Representation of letter position in spelling: Evidence from acquired dysgraphia

Abstract

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. Keywordsletter position coding; dysgraphia; spelling; letter perseveration errors; orthographic processing Many cognitive functions require the ability to represent and process sequences of items or events. Sequence information is essential, for example, in recalling a telephone number, reasoning about causes and effects, navigating a route through an environment, or producing a sentence. As Karl Lashley pointed out more than 50 years ago in The problem of serial order in behavior (Lashley, 1951), the question of how the brain represents and processes ordered sequences is far from trivial; and this question remains a central concern for research in a variety of cognitive domains (e.g., working memory: Henson, 1998; motor control: Bullock, 2004; reading: Grainger & Whitney, 2004; music performance: Palmer, 2005; spoken language production: Dell, Burger & Svec, 1997).This article addresses the serial order issue in the context of spelling. Spelling a word requires not only information about the identities of the letters in the word, but also information about the ordering of those letters. This ordering information could be encoded in a variety of ways. In the word PENCIL, for example, the letter E could be represented as the second letter in the word, the letter five positions from the end of the word, the letter in the nucleus of the first (orthographic) syllable, or the letter that follows P and precedes N. In each case the E's position * Corresponding author: Department of Cognitive Science, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, Tel: 410-516-7625, Fax: 410-516-8020, fischerbaum@cogsci.jhu.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form....

Shared versus separate processes for letter and digit identification

“…Second, systematic character perseveration errors were apparent in the substitution errors for both letter and digit strings. Using methods described in detail in McCloskey, Macaruso, andRapp (2006), Fischer-Baum, McCloskey, andRapp (2010), and McCloskey, Fischer-Baum, and Schubert (in press), we conducted perseveration analyses separ ately for digit and letter strings. The analyses revealed that far more often than expected by chance (p < .0001 for both letter and digit ana lyses), erroneous digits and letters (e.g., the 5 in the 148479 -» ■ 158479 error, and the D in the FVMXGY -> FDMXGY error) were present in one or both of the two immediately preceding responses.…”

Both-edges representation of letter position in reading

“…From these results, Fischer-Baum et al (2010) argued for both-edges representations of letter position in spelling. According to this scheme, a letter's position is encoded relative to both the beginning and the end of the word, such that the A in CARPET has position representations B + 2 and E-5.…”

“…In the domain of spelling, Fischer-Baum, McCloskey, and Rapp (2010) used letter perseveration errors to contrast position representation schemes. Two participants with acquired dysgraphia (CM and LSS) intruded letters from prior spelling responses into subsequent responses when spelling to dictation.…”

On the time-course of adjacent and non-adjacent transposed-letter priming

“…Location-specific letter representations indicate that a given letter identity is present in the stimulus at a particular location relative to eye fixation, but do not inform about the position of letters in the stimulus. This information is carried by location-invariant sublexical representations in two different ways: by coding for ordered combinations of contiguous and non-contiguous letter sequences (open-bigrams), and by coding for precise position-in-string information using space-letter and letter-space combinations (akin to the both edges coding scheme of Fischer-Baum, McCloskey & Rapp, 2010; Fischer-Baum, Charny, & McCloskey, 2011; see Hannagan & Grainger, 2012, for more details). The first scheme provides positional flexibility (referred to as coarse-grained orthography by Grainger and Ziegler, 2011), while the second provides positional precision in the same way as location-specific letter representations, except that positional information is now stimulus-centered rather than gaze-centered.…”