Nonlinguistic learning in individuals with aphasia: effects of training method and stimulus characteristics

The role of cognitive control and naming in aphasia

The classical aphasia literature has placed considerable emphasis on the language-centered understanding of aphasia and failed to consider the role of executive functions (EFs) regarding different aspects of patients' performance. Many current studies suggest deficits in EFs in individuals with aphasia, however, the available data is still limited. Here, our aim was to investigate the impairment of EFs and its potential negative effects on naming (slower performance, increased reaction time and/or decreased accuracy). We sought to determine whether the poor performance observed in word fluency task correlated with similar outcomes in naming. Our study involved five Hungarian post stroke aphasic patients (2 males and 3 females) between the ages of 60 and 70, as well as a control group matched for age and gender. The participants were diagnosed with different types of aphasia (global, Wernicke's, anomic and conduction). This study employed various neuropsychological and linguistic batteries. By comparing the patients' performance to that of the control group, we aimed to investigate the impacts of stroke. Within the aphasia group, we observed difficulties in following complex commands and a connection between general slowness and reduced accuracy in naming. We concluded that impairment of executive functions may have a negative impact on naming, comprehension, and fluency. Therefore, it is important to consider functional variations in neural networks, and to base our interpretations on the available psychophysiological data in literature. Our findings provide an alternative perspective to the traditional assessment of aphasia and highlight the importance of considering the role of executive functions.

Aging effects and feasibility of statistical learning tasks across modalities

Knowledge on statistical learning (SL) in healthy elderly is scarce. Theoretically, it is not clear whether aging affects modality-specific and/or domain-general learning mechanisms. Practically, there is a lack of research on simplified SL tasks, which would ease the burden of testing in clinical populations. Against this background, we conducted two experiments across three modalities (auditory, visual and visuomotor) in a total of 93 younger and older adults. In Experiment 1, SL was induced in all modalities. Aging effects appeared in the tasks relying on an explicit posttest to assess SL. We hypothesize that declines in domain-general processes that predominantly modulate explicit learning mechanisms underlie these aging effects. In Experiment 2, more feasible tasks were developed for which the level of SL was maintained in all modalities, except the auditory modality. These tasks are more likely to successfully measure SL in elderly (patient) populations in which task demands can be problematic.

The role of the hippocampus in statistical learning and language recovery in persons with post stroke aphasia

Although several studies have aimed for accurate predictions of language recovery in post stroke aphasia, individual language outcomes remain hard to predict. Large-scale prediction models are built using data from patients mainly in the chronic phase after stroke, although it is clinically more relevant to consider data from the acute phase. Previous research has mainly focused on deficits, i.e., behavioral deficits or specific brain damage, rather than compensatory mechanisms, i.e., intact cognitive skills or undamaged brain regions. One such unexplored brain region that might support language (re)learning in aphasia is the hippocampus, a region that has commonly been associated with an individual's learning potential, including statistical learning. This refers to a set of mechanisms upon which we rely heavily in daily life to learn a range of regularities across cognitive domains. Against this background, thirty-three patients with aphasia (22 males and 11 females, M = 69.76 years, SD = 10.57 years) were followed for 1 year in the acute (1-2 weeks), subacute (3-6 months) and chronic phase (9-12 months) post stroke. We evaluated the unique predictive value of early structural hippocampal measures for short-term and long-term language outcomes (measured by the ANELT). In addition, we investigated whether statistical learning abilities were intact in patients with aphasia using three different tasks: an auditory-linguistic and visual task based on the computation of transitional probabilities and a visuomotor serial reaction time task. Finally, we examined the association of individuals' statistical learning potential with acute measures of hippocampal gray and white matter. Using Bayesian statistics, we found moderate evidence for the contribution of left hippocampal gray matter in the acute phase to the prediction of long-term language outcomes, over and above information on the lesion and the initial language deficit (measured by the ScreeLing). Non-linguistic statistical learning in patients with aphasia, measured in the subacute phase, was intact at the group level compared to 23 healthy older controls (8 males and 15 females, M = 74.09 years, SD = 6.76 years). Visuomotor statistical learning correlated with acute hippocampal gray and white matter. These findings reveal that particularly left hippocampal gray matter in the acute phase is a potential marker of language recovery after stroke, possibly through its statistical learning ability.

Mechanisms underlying anomia treatment outcomes

Treatments for anomia have demonstrated short- and long-term efficacy. However, individual outcomes can be variable, and evidence for treatment generalization is limited. We investigated whether treatment-related measures of access to- and learning of language, namely, a) responsiveness to cues, and b) during-treatment improvements in naming, are good predictors of treatment outcomes. In addition, we investigated mechanisms underlying treatment generalization. Ten adults with chronic, post-stroke aphasia received a phonological treatment for anomia three times a week for five weeks. Naming accuracy of treated and untreated words was assessed pre- and post-treatment and at four- and eight-week follow-ups. Generalization to an untrained naming task, which involved analyses of naming accuracy and speech errors, was also assessed; speech errors were analyzed according to the Interactive Activation (IA) model of word retrieval. Group analyses indicate significant improvements in naming treated compared to untreated words, at all timepoints after therapy. Additional analyses showed significant long-term improvements in naming untreated words. Initial responsiveness to cueing and early improvement emerged as significant predictors of overall pre- to post-treatment improvements in naming treated words; naming improvements made early-on in treatment were also predictive of improvements in naming of the untreated words at follow-up. Furthermore, our study is the first to demonstrate that generalization after a phonological treatment for anomia may be driven by a strengthening of lexical-phonological connections. This study provides novel insights regarding mechanisms driving anomia treatment outcomes. Understanding such mechanisms is critical to improving existing assessment practices, optimizing treatment selection and building treatment protocols that are more likely to generalize.

Implicit learning and implicit treatment outcomes in individuals with aphasia

BACKGROUND

Implicit learning is a process of learning that occurs outside of conscious awareness and may be involved in implicit, exposure-based language training. However, research shows that implicit learning abilities are variable among individuals with aphasia, and it remains unknown whether individuals who show basic implicit learning abilities also benefit from implicit language training.

AIMS

The aims of this series of experiments were to test implicit learning in individuals with agrammatic aphasia, examine the effects of a novel implicit language treatment, and investigate whether individuals with aphasia who show implicit learning ability also benefit from implicit treatment focused on passive sentence comprehension.

METHODS & PROCEDURES

Nine participants with chronic agrammatic aphasia and 21 neurologically intact participants completed a visuomotor serial reaction time test of implicit learning (Experiment 1). The participants with aphasia also completed a short-term novel implicit sentence comprehension treatment (Experiment 2) that consisted of five sessions of repeated exposure to grammatically correct passive sentences and matching photographs. Sentence comprehension was tested in multiple baseline sessions and on each day of training using a sentence-picture matching task. The relation between participants' learning patterns across experiments was also examined.

OUTCOMES & RESULTS

Individuals with agrammatic aphasia as well as neurologically intact adults demonstrated significant implicit sequence learning in the serial reaction time task. However, the participants with aphasia did not show concomitant improvement in sentence comprehension as a result of the implicit treatment protocol.

CONCLUSIONS

This study suggests that individuals with agrammatic aphasia demonstrate implicit learning ability; however, this ability does not necessarily promote successful outcomes in treatment that is based solely on implicit training methods.