FACILITATING READING IN POSTERIOR CORTICAL ATROPHY

Abstract

Posterior cortical atrophy (PCA) is a neurodegenerative syndrome characterised by progressive visual impairment and parietal and occipital brain atrophy. Most frequently a consequence of underlying Alzheimer's disease (AD) pathology, PCA involves prominent visuoperceptual and visuospatial impairment with relatively spared episodic memory and insight. Reading problems, particularly when reading passages of text, are a common and debilitating early symptom of PCA, occurring as a result of deficits including visual disorientation, visual crowding, and a reduced effective field of vision. This project intends to 1) conduct the first quantitative investigation of passage reading deficits in PCA; 2) maximise reading ability in PCA by manipulating the presentation of text in order to circumvent dementia-related visual deficits. 15 PCA, 6 typical AD and 6 healthy control participants read aloud news articles presented normally or under two reading interventions (single- and double-word). Reading interventions were developed based on the notion that reducing the spatial, perceptual and oculomotor demands of passage reading would support poor reading in PCA. The efficacy of reading interventions was evaluated through reading performance (accuracy, latency and independent ratings of global comprehension), measures of eye tracking (fixations and saccades) and self-rated measures of reading ability (ease and comprehension). PCA patients' mean reading accuracy for normal passage text was 57.2% in contrast to near-ceiling accuracy in typical AD patients (97.5%) and healthy controls (99.4%); spatial aspects of text were the primary determinants of passage reading ability in PCA (see Figure 1). PCA patients made more saccades, more fixations and longer fixations than typical AD patients (p<.05) and healthy controls (p<.005; see Table 1). The interventions led to considerable and consistent gains in PCA patients' reading accuracy (both p<.001). Under the single-word intervention, mean reading accuracy increased from 57.2% to 95.6%. PCA patients' fixations were of increased duration and saccades were of decreased amplitude (both p<.05). Both interventions also resulted in improvements on self-rated measures of reading (ease: both p<.005; comprehension: both p<.005; pleasantness; both p<.05). Findings highlight the contribution of various visual and oculomotor deficits in limiting reading above the single-word level in PCA and provide a basis for developing software-based reading aids. A) Heatmap of PCA accuracy data from a sample passage (mean group accuracy rates: PCA=75%, tAD=98%, controls=100%). Lighter colours indicates the location of words most commonly missed or mis-read, and indicates spatial blases towards worse reading in later paragraph and lines and in the centre of dense, crowded passages of text. B) Order of first forty words read by i) a PCA patient with MMSE score = 13/30; and, ii) a PCA patient with MMSE score = 22/30. Transcripts of the participants' corresponding spoken output are beneath each example (Italicised text). Numbers refer to where words were repeated. Each hyphen (-) in the transcript beneath each example indicates a pause of 3 seconds.