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

Abstract

Purpose Typical language users can engage in a lively internal monologue for introspection and task performance, but what is the nature of inner speech among individuals with aphasia? Studying the phenomenon of inner speech in this population has the potential to further our understanding of inner speech more generally, help clarify the subjective experience of those with aphasia, and inform clinical practice. In this scoping review, we describe and synthesize the existing literature on inner speech in aphasia. Method Studies examining inner speech in aphasia were located through electronic databases and citation searches. Across the various studies, methods include both subjective approaches (i.e., asking individuals with aphasia about the integrity of their inner speech) and objective approaches (i.e., administering objective language tests as proxy measures for inner speech ability). The findings of relevant studies are summarized. Results Although definitions of inner speech vary across research groups, studies using both subjective and objective methods have established findings showing that inner speech can be preserved relative to spoken language in individuals with aphasia, particularly among those with relatively intact word retrieval and difficulty primarily at the level of speech output processing. Approaches that combine self-report with objective measures have demonstrated that individuals with aphasia are, on the whole, reliably able to report the integrity of their inner speech. Conclusions The examination of inner speech in individuals with aphasia has potential implications for clinical practice, in that differences in the preservation of inner speech across individuals may help guide clinical decision making around aphasia treatment. Although there are many questions that remain open to further investigation, studying inner speech in this specific population has also contributed to a broader understanding of the mechanisms of inner speech more generally.

Figures

Figure 1.

A model of naming. This model includes the most consistent aspects of various processing models of naming that have been published over the past several decades. The arrow indicating “self-monitoring” is the level at which inner speech arises and becomes available to conscious monitoring by the speaker (figure from Fama, 2018).

Figure 2.

Methods of studying inner speech in aphasia. This figure is a conceptual representation of the mental processes required for the various approaches and the potential biases inherent to each approach. Objective approaches involve asking participants to make phonological judgments (e.g., rhymes, homophones) on either written words (left) or pictures (right). Subjective approaches involve asking participants to provide self-reports of success during a silent picture-naming task. Interview-based methods are not directly represented in the diagram but are subject to the same potential biases as other subjective approaches.