The Subjective Experience of Inner Speech in Aphasia Is a Meaningful Reflection of Lexical Retrieval

Abstract

Purpose: Individuals with aphasia often report that they feel able to say words in their heads, regardless of speech output ability. Here, we examine whether these subjective reports of successful "inner speech" (IS) are meaningful and test the hypothesis that they reflect lexical retrieval. Method: Participants were 53 individuals with chronic aphasia. During silent picture naming, participants reported whether or not they could say the name of each item inside their heads. Using the same items, they also completed 3 picture-based tasks that required phonological retrieval and 3 matched auditory tasks that did not. We compared participants' performance on these tasks for items they reported being able to say internally versus those they reported being unable to say internally. Then, we examined the relationship of psycholinguistic word features to selfreported IS and spoken naming accuracy. Results: Twenty-six participants reported successful IS on nearly all items, so they could not be included in the item-level analyses. These individuals performed correspondingly better than the remaining participants on tasks requiring phonological retrieval, but not on most other language measures. In the remaining group (n = 27), IS reports related item-wise to performance on tasks requiring phonological retrieval, but not to matched control tasks. Additionally, IS reports were related to 3 word characteristics associated with lexical retrieval, but not to articulatory complexity; spoken naming accuracy related to all 4 word characteristics. Six participants demonstrated evidence of unreliable IS reporting; compared with the group, they also detected fewer errors in their spoken responses and showed more severe language impairments overall. Conclusions: Self-reported IS is meaningful in many individuals with aphasia and reflects lexical phonological retrieval. These findings have potential implications for treatment planning in aphasia and for our understanding of IS in the general population. A phasia is a language disorder, acquired through stroke or other brain injury, that typically has chronic effects and a significant negative impact on long-term quality of life (Berthier, 2005; Engelter et al., 2006; Hilari et al., 2010). The specific language difficulties associated with aphasia can vary from person to person, but a relatively universal deficit is anomia, an impairment of naming and word-finding (Laine & Martin, 2006; Maher & Raymer, 2004). Here, we are interested in a common clinical phenomenon in which some individuals with aphasia and anomia report that they can say words in their head that they cannot say out loud. This anecdotal sense of "inner speech" (IS) is supported by some objective prior work suggesting that IS can exceed overt speech abilities in people with aphasia (Fama, Hayward, Snider, Friedman, & Turkeltaub,

Self-reported inner speech relates to phonological retrieval ability in people with aphasia

“…We found significant relationships between item-level reports of successful IS during silent picturenaming and accuracy/error type on a spoken naming task in a small group of individuals with aphasia (Hayward, 2016;Hayward et al, 2016). Using similar methods, we then replicated these findings in a larger participant group, again showing that self-reported IS is closely related to lexical retrieval (Fama et al, 2019). These same studies also revealed preliminary evidence that IS does not relate to post-lexical output processing.…”

“…These same studies also revealed preliminary evidence that IS does not relate to post-lexical output processing. Self-reported IS related to word features primarily associated with retrieval, but did not relate to the articulatory complexity of words (Fama et al, 2019;Hayward, 2016). In a separate line of research using an interview-based approach, we found that the experience of successful IS in the specific context of anomia (where successful IS is followed by a failure of spoken output) relates to phonological output processing and to lesions in left ventral sensorimotor cortex (Fama, Hayward, Snider, Friedman, & Turkeltaub, 2017).…”

“…The goal of this study was to clarify individual differences in the self-reported experience of successful inner speech (successful IS) in aphasia. Building on the findings from prior work (Fama et al, 2019(Fama et al, , 2017, we examined the relationship between the subjective experience of IS and task-level performance on objective measures of different aspects of the mental process of naming. We found that the frequency of successful IS reported by an individual relates to their phonological retrieval ability and not to their speech production ability.…”

“…While these previous studies have provided promising evidence for our hypotheses, the scope of the conclusions drawn have been relatively limited, due to small number of participants (Hayward, 2016;Hayward et al, 2016), large proportion of participants excluded from main analysis (Fama et al, 2019), or examination of successful IS only in the specific context where it precedes anomia (Fama et al, 2017). In the current study, we approached the study of self-reported IS at the level of overall task performance, which allowed us to examine relationships between the experience of successful IS during silent picture naming and both lexical retrieval and speech production ability.…”

“…All tests were normed in healthy, older adults and any specific items or trials missed by more than 25% of participants in the norming sample were removed from analysis. For a complete description of the stimuli used for this study, including psycholinguistic features as well as sources of picture stimuli, please see Fama et al (2019).…”