Elsevier

Cognition

Volume 115, Issue 3, June 2010, Pages 466-490
Cognition

Representation of letter position in spelling: Evidence from acquired dysgraphia

https://doi.org/10.1016/j.cognition.2010.03.013Get rights and content

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.

Introduction

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, Svec, & Burger, 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 is specified according to a different representational scheme. If we say that the E is the second letter in the word, we implicitly adopt a left-edge based scheme, in which a letter’s position is defined in terms of distance in letters from the left edge of the word. By this positional scheme, P is the first letter, E is the second, and so forth. Alternatively, if we say that E is the letter following P and preceding N, we are using a letter-context scheme, in which a letter’s position is specified with respect to the surrounding letters.

The goal of present study was to identify the scheme for representing letter position in the graphemic representations that underlie spelling performance. Several researchers have offered hypotheses about the representation of letter position in spelling (e.g., Brown and Loosemore, 1994, Caramazza and Hillis, 1990, Glasspool, 1998, Glasspool and Houghton, 2005, Houghton et al., 1994, Houghton and Zorzi, 2003). However, the relevant empirical evidence is sparse, and no studies have directly compared the alternative proposals. In the present study we examine a broad range of positional schemes in light of data from two individuals with acquired dysgraphia, LSS and CM. In spelling tasks LSS and CM made frequent letter perseveration errors, in which letters from prior responses intruded into subsequent responses. We argue that these letter perseveration spelling errors motivate strong conclusions about the representational scheme used for specifying letter position in spelling.

Perseveration errors – both from impaired and unimpaired individuals – have been used in a variety of domains to infer how the positions of elements in a sequence are represented (e.g., Boomer and Laver, 1968, Cohen and Dehaene, 1990, Henson, 1999). In the present study extensive testing of LSS and CM provided large sets of letter perseveration errors that allowed us to contrast alternative hypotheses of letter position representation in spelling. Additional aspects of the participants’ spelling performance localized their perseveration errors to the level of abstract letter representation – what we call the level of graphemic spelling representation. This localization places some constraints on the levels of processing at which the implicated letter position representations may be active.

Patterns of performance in individuals with dysgraphia acquired as a result of neural insult (e.g., stroke) have been used extensively as a basis for conclusions about the cognitive representations and processes that support spelling in the intact brain (e.g., Caramazza and Hillis, 1990, Caramazza and Miceli, 1990, McCloskey et al., 1994, McCloskey et al., 2006, Rapp et al., 1997, Tainturier and Caramazza, 1996, see McCloskey (2003) for discussion). The logic by which impaired performance can be used to draw inferences about normal cognition has been discussed at length elsewhere, and we refer the interested reader to those sources (e.g., Caramazza, 1984, Caramazza, 1986, Caramazza, 1992, Caramazza and Coltheart, 2006, McCloskey, 1993, McCloskey, 2001, McCloskey, 2003, McCloskey and Caramazza, 1988). In accord with this logic we assume that the brain damage suffered by LSS and CM has caused their previously-normal spelling processes to malfunction (leading to perseverations and other errors), but has not resulted in creation of novel representational schemes for specifying letter position. Given this assumption we can use the perseveration errors to draw conclusions about representation of letter position in the normal spelling system. An important advantage of studying impaired performance is that, as in the present study, one can often accumulate large corpora of errors that arise from a single level of representation, and are highly informative about the nature of the representations at that level.

The question of how the position of an element in a sequence is represented is critical for all domains that rely on sequence processing. In the past few years, this question has received a great deal of attention in the domain of reading (e.g., Davis, 1999, Davis and Bowers, 2004, Davis and Bowers, 2006, Grainger et al., 2006, Grainger and van Heuven, 2003, Gomez et al., 2008, Kinoshita and Norris, 2009, Perea and Lupker, 2003, Perea and Lupker, 2004, Schoonbaert and Grainger, 2004, Van Assche and Grainger, 2006, Whitney, 2001). The research on reading provides a source of hypotheses regarding position representation in orthographic processing generally. However, it is important to emphasize that our results and conclusions are specific to spelling. Because we do not know whether reading and spelling use the same scheme for representing letter position (and because we did not study LSS’s or CM’s reading in detail), we make no claims about position representation in reading.

As a framework for subsequent discussion, we begin by sketching a theory of the cognitive mechanisms involved in spelling, and then lay out a variety of hypotheses concerning the encoding of letter position in graphemic spelling representations. Next we offer case histories for CM and LSS, and characterize their spelling deficits. Following this introductory material we present results demonstrating that both participants often perseverate letters from spelling responses into subsequent responses. We then report an extensive series of analyses that use the letter perseveration phenomenon as a tool for probing the representation of letter position in graphemic spelling representations. Finally, we conclude with a brief discussion of issues arising from our results and conclusions.

Section snippets

A cognitive spelling theory

Most of the data we report come from a writing to dictation task, in which a word or nonword is dictated, and the participant produces a written spelling response. Consequently, we describe the cognitive spelling theory in the context of this task (see Miceli and Capasso, 2006, Tainturier and Rapp, 2001).

The theory assumes that when a familiar word (e.g., “table”) is dictated, the corresponding phonological lexeme is activated in a phonological lexicon (see Fig. 1). This lexeme then activates a

Representation of letter position

The letter perseveration errors produced by CM and LSS provide an opportunity to explore how letter position is encoded at the level of graphemic representations. In this article we address two specific questions. First, relative to what reference point (or points) is the position of a letter defined? Second, are letter position representations discrete, such that each position has a representation that is entirely distinct from that of every other position; or are position representations

Case histories and neuropsychological assessments

CM was a right-handed man with a Ph.D. in electrical engineering. He worked as a university professor until suffering a stroke in September 1986 at age 59. LSS was a left-handed man with a Master’s degree in psychology. He worked as a regional sales representative for a health services company until a stroke in July 2003 at age 54. For both participants CT scan showed extensive cortical and subcortical damage in the distribution of the left middle cerebral artery. Both reported excellent

Letter perseveration errors

Most of the spelling errors produced by LSS and CM contained intruded letters – that is, letters that did not appear in the correct spelling of the target word. Letter intrusions may take the form of substitutions or insertions. For example, in the substitution error “head”  HEAT, the T is an intruded letter, as is the I in the insertion error “spend”  SPIEND.

For both participants, intruded letters were often present in one or more of the preceding responses, raising the possibility that at least

Letter position analyses

In this section we present analyses that use CM’s and LSS’s letter perseveration errors as a basis for inferences about the positional scheme used in graphemic spelling representations. Before presenting these analyses, we first need to introduce some terminology. We refer to a response with a perseverated letter as a perseveration response, and the prior response from which the letter was perseverated as the source response. For example, assuming that the R in CM’s error “edge”  ERGE was a

General discussion

The aim of the present study was to identify the cognitive scheme for encoding letter position in the orthographic representations that underlie the ability to spell. We considered more than ten candidate schemes falling into three categories: content-independent, letter context, and syllabic. The candidate schemes also varied regarding whether the postulated position representations were discrete or graded. We evaluated the candidate positional schemes through analyses of letter perseveration

Acknowledgements

This research was supported by NIH Grants NS22201 and DC 006740. We thank Paul Smolensky, Manny Vindiola, Ariel Goldberg, Özge Gürcanlı and members of the JHU CogNeuro Lab for feedback and suggestions, Donna Aliminosa, Tony Pastor, Sumin Lee, Jenna Rowen and Julia Thorn for help with data analysis and testing, as well as two anonymous reviewers for their helpful suggestions. We especially thank LSS and CM for their cheerful participation; working with them was truly a pleasure.

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