Does semantic impairment explain surface dyslexia? VLSM evidence for a double dissociation between regularization errors in reading and semantic errors in picture naming
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1
Medical College of Wisconsin, Neurology, United States
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2
Rosalind Franklin University of Medicine and Science, United States
The correlation between semantic deficits and exception word regularization errors ("surface dyslexia") in semantic dementia has been taken as strong evidence for involvement of semantic codes in exception word pronunciation. Rare cases with semantic deficits but no exception word reading deficit have been explained as due to individual differences in reading strategy, but this account is hotly debated. Semantic dementia is a diffuse process that always includes semantic impairment, making lesion localization difficult and independent assessment of semantic deficits and reading errors impossible. We addressed this problem using voxel-based lesion symptom mapping in 38 patients with left hemisphere stroke. Patients were all right-handed, native English speakers and at least 6 months from stroke onset. Patients performed an oral reading task that included 80 exception words (words with inconsistent orthographic-phonologic correspondence, e.g., pint, plaid, glove). Regularization errors were defined as plausible but incorrect pronunciations based on application of spelling-sound correspondence rules (e.g., 'plaid' pronounced as "played"). Two additional tests examined explicit semantic knowledge and retrieval. The first measured semantic substitution errors during naming of 80 standard line drawings of objects. This error type is generally presumed to arise at the level of concept selection. The second test (semantic matching) required patients to match a printed sample word (e.g., bus) with one of two alternative choice words (e.g., car, taxi) on the basis of greater similarity of meaning. Lesions were labeled on high-resolution T1 MRI volumes using a semi-automated segmentation method, followed by diffeomorphic registration to a template. VLSM used an ANCOVA approach to remove variance due to age, education, and total lesion volume.
Regularization errors during reading were correlated with damage in the posterior half of the middle temporal gyrus and adjacent posterior inferior temporal gyrus (blue in figure 1). In contrast, semantic errors during picture naming (red and pink in figure 1) and impaired performance on the semantic matching task (yellow and pink in figure 1) were correlated with more anterior temporal lobe damage and with inferior frontal gyrus involvement. There was substantial overlap between lesion correlates for the two explicit semantic tasks (pink in figure 1), but none between these areas and those correlated with regularization errors.
This double dissociation is difficult to accommodate in terms of a common impairment underlying semantic deficits and regularization errors. Lesions in relatively anterior temporal regions appear to produce semantic deficits but not regularization errors, whereas more posterior temporal lesions produce regularization errors but not explicit semantic errors. One possibility is that this posterior temporal region stores whole word representations that do not include semantic information. Alternatively, these representations may include highly abstract and word-specific semantic information useful for computing phonology but not for more complex semantic tasks.
Acknowledgements
Funding sources: AHA grant 13PRE16510003, NIH grants: RO1NS033576, RO1DC003681, RO3NS054958
Keywords:
VLSM,
Aphasia,
surface dyslexia,
semantics,
paraphasias
Conference:
Academy of Aphasia -- 52nd Annual Meeting, Miami, FL, United States, 5 Oct - 7 Oct, 2014.
Presentation Type:
Platform or poster presentation
Topic:
Student award eligible
Citation:
Pillay
S,
Humphries
C,
Stengel
B,
Book
D,
Rozman
M and
Binder
JR
(2014). Does semantic impairment explain surface dyslexia? VLSM evidence for a double dissociation between regularization errors in reading and semantic errors in picture naming.
Front. Psychol.
Conference Abstract:
Academy of Aphasia -- 52nd Annual Meeting.
doi: 10.3389/conf.fpsyg.2014.64.00084
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Received:
30 Apr 2014;
Published Online:
04 Aug 2014.
*
Correspondence:
Mrs. Sara Pillay, Medical College of Wisconsin, Neurology, Milwaukee, WI, 53226, United States, sapillay@mcw.edu