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1.  Temporal stability and representational distinctiveness: Key functions of orthographic working memory 
Cognitive neuropsychology  2012;28(5):338-362.
A primary goal of working memory research has been to understand the mechanisms that permit working memory systems to effectively maintain the identity and order of the elements held in memory for sufficient time as to allow for their selection and transfer to subsequent processing stages. Based on the performance of two individuals with acquired dysgraphia affecting orthographic WM (the graphemic buffer) we present evidence of two distinct and dissociable functions of orthographic WM. One function is responsible for maintaining the temporal stability of letters held in orthographic WM, while the other is responsible for maintaining their representational distinctiveness. The failure to maintain temporal stability and representational distinctiveness give rise, respectively, to decay and interference effects that manifest themselves in distinctive error patterns, including distinct serial position effects. The findings we report have implications beyond our understanding of orthographic WM, as the need to maintain temporal stability and representational distinctiveness in WM is common across cognitive domains.
PMCID: PMC3427759  PMID: 22248210
working memory; spelling; dysgraphia; orthographic representations
2.  Underlying Cause(s) of Letter Perseveration Errors 
Neuropsychologia  2011;50(2):305-318.
Perseverations, the inappropriate intrusion of elements from a previous response into a current response, are commonly observed in individuals with acquired deficits. This study specifically investigates the contribution of failure-to activate and failure-to-inhibit deficit(s) in the generation of letter perseveration errors in acquired dysgraphia. We provide evidence from the performance 12 dysgraphic individuals indicating that a failure to activate graphemes for a target word gives rise to letter perseveration errors. In addition, we also provide evidence that, in some individuals, a failure-to-inhibit deficit may also contribute to the production of perseveration errors.
PMCID: PMC3259193  PMID: 22178232
letter perseveration errors; dysgraphia; spelling; inhibition
3.  Representation of Letter Position in Spelling: Evidence from Acquired Dysgraphia 
Cognition  2010;115(3):466-490.
The graphemic representations that underlie spelling performance must encode not only the identities of the letters in a word, but also the positions of the letters. This study investigates how letter position information is represented. We present evidence from two dysgraphic individuals, CM and LSS, who perseverate letters when spelling: that is, letters from previous spelling responses intrude into subsequent responses. The perseverated letters appear more often than expected by chance in the same position in the previous and subsequent responses. We used these errors to address the question of how letter position is represented in spelling. In a series of analyses we determined how often the perseveration errors produced maintain position as defined by a number of alternative theories of letter position encoding proposed in the literature. The analyses provide strong evidence that the grapheme representations used in spelling encode letter position such that position is represented in a graded manner based on distance from both edges of the word.
PMCID: PMC2953246  PMID: 20378104
letter position coding; dysgraphia; spelling; letter perseveration errors; orthographic processing

Results 1-3 (3)