![]() The presence of an incongruous homonymous hemianopia in a single patient afforded us the opportunity to investigate the role that right foveal and parafoveal vision play in reading. 11– 13 It is likely that both “bottom-up” (visual) and “top-down” (linguistic and attentional) factors modify reading scanpaths. Some authors have argued that the pattern of each reading scanpath is mainly dictated by the visual characteristics of the text, such as the length of the next word and the distance from one optimal viewing point to the next 8– 10 while others have stressed linguistic factors such as sentential meaning. Therefore, an appreciable proportion of fixation time during text reading is presumably devoted to planning reading saccades. 7 Fixation times during text reading average about 250 ms per word, many times longer than would be expected if the rate limiting step in reading was word recognition. 5įor over a century it has been known that normal subjects can recognise single words as fast as single letters, 6 and more recently it has been discovered that single words can be read with exposure times as short as 50 ms. 1– 4 Thus, word identification and the planning of reading saccades occur in parallel during normal reading. Simultaneously, an implicit spatial attentional window, which extends asymmetrically into right parafoveal vision, serves two purposes, providing preparatory partial word identification as well as assisting the planning of reading saccades to the next viewing point in the sentence. The influence of top-down attentional processes during text reading can be visualised in parafoveal V1 using PET.ĭuring left to right text reading, identification of words is dependent on the high visual acuity afforded by foveal vision extending 1° either side of fixation. Right parafoveal vision is not critically involved in single word identification, but is when planning left to right reading saccades. ![]() Binocular single word reading produced activity in the representation of foveal V1 bilaterally however, text reading with the left eye only was associated with activation in left but not right parafoveal V1, despite there being visual stimuli in both visual fields.Ĭonclusions: The presence of a word length effect (typically associated with pure alexia) can be caused by a macular splitting hemianopia. ![]() The PET data provided evidence of “top-down” processes involved in reading. His eye movement patterns were more orderly when reading text with his left eye, making fewer saccades. A small word length effect was present in his right eye but not his left. Results: The patient was faster at reading single words and text with his left eye compared with his right. Eye movements were recorded while reading three passages of text, and PET data were gathered while the subject performed a variety of reading tasks in the camera. Single word reading speeds were monitored using a “voice-trigger” system. Methods: The patient, a 48 year old right handed male with a macular sparing hemianopia in his left eye and a macular splitting hemianopia in his right eye, performed various reading tasks. Objective: To investigate the role right foveal/parafoveal sparing plays in reading single words, word arrays, and eye movement patterns in a single case with an incongruous hemianopia. ![]()
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