Inner Speech

 

What do we study?

Inner speech is the internal dialogue (or, monologue) we engage in with ourselves. Interestingly, some of the population does not experience inner speech and those that do tend to vary in how often they engage with inner speech, and for what purposes. Inner speech has long been studied through interdisciplinary lenses (philosophy, neuroscience, linguistics, psychology), and therefore many methods and designs have been used to explore it. While it has most typically been explored in cognitively healthy young adults, our lab has a particular interest in studying inner speech in persons with post-stroke aphasia, a language disorder, because it may be intact compared to aloud speaking or even comprehension abilities. See below for a sample of publications from our lab about inner speech.


Research from the lab

The goal of this line of research is to broadly characterize the role of inner speech in aphasia recovery. Inner speech is our inner voice, a cognitive process that interdisciplinary research has related to not only language processes but also to self-awareness, problem solving, and motivation. My early work (Stark, Geva & Warubrton, 2017) demonstrated that individuals with aphasia can have relatively preserved inner speech whilst having severe verbal/oral impairments.

More recently, I have taken two approaches to evaluating inner speech in aphasia. The first approach examines the role of inner speech in treated naming recovery. I hypothesized that pictures which have preserved inner speech, but which cannot be orally named pre-therapy, will be more likely to be orally named post-therapy, in comparison to pictures that did not have inner speech pre-therapy. National Institute on Disability, Independent Living, and Rehabilitation Research (NIDILRR) funding enabled us to empirically evaluate this hypothesis. In the currently collected sample (N=15; final goal to collect N=20), we confirmed that preserved inner speech at baseline significantly predicted post-treatment oral naming accuracy for those items. Further, we found that inner speech was a better predictor of post-treatment naming accuracy than aphasia severity. These preliminary results suggest that preserved inner speech is a potentially powerful predictor for identifying which items might best be relearned with lexical therapy.

In the second approach, thanks to NIDILRR funding, my lab characterizes how often, in what situations, and for what reasons individuals with aphasia experience and use inner speech in daily life. We used experience sampling, thought listing, surveys, and interviews across three weeks and 33 total time-points to dynamically evaluate the experience of inner speech in 24 individuals with aphasia (Alexander, Hetrick & Stark, 2024). We had low attrition (8%) and high compliance (96%), suggesting that the multiple timepoint study was feasible. We found that participants experienced inner speech in most sampled instances. When asked to reflect about their inner speech content, functions and activities during the week, common themes were when remembering, to plan, and to motivate oneself. We didn’t identify a significant relationship between aphasia severity and inner speech but did identify that people with probable anosognosia (lack of insight about their aphasia) had significantly fewer experiences of inner speech across experience sampling. These findings led us to the conclusion that adults with aphasia, no matter the severity, experience inner speech often and use inner speech to explore shared, common themes (e.g., to plan), but that a lack of insight into aphasia hampers the experience of inner speech. We also identified that our sample of people with aphasia used inner speech to explore themes that were not as commonly identified in studies involving young adults, such as talking to themselves about health. Our 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 extent to which inner speech themes are unique to aphasia.

We have also published a perspective on investigating inner speech via interdisciplinary approaches, in European Journal of Neuroscience (preprint: https://osf.io/athr9). 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.


Resources for the above projects can be found:


Multimedia presentations on inner speech from our lab

Dr. Stark discusses our inner speech work through an invited presentation at the Center for Research Excellence (CRE) in Australia:

Funding

Thank you to the following for supporting this research!

Further reading from outside the lab

Highly encourage you to read more on inner speech from:

  • Mackenzie Fama

  • Alain Morin & Famira Racy

  • Thomas Brinthaupt

  • Russell Hurlburt

  • Sharon Geva

  • Peter Langland-Hassan

  • Ben Alderson-Day & Charles Fernyhough

  • Lev Vygotsky

  • Peter Carruthers