Inner Speech in Aphasia: Current Evidence, Clinical Implications, and Future Directions

Theory of mind deficits in non-fluent primary progressive aphasia

Theory of Mind (ToM) is a complex socio-cognitive subdomain that is under-researched in neurodegenerative disorders, particularly in persons with primary progressive aphasia. We studied 14 persons with non-fluent/agrammatic variant primary progressive aphasia (nfaPPA), and asked two questions: (1) whether persons with nfaPPA have intact or impaired ToM, with emphasis on their false belief attribution abilities, relative to healthy controls; and (2) whether false-belief attribution (a component of ToM) is associated with their syntactic and executive function (EF) abilities. False belief understanding was tested through nonverbal videos, with participants deciding whether the story ending was an appropriate end of each video scenario or not. Syntactic production abilities were measured through repetition of syntactically simple and complex sentences (comprising length-matched complement and adjunct sentences), and EF tasks, specifically, a digit-back and an attention-shifting task. Persons with nfaPPA were less accurate than controls in adapting their reasoning to the false beliefs of other agents in the nonverbal videos of the false belief attribution task. Their false belief attribution performance was significantly predicted primarily by their syntactic production, followed by their EF. The overall findings suggest that persons with nfaPPA may have impaired performances in ToM tasks, due to impairments in basic non-social cognitive functioning, such as syntactic and EF abilities.

Learning to operate an imagined speech Brain-Computer Interface involves the spatial and frequency tuning of neural activity

Brain-Computer Interfaces (BCI) will revolutionize the way people with severe impairment of speech production can communicate. While current efforts focus on training classifiers on vast amounts of neurophysiological signals to decode imagined speech, much less attention has been given to users' ability to adapt their neural activity to improve BCI-control. To address whether BCI-control improves with training and characterize the underlying neural dynamics, we trained 15 healthy participants to operate a binary BCI system based on electroencephalography (EEG) signals through syllable imagery for five consecutive days. Despite considerable interindividual variability in performance and learning, a significant improvement in BCI-control was globally observed. Using a control experiment, we show that a continuous feedback about the decoded activity is necessary for learning to occur. Performance improvement was associated with a broad EEG power increase in frontal theta activity and focal enhancement in temporal low-gamma activity, showing that learning to operate an imagined-speech BCI involves dynamic changes in neural features at different spectral scales. These findings demonstrate that combining machine and human learning is a successful strategy to enhance BCI controllability.

Evidence from aphasia suggests a bidirectional relationship between inner speech and executive function

Research over the past several decades has revealed that non-linguistic cognitive impairments can appear alongside language deficits in individuals with aphasia. One vulnerable cognitive domain is executive function, an umbrella term for the higher-level cognitive processes that allow us to direct our behavior towards a goal. Studies in healthy adults reveal that executive function abilities are supported by inner speech, the ability to use language silently in one's head. Therefore, inner speech may mediate the connection between language and executive function deficits in individuals with aphasia. Here, we investigated whether inner speech ability may link language and cognitive impairments in 59 adults with chronic, post-stroke aphasia. We used two approaches to measure inner speech: one based on internal retrieval of words and one based on internal retrieval plus silent manipulation of the retrieved phonological forms. Then, we examined relationships between these two approaches to measuring inner speech and five aspects of executive function ability: response inhibition, conflict monitoring/resolution, general task-switching ability, phonological control, and semantic control. We also looked for dissociations between inner speech ability and executive function ability. Our results show tentative relationships between inner speech (across multiple measurement approaches) and all aspects of executive function except for response inhibition. We also found evidence for a double dissociation: many participants show intact executive function despite poor inner speech, and vice versa, so neither process is strictly reliant on the other. We suggest that this work provides preliminary evidence of a bidirectional relationship between inner speech and executive function: inner speech supports some aspects of executive function via internal self-cueing and certain aspects of executive function support performance on complex inner speech tasks.

Interdisciplinary approaches to understanding the inner speech, with emphasis on the role of incorporating clinical data

Neuroscience has largely conceptualized inner speech, sometimes called covert speech, as being a part of the language system, namely, a precursor to overt speech and/or speech without the motor component (impoverished motor speech). Yet interdisciplinary work has strongly suggested that inner speech is multidimensional and situated within the language system as well as in more domain general systems. By leveraging evidence from philosophy, linguistics, neuroscience and cognitive science, we argue that neuroscience can gain a more comprehensive understanding of inner speech processes. We will summarize the existing knowledge on the traditional approach to understanding the neuroscience of inner speech, which is squarely through the language system, before discussing interdisciplinary approaches to understanding the cognitive, linguistic and neural substrates/mechanisms that may be involved in inner speech. Given our own interests in inner speech after brain injury, we finish by discussing the theoretical and clinical benefits of researching inner speech in aphasia through an interdisciplinary lens.

Inner speech in the daily lives of people with aphasia

Introduction

This exploratory, preliminary, feasibility study evaluated the extent to which adults with chronic aphasia (N = 23) report experiencing inner speech in their daily lives by leveraging experience sampling and survey methodology.

Methods

The presence of inner speech was assessed at 30 time-points and themes of inner speech at three time-points, over the course of three weeks. The relationship of inner speech to aphasia severity, demographic information (age, sex, years post-stroke), and insight into language impairment was evaluated.

Results

There was low attrition (<8%) and high compliance (>94%) for the study procedures, and inner speech was experienced in most sampled instances (>78%). The most common themes of inner speech experience across the weeks were 'when remembering', 'to plan', and 'to motivate oneself'. There was no significant relationship identified between inner speech and aphasia severity, insight into language impairment, or demographic information. In conclusion, adults with aphasia tend to report experiencing inner speech often, with some shared themes (e.g., remembering, planning), and use inner speech to explore themes that are uncommon in young adults in other studies (e.g., to talk to themselves about health).

Discussion

High compliance and low attrition suggest design feasibility, and results emphasize the importance of collecting data in age-similar, non-brain-damaged peers as well as in adults with other neurogenic communication disorders to fully understand the experience and use of inner speech in daily life. Clinical implications and future directions are discussed.

Repetition Priming Treatment for Anomia: Effects of Single- and Multiple-Exemplar Protocols

INTRODUCTION

Repetition priming can lead to improved naming ability in people with aphasia, but concerns have arisen from prior research about using only a single picture exemplar for each target. Specifically, it is unclear whether the observed improvements were due to learning simple correspondences between particular words and pictures rather than changes at a deeper level of lexical-semantic processing. In addition, implications for generalization after training with single exemplars were unclear. This study replicated and extended previous work to address these questions.

METHOD

Five participants with chronic aphasia participated in this repeated-measures design study, which repeatedly paired words and pictures with no feedback provided. Two participants engaged in a single-exemplar condition, with a single picture exemplar of each target used for every presentation of that target. The remaining three participants engaged in a multiple-exemplar condition, with several different pictures used for each target. Half of these targets used training pictures during naming probes, whereas half did not.

RESULTS

Primed items led to greater improvements in naming than items that were practiced but not primed. The data indicate that improvements may extend beyond stimulus-specific correspondences. Maintenance and generalization effects were mixed.

CONCLUSIONS

These data provide further support for the efficacy of repetition priming treatment for anomia. Implications and future directions are discussed.

Self-talk: research challenges and opportunities

In this review, we discuss major measurement and methodological challenges to studying self-talk. We review the assessment of self-talk frequency, studying self-talk in its natural context, personal pronoun usage within self-talk, experiential sampling methods, and the experimental manipulation of self-talk. We highlight new possible research opportunities and discuss recent advances such as brain imaging studies of self-talk, the use of self-talk by robots, and measurement of self-talk in aphasic patients.

Listening to Yourself and Watching Your Tongue: Distinct Abilities and Brain Regions for Monitoring Semantic and Phonological Speech Errors

Despite the many mistakes we make while speaking, people can effectively communicate because we monitor our speech errors. However, the cognitive abilities and brain structures that support speech error monitoring are unclear. There may be different abilities and brain regions that support monitoring phonological speech errors versus monitoring semantic speech errors. We investigated speech, language, and cognitive control abilities that relate to detecting phonological and semantic speech errors in 41 individuals with aphasia who underwent detailed cognitive testing. Then, we used support vector regression lesion symptom mapping to identify brain regions supporting detection of phonological versus semantic errors in a group of 76 individuals with aphasia. The results revealed that motor speech deficits as well as lesions to the ventral motor cortex were related to reduced detection of phonological errors relative to semantic errors. Detection of semantic errors selectively related to auditory word comprehension deficits. Across all error types, poor cognitive control related to reduced detection. We conclude that monitoring of phonological and semantic errors relies on distinct cognitive abilities and brain regions. Furthermore, we identified cognitive control as a shared cognitive basis for monitoring all types of speech errors. These findings refine and expand our understanding of the neurocognitive basis of speech error monitoring.

The Self Course: Lessons Learned from Students' Weekly Questions

In this paper, I tentatively answer 50 questions sampled from a pool of over 10,000 weekly questions formulated by students in a course entitled "The Self". The questions pertain to various key topics related to self-processes, such as self-awareness, self-knowledge, self-regulation, self-talk, self-esteem, and self-regulation. The students' weekly questions and their answers highlight what is currently known about the self. Answers to the student questions also allow for the identification of some recurrent lessons about the self. Some of these lessons include: all self-processes are interconnected (e.g., prospection depends on autobiography), self-terms must be properly defined (e.g., self-rumination and worry are not the same), inner speech plays an important role in self-processes, controversies are numerous (are animals self-aware?), measurement issues abound (e.g., self-recognition as an operationalization of self-awareness), deficits in some self-processes can have devastating effects (e.g., self-regulatory deficits may lead to financial problems), and there are lots of unknowns about the self (e.g., gender differences in Theory-of-Mind).

A voice without a mouth no more: The neurobiology of language and consciousness

Most research on the neurobiology of language ignores consciousness and vice versa. Here, language, with an emphasis on inner speech, is hypothesised to generate and sustain self-awareness, i.e., higher-order consciousness. Converging evidence supporting this hypothesis is reviewed. To account for these findings, a 'HOLISTIC' model of neurobiology of language, inner speech, and consciousness is proposed. It involves a 'core' set of inner speech production regions that initiate the experience of feeling and hearing words. These take on affective qualities, deriving from activation of associated sensory, motor, and emotional representations, involving a largely unconscious dynamic 'periphery', distributed throughout the whole brain. Responding to those words forms the basis for sustained network activity, involving 'default mode' activation and prefrontal and thalamic/brainstem selection of contextually relevant responses. Evidence for the model is reviewed, supporting neuroimaging meta-analyses conducted, and comparisons with other theories of consciousness made. The HOLISTIC model constitutes a more parsimonious and complete account of the 'neural correlates of consciousness' that has implications for a mechanistic account of mental health and wellbeing.

Distinguishing semantic control and phonological control and their role in aphasic deficits: A task switching investigation

People use cognitive control across many contexts in daily life, yet it remains unclear how cognitive control is used in contexts involving language. Distinguishing language-specific cognitive control components may be critical to understanding aphasia, which can co-occur with cognitive control deficits. For example, deficits in control of semantic representations (i.e., semantic control), are thought to contribute to semantic deficits in aphasia. Conversely, little is known about control of phonological representations (i.e., phonological control) in aphasia. We developed a switching task to investigate semantic and phonological control in 32 left hemisphere stroke survivors with aphasia and 37 matched controls. We found that phonological and semantic control were related, but dissociate in the presence of switching demands. People with aphasia exhibited group-wise impairment at phonological control, although individual impairments were subtle except in one case. Several individuals with aphasia exhibited frank semantic control impairments, and these individuals had relative deficits on other semantic tasks. The present findings distinguish semantic control from phonological control, and confirm that semantic control impairments contribute to semantic deficits in aphasia.

Web-based Oral Reading for Language in Aphasia (Web ORLA®): A pilot randomized control trial

OBJECTIVE

To investigate an intensive asynchronous computer-based treatment delivered remotely with clinician oversight to people with aphasia.

DESIGN

Single-blind, randomized placebo-controlled trial.

SETTING

Free-standing urban rehabilitation hospital.

PARTICIPANTS

Adults with aphasia (at least six months post-onset).

INTERVENTIONS

Experimental treatment was Web ORLA^® (Oral Reading for Language in Aphasia) which provides repeated choral and independent reading aloud of sentences with a virtual therapist. Placebo was a commercially available computer game. Participants were instructed to practice 90 minutes/day, six days/week for six weeks.

MAIN MEASURES

Change in Language Quotient of the Western Aphasia Battery-Revised from pre-treatment to post-treatment and pre-treatment to six weeks following the end of treatment.

RESULTS

32 participants (19 Web ORLA^®, 13 Control) completed the intervention and post-treatment assessment; 27 participants (16 Web ORLA^®, 11 Control) completed the follow-up assessment six weeks after treatment had ended. Web ORLA^® treatment resulted in significant improvements in language performance from pre-treatment to immediately post-treatment (X = 2.96; SD = 4.32; P < 0.01; ES = 0.68) and from pre-treatment to six weeks following the end of treatment (X = 4.53; SD = 3.16; P < 0.001; ES = 1.43). There was no significant difference in the gain from pre-treatment to post-treatment for the Web ORLA^® versus Control groups. However, the Web ORLA^® group showed significantly greater gains at the six-week follow-up than the control group (X = 2.70; SD = 1.01; P = 0.013; ES = 1.92).

CONCLUSION

Results provide evidence for improved language outcomes following intensive, web-based delivery of ORLA^® to individuals with chronic aphasia. Findings underscore the value of combining clinician oversight with the flexibility of asynchronous practice.