Subjective experience of inner speech in aphasia: Preliminary behavioral relationships and neural correlates

Abstract

Many individuals with aphasia describe anomia with comments like "I know it but I can't say it." The exact meaning of such phrases is unclear. We hypothesize that at least two discrete experiences exist: the sense of (1) knowing a concept, but failing to find the right word, and (2) saying the correct word internally but not aloud (successful inner speech, sIS). We propose that sIS reflects successful lexical access; subsequent overt anomia indicates post-lexical output deficits. In this pilot study, we probed the subjective experience of anomia in 37 persons with aphasia. Self-reported sIS related to aphasia severity and phonological output deficits. In multivariate lesion-symptom mapping, sIS was associated with dorsal stream lesions, particularly in ventral sensorimotor cortex. These preliminary results suggest that people with aphasia can often provide meaningful insights about their experience of anomia and that reports of sIS relate to specific lesion locations and language deficits.

Keywords: Anomia; Aphasia; Inner speech; Language; Lesion-symptom mapping; Self-report; Stroke.

Figure 1

Simplified model of naming, demonstrating a distinction between access, which is necessary and sufficient for sIS, and output, which is then required for successful aloud naming.

Figure 2

Picture support for the concepts of sIS and IwW. No pictorial support was given for ToT.

Figure 3

sIS and other anomia ratings.

Figure 4

A. Lesion overlay map (N=36). B. SVR-LSM results showing lesion locations associated with higher reports of sIS, IwW, and ToT (p < .01, see figure legend for color representations). C. SVR-LSM results at p < .10 to illustrate the minimal overlap between lesions associated with sIS and IwW. Total lesion volume was controlled in both maps, using the direct lesion volume control method.