“I know it but I can’t say it”: Clarifying the subjective experience of inner speech in aphasia

• ¹ Georgetown University, United States
• ² MedStar National Rehabilitation Hospital, Research Division, United States

Nearly all individuals with aphasia suffer from anomia. Anecdotally, many individuals with aphasia report that impairments in out loud speech are a poor reflection of their inner speech abilities, often making comments such as, “I know it but I can’t say it.” While there is some research on inner speech in aphasia, no studies to date have investigated exactly what individuals mean when reporting this feeling and whether their intended message may have clinical relevance in diagnosis and treatment of anomia. We hypothesized that people with aphasia can distinguish between at least two discrete internal experiences of anomia, including the feeling of recognizing an object or concept but failing to find its name (“I know what it is in my head”) and the feeling of finding the name and saying it correctly in one’s head but not out loud (“I can say it in my head” i.e., successful inner speech). Furthermore, we hypothesize these to be distinct from the sense of knowing a word without being able to call it to mind, i.e., tip-of-the-tongue. A structured questionnaire was administered to individuals with aphasia by a speech-language pathologist using gestural, pictorial, and written support to help them describe more precisely their internal perceptions about word-finding. It begins with “Do you ever know what you want to say but you can’t say it?” followed by opportunity for open-ended description. The investigator then describes the different perceptions reflected by our hypothesis, i.e., knowing it in one’s head vs. successful inner speech (sIS) vs. tip-of-the-tongue (ToT). We ask subjects how frequently they perceive each of these distinct experiences of anomia on a scale of 0 (never) to 4 (almost always). Subjects (N=18) are adults with chronic aphasia resulting from unilateral stroke. To date, 100% of subjects across a wide range of aphasia severity and subtype have endorsed the general phenomenon, “I know it but I can’t say it.” Of these, 82% endorse the specific experience of sIS. Based on self-report data, the frequency of sIS was correlated with the frequency of ToT but was not related to reported frequency of “knowing it.” Additionally, preliminary voxel-based lesion-symptom mapping suggests that the reported frequency of sIS is associated with different lesion locations than the reported frequency of simply “knowing it” in one’s head. Overall, we have demonstrated that individuals with aphasia can describe a perceived mismatch between their inner and out loud speech. Their frequency ratings suggest that they can distinguish between different specific internal experiences of anomia, when given the opportunity to do so. These results, along with preliminary lesion-symptom mapping, further suggest that sIS shares characteristics with ToT and that both are discrete from simply recognizing an object or concept. We suggest that this difference reflects a reliance of both sIS and ToT on some level of phonological access, whereas the perception of “knowing it” relies only on semantic access. Continuing to explore subjective experiences of anomia has significant implications for future research, potentially improving our understanding and treatment of this pervasive deficit.