The analysis of perseverations in acquired dysgraphia reveals the internal structure of orthographic representations

Abstract

At a minimum, our long-term memory representations of word spellings consist of ordered strings of single letter identities. While letter identity and position must certainly be represented, it is by no means obvious that this is the only information that is included in orthographic representations, nor that representations necessarily have a one-dimensional “flat” structure. Evidence favours the alternative hypothesis that orthographic representations, much like phonological ones, are internally rich, complex multidimensional structures, though many questions remain regarding the precise nature of the internal complexity of orthographic representations. In this investigation, we test competing accounts of the internal structure of orthographic representations by analysing the perseveration errors produced by an individual with acquired dysgraphia, L.S.S. The analysis of perseveration errors provides a novel and powerful method for investigating the question of the independence of different representational components. The results provide clear support for the hypothesis that letter quantity and syllabic role information are associated with, but separable from, letter identity information. Furthermore, the results indicate that digraphs—letter pairs associated with a single phoneme (e.g., the SH in FISH)—are units of orthographic representation. These results contribute substantially to the further development of the multidimensional hypothesis, providing both new and converging evidence regarding the nature of the internal complexity of orthographic representations.

Keywords:

• Perseveration
• Spelling
• Orthographic representation.

Notes

¹ Elsewhere in the literature, the term grapheme has been used to describe any single letter or letter group that corresponds to a phoneme (B and SH are both graphemes, as they each map to a single phoneme, /b/ and /∫/ respectively). One of the goals of this paper is to examine whether multiletter units like SH have a unitary representation at a level of abstract letter identity. We therefore simply refer to the units at this level of representation as graphemes and consider the additional hypothesis that there are graphemes composed of multiple letters.

² In Figure 1, all graphemes are marked with either a [SGL] or a [DBL] in the grapheme quantity dimension. Alternatively, it is possible that [DBL] is marked in the grapheme quantity dimension, and [SGL] is the unmarked default quantity.

³ These analyses are carried out over the identical corpus of spelling trials for L.S.S. described in Fischer-Baum et al. (2010). However, we constrained the analysis here to the perseveration of only single consonant intrusions—leaving out vowel intrusions and multiletter intrusions—as these results will serve as an appropriate comparison for the later analyses reported in this investigation.

⁴ Results similar to those reported in this paper were obtained when we allowed control responses to be drawn from the entire corpus of L.S.S.'s spelling errors. However, we believe constraining the control responses to the same testing session is a more conservative analysis. Consider a testing day in which L.S.S. (for whatever reason) had produced (for whatever reason) a far larger number of Fs than usual. If control responses are taken only from that testing day, many of the control responses would contain the letter F. If the control responses are taken from the entire corpus, fewer of the control responses would contain the letter F. Therefore, for a single perseveration-source pair involving an F that was produced during the “F-intensive” session, an analysis that included control responses from the entire corpus might overestimate the probability that it was a true perseveration.

⁵ It may be possible to explain the error by assuming that what perseverates between one response and the next is the “fact” that there is a single grapheme associated with two positions, separate from information about either identity or the position of that double. However, if information about the fact that a grapheme is doubled is represented separately from both identity and position information, it is unclear how this is substantively different from an account that assumes separate dimensions of quantity, position, and identity information.

⁶ Unlike the other analyses reported here, we restricted our window of perseveration to a single preceding trial (E−1) rather than the two immediately preceding trials. Expanding the analysis to a larger window reduced the power of our analysis as it was very likely that one of two randomly chosen responses would contain word-initial onsets or word-final codas, increasing chance proportions to near ceiling levels. By limiting our window of perseveration to a single preceding trial, we lower the probability of observing word-onsets and word-codas in the perseveration window by chance. This more limited analysis allows us to evaluate whether word-onsets and word-codas appear in previous responses more than would be expected by chance without concerns about ceiling effects. Nonetheless, it is worth noting that when the larger perseveration window was used, the result approached significance (p < .1).

⁷ We restricted intrusions to those that appeared in the same syllable because of the possibility that pairs of consonants that are pronounced with a single phoneme when they appear in the same syllable (e.g., the MB in LAMB) may be pronounced with two phonemes when the same letter pair crosses a syllable boundary (e.g., the MB in AM.BER), creating some ambiguity as to whether or not they would be represented as digraphs by the orthographic system.

⁸ Consonant clusters that could either be digraphs or not depending on the word (e.g., SC in SCOUT versus SCIENCE) were excluded from the analysis. The set of possible consonant clusters was: {bl; br; cl; cr; ct; dr; fr; ft; gl; gr; kl; kr; lb; ld; lg; lk; lp; lt; mp; nd; nk; nt; pl; pr; pt; rb; rd; rf; rg; rk; rl; rm; rn; rp; rt; sk; sl; sm; sn; sp; st; sw; tr; wn}. The set of possible consonant digraphs was: {ch; ck; dg; gh; gn; kn; mb; mn; ng; ph; ps; sh; th; wh; wr}.