Post-lexical representations and processes in writing: Evidence from peripheral dysgraphia
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1
Johns Hopkins University, Cognitive Science Department, United States
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2
Macquarie University, Cognitive Science Department, Australia
Multiple levels of representation are implicated in writing a word (Fig. 1A). According to most theorists, the word’s spelling is first activated as a sequence of abstract letter identities. These abstract representations activate effector-independent graphic motor plans, which represent the writing movements for specific letter shapes (e.g., lower-case print a) in a form not tied to a particular effector (e.g., right or left hand). The graphic motor plans in turn activate effector-specific motor programs, which mediate the execution of writing movements with the chosen effector.
We report findings from NGN, a 77-year-old man with a left ventro-medial lesion resulting from stroke. NGN is intact in spelling words aloud (92% correct), yet severely impaired in writing the same words (62% correct, p < .001). NGN is also impaired in writing pseudowords, single letters, and letter strings. Further, he is impaired in writing with the left or right hand, and with eyes open or closed. NGN’s errors are predominantly letter substitutions, but also include occasional malformed letters (Fig. 1B). NGN shows no signs of apraxia, and is intact in copying shapes and letters. Taken together, these results indicate a deficit at the level of effector-independent graphic motor plans.
In writing to dictation tasks NGN wrote 6463 words and 1444 single letters on a graphics tablet. We explore three phenomena apparent in his performance. First, most incorrect letters shared writing strokes with the corresponding target letters (e.g., R written as B). Second, the dynamics of the writing process were significantly different for correct and incorrect letters: Letters written in error (e.g., the A in AUMBER; Fig. 1B) were produced with lower stroke velocities and more hesitations than the same letters produced as correct responses (e.g., the A in ANSWER). Furthermore, stroke direction and sequencing were often different for incorrect letters than for the same letters written as correct responses (Fig. 1C). Third, NGN’s error rate was much higher for the first letter in a word than for subsequent letters (Fig. 1D). This serial position effect was not a manifestation of left neglect.
These phenomena speak to cognitive mechanisms in normal and impaired writing. We propose that graphic motor plans are componential, separately representing the location, direction, and ordering of strokes; and consequently, that activation or maintenance in working memory may fail for one or more specific components of a motor plan. For NGN, we suggest, degraded graphic motor plans often stall the writing process, and efforts to complete the letter result in malformed characters or, more often, well-formed but erroneous letters produced with unusual stroke patterns and temporal dynamics.
In light of NGN’s serial position effect (Fig. 1D) we propose further that during the writing of a word, graphic motor plans for multiple positions in the word are activated concurrently and held in a working memory. NGN, we suggest, suffers from a position-specific impairment of the graphic-plan working memory, such that activation or maintenance of graphic motor plans is more severely impaired for the first position in a word than for subsequent positions.
Keywords:
Writing,
dysgraphia,
Peripheral dysgraphia,
spelling,
cognitive neuropsychology
Conference:
54th Annual Academy of Aphasia Meeting, Llandudno, United Kingdom, 16 Oct - 18 Oct, 2016.
Presentation Type:
Platform Sessions
Topic:
Academy of Aphasia
Citation:
Mccloskey
M,
Schubert
T and
Reilhac
C
(2016). Post-lexical representations and processes in writing: Evidence from peripheral dysgraphia.
Front. Psychol.
Conference Abstract:
54th Annual Academy of Aphasia Meeting.
doi: 10.3389/conf.fpsyg.2016.68.00055
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Received:
26 Apr 2016;
Published Online:
15 Aug 2016.
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Correspondence:
Dr. Michael Mccloskey, Johns Hopkins University, Cognitive Science Department, Baltimore, United States, michael.mccloskey@jhu.edu