The word-length effect in acquired alexia, and real and virtual hemianopia

• Published in: Neuropsychologia Vol. 50; no. 5; pp. 841 - 851
• Main Authors: Sheldon, Claire A., Abegg, Mathias, Sekunova, Alla, Barton, Jason J.S.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.04.2012; Elsevier
• Subjects: Adult; Adult and adolescent clinical studies; Alexia; Analysis of Variance; Biological and medical sciences; Brain - pathology; Brain - physiopathology; Control Groups; Correlation; Data processing; Disorders of higher nervous function. Focal brain diseases. Central vestibular syndrome and deafness. Brain stem syndromes; Dyslexia; Dyslexia, Acquired - pathology; Dyslexia, Acquired - physiopathology; Experiments; Eye Movements; Female; Fixation; Fixation, Ocular; Hemianopsia - pathology; Hemianopsia - physiopathology; Humans; Image Processing, Computer-Assisted; Intervention; Language; Magnetic Resonance Imaging; Male; Medical sciences; Middle Aged; Nervous system (semeiology, syndromes); Neurological Impairments; Neurology; Organic mental disorders. Neuropsychology; Patients; Photic Stimulation; Psychology. Psychoanalysis. Psychiatry; Psychopathology. Psychiatry; Reaction Time; Reading; Reading Comprehension; Receptive field; Rehabilitation; Rehabilitation Programs; Saccade; Time Factors (Learning); User-Computer Interface; Vision; visual field; Visual Fields - physiology; Vocabulary; Word; Word Recognition; Saccade; Reading; Alexia; Word; Fixation; Human; Nervous system diseases; Visual fixation; Hemianopsia; Word length; Experimental study; Language disorder; Cerebral disorder; Saccadic eye movement; Communication disorder; Language; Central nervous system disease
• ISSN: 0028-3932; 1873-3514
• DOI: 10.1016/j.neuropsychologia.2012.01.020

► We examined the contribution of homonymous visual field loss to reading speed. ► We simulated hemianopia in healthy subjects with a gaze-contingent paradigm during an eye-tracking experiment. ► In healthy subjects, the 95% upper prediction limits were 51ms/letter with full fields and 161ms/letter with simulated right hemianopia. ► With these criteria, we examined six paradigmatic patients with acquired peripheral alexias. ► In these subjects, our findings clarified the magnitude of the word-length effect that originates from hemianopia alone. A word-length effect is often described in pure alexia, with reading time proportional to the number of letters in a word. Given the frequent association of right hemianopia with pure alexia, it is uncertain whether and how much of the word-length effect may be attributable to the hemifield loss. To isolate the contribution of the visual field defect, we simulated hemianopia in healthy subjects with a gaze-contingent paradigm during an eye-tracking experiment. We found a minimal word-length effect of 14ms/letter for full-field viewing, which increased to 38ms/letter in right hemianopia and to 31ms/letter in left hemianopia. We found a correlation between mean reading time and the slope of the word-length effect in hemianopic conditions. The 95% upper prediction limits for the word-length effect were 51ms/letter in subjects with full visual fields and 161ms/letter with simulated right hemianopia. These limits, which can be considered diagnostic criteria for an alexic word-length effect, were consistent with the reading performance of six patients with diagnoses based independently on perimetric and imaging data: two patients with probable hemianopic dyslexia, and four with alexia and lesions of the left fusiform gyrus, two with and two without hemianopia. Two of these patients also showed reduction of the word-length effect over months, one with and one without a reading rehabilitation program. Our findings clarify the magnitude of the word-length effect that originates from hemianopia alone, and show that the criteria for a word-length effect indicative of alexia differ according to the degree of associated hemifield loss.