importance as communication in everyday life
           fluctuates in processing time.

           Moreover, an overwhelming amount of STM measures (standardised and experimental) are
           used in aphasia research. However, diversity in STM tests makes it harder to compare
           discrepant findings and makes it more difficult for clinicians to select appropriate
           assessment tools. Furthermore, the validity and reliability of used STM tools are
           questioned in the aphasic population. Thus, the establishment of a Dutch verbal STM
           assessment tool is crucial to better comprehend the nature of aphasia as a processing
           disorder, and has the purpose to serve as a practical tool to help Dutch clinicians and
           speech pathologists diagnose STM deficits more specifically, which can lead to optimized
           speech therapy.

           1.3. Objective of the study

           The first aim of the present study is to develop a Dutch clinical verbal STM assessment
           tool, based on the third part of the TALSA battery, to assess STM deficits at all levels
           of severity. With this intention, the investigators hope to better comprehend the nature
           of aphasia and the impact of STM deficits which may ameliorate treatment techniques.
           Importantly, this test focuses on clinical use and administration, in which despite the
           patient's language problems, the test must be understandable and applicable (e.g., test
           duration and response modality).

           The second aim is to run a pilot test on the aphasic population and the healthy
           population. Running a pilot test will validate the stimuli and the wording of the tasks.
           Confounded items (e.g., ambiguous stimuli, poor wording) will be revised or eliminated
           if necessary.

           The third aim is to evaluate the verbal STM assessment tool with respect to important
           psychometric properties, as the methodological quality of a test affects the
           interpretation of the results.

        2. Method

      2.1. Study population

      The investigators will include a maximum of 100 patients with aphasia in the acute to
      subacute phase after an ischemic or hemorrhagic stroke. The patients will be directly
      recruited in the Ghent University hospital at the Stroke unit. Furthermore, 20 healthy
      controls will be recruited via social media platforms. Healthy participants will be matched
      to the aphasic group for gender, age and education. All participants will voluntarily
      participate in this research project and sign an informed consent.

      2.2. Verbal STM assessment tool development (first aim)

      The first step towards the development of a Dutch clinical verbal STM assessment tool is to
      carefully select the most crucial verbal STM subtests of the original English TALSA battery.
      This is because the original TALSA battery is quite long and is not yet developed for
      administration in clinical settings. In particular, the Dutch verbal STM assessment tool will
      be based on the third part of the TALSA battery which involves verbal STM span tasks. The
      third part of the TALSA battery, moreover, evaluates phonological and semantic language
      representations by varying word characteristics of the items. Thus, the Dutch verbal STM
      assessment tool will consist of verbal STM span tasks with linguistic variations
      (phonological and semantic representations).

      The stimuli in the original TALSA battery consist of pictures and recordings of words,
      nonwords, sentences, and sequences of words, nonwords, and digits. However, literally
      translating the TALSA test-battery is inappropriate because there is not a one-to-one match
      between words and syntactic structures across any two languages. In particular, it is
      important to take into account word characteristics, such as word frequency, syllables,
      imageability and age of acquisition, that influence the degree of success in word retrieval
      in aphasia. Therefore, the verbal STM assessment tool will rely on the same subset tasks of
      part 3 of the TALSA battery, but with the careful selection of new Dutch stimuli with respect
      to important word characteristics.

      In the original TALSA battery, the authors took word frequency, syllables and imageability
      into account. However, research showed that age of acquisition (AoA) is also a crucial word
      characteristic in success of word retrieval in aphasia, thus AoA will be included during the
      stimuli selection procedure. In order to collect stimuli that meet these general word
      characteristics, word databases will be consulted, such as the Dutch Lexicon Project 2.

      2.3. Pilot test (second aim)

      Once the test-battery is developed, pilot testing will be of crucial importance in the
      clinical setting and healthy population to adapt and improve the test-battery where
      necessary.

      Particularly in the clinical setting, patients with aphasia will be recruited according to
      the inclusion and exclusion criteria. Specifically, all patients who are eligible will be
      asked for informed consent to participate in this trial. Subsequently, the Oxford Cognitive
      screen, the Token Test and the Dutch verbal STM assessment tool will be administered.

      The Token Test determines the severity of aphasia and investigates sentence comprehension.
      The Oxford Cognitive screen is a short cognitive screening tool that is administered in the
      acute phase of stroke. The outcomes on the Token Test and Oxford Cognitive Screen can serve
      as a support to interpret the results of the Dutch verbal STM assessment tool.

      It is worth noting that the Dutch verbal STM assessment tool, the Token Test and the Oxford
      Cognitive screen will be administered over a time span of maximum two consecutive days
      depending on how fatigued the patient is during testing. The total test duration on patients
      is estimated to take approximately two hours. The total test duration on healthy controls is
      estimated to take approximately 1 hour. During administration of the Dutch verbal STM
      assessment tool, audio recordings will be made of the patient. In this way, it is possible to
      reevaluate misunderstandings during the scoring of the subtests.

      In order to verify or adapt the difficulty of the items, it is critical that the Dutch verbal
      STM assessment tool will also be tested on healthy controls. Results of the original TALSA
      battery revealed that healthy controls performed near ceiling on most of the subtests.
      However, in some of the subtests (e.g., nonword span), healthy controls showed a similar
      results pattern as aphasia patients, which questions the contribution of those subtests.

      To conclude, running a pilot test provides the opportunity to reevaluate items that stand out
      from the distribution of scores (e.g., sufficient number of healthy controls respond
      incorrectly to an item). Specifically, these items may be confounded and need to be
      eliminated or adapted (e.g., ambiguous stimuli).

      2.4. Psychometric properties (third aim)

      Reliability and validity are important psychometric properties. Reliability refers to the
      consistency, stability and accuracy of an assessment tool. Validity of a test refers to
      whether the assessment tool measures what it intends to measure.

        -  Internal consistency: To verify the reliability of the Dutch verbal STM assessment tool,
           the internal consistency of the test will be estimated using the split-half reliability
           procedure. In this way, the constancy of results across items within a subtest can be
           analyzed.

        -  Face validity: The TALSA battery is developed to approach aphasia as a processing
           disorder, supported by cognitive models of language processing. Therefore, the test
           battery focuses on component stages of word processing (e.g., semantic or phonological)
           and, moreover, with an emphasis on processes related to access, retrieval and short-term
           maintenance of language representations.

        -  Concurrent validity: The results of the Dutch verbal STM assessment tool will be
           compared with the results of the original TALSA battery to verify the concurrent
           validity. High correlations between the subtests of the original TALSA battery and Dutch
           verbal STM assessment tool suggest a good concurrent validity.

      To conclude, throughout the process of pilot testing, the Dutch verbal STM assessment tool
      will be modified and improved where necessary and will be psychometrically evaluated (e.g.,
      reliability, validity and item analysis).
    

Intervention name(s): short term memory assessment; Oxford cognitive screen; Token Test; Montreal cognitive assessment
Intervention type(s): Diagnostic Test; Diagnostic Test; Diagnostic Test; Diagnostic Test
Intervention description(s): Aphasia group: The Dutch verbal STM assessment tool will be administered over a time span of maximum two consecutive days depending on how fatigued the patient is during testing.
Healthy control group: the Dutch verbal STM assessment tool will be administered.; Evaluation of the cognitive abilities of the patients with aphasia.; Evaluation of the severity of the aphasia in patients with aphasia.; Evaluation of cognitive dysfunction in the group of healthy volunteers.
Allocation: Non-Randomized
Intervention model: Parallel Assignment
Masking: None (Open Label)
Primary purpose: Diagnostic
Keywords: aphasia; short-term memory; assessment