Table 1.

Studies on inner speech (IS) in aphasia.

Paper	Participants (N; aphasia subtypes)	Approach to studying IS	Methods	Results and outcomes
Goodglass et al. (1976)*	N = 42 Various	Mixed (subjective reports of tip-of-the-tongue, ToT)	• Participants completed a picture-naming task. For incorrect trials, participants were asked (a) whether they had an idea of the word (ToT), (b) to identify the number of syllables and the first letter, and (c) to select the word from multiple choices.	• Individuals with Broca's and conduction aphasia reported ToT > 50% of the time and were able to demonstrate some knowledge of words they were unable to say aloud (via syllable counting and first letter identification). • Individuals with Wernicke's aphasia reported high levels of ToT but low levels of phonological knowledge. • Individuals with anomic aphasia rarely reported ToT.
Feinberg et al. (1986)	N = 5 Conduction	Objective	• IS tasks = rhyme and homophone judgments (2AFC) and word length comparisons, all based on pictures (requiring word retrieval).	• 4/5 patients were able to perform well on all three IS-based tasks, despite poor overt picture naming. • Conclusion: “Four patients had access to the phonological representation of words at a higher level than their verbal production indicated” (Feinberg et al., 1986).
Oomen et al. (2001)*	N = 11 Broca's	N/A (self-monitoring)	• Participants completed speech production tasks under normal conditions and with auditory masking present, in order to compare monitoring ability.	• Results show that individuals with Broca's aphasia have more preserved error monitoring in the presence of white noise, when compared to age-matched controls (N = 11). • Authors conclude that individuals with Broca's aphasia primarily use pre-articulatory monitoring to detect errors.
Geva, Bennett, et al. (2011)	N = 29 Various	Objective	• IS tasks = Y/N rhyme judgment (real words) and homophone judgment (real words and pseudowords), all performed on written words (adapted from the PALPA). • IS task performance was compared to oral reading, spoken sentence comprehension, and repetition.	• Patients as a group performed worse than age-matched controls (N = 27) on all three IS tasks. • Some patients showed dissociation between inner and overt speech (IS tasks vs. oral reading), in both directions (i.e., inner > overt and inner < overt). • Preserved inner speech relative to overt speech is attributed either to apraxia or to impairments in translating the phonological code into articulatory code.
Geva, Jones, et al. (2011)	N = 17 Various	Objective	• Behavioral = same as above, except for the pseudoword homophone judgment task. • Patients underwent structural MRI scanning for the purposes of voxel-based lesion–symptom mapping (VLSM).	• VLSM showed that performance on the IS tasks was associated with lesions to areas in the left inferior frontal gyrus, pre- and postcentral gyrus, anterior supramarginal gyrus, and adjacent white matter.
Langland-Hassan et al. (2015)	N = 11 Various	Objective	• IS task = silent rhyme judgment task based on pictures (requiring word retrieval). • Patients also completed the WAB-R and portions of the CLQT.	• Patients performed worse than age-matched controls (N = 12) on the silent rhyme judgment task, despite relatively intact ability to perform an auditory rhyme judgment task. • No correlation between IS task performance and confrontation or generative naming tasks.
Hayward et al. (2016)	N = 2 Both fluent	Mixed	• IS task = self-report during silent picture naming. • Participants also completed overt naming and later participated in a paired-associate naming treatment on a subset of unsuccessful items from the naming task.	• At the item level, self-reported successful IS predicted success of spoken naming as well as the likelihood of phonological errors in cases where naming failed. • During naming treatment, participants successfully learned more words that had been reported as successful vs. unsuccessful IS on the IS task.
Hayward (2016)	N = 6 Various	Mixed	• IS task = same as above. • Self-reported success of IS was analyzed with respect to psycholinguistic variables of the word stimuli.	• Successful vs. unsuccessful IS items differed on frequency and age of acquisition, but not articulatory complexity, triphone probability, phonological neighbors, or length in phonemes or syllables. • Author concluded that IS relates to phonological retrieval and not to output processing.
Stark et al. (2017)	N = 38 Various	Objective	• IS tasks = Y/N homophone and rhyme judgment, both performed on written words (stimuli taken in part from the PALPA). • Overt speech measured via oral reading. • Participants with preserved IS were divided into groups based on overt speech ability and IS scores were compared to CAT tasks.	• Eight participants showed preserved IS/poor overt speech, i.e., dissociation of inner/overt speech.  • IS rhyme scores related to spoken naming; IS homophone scores related to MLU (picture description). • 21 participants showed preserved IS/good overt speech.  • No significant correlations with CAT tasks, when correcting for multiple comparisons.
Fama et al. (2017)	N = 37 Various	Subjective	• Self-report of the experience of successful IS during anomia (i.e., successful IS but failure to name) based on a structured interview. • Participants also completed an objective language battery and underwent structural MRI scanning for the purposes of multivariate lesion–symptom mapping.	• Successful IS during anomia was subjectively dissociable from other experiences of anomia, e.g., having an idea but not being able to think of the word. • Self-reported experience of IS during anomia in the context of daily life was related to measures of output processing (as predicted), but also to overall severity of language impairments (not predicted). • Multivariate lesion–symptom mapping analysis demonstrated that the experience of successful IS followed by anomia is associated with damage to brain regions supporting speech output.
Fama, Snider, et al. (2019)	N = 53; N = 27 included in all analyses Various	Mixed	• IS task = self-report during silent picture naming (divided across 2 days). • Participants also completed three picture-based tasks requiring word retrieval (spoken naming, first letter identification, syllable counting), as well as three matched auditory tasks (repetition instead of naming), all using the same stimuli.	• Overall levels of self-reported successful IS were stable across days in most participants. • Participants performed better on the picture-based tasks for words that were reported as successful vs. unsuccessful IS (analysis performed at the item level). • Authors concluded that self-reported IS is a meaningful reflection of lexical retrieval.
Fama, Henderson, et al. (2019)	N = 53 Various	Mixed	• IS task = self-report during silent picture naming. • Participants also completed tasks relying heavily on word retrieval (e.g., picture-based rhyme judgment, controlling for performance on a matched auditory version) and tasks relying heavily on output processing (e.g., oral reading and repetition).	• Overall self-reported IS related to performance on retrieval-based tasks, but not to tasks relying on output processing (analysis performed at the task level). • In a hierarchical regression analysis, self-reported IS was a better predictor of spoken naming than the objective, retrieval-based tasks. • Successful IS related to overall levels of phonological errors on a spoken naming task (not semantic errors).

Note. The table shows the number of participants with aphasia (if controls were included, they are not listed here) and aphasia subtypes, general approach to studying inner speech (subjective, objective, or mixed subjective/objective), methods, and relevant outcomes. Studies marked with an asterisk (*) are not framed by the researchers as investigations of inner speech, per se; Goodglass et al. (1976) studied “tip-of-the-tongue,” and Oomen et al. (2001) studied pre- and postarticulatory monitoring. 2AFC = Two-alternative forced choice; PALPA = Psycholinguistic Assessments of Language Processing in Aphasia; WAB-R = Western Aphasia Battery–Revised; CLQT = Cognitive Linguistic Quick Test; MLU = mean length of utterance; CAT = Comprehensive Aphasia Test.