Exploratory examination of lexical and neuroanatomic correlates of neglect dyslexia

Abstract

Objective: This study examined lexical and neuroanatomic correlates of reading errors in individuals with spatial neglect, defined as a failure to respond to stimuli in the side of space opposite a brain lesion, causing functional disability.

Method: One-hundred and ten participants with left spatial neglect after right-hemisphere stroke read aloud a list of 36 words. Reading errors were scored as "contralesional" (error in the left half of the word) or as "other." The influence of lexical processing on neglect dyslexia was studied with a stepwise regression using word frequency, orthographic neighborhood (number of same length neighbors that differ by 1 letter), bigram and trigram counts (number of words with the same 2- and 3-letter combinations), length, concreteness, and imageability as predictors. MRI/CT images of 92 patients were studied in a voxelwise lesion-symptom analysis (VLSM).

Results: Longer length and more trigram neighbors increased, while higher concreteness reduced, the rate of contralesional errors. VLSM revealed lesions in the inferior temporal sulcus, middle temporal and angular gyri, precuneus, temporal pole, and temporo-parietal white matter associated with the rate of contralesional errors.

Conclusions: Orthographic competitors may decrease word salience, while semantic concreteness may help constrain the selection of available word options when it is based on degraded information from the left side of the word. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Trial registration: ClinicalTrials.gov NCT00990353 NCT00350012 NCT00989430.

Figures

Figure 1.

Lesion coverage map. Color bar represents lesion overlap among participants (1 – single participant, 55 - 55 participants with lesion in the area). Image in neurological convention.

Figure 2.

VLSM results. A). Lesions associated with higher contralesional reading errors, controlling for rate of other reading errors and log lesion volume. B). Lesions associated with higher other error rate, controlling for the rate of contralesional reading errors and log lesion volume. T map with voxelwise threshold of p < 0.005. Images in neurological convention.

Figure 3.

Bivariate correlations of word properties and reading errors. Correlations not significant at p

Figure 4.

Item-wise multiple regression plot: Increased word length and trigram count amplify contralesional reading errors. Three-dimensional plane is superimposed on mean-centered regression coefficients to facilitate visualization.

Figure 5.

Tentative neurocognitive model of visuospatial and linguistic processing during single word reading. See Cohen et al., (2003) for a similar model. Contralateral hemisphere processes each half of the centrally presented word through a cascade of activation in the visual areas. Activation of bigrams and trigrams (2- and 3-letter clusters) is modulated by inhibition form orthographic competitors. Bigram, trigram, and word form information is processed in the ventral occipitotemporal cortex up to the level of the left Visual Word Form Area (VWFA). For word segments on the left, information is relayed to the left VWFA through interhemispheric connections via the corpus callosum. VWFA projects to brain structures involved in phonological and semantic processing. Thus, reading arises as an interactive activation of orthographic, phonological and semantic representations in the left hemisphere. The right hemisphere homologue of the VWFA supports abstract letter identification and higher order association areas in the right hemisphere may support semantic analysis. Visuospatial processing interacts with word recognition at each processing level. Arrow weight and outline represents the relative role of a given input in the reading process. (STG – superior temporal gyrus; ITG – inferior temporal gyrus; MTG – middle temporal gyrus; AG – angular gyrus, TP – temporal pole; V1-V4 – primary visual and visual association areas).