Deficient morphological processing in adults with developmental dyslexia: another barrier to efficient word recognition?

Copyright # 2006 John Wiley & Sons, Ltd. DYSLEXIA 13: 110–129 (2007)

Published online 13 March 2006 in Wiley InterScience(www.interscience.wiley.com). DOI: 10.1002/dys.322

& Deficient MorphologicalProcessing in Adults withDevelopmental Dyslexia:Another Barrier to EfficientWord Recognition?Rachel Schiff1,* and Michal Raveh2

1 School of Education and Haddad Center for Research in Dyslexia, Bar Ilan University,Israel2 Psychology Department and the Gonda Brain Research Center, Bar Ilan University, Israel

Research on dyslexia has focused on the phonological level oflinguistic analysis. Here we extend the investigation of the linguisticcompetence of individuals with dyslexia to the morphological levelof linguistic analysis. We examine whether adult Hebrew readerswith dyslexia extract and represent morphemic units similarly tonormal readers. Using the priming paradigm in the word fragmentcompletion task, we measured the magnitude of morphologicalpriming and contrasted this effect with the repetition priming effect.Students with normal reading ability showed the typical repetitionpriming effect. A comparable repetition priming effect was alsofound for the dyslexic group as a whole. However, when thedyslexics were classified into three subtypes according to theirphonological and orthographic decoding skills, repetition primingeffects were significant only for the phonological dyslexia subgroupbut not for the surface or mixed dyslexia subgroups. Furthermore,students with normal reading ability showed strong morphologicalpriming, comparable in strength to the repetition priming effect. Incontrast, the dyslexic readers did not show morphological priming,neither the dyslexia group as a whole, nor any of the subgroups.Our results highlight an additional source for dyslexics’ difficultieswith word recognition which lie at the level of morphologicalprocessing. Copyright # 2006 John Wiley & Sons, Ltd.

Keywords: morphology; priming; reading; adults; developmental dyslexia; subtypes

*Correspondence to: Rachel Schiff, Haddad Center, School of Education, Bar IlanUniversity, Ramat-Gan 52900, Israel. Tel.: +972-3-5318705; fax: +972-3-5351049; e-mail:[email protected]; Contract/grant sponsor: Israel Science Foundation; Contract/grantnumber: 885/04

INTRODUCTION

Developmental dyslexia is the specific functional failure to acquire age-appropriate reading skills by otherwise normally developing childrenwith adequate intelligence and socio-cultural opportunity (Curtin,

Manis, & Seidenberg, 2001; Stanovich, 1988; Vellutino, 1979). Adults withdevelopmental dyslexia typically have major difficulties in phonologicalprocessing (e.g. Adams, 1990; Stanovich, 1991; Vellutino, 1979), showing, forexample, poor performance in non-word repetition (e.g. Snowling, 1981), non-word reading (e.g. Rack, Snowling, & Olson, 1992) and phonological awarenesstasks (e.g. Bradley & Bryant, 1985; Liberman, 1987; Mann, 1991). Consequently, awidely held view is that the core problem in developmental dyslexia involvesinadequate representation and use of phonological information (Lyon, 1995;Mann, 1998; Morris et al., 1998; Shankweiler et al., 1995; Stanovich, 1989; Wagner& Torgesen, 1987).

Orthographic alphabetic systems also represent morphemic as well asphonemic units. Readers’ morphological knowledge may thus also play a rolein their word decoding ability (e.g. Carlisle, 1995; Elbro & Arnbak, 1996; Singson,Mahony, & Mann, 2000). Morphological structure is an especially importantanchor for the reader in ‘deep’ orthographies, such as English and unvocalizedHebrew. The phonological structure of words in these languages is not entirelytransparent and hence word reading entails inconsistent grapheme-to-phonemeconversion (Elbro & Arnbak, 1996). Accuracy and speed of word decoding areaffected by the complexity of the morphological structure, as manifested in thedegree of transparency and productivity (Schiff, 2003; Shimron & Vaknin, 2005).While the relationship between phonology and reading disability has beenextensively researched, much less is known about the relationship betweenmorphological knowledge and reading disability. The major goal of our researchis to extend the investigation of the linguistic competence of dyslexic adults to themorphological level of linguistic analysis.

Studies using a variety of alphabetic writing systems and different readingtasks have illustrated the fundamental effects of morphology on reading (Anglin,1993; Feldman, 1995; Koda, 2000; Leong, 1989; Nagy & Anderson, 1984; Nagy,Anderson, Schommer, Scott, & Stallman, 1989; Schiff, 2003; Tyler & Nagy, 1986).Readers’ ability to reflect upon the meaning of morphemes and their ability toparse and manipulate them, termed ‘morphological awareness’, contribute toreading ability over and above the contribution of phonological awareness (e.g.Singson, Mahony, & Mann, 2000; see Mann, 2000, for review). Moreover, evidencefrom different languages shows that morphological awareness increases inimportance for reading throughout the school years (e.g. Carlisle, 1995, 2000;Mahony, Singson, & Mann, 2000; Shankweiler et al., 1995; Singson et al., 2000) aswell as in Hebrew (Levin, Ravid, & Rapaport, 2001; Ravid & Avidor, 1998; Ravid& Malenky, 2001). Reading vocabulary progressively gathers more multi-morphemic words in later school years (Mann, 2000) and readers may use themeaning of morphemes to analyse the meaning of complex words, thusachieving greater text comprehension. If morphological structure is significantin the acquisition of reading in Indo-European languages like English, it shouldbe all the more so in the Semitic languages, Hebrew and Arabic, whereword structure expresses a rich array of semantic notions (Bolozky, 1999;

Deficient Morphological Processing 111


Boudelaa & Marslen-Wilson, 2000, Deutsch & Frost, 2002; Ravid & Malenky, 2001).We have therefore examined the influence of morphological structure in Hebrew.

The role played by morphology in reading has been demonstrated extensively inword recognition literature, suggesting that morphological structure is one of theorganizing principles of the mental lexicon (Deutsch & Frost, 2003; Feldman, 1995;Schreuder & Baayen, 1995). One important method that has proved especiallyrevealing is the priming paradigm, in which the presentation of a target word ispreceded by the same word (i.e. repetition priming, e.g. scan–scan) or by a relatedword (see Feldman, 1994 for review). The significant result is that a morphologicallyrelated word (e.g. scanner–scan) improves both the speed and the accuracy of targetidentification. Morphologically related words are typically related by both form(orthography and phonology) and meaning. It should be therefore stressed that,under the same priming conditions, morphologically unrelated primes that are onlyorthographically or semantically similar to the target have little or no effect on theidentification of the target (Bentin & Feldman, 1990; Drews & Zwitserlood, 1995;Feldman, 2000; Napps, 1989). In addition, the morphological priming effect istypically measured relative to orthographically related primes that are as similar tothe targets as the morphological primes (e.g. scanner–scan vs scandal–scan). Thisensures that the observed morphological priming effect is over and above the effectof orthographic similarity. Based on these considerations, the morphologicalpriming effect is considered a morphological effect, resulting from the morpholo-gical relationship between the prime and the target words.

This facilitatory effect of morphological primes is taken as evidence for thesensitivity of readers to the morphological structure of words. It is thought toreflect a transfer effect; that is, the information related to the shared basemorpheme is extracted from the prime and transferred to the processing of thetarget. Results from numerous studies show that morphological priming is arobust effect that may serve as an important tool for investigating howmorphological information is represented in the mental lexicon and manipulatedin the course of word recognition (Deutsch & Frost, 2003; Schreuder & Baayen,1995). The representations of morphological units, such as the root in Hebrew,and the manipulation of these units constitute procedural morphologicalknowledge; the reader decomposes words into their constituent morphemesand recombines these morphemes to obtain the meaning of the whole word(Chialant & Caramazza, 1995; Frost, Forster, & Deutsch, 1997; Schreuder& Baayan, 1995; Stanners, Neiser, Hernon, & Hall, 1979). In contrast to theexplicit morphological knowledge reflected in morphological awareness tasks,we refer to these procedures as implicit morphological knowledge because theyare part of the reader’s linguistic knowledge and are unconscious and automatic.

Here we examine the quality of the implicit morphological knowledge ofadults with developmental dyslexia who are native Hebrew speakers. Using thepriming paradigm we investigate whether they are sensitive to the morpholo-gical structure of words they read and whether they extract and representmorphemic units during the reading process similarly to normal readers.

Hebrew Morphology

We first briefly describe the relevant characteristics of Hebrew morphologyto illustrate the complexities of the morphological structure of Hebrew

R. Schiff and M. Raveh112


words and the challenge they pose for the decomposition process in wordrecognition.

Hebrew words are constructed from two basic morphemes, the root and theword pattern. The Semitic root, consisting of three or four consonants (e.g. g-d-lor p-r-s-m), reflects the core meaning shared by all the words formed from thisroot. The root is thus considered a core phonological and semantic unit thatrelates the members of its morphological family by supplying basic lexicalcontent and a consonantal skeleton of the word (Berman, 1987; Ravid, 1996;Schwarzwald, 2001). Neither root nor pattern has an independent lexical statusand only in their combined form do they constitute a lexeme. However, unlikewords in English, these basic morphemes are non-concatenative, that is they arenot sequentially ordered. The roots are interwoven with word patterns to createwords; for example, the root g-d-l ‘grow’ and the word pattern CaCoC combinetogether to yield the adjective GaDoL ‘big’.

Hebrew is a derivationally rich language. Derivations of numerous relatedwords all cluster around the same root; in other languages these may beexpressed by non-related lexemes (Ravid, 2002; Schwarzwald, 2001). Forexample, the root g-d-l carries the basic meaning of grow and serves to relate alarge morphological family of verbs, nouns and adjectives: gadal ‘grew’, gidel‘raised’, gudal ‘was raised’, higdil ‘enlarge’, hugdal ‘was enlarged’, gdila‘growing’, gidul ‘growth’, hagdala ‘magnification’, gdula ‘eminence’, godel‘size’, migdal ‘tower’, megadel ‘grower’, magdelet ‘magnifying glass’, gadol ‘big’,megudal ‘grown’.

Given the central role of the root in Semitic word structure, it is no wonder thatroot perception is an inherent component of Semitic lexical and morphologicalknowledge. There is ample evidence that the root has a central role in theorganization of the mental lexicon of Hebrew and Arabic speakers (Abu-Rabia,2002; Boudelaa & Marslen-Wilson, 2001; Ravid, 2002) and that root perception isessential component in reading and writing processes (Frost et al., 1997; Ravid,2002). Using the priming paradigm in Hebrew shows that the exposure to theroot morpheme (e.g. ZMR) facilitates the identification of words derived fromthat root (e.g. /tiZMoRet/, meaning orchestra) (Deutsch, Frost, & Forster, 1998;Frost et al., 1997). The priming effect indicates that the root is extracted from theprinted word during word recognition. Languages like Hebrew, with a rich andcomplex morphology, thus pose a distinct challenge for morphological analysis inreading, all the more so for dyslexics.

Morphological Processing and Dyslexia

Morphological processing in individuals with developmental dyslexia has notbeen studied in detail. The few studies, focusing mostly on explicit morphologicalawareness, show that children with familial risk for dyslexia exhibit poor masteryof inflectional morphology at an early age and are at higher risk for impairmentin subsequent language development (Lyytinen & Lyytinen, 2004). The languageimpairment of dyslexic children and adults is not limited to phonologicalprocessing but also extends to morphological awareness (Arnbak & Elbro, 2000;Ben-Dror, Bentin & Frost, 1995; Carlisle, 1987; Elbro & Arnbak, 1996; Joanisse,Manis, Keating, & Seidenberg, 2000; Leong & Parkinson, 1995; Schiff & Ravid,submitted).



However, the quality of dyslexics’ implicit morphological knowledge hasreceived scant attention. Leong (1999) demonstrated marked latency differencesin a morphographic lexical decision task between dyslexic students and theirchronological-age controls. In the present study we use the priming paradigm tofurther examine dyslexics’ implicit and procedural reading skills. Our study thusdiffers from the previous studies that have depended mostly on consciousmorphological analysis. Our aim here is to examine whether dyslexics have intactimplicit morphological knowledge and whether they use morphologicalprocesses similar to those used by normal readers.

Morphological priming has not been examined in dyslexics, although there aresome studies of repetition priming (i.e. where the prime and the target words areidentical). Samuelsson, Gustafson, and Ronnberg (1998) testing a group ofchildren and adolescents (aged 9–15 years) with developmental dyslexia, showedthat repetition priming varied as a function of the subtype of dyslexia (definedaccording to the subjects’ orthographic and phonological decoding skills).Specifically, the ‘phonological’ subgroup, with impaired phonological decodingbut intact orthographic word decoding, showed strong repetition priming forprinted words. In contrast, the ‘surface’ subgroup, with impaired orthographicword decoding, did not show repetition priming for printed words but producedrepetition priming for spoken words (see also Carlesimo, Fadda, Sabbadini,& Caltagirone, 1994; Samuelsson, Bogges, & Karlsson, 2000; Whatmough& Arguin, 1998). Children with weaknesses in both orthographic andphonological word decoding showed low levels of priming for both auditoryand visually presented words.

Samuelsson et al. assume that repetition priming effects are mediated bytwo separate word-form systems. The observed level of priming should thusbe seen as an indicator of the strength with which visual and auditoryinformation is implicitly extracted and represented in these systems. Puresubtypes of dyslexia (phonological and surface) can therefore be explained bypostulating a selective impairment in one of the input systems, while the mixedsubtype (the majority of subjects in their study) appear to have impairment inboth systems.

These results are theoretically and methodologically important for theinvestigation of the quality of morphological processes of dyslexics. If, as theseresults suggest, dyslexia involves impairment at the word form level of thereading process, the major question is what effect this impairment has onprocessing at higher levels of the lexical system, i.e. on the subsequent extractionof morphological information. Recent results with normal adult readers suggestthat morphological processing is influenced by orthographic and phonologicalfactors (Feldman, Rueckl, DiLiberto, Pastizzo, & Vellutino, 2002; Rueckl,Mikolinski, Raveh, Miner, & Mars, 1997). For example, Rueckl et al. (1997)demonstrated stronger morphological priming for morphological relatives thatare more similar in surface form (e.g. made–make) than pairs from the samemorphological class (irregular inflections) that are less similar in form (e.g. took–take). These findings therefore suggest that morphological processing interactswith, and hence should be affected by, the quality of lower levels of formalprocessing.

In summary, the major goal of the research presented here is to examine thequality of the implicit morphological knowledge of adults with developmental



dyslexia. We use the priming paradigm and extend the methodology used bySamuelsson et al. (2000) to study morphological processing. We investigatedwhether dyslexic readers are sensitive to the morphological structure of thewords they read and whether they extract and represent morphemic units duringreading as do normal readers. Specifically, we divided the dyslexic subjects intosubtypes based on decoding skills (pure surface, pure phonological, and mixeddyslexia), then examined both repetition and morphological priming effects. Thecomparison between repetition and morphological priming effects may provideimportant insights into the relationship between the formal level of processing(orthographic and phonological) and the higher level of morphologicalprocessing. This comparison may also help elucidate the specific pattern ofdeficits in different subtypes of dyslexia.

METHOD

Subjects

Sixty-four undergraduate students at Bar Ilan University volunteered toparticipate in this study. All participants were native speakers of Hebrew withno reported signs of sensory or neurological deficiencies. The dyslexic groupconsisted of 30 students randomly selected from a group of students involved ina dyslexic support group at the Haddad Centre for Research in Dyslexia andReading Disorders at Bar Ilan University. This center provides the students withremedial teaching to support their second language studies (English). Thestudents had all been previously diagnosed as dyslexic by trained diagnosticiansand had records documenting reading problems from childhood. Their lastdiagnosis was performed within the three years prior to attending the universityor while attending the university. Diagnoses showed that the students all hadnormal IQ scores. There were ten women and twenty men in the dyslexia groupwith mean age of 25 years (S.D. 4.13). The control group consisted of 34 age-matched undergraduates with a mean age of 26 (S.D. 3.88), eight women andtwenty-two men. The control students, who volunteered to participate in thisstudy, reported that they had no history of learning or reading problems and thatthey were not taking medication.

We used a word reading task (adopted from Brande, 1997) to exclude controlsubjects with poor reading ability and to demonstrate differences in readingability between the dyslexia and the control group. In this task the participantswere given a list of 200 words and were asked to read them aloud as quickly andas accurately as possible within a time limit of one minute. A fluency score, thenumber of words correctly read within the minute, and an accuracy score, thenumber of errors, were registered.

Four students, who by their self-report were normal readers, were excludedfrom the control group because the number of words they read correctly wasbelow the 15th percentile of their group. The dyslexic group read fewer wordscorrectly than the control group within the time limit (82 vs 119, respectively;tð58Þ ¼ 7:16, p50:001) and made more errors than the control group (3.5 vs 1.2,respectively; tð58Þ ¼ 3:27, p50:01).



Classification into subgroups of dyslexiaWe classified the dyslexic students into three subtypes } surface, phonologicaland mixed dyslexics}according to their performance in orthographic andphonological judgment tasks (after Olson, Kliegl, Davidson, & Foltz, 1985).Following the word reading task, all students performed two tests of worddecoding skills. The first was an orthographic-decoding task in which they werepresented with 30 word–pseudoword pairs one at a time on the computer screenand were asked to decide as quickly and as accurately as possible which wasspelled correctly. Since the phonological code of the two stimuli was identical,the judgment had to rely on stored orthographic representations of specificwords. Pseudowords were created by changing one letter in real words. AnEnglish equivalent example is brain–brane. An Hebrew example is the wordTRUMH, /truma/, ‘contribution’ (the orthographic, phonological forms and themeaning, respectively). The first phoneme /t/ of the word is written with theletter ‘taf’ and has a homophonic letter ‘tet’ that was used to create the distractorpseudoword. Modern Hebrew has several such letter pairs with identicalpronunciation. We used 5 letter pairs that were represented in equal numberswithin the stimulus list. The position of the changed letter (initial, middle orfinal) was also balanced across the list.

The second decoding task was a phonological decoding task in which thestudents were presented with 30 pseudoword–pseudohomophone pairs and wereasked to decide as quickly and as accurately as possible which sounded like a realword. Because both pseudowords were visually unfamiliar, they could not beidentified orthographically and, hence, the decision had to be based on aphonological decoding strategy. The two pseudowords had identical letters andwere written with the diacritic marks of Hebrew that convey vowel sounds withone mark difference between them. A nearly equivalent example in English wouldbe trune–trane, where the second word sounds like the real word train. A Hebrewexample is: both pseudowords in the pair contain the same 5 letters RMKOL butdiffer in one diacritical mark, a difference that results in two phonological forms,/rimkol/ which is a nonsense string and /ramkol/ which sounds like the real wordmeaning ‘loudspeaker’. The sound change specified by the diacritical marks andtheir position within the pseudoword was balanced across all stimulus pairs.

Raw reaction times in the two tasks were transformed to standard z-scores forpurposes of comparison and served as the basis for classification of dyslexicsubtype. Discrepancy scores between the standard scores of the orthographic andphonological decoding tests were used as a classification criterion with a cut-offof one standard deviation difference between the two tasks (for a similar methodof classification see Curtin et al., 2001; Samuelsson et al., 1998). The phonologicalsubgroup was defined as dyslexics with low performance in the phonologicaljudgment task relative to their performance in the orthographic judgment task.The surface subgroup was defined as dyslexics with low performance in theorthographic judgment task relative to their performance in the phonologicaljudgment task. Finally, the mixed subgroup was defined as those with equallypoor performance in both orthographic and phonological tasks. This procedureyielded 10 phonological, 6 surface and 14 mixed dyslexics.

The dyslexia group as a whole were significantly slower than the control groupin carrying out both the orthographic test (tð58Þ ¼ 6:97, p50:001) and thephonological test (tð58Þ ¼ 9:70, p50:001). Dyslexic participants also made more



errors than the control group, but the difference in error rates was significant onlyin the phonological test (tð58Þ ¼ 20:07, p50:05). The mean reaction times anderrors for the control and the three dyslexia subgroups in the two judgment tasksare presented in Table 1.

A series of one-way ANOVAs on the reaction times with subgroup asindependent factor (control, phonological, orthographic, mixed) revealed that thesubgroups differed in their performance in the orthographic (Fð3,56Þ ¼ 24,p50:001) and phonological judgment tasks (Fð3,56Þ ¼ 40:9, p50:001). Plannedcomparisons (Tukey) showed that the control group differed significantly fromthe three dyslexia subgroups in each of the two tasks. In addition, in theorthographic task, the phonological subgroup performed better than boththe surface (p50:01) and the mixed (p ¼ 0:06) subgroups. The performance ofthe surface and the mixed subgroups was comparable in this task. In thephonological task, the surface subgroup performed better than both thephonological (p50:01) and the mixed (p ¼ 0:064) subgroups. The performanceof the phonological and the mixed subgroups was comparable in this task. Thefour subgroups differ in their performance in the word reading task(Fð3,56Þ ¼ 18:43, p50:001). Planned comparisons (Tukey) revealed that only thecontrol group differed significantly from the three dyslexia subgroups and therewere no differences among the dyslexia subgroups. The analysis of the errorrate in the two judgment tasks showed that the four subgroups differed inthe orthographic task (Fð3,56Þ ¼ 5:17, p50:01) but not in the phonological task.Planned comparisons (Tukey) showed that the surface subgroup made signifi-cantly more errors in the orthographic task than each of the other three subgroups.

The priming Task

The priming condition (repetition, morphological, unprimed, orthographic) wasmanipulated as a within-subjects independent variable and group or subgroup as

Table 1. Mean reaction times (and S.D.) in the orthographic and phonological judgmenttasks and mean (and S.D.) word reading performance for the control group and the threesubgroups of dyslexics

Control Phonological Surface Mixedn ¼ 30 n ¼ 10 n ¼ 6 n ¼ 14

Phonological judgmentRT 1652 3851 2667 3487S.D. (310) (950) (805) (888)Error 1 2.4 1.66 2.57S.D. (1.55) (2.87) (2.42) (3.75)

Orthographic judgmentRT 1066 1558 2427 2032S.D. (236) (354) (847) (606)Error 0.87 0.9 3 1.07S.D. (1.01) (0.8) (2) (1.49)

Reading words/minMean 119 88.6 70.5 81.6S.D. (20) (13.3) (21.5) (24)Error 1.2 2.9 6.66 2.5S.D. (1.2) (2.9) (5.95) (1.87)



a between-subjects independent variable. The dependent variable was thepercentage of target completions in the word fragment completion test; that is,the rate at which the target word was given as he first completion for thefragment presented at test.

MaterialsThe stimuli consisted of 44 target words with nominal root derivations 4–6 letterslong. To create four priming conditions, these target words were paired with 44sets of three primes each: a word identical to the target for the repetition primingcondition, a word derived from the same root as the target for the morphologicalpriming condition and, for the orthographic baseline condition, a wordorthographically related to the target but unrelated morphologically. In theunprimed condition, no related primes were presented during the study phase.The orthographic baseline primes had the same number of letters as themorphologically related prime but a different root. Thus, the morphologicallyrelated prime and the orthographic baseline prime shared the same number ofletters with the target. Each target was paired with each of its four primes and thetest items were counterbalanced across participants such that participants did notsee any prime or target more than once. An English equivalent example is scan–scanner–scandal for the repetition, morphological and orthographic primes,respectively, for the target word scan; an example of a Hebrew set is givenin Table 2.

The priming task consisted of a study phase followed by a test phase with aword fragment completion task. In the study phase, participants were exposed to33 primes, 11 of each of the three priming conditions, repetition, morphologicaland orthographic. In addition, there were 22 filler words in the study list in orderto obscure the relationship between the primes and the targets. In the test phase,participants were exposed to 44 fragmented targets and 18 filler fragments.A fragment was created by omitting one letter of the target word, either frominitial, middle, or final position (e.g. sca ). Each resulting fragment could becompleted in at least three possible ways, of which the target word is not thehighest in frequency. Fragments were pre-tested to ensure that the target wordwas given as a completion only about 20–30% of the times. This ensured that the

Table 2. An example of a stimulus set for the priming task. Root letters appear inuppercase and word pattern in lowercase letters. The words appear first in theirorthographic form, then their /phonetic form/ and meaning

Priming Condition

Repetition Morphological Orthographic Unprimed

PrimeOrthography MHiRut nMHR YHiR }Phonetics /mehirut/ /nimhar/ /yahir/Meaning ‘speed’ ‘hasty’ ‘arrogant’

TargetOrthography MHiRut MHiRut MHiRut MHiRutPhonetics /mehirut/ /mehirut/ /mehirut/ /mehirut/Meaning ‘speed’ ‘speed’ ‘speed’ ‘speed’



baseline target completion rate would not be too high and would leave room forthe primes to affect performance. All stimuli appeared white in the middle of ablack computer screen in 20 points Ariel font.

ProcedureIn the study task, participants were presented with the 55 words one at a time for3000 ms each. They were asked to rate the frequency of use of each word on ascale of 1–5. This phase was followed immediately by the test in which they sawthe 62 fragments one at a time and were asked to say the first word that came totheir mind to correctly complete the fragment. The oral response terminated thetrial and then the next fragment appeared. If the participant did not respondwithin 3000 ms, the program moved to the next trial. The responses in both thestudy and the test were oral and were recorded. The presentation of the stimuliand the recording of the responses were controlled by the computer programDMDX developed by Forster and Forster at the University of Arizona.

RESULTS

Analysis by Group

We first present the analysis of repetition and morphological priming of thedyslexic group as a whole compared to the control group. For the measure of thetarget completion rate we counted only those fragment completions that wereidentical to the target word. The mean target completion rates as a function ofpriming condition are presented in Figure 1.

Figure 1 shows that for both the dyslexic and control groups the proportion oftarget completion varied as a function of priming condition and was highest inthe repetition priming condition, followed by the morphological, orthographic,and unprimed conditions in that order. A repeated analysis of variance (ANOVA)with priming condition as a within-subjects and group as between-subjects

0

5

10

15

20

25

30

35

40

Repetition Morphological Orthographic Unprimed

Priming condition

% T

arg

et c

om

ple

tio

n

Control

Dyslexia

Figure 1. Percentage of target completion in the four priming conditions for the controland dyslexia groups.



variables revealed a significant effect of priming condition (Fð3,174Þ ¼ 18:13,p50:001), a significant effect of group (Fð1,58Þ ¼ 12:94, p50:001), and asignificant interaction of priming condition and group (Fð3,174Þ ¼ 2:68, p50:05).

Planned comparisons (Bonferroni) revealed that the repetition primingcondition differed significantly from both baseline conditions (orthographicand unprimed conditions) for the control group as well as for the dyslexia group(p50:05), indicating that the repetition priming effects for the two groups weresignificant. The source of the interaction lies at the morphological primingcondition. The control group showed significant morphological priming effect:The morphological priming condition differed significantly from the baselineconditions, p50:05: In contrast, the morphological priming effect for the dyslexiagroup was not significant.

It is important to note that the two baselines, the orthographic and theunprimed conditions, did not significantly differ from one another and werestatistically equivalent for the control and the dyslexia group. Thus anydifference between the two groups cannot be attributed to differences at thebaseline performance but must indeed be attributed to differences in the primingeffects.

Several repeated measures ANOVAs further demonstrated the differences inthe priming effects between the dyslexia and control groups. An ANOVA withpriming condition (Repetition, Unprimed) as within-subjects variable and group(Dyslexia, Control) as a between-subjects variable revealed that the interactionbetween group and priming condition was not significant (Fð1,58Þ ¼ 1:33,p > 0:05). A similar result was obtained for comparison with the orthographicbaseline (Fð1,58Þ ¼ 0:163, p > 0:05). Thus, the repetition priming effects of thedyslexia and control groups were comparable. In contrast, an ANOVA withpriming condition (Morphological, Unprimed) as within-subjects variable andgroup (Dyslexia, Control) as a between-subjects variable revealed a significantinteraction between group and priming condition (Fð1,58Þ ¼ 8:97, p50:01).A significant interaction was also obtained when the morphological primingcondition was compared with the orthographic baseline (Fð1,58Þ ¼ 4:89, p50:05).These interactions indicate that morphological priming had different effects onthe two groups, showing significantly stronger effects in the control group thanin the dyslexia group.

Analysis by Dyslexia Subtype

Table 3 presents the mean target completion rates in the different primingconditions for the three dyslexia subtypes. A repeated measures ANOVA withpriming condition as a within-subjects variable and subgroup as a between-subjects variable (control, phonological, surface, mixed) revealed a main effect ofpriming condition (Fð3,168Þ ¼ 13:00, p50:001), a main effect of subgroup(Fð1,56Þ ¼ 4:56, p50:01), and a marginal interaction between priming conditionand subgroup (Fð9,168Þ ¼ 1:91, p ¼ 0:053).

Planned comparisons (Bonferroni) revealed that the repetition primingcondition was significantly different from both baseline conditions (orthographicand unprimed conditions) only for the control group and the phonologicalsubgroup, indicating significant repetition priming effects for these two



subgroups. The morphological priming condition was significantly differentfrom both baseline conditions only for the control group. Note that the twobaselines, the orthographic and the unprimed conditions, did not significantlydiffer from one another in any of the subgroups and were statistically equivalentfor all subgroups.

The repetition and morphological priming effects were separately examinedfor the phonological versus the surface subgroups and for the phonologicalversus the mixed subgroups. An ANOVA with priming condition (Repetition,Unprimed) and subgroup (Phonological, Surface) revealed no significantinteraction between subgroup and priming condition (Fð1,14Þ ¼ 0:18, p > 0:05).A similar result was obtained by comparing to the orthographic baseline(Fð1,14Þ ¼ 0:09, p > 0:05). Thus the repetition priming effects of the phonologicaland surface subgroups were not statistically different. An ANOVA with primingcondition (Repetition, Unprimed) and subgroup (Phonological, Mixed) revealeda marginally significant interaction between subgroup and priming condition(Fð1,22Þ ¼ 4:18, p ¼ 0:053). A significant interaction was obtained by comparingrepetition priming with the orthographic baseline (Fð1,22Þ ¼ 4:89, p50:05). Thus,the repetition priming effect of the phonological subgroup was stronger than theeffect of the mixed subgroup.

No interactions were found for the comparison between the morphologicalpriming and the baseline conditions for each pair of dyslexia subgroups,indicating that the subgroups showed comparable (weak) morphologicalpriming effects.

DISCUSSION

We have used the priming paradigm to examine the implicit morphologicalrepresentations and procedures of adults with dyslexia. The magnitude of themorphological priming effect was measured in the word fragment completiontask (e.g. scanner–scan), and was then contrasted with the repetition primingeffect (e.g. scan–scan). This contrast was examined for the dyslexia group as awhole, as well as separately for different subtypes of dyslexics defined by thediscrepancy between their phonological and orthographic skills.

In general, the dyslexic and the control groups differed in their patterns ofrepetition and morphological priming effects. Students with normal readingability showed the typical repetition priming effect, i.e. repeated primessubstantially facilitated the completion of targets in the test phase. A comparablerepetition priming effect was also found for the dyslexic group as a whole.

Table 3. Percentage of target completion (and S.D.) in the different priming conditions forthe three subtypes of dyslexia

Phonological Surface Mixed

Priming condition:Repetition 37.25 (13.20) 31.82 (12.53) 24.03 (13.15)Morphological 24.52 (10.53) 24.24 (9.38) 18.83 (15.73)Orthographic 16.34 (8.31) 13.64 (9.53) 20.78 (13.06)Unprimed 16.35 (5.74) 12.12 (11.01) 20.13 (13.40)



However, further analysis of the dyslexia subtypes revealed significant repetitionpriming effects only for the phonological dyslexia subgroup but not for thesurface or mixed dyslexia subgroups. Furthermore, students with normal readingability showed morphological priming that was as strong as their repetitionpriming effect. In contrast, the interaction between group and priming clearlyrevealed different morphological priming effects in dyslexic and normal readers.Dyslexic readers did not show morphological priming, neither the dyslexiagroup as a whole, nor any of the subgroups.

Repetition priming reflects the ability of readers to extract visual andorthographic features from the printed word and to activate appropriaterepresentations in the visual word-form system (Roediger, 1990; Schacter, 1990;Tulving & Schacter, 1990). Analysis of the repetition priming effect of the dyslexiagroup as a whole suggests that dyslexics show intact repetition priming.However, subsequent analysis by subtypes showed that this was true only for thephonological dyslexia subgroup. The surface and the mixed subgroups did notshow repetition priming. These differential results can be revealing with respectto the underlying functionality of the input representation system. Impairment atthe word-form input system of the surface and the mixed dyslexics may explainboth their weakness in the orthographic decoding task (Castles & Coltheart, 1993;Rack et al., 1992; Stanovich & West, 1989; Seymour & MacGregor, 1984) and theirnull visual repetition priming effects.

The weak repetition priming effects demonstrated by the surface and mixeddyslexics suggest that these readers cannot fully exploit the benefitsfrom repeated exposures to printed words. In contrast, the phonologicalsubgroup, who exhibited good orthographic decoding skills, did show therepetition priming, suggesting that they have an intact visual word-form systemand the ability to extract and represent the orthographic features of printedwords. Their weakness lies at the phonological level of analysis (Castles &Coltheart, 1993; Rack et al., 1992; Stanovich & West, 1989; Seymour & MacGregor,1984).

Although the repetition priming effect of the surface subgroup was notstatistically significant, it was numerically comparable to the effect produced bythe phonological subgroup. Given the small number of subjects in the surfacesubgroup, the interpretation of this null effect should be made with caution.Nonetheless, the fact that the pattern of repetition priming across the dyslexiasubgroups replicates that found by Samuelsson et al. (1998) with respect toprinted words supports the validity of this finding.

In addition to confirming the well documented phonological difficulties indyslexia, the present investigation provides new information on the quality of therepresentations at levels higher than the perceptual level, that is, at the levels ofmorphological representation and analysis. Students with normal reading abilitydemonstrated a strong morphological priming effect, consistent with themorphological priming effects reported elsewhere in the fragment completiontask (Feldman et al., 2002; Raveh & Rueckl, 2000; Rueckl, et al., 1997; Weldon,1991). Using an orthographic baseline and the long-term priming methodallowed us to rule out formal similarity or semantic similarity as a source for theobserved priming. In the long-term priming method, where the prime and thetarget words are separated by several intervening words, primes that are onlyorthographically or semantically related to the targets do not affect the



identification of the targets (Henderson, Wallis, & Knight, 1984; Napps, 1989;Stolz & Feldman, 1995). The orthographic baseline condition ensures that theobserved priming effect is not just due to orthographic similarity, but must stemfrom the morphological relationship between the prime and the target words, i.e.their shared root.

The major question we addressed here was whether well-compensatedundergraduate students with dyslexia use morphological procedures duringlexical access similar to those of normal readers. We found that, in sharp contrastto the strong morphological priming found for the normal readers, none of thedyslexia subgroups showed morphological priming. Morphologically relatedprimes did not influence their target completion rate.

To interpret this finding, we first need to consider the basis of themorphological priming effect. In dual route models of morphological processing,lexical access involves two word identification processes that work in parallel,lexical retrieval of the whole word and morphological decomposition (Burani &Laudanna, 1992; Deutsch & Frost, 2003; Schreuder & Baayen, 1995). The whole-word route involves the activation of whole-word representations in the mentallexicon, and the decomposition route involves the extraction of the constituentmorphemes of the word. The mental lexicon of adults, according to thisapproach, is therefore organized according to morphological principles: itcontains morphemic units in addition to word units, with connectionsbetween the two types of representations. Based on a series of priming studiesin Hebrew (Deutsch et al., 1998; Frost et al., 1997; for a review see Deutsch& Frost, 2003), Frost and colleagues claim that, for nominal forms, thedecomposition involves the extraction of the root morpheme and the activationof the root unit in the mental lexicon. The fact that the morphological primingeffect of the normal readers in our research was as strong as the repetitionpriming effect underscores the significance of the root extraction for theidentification of the whole word.

Our working assumption is that morphological priming reflects the psycho-logical reality of the root morpheme and its role in lexical organization and lexicalaccess. Therefore, the lack of morphological priming in dyslexics suggests thattheir lexical access does not involve morphological decomposition. It is possiblethat the impaired morphological decomposition is due to their difficulty in thevisual encoding of the printed word, i.e. segmenting the orthographic accessrepresentation to extract the root morpheme. Alternatively, difficulties may bephonological in nature, such that inadequate processing of the phonologicalrepresentation in the verbal short-term memory (see Jeffries & Everatt, 2004;Meyler & Breznitz, 2005; Ransby & Swanson, 2003) hinders the segmentationof morphologically complex words and the extraction of the root morpheme.In any case, such encoding failures may result in that root morphemes may notbe or may be inadequately represented in the mental lexicon of readerswith dyslexia.

This lack of morphological priming in dyslexics is highly revealing sincemorphological priming is found in children as young as 2nd grade (Raveh& Yamin, 2004; Raveh, Schiff, & Kahta, submitted). Thus, there appears to bemorphological decomposition of printed words even at the early stages of normalreading acquisition. The low level of morphological processing reflected by thelack of morphological priming does not appear to be due to delayed linguistic



development, but rather to a deficit specific to dyslexia. Our findings imply thatthe word recognition procedures performed by adults with dyslexia, at least atthe morphological level of processing, are qualitatively very different from theprocedures used by normal readers, even by young readers. The use ofmorphologically unsophisticated word recognition procedures anchored inlexical access, which is based largely on whole-word representations, rendersreading performance inefficient, especially when the texts encountered becomericher and more complex.

The contrast between the pattern of results in the repetition and themorphological priming conditions across the different subtypes of dyslexia hasinteresting theoretical implications. As discussed above, whereas repetitionpriming effects tap into the perceptual level of word form, morphological effectsare assumed to reflect higher levels of processing. Dual route models suggest thatthey reflect the representations and processing at a specific morphological level(Burani & Laudanna, 1992; Deutsch & Frost, 2003; Schreuder & Baayen, 1995),while connectionist models of word recognition suggest they reflect theinteraction between the form and semantic level of processing (Cottrell& Plunkett, 1994; Plaut & Gonnerman, 2000; Raveh, 2002; Reuckl et al., 1997;Reuckl & Raveh, 1999). The classification into dyslexic subtypes revealed thatphonological dyslexics do show repetition priming but weak or no morpholo-gical priming. This suggests that adequate activation at the level of word form isnot a sufficient condition for adequate processing at higher levels. Furtherexamination of morphological priming using different priming methods anddifferent modality (e.g. short-term priming, auditory priming) is needed toclarify the relationship between perceptual and morphological levels ofprocessing.

The growing research literature on students with dyslexia suggests that theydemonstrate persistent deficits in single word recognition (Ben-Dror, Pollatsek,& Scarpati, 1991; Booth, Perfetti, MacWhinney, & Hunt, 2000; Bruck, 1990, 1993;Leong, 1999, Maughan, 1995; Ransby & Swanson, 2003). However, most of theresearch has focused on the impaired phonological processes underlying theirword recognition deficits. Our results, along with earlier findings of Leong(1999), highlight an additional source for dyslexics’ difficulties with wordrecognition, namely impairment at the level of morphological processing. Furtherresearch is needed to investigate whether there is a relationship between theirdeficits in phonological and morphological processing. Finally, adult dyslexicsshow difficulties in explicit tests of morphological knowledge (Leong, 1999; Schiff& Ravid, submitted). Our research adds the implicit aspect of morphologicalknowledge involved in automatic lexical access. We are currently examiningwhether these two aspects are related, that is, whether deficits in morphologicalawareness are associated with inadequate implicit morphological procedures andhow these two aspects affect readers’ decoding accuracy and fluency.

ACKNOWLEDGEMENTS

This research was supported by the Israel Science Foundation (Grant No. 885/04).We thank the staff and students of Haddad Center for Research in Dyslexia and

Reading Disorders for their contribution to this research.



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Deficient morphological processing in adults with developmental dyslexia: another barrier to efficient word recognition?