Words don't come easy: On the cerebral specialization of visual word recognition

TY - BOOK

T1 - Words don't come easy

T2 - On the cerebral specialization of visual word recognition

AU - Starrfelt, Randi

PY - 2008

Y1 - 2008

N2 -  This dissertation comprises a brief theoretical review and four empirical studies relating to the question of whether cerebral areas can be specialized for reading. This question has been studied within the broader context of cognitive neuroscience, both in patients with acquired disorders of reading, and with the use of functional imaging techniques. Extant evidence for (and against) cerebral specialization for visual word recognition is briefly reviewed and found inconclusive.                      Study I is a case study of a patient with a very selective alexia and agraphia affecting reading and writing of letters and words but not numbers. This study raised questions of "where" in the cognitive system such a deficit may arise, and whether it can be attributed to a deficit in a system specialized for reading or letter knowledge. The following studies investigated these questions in the visual domain.                      An important account postulates that an area in the mid-fusiform gyrus - The visual word form area - is specialized for reading (in literate adults). Study II is a PET study investigating activity in this area during performance of tasks with pictures and words. This study concludes that there is something special about word processing in this area, but that this may relate to the relative automaticity in the reading process, rather than reflect true cerebral specialization for reading. We suggest that the process of shape integration, which is common to both word and object processing, may explain the pattern of activations found in our and other functional imaging studies of the visual word form area.                       Study III reports a patient (NN) with pure alexia. NN is not impaired in object recognition, but his deficit(s) affects processing speed and visual apprehension span for both letters and digits. Thus, his visual deficits are not specific to alphabetical material. NN is also impaired in the categorization of fragmented drawings, suggesting a subtle deficit in the process of shape integration. We suggest that this subtle deficit can explain why words seem to be reduced to their constituent parts (letters) in pure alexia.                      Study IV reports four patients with mild pure alexia, and shows that they are all impaired in processing of both single letters and digits in the central visual field. Furthermore, all four patients have reduced visual apprehension span for both letters and digits, as well as subtle deficits with pictorial stimuli. This study supports the notion that pure alexia is associated with a general visual deficit that affects other stimuli than letters and words. We suggest that the reduced recognition efficiency in the central part of the visual field observed in our patients is the most important factor contributing to their reading problems.                      In sum, the empirical studies do not support the notion of selectivity for word or letter processing in the visual domain. However, the findings do suggest that reading may be disproportionately affected by damage to more general purpose visual recognition processes.

AB -  This dissertation comprises a brief theoretical review and four empirical studies relating to the question of whether cerebral areas can be specialized for reading. This question has been studied within the broader context of cognitive neuroscience, both in patients with acquired disorders of reading, and with the use of functional imaging techniques. Extant evidence for (and against) cerebral specialization for visual word recognition is briefly reviewed and found inconclusive.                      Study I is a case study of a patient with a very selective alexia and agraphia affecting reading and writing of letters and words but not numbers. This study raised questions of "where" in the cognitive system such a deficit may arise, and whether it can be attributed to a deficit in a system specialized for reading or letter knowledge. The following studies investigated these questions in the visual domain.                      An important account postulates that an area in the mid-fusiform gyrus - The visual word form area - is specialized for reading (in literate adults). Study II is a PET study investigating activity in this area during performance of tasks with pictures and words. This study concludes that there is something special about word processing in this area, but that this may relate to the relative automaticity in the reading process, rather than reflect true cerebral specialization for reading. We suggest that the process of shape integration, which is common to both word and object processing, may explain the pattern of activations found in our and other functional imaging studies of the visual word form area.                       Study III reports a patient (NN) with pure alexia. NN is not impaired in object recognition, but his deficit(s) affects processing speed and visual apprehension span for both letters and digits. Thus, his visual deficits are not specific to alphabetical material. NN is also impaired in the categorization of fragmented drawings, suggesting a subtle deficit in the process of shape integration. We suggest that this subtle deficit can explain why words seem to be reduced to their constituent parts (letters) in pure alexia.                      Study IV reports four patients with mild pure alexia, and shows that they are all impaired in processing of both single letters and digits in the central visual field. Furthermore, all four patients have reduced visual apprehension span for both letters and digits, as well as subtle deficits with pictorial stimuli. This study supports the notion that pure alexia is associated with a general visual deficit that affects other stimuli than letters and words. We suggest that the reduced recognition efficiency in the central part of the visual field observed in our patients is the most important factor contributing to their reading problems.                      In sum, the empirical studies do not support the notion of selectivity for word or letter processing in the visual domain. However, the findings do suggest that reading may be disproportionately affected by damage to more general purpose visual recognition processes.

M3 - Ph.D. thesis

BT - Words don't come easy

PB - Museum Tusculanum

CY - Kbh.

ER -