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 DOI: 10.1177/002221940003300409

2000 33: 387J Learn DisabilMaryanne Wolf, Patricia Greig Bowers and Kathleen Biddle

Naming-Speed Processes, Timing, and Reading : A Conceptual Review  

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Naming-Speed Processes,Timing, and Reading:A Conceptual Review

Maryanne Wolf, Patricia Greig Bowers, and Kathleen Biddle

Note. Although it is conceptualized as the summary article, readers with little background in this area may find it helpful to read thisarticle immediately following the introductory article.

This article integrates the findings in the special issue with a comprehensive review of the evidence for seven central questions about therole of naming-speed deficits in developmental reading disabilities. Cross-sectional, longitudinal, and cross-linguistic research onnaming-speed processes, timing processes, and reading is presented. An evolving model of visual naming illustrates areas of differenceand areas of overlap between naming speed and phonology in their underlying requirements. Work in the cognitive neurosciences isused to explore two nonexclusive hypotheses about the putative links between naming speed and reading processes and about the sourcesof disruption that may cause subtypes of reading disabilities predicted by the double-deficit hypothesis. Finally, the implications of thework in this special issue for diagnosis and intervention are elaborated.

he research in this article and

special issue represents a shift in-M- perspective from the direction

of reading disabilities research over thelast decade and a half. Until recently,the assumption in the field of readingdisabilities has been that phonologicalprocessing deficits lie at the core of read-ing failure. The research that is pre-sented here extends this view to in-

corporate an additional, second coredeficit in the processes underlyingnaming speed. In evaluating such a

view, it is essential to address both

very basic and highly complex ques-tions. The first purpose of this final ar-ticle in the special issue is to raise themost important of these questions andto document our increasing knowl-edge about them. Seven major ques-tions, ranging from the most re-

searched to the most speculative, areposed in theoretical and applied do-mains. The article’s second purpose isto summarize and integrate the workof the authors in this special issue re-garding the evidence for these ques-tions.

As noted in the introductory article(Wolf & Bowers, this issue), the double-deficit hypothesis represents an evolv-ing, alternative conceptualization of

reading disabilities that integrates pre-vious work on phonological deficitswith research on naming-speed defi-cits. Three subtypes of impaired read-ers are presently categorized underthis hypothesis, characterized respec-tively by phonological deficits, naming-speed deficits, and a combination ofboth. The latter, double deficit, appearsto accompany the most serious formsof reading disability.

It is important to note from the out-set that at no point do we suggest thatphonological skills and processes un-derlying naming speed represent theonly deficits that can disrupt readingdevelopment. Rather, we believe that amore refined understanding of theunique and combined contributions ofboth sets of processes will prove essen-tial for an ultimately more differenti-ated view of reading failure and, veryimportant, a more comprehensive ap-proach to reading intervention, which

will be the subject of the last questionin this review.

Question 1

What are naming-speed deficits,how are they measured, and how ex-tensive are they among children andadults with reading disabilities? Arethey found among dyslexic readers inother languages? Almost 3 decades ofresearch now demonstrate that the vast

majority of children and adults withreading disabilities have pronounceddifficulties when asked to name rap-idly the most familiar visual symbolsand stimuli in the language: letters,numbers, colors, and simple objects.Many of these children and adults donot have blatant word-finding difficul-ties but are nevertheless significantlyslower than their average-reading peerson continuous naming or naming-speed tasks, in which they are requiredto retrieve names for common, seriallypresented stimuli under conditions re-quiring time (see Figure 1).

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388

FIGURE 1. Example of most commonly used naming-speed task, the RapidAutomatized Naming (RAN) test.

The research in this area is based

originally on work in the neurosci-ences, stemming from a hypothesisabout color naming by Geschwind(1965). Geschwind (1965) suggestedthat the cognitive components in-

volved in color naming-that is, thosecomponents involved in attaching averbal label to an abstract, visual stim-ulus-would make a good early pre-dictor of later reading performance,which poses similar cognitive require-ments. This hypothesis was investi-gated and developed by Denckla (1972)who, in collaboration with Rudel

(Denckla & Rudel, 1974, 1976a, 1976b),found that the speed with which nameswere retrieved, rather than the accu-

racy in color naming or the namingitself, differentiated dyslexic readersfrom others. These researchers werethe first to design a rapid automatizednaming (RAN) task to measure con-tinuous, serial naming-speed perfor-mance on common visual stimuli. TheRAN tasks measure the speed withwhich children can verbally name a se-

rial array of the most basic visual sym-bols (see Figure 1) and are the proto-typical tasks used in most of the citedresearch (for task variations that do notrely on alphanumeric symbols withlanguage-impaired children, see Wiig,Zureich, & Chan, in this issue).The cumulative cross-sectional, lon-

gitudinal, and cross-linguistic researchon RAN or RAN-like tasks has demon-strated that processes underlying nam-ing speed differentiate dyslexic readersfrom

1. average readers (Berninger, inpress; Berninger et al., 1995;Bowers, Steffy, & Tate, 1988;Denckla & Rudel, 1976a, 1976b;Grigorenko et al., 1997; Snyder &

Downey, 1995; Spring & Capps,1974; Spring & Davis, 1988; Wolf,1982; Wolf, Bally, & Morris, 1986;Wolff, Michel, & Ovrut, 1990a,1990b, 1990c);

2. nondiscrepancy or &dquo;garden-variety&dquo; poor readers (describedby Gough and Tunmer, 1986, as

readers whose low reading levelis not discrepant with their IQ orachievement scores; Ackerman &

Dykman, 1993, 1995; Badian, 1994,1995, 1996a, 1996b; Wolf &Obreg6n, 1992); and

3. readers with other learning disabil-ities (Ackerman & Dykman, 1993,1995; Denckla & Rudel, 1976b; Fel-ton & Brown, 1990; Wood & Felton,1994).

There are mixed results concerning thequestion whether naming speed differ-entiates dyslexic readers from reading-age-matched readers. This method

employs comparisons with younger,average readers who read at the samelevel as the older dyslexic group. Ack-erman and Dykman (1993), Biddle

(1996), Segal and Wolf (1993), and Wolf(1991; Wolf & Segal, 1997) found thatchildren with dyslexia performed sig-nificantly slower than reading-age-matched children, but Badian (1996a)and Olson (1995) reported no differ-ences. A more comprehensive sum-mary of the research on naming speedwith more detailed information on

specific populations and findings is

provided in Table 1.Naming-speed differences have been

demonstrated among dyslexic readersacross languages of varying degreesof orthographic regularity, includingGerman (Ndslund & Schneider, 1991;Wimmer, 1993; Wolf, Pfeil, Lotz, & Bid-

dle, 1994), Finnish (Korhonen, 1995),Dutch (Van den Bos, 1998; Yap & Van

der Leij, 1993), and Spanish (Novoa,1988; Novoa & Wolf, 1984). In bothGerman (Wimmer, 1993) and Dutch(Van den Bos, 1998)-two languageswith a more transparent or regularorthography than English-namingspeed appears a more robust predictorof reading performance than phonolog-ical awareness measures. The impor-tance of these cross-linguistic findingsis that they eliminate the irregularity ofEnglish orthography as a possible ex-planatory factor in the naming-speedfindings. Moreover, they suggest that,in languages where a regular structurecan be decoded using relatively lower

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389

TABLE 1

Summary of Selected Studies of Naming Speeds

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390

(Table 1 continued)

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391

(Table 1 continued)

Note. RAN = rapid automatizing naming tasks: i.e., serial or continuous naming measures; RAS = rapid alternating stimulus tasks: i.e., alternating stimuli sets in aRAN format; ADD = attention-deficit disorder; LD = learning disabled; CA = chronological age; RA = reading age; RD = reading disabled; NRD = non-readingdisabled; Ll = language impairment.

levels of phonological skill than neededin English, the speed-of-processingvariable emerges as a stronger predic-tor of reading performance than pho-nological awareness tasks.

Efforts to understand the sources of

naming-speed deficits have indicatedthat naming speed’s differentiation ofdyslexic readers from controls cannoteasily be ascribed to differences in ar-ticulation rate (Ackerman & Dykman,1993; Ellis, 1985; Obreg6n, 1994; Stano-vich, Nathan, & Zolman, 1988; Wagner,Torgesen, Laughon, Simmons, & Ra-

shotte, 1993; Wimmer, 1993), short-term memory difficulties (Bowerset al., 1988; Wimmer, 1993), or visual

scanning problems that might resultfrom the continuous naming format.(See, however, differences for dyslexicsin articulation rate for non-namingtasks in Nicolson & Fawcett, 1995; Sny-der & Downey, 1995; Wolff et al.,1990b.) To investigate these articula-tory and end-of-line visual scanninghypotheses, Obreg6n (1994) in our labdesigned a highly sophisticated com-puter program to digitize the speechstream of children during RAN tasks.

He found no differences between

reader groups in isolated time to artic-ulate the verbal labels, nor for time toscan from the end of one line to the be-

ginning of the next line. Significant dif-ferences were found, however, for chil-dren with dyslexia in the interstimulusintervals (ISI)-that is, the time it takesdyslexic readers to disinhibit from theprevious stimulus, perceive and recog-nize the present stimulus, activate lex-ical access and retrieval processes for

its verbal label, and move to the nextstimulus. The locus of reader differ-

ences for naming speed in the ISI is animportant finding with potential linksto similar findings in timed visual andauditory tasks. This is discussed in

more detail under Question 5.To summarize, naming-speed defi-

cits are consistently found in childrenand adults with reading disabilities

across all languages tested, alongsidethe better understood phonologicalawareness-based deficits. These defi-cits cannot be attributed to English or-thography, articulation, or short-termmemory, although more work is neededwith regard to rate of articulation.

Question 2

Can children with developmentaldyslexia be categorized in subtypesaccording to the presence or absenceof phonological and naming-speeddeficits? The extensive literature on

phonological disabilities in childrenwith reading disabilities representsone of the most well-known areas of re-search in reading disabilities and is notreviewed here (see, e.g., Blachman, 1997;Catts, 1996; Lyon, 1995; Stanovich &

Siegel, 1994; Torgesen, Wagner, & Ra-

shotte, 1994). A parallel body of re-search on naming-speed deficits is

summarized in Table 1 and discussedin Wolf and Bowers (1999). Until re-cently, there have been few efforts todiscuss the ramifications of the co-

occurrence of these deficits in the samechild (see Blachman, 1994). Lovett

(1984) may have been the first to ad-dress this convergence in her subtypedescriptions of accuracy-disabled andrate-disabled readers. As discussed inthe introductory article, Lovett’s rate-disabled readers showed poor nam-

ing speed but age-appropriate word

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392

identification scores. The accuracy-disabled readers were more severelyimpaired than average or rate-disabledreaders on both accuracy and rate

for all reading and naming-speed mea-sures.

In both the school-based and the

clinically-referred samples included inthis special issue, the reanalysis of par-ticipants along the lines of the double-deficit hypothesis resulted in four sub-groups of readers whose differenceswere clear-cut. These included a groupof children with no deficit, two groupswith a deficit in one but not in the other

process, and a group with deficits inboth processes. In the school-based sam-

ples, readers in the age-appropriaterange on phonological and naming-speed dimensions differed signifi-cantly from those with combineddeficits on all aspects of reading tested,including word attack, word identifi-cation accuracy and latency for con-crete words and for exception words,oral reading, and reading comprehen-sion. Either deficit could appear singlyin a child with reading disabilities. Thevast majority of single-deficit childrenin the school-referred databases (seeBowers, 1995; Manis, Doi, & Bhadha, inthis issue; Wolf & Bowers, 1999) wouldbe described as having modest readingimpairments, with the phonological-deficit subtype somewhat more im-paired than the subtype with naming-speed deficits.

It is important to note that in theclinically-referred populations, Lovett(1995; Lovett, Steinbach, & Frijters, inthis issue) has shown that singledeficits can also be implicated in moreserious cases of reading disability. It

was unknown until this time whether

single-deficit subtypes would appearin these very impaired children. Aswould be predicted, however, the ma-jority of Lovett et al.’s population wereclassified as children with a doubledeficit: &dquo;The most striking findingfrom diagnostic comparisons of thethree subgroups was the extent to

which the two deficits in combination

depressed all aspects of written lan-guage acquisition for affected chil-

dren&dquo; (Lovett, Steinbach, & Frijters, inthis issue). In Wolf and Bowers’ (1999)school-based population, double-deficitreaders were approximately 2.5 to 3years below grade-level expectationson six aspects of reading (see similarfindings in Krug, 1996). Across bothclinical and school populations, there-fore, the double-deficit subtype wasthe most impaired of all subtypes onall measures of reading. With fewexceptions, double-deficit readers per-formed worse than single-deficit read-ers in the phonological and naming-speed subtypes on both rate and

phonological measures.Research on these subtypes is rap-

idly increasing. Several emerging data-bases by Badian (1996a, 1996b), Ber-ninger et al. (1995), Biddle (1996), Krug(1996), and Meyer, Wood, Hart, andFelton (1998) have shown findingsconsistent with those reported in thisissue. Furthermore, cross-linguisticstudies that indicate similar subtypeshave begun in Dutch (Van den Bos,1998), German (Wolf et al., 1994), andHebrew (Breznitz, personal communi-cation, June 1999). Recently, Morriset al. (1998) applied clustering tech-niques to classify reading disabilitysubgroups in their large study. Consis-tent with their original theoretical pre-dictions, phonological deficits played acentral role in the classification of their

subtypes. Less predicted in their origi-nal hypotheses, naming-speed deficitsalso played a major role in their classi-fications and, when co-occurring withphonological deficits, characterizedtheir two most profoundly impairedsubtypes. According to Morris et al.,these findings &dquo;attest to the primaryimpairments of phonological processesand serial naming speed-as opposedto IQ scores-in explaining variabilitywithin groups of disabled readers.These results suggest that serial nam-ing deficits and more general rate-

based factors must be considered in ex-

amining reading outcomes for childrenwith reading disabilities&dquo; (1998, p. 24).

Earlier data reports of combineddeficits are also supportive of double-deficit hypothesis subtypes. Blachman

(1994) quoted Wood in questioningwhether the early co-occurrence of pho-nemic awareness and naming-speeddeficits is a better marker for the most

impaired readers than simply phone-mic awareness alone: &dquo;Poor phonemeawareness may get the child into a re-medial reading program, but also hav-ing a naming rate deficit may be whatkeeps the child in the program&dquo; (Wood,cited in Blachman, 1994, p. 290).The results in this section indicate

that naming-speed deficits and phono-logical deficits can be found indepen-dently and in combined forms. Theyunderscore the importance of includ-ing rapid naming criteria in our identi-fication of subgroups. Very important,if future research consistently demon-strates that single-deficit readers aremore frequently modestly impairedand that double-deficit readers are themost profoundly impaired, then criti-cal studies about possible compensa-tory skills can be pursued. Furthermore,longitudinal research from kinder-garten to middle grades will be im-portant to understand cognitive-developmental differences betweendouble-deficit readers who continue tohave both deficits over time and thosewho resolved their deficits in earlygrades. We are particularly interestedin double-deficit readers whose pho-nological decoding problems are re-

solved with intervention, reclassifyingthem into a naming-speed deficit sub-type with more discrete fluency andcomprehension problems.To summarize the evidence for the

second question, naming-speed defi-cits or phonological deficits can oc-cur independently in cases of mod-est or serious reading disability. Theco-occurrence of both deficits-thedouble-deficit subtype-characterizesthe most difficult forms of reading dis-ability. Current research on subtypesincreasingly reflects both dimensions.

Question 3

Should naming-speed processes besubsumed under phonological pro-

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393

cesses, as is current practice in mostresearch on reading disabilities? If

not, what are the distinctive prop-erties of naming-speed processesthat separate them from phonology?Researchers who work within a pho-nological core deficit framework regu-larly acknowledge the independentcontributions of naming speed to read-ing, but they tend to categorize namingspeed as &dquo;part of the phonological fam-ily&dquo; (Torgesen, Wagner, Rashotte, Bur-gess, & Hecht, 1997, p. 84). Depicted asthe retrieval of phonological codes inearlier characterizations (Wagner et al.,1993), naming speed was conceptual-ized with good reason as a phonologi-cal process, including some sharedvariance (to be described) between thetwo variables. Naming speed, like anylinguistic task (e.g., semantic genera-tion, expressive vocabulary), involvesaccessing a phonological code; how-ever, we believe this to be insufficientreason to categorize and subsumenaming speed under phonology.

Cognitive RequirementsThe rationale for emphasizing the dif-ferences between naming speed andphonology is embedded in the com-plex cognitive structure of naming andalso in the importance of timing withinand across each of naming’s multiplesubprocesses. A brief examination ofthis structure in a model of letter nam-

ing illustrates how naming and serialnaming speed’s internal complexity gobeyond phonological processes (seeFigure 2).As depicted in Figure 2, visual nam-

ing represents a demanding array ofattentional, perceptual, conceptual,memory, lexical, and articulatory pro-cesses (see earlier model in Wolf, 1982;see detailed discussion of this model’s

components in Wolf & Bowers, 1999).The model begins with the activationof attentional processes that, in turn,activate bihemispheric visual process-ing at multiple levels. For example,components responsible for lower spa-tial frequencies provide information

about the global shape of the stimulusand are operating within 60 to 80 msof stimulus presentation (Chase, 1996;Legge, 1978). Visual components re-

sponsible for higher spatial frequen-cies operate somewhat more slowly,within 150 to 200 ms, and provide in-formation about the finer details of thestimulus. This, in turn, allows for iden-tification or recognition processes thatintegrate information about the pres-ent stimulus with known mental rep-resentations, the quality of which willinfluence the speed of the processing(see Perfetti, 1992). Additional compo-nents that may influence the integra-tion of the cumulative visual and rep-resentational information are affectivefactors and associative input fromother sensory modalities (see concept ofcumulative modality threshold in Wolf,1982). Lexical processes-including se-mantic, phonological access, and re-

trieval processes-are integrated withthe cumulative information. Motorcommands translate this phonologicalinformation into an articulated name.The entire process occurs within 500 ms

(Wingfield, 1968).One purpose of this evolving model

is to give a visual heuristic for under-standing the complexity of naming’sstructural requirements (see also mod-els of naming in Johnson, Paivio, &

Clark, 1996; Seymour, 1973; Wolf,1982). It exemplifies both the impor-tance of access to the phonologicalcode in naming and the fact that

phonological processes represent onlyone subset of the multiple processes in-volved in naming.The second purpose of the model is to

demonstrate the extent of processing-speed requirements (PSRs) that accom-pany each of the components in nam-

ing. Continuous naming-speed tasks addto the visual naming model the extrademands of rapidity and serial process-ing to the ordinary PSRs found in eachsubprocess. The complexity of this un-derlying structure, the extent of ordi-nary processing speed demands, andthe addition of rapid rate and seriationto PSRs make naming speed a differentcognitive task from phonology.

By the same token, this particularcombination of requirements makesnaming speed a significant predictor ofreading. This is because naming speed(particularly serial naming speed) pro-vides an early, simpler approximationof the reading process (see Blachman,1984), with reading’s similar combina-tion of rapid, serial processing andintegration of attentional, perceptual,conceptual, lexical, and motoric sub-processes. The demands in reading forhigher-level comprehension processesgo far beyond those in naming speed.Nevertheless, it is the intrinsic cogni-tive complexity of naming speed andreading that we wish to emphasize inour arguments here-a complexitythat is obscured by referring to namingspeed as a phonological process. Fur-thermore, just as in reading, the multi-ple underlying component structure ofnaming speed obviates unitary ex-

planations for its breakdown. These

explanations include phonologicalprocessing problems for both namingspeed and reading; there are, however,other potential causes for failure in

naming speed and reading that are

based on the complexity described.Thus, throughout this work the em-phasis is not so much on naming speedbut rather on the multiple processes un-derlying it.

Independent Prediction

In addition to the cognitive-structuraldifferences modeled above, severalother types of evidence support thedifferentiation between naming speedand phonology. First, the interrelation-ships found between phonologicalmeasures and rapid naming tasks aremodest (Blachman, 1984; Bowers, 1995;Cornwall, 1992; Felton & Brown, 1990;Wimmer, 1993) or sometimes insignifi-cant (Mann, 1984). There is variabilityin this finding, as described in twostudies by Wagner and Torgesen. Inone study, Wagner et al. (1993) foundthat by Grade 2 the relationship be-tween phonological and naming-speedmeasures was small; in a subsequent,

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FIGURE 2. Model of visual naming.

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395

longitudinal sample (Wagner, Torge-sen, & Rashotte, 1994), the relation-

ships appeared stronger in youngerchildren. This variability may be de-velopmentally determined such that

stronger relationships appear in pre-and early reading stages with de-creased relationships as naming speedapproaches relatively automatic ratesin average readers between Grades 1and 2 (see Biddle, 1996; McBride-

Chang & Manis, 1996; Wolf, 1991). Asemphasized by Manis, Doi, andBhadha (in this issue) and by McBride-Chang and Manis (1996), the variabil-ity in this finding is also influenced bythe reading characteristics of the pop-ulation studied. Manis, Doi, and their

colleagues (McBride-Chang & Manis,1996) have contributed an importantdimension to this issue with their em-

phasis on accounting for developmen-tal age and severity of reading disabil-ity in any analysis of the separatecontributions of both variables to vari-ous reading outcomes.Second, there are different patterns

of relationships with specific readingsubskills that characterize namingspeed and phonological variables (seeCronin & Carver, 1998). In a series ofstudies (Bowers, 1993, 1995; Bowers &

Swanson, 1991), Bowers and her col-leagues reported that phonologicaltasks strongly predicted word andnonword decoding but not word andtext reading speed. Naming speed pre-dicted accuracy and latency for wordidentification, expressiveness, and

speed reading text passages (Young &

Bowers, 1995). Bowers (1995) found in-dependent contributions to oral read-ing and to word identification accu-racy for regular and irregular words byboth variables. Naming speed alonecontributed to speed on reading mea-sures, whereas phonological decodingcontributed solely to comprehension.Cornwall (1992) found similar differen-tial patterns of relationships for naming-speed and phonological tasks with

reading subskills and concluded thatnaming-speed abilities &dquo;may representunique aspects of the reading process,

as opposed to an overall phonologicalability&dquo; (1992, p. 537).

In this issue, Manis, Doi, and Bhadha

(see their Tables 2 and 3) conductedcommonality analyses to determinethe amount of shared and unique vari-ance of phonemic awareness and nam-ing speed with various reading tasks.These analyses consistently indicatedthat both naming-speed and phono-logical variables predict unique, inde-pendent variance in every readingmeasure in addition to significant com-mon variance. In orthographic vari-ables, naming speed accounted formore variance in the &dquo;purer&dquo; ortho-

graphic tasks than the phonologicalvariable and a similar amount of vari-

ance in tasks that included both ortho-

graphic and phonological components(e.g., word identification).A third and related type of evidence

is a matter of ongoing debate in the lit-erature. Controlling for the effects ofGrade 2 word identification on later

reading skills, Torgesen et al. (1997)found that phonological measures-but not naming speed-predictedsmall but significant variance in laterreading beyond the contribution ofGrade 2 reading variables. Meyer et al.(1998) in a similar analysis found thatonly naming speed predicted later

reading in a severely impaired popula-tion when controlling for Grade 4

word identification.Most recently, Manis (personal com-

munication, August 15, 1998) con-ducted a study with participants moresimilar in age to Torgesen et al.’s (1997)sample, and more similar in severity ofimpairment to Meyer et al.’s (1998) pop-ulation. Unlike Torgesen et al. (1997),Manis and his colleagues (in this issue)found significant variance in Grade 2orthographic skill explained by bothnaming-speed and phonological aware-ness measures after controlling for theautoregressive effects of Grade 2 read-ing skills. Although the complex fac-tors in this area of research are beyondthe scope of this article (see discus-sions in Torgesen et al., 1997; Wolf &

Bowers, 1999), this literature indicates

that it is critical to take into account the

following:

1. the severity of reading impairmentand sample characteristics (includ-ing, as noted by Torgesen et al.,1997, the quality of reading in-struction) ;

2. the distinctions among word iden-

tification, word attack, word recog-nition, and reading speed vari-ables ; and

3. the developmental factors that in-corporate information about whenvarious processes approach auto-matic levels (Biddle, 1996; Carver,1991; Cronin & Carver, 1998; Kail& Hall, 1994; McBride-Chang &

Manis, 1996).

To summarize the arguments in thisarea, naming speed is conceptualizedas a complex ensemble of attentional,perceptual, conceptual, memory,phonological, semantic, and motoric

subprocesses that places heavy em-phasis on precise timing requirementswithin each component and across all

components. Phonological processesplay an ineluctably important role innaming speed, but represent only onecomponent area among many. Thereseem to be strong relationships be-tween naming speed and word andtext fluency and between phonologicalawareness and word attack (real wordand nonword). Both variables con-

tribute uniquely to word identificationand also have some variance in com-mon. There appear to be strong devel-opmental trends with average readers,who approach levels of automaticity(see Note 1) on symbol-speed mea-sures by Grade 2, significantly earlierthan dyslexic readers. Nondiscrepantor garden-variety poor readers appearto be much closer to average readers intheir development of automaticity forsymbols, but further work is necessaryto understand the effects of IQ. Nam-ing speed is a weaker predictor of laterreading for nondiscrepant poor read-ers and average reader groups afterGrade 2. For severely impaired dys-

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396

lexic readers, naming speed appears tobe a powerful-and sometimes the

strongest-predictor of later readingwell into Grade 8 (Meyer et al., 1998).Given this evidence, continuing to sub-sume naming speed under phonologyobscures its separate role in readingfailure.

Question 4

What links naming-speed processesto reading? Although the phonologi-cal core deficit perspective rests on anextensive research tradition and goodcommon sense (e.g., learning grapheme-phoneme correspondence rules re-

quires an awareness of and an abilityto analyze and blend the soundswithin words), no such straightfor-ward conceptualization exists to ex-

plain how the processes underlyingnaming speed affect word identifica-tion and word attack. Toward that end,in the next two sections we brieflysummarize two nonexclusive hypothe-ses on the possible roles of orthogra-phy or general timing processes in ex-plaining the relationships betweennaming-speed deficits and readingbreakdown. The arguments in thesesections are highly speculative andrepresent work in progress (see moreelaborate discussions in Bowers &

Wolf, 1993; Wolf & Bowers, 1999).Considerable further work from a va-

riety of perspectives is needed beforethese relationships will be sufficientlyclarified.

Orthographic Pattern ..

RecognitionIn our first hypothesis, we considerwhether naming speed and reading areconnected through orthographic pro-cesses. (The second hypothesis is thesubject of Question 5.) In an earlierarticle (Bowers & Wolf, 1993), we hy-pothesized that processes underlyingslow naming speed could contribute toreading failure in three related ways:

1. by preventing the appropriateamalgamation (see Ehri, 1992) of the

connections between phonemesand orthographic patterns atsubword and word levels of

representation;2. by limiting the quality of ortho-

graphic representations in long-term memory (see Perfetti, 1992);and

3. by increasing the amount of re-peated practice needed before anorthographic code is learned as alexical or sublexical unit and before

representations of sufficient qualityare achieved.

For some time, we have each at-

tempted to examine this question atdifferent levels of analysis. Based inpart on Adams’ (1981) orthographic re-dundancy model, Bowers, Golden,Kennedy, and Young (1994) have em-phasized the importance of the learnedassociations between letters in the de-

velopment of orthographic representa-tions : &dquo;If a beginning reader is slow inidentifying individual letters (as in-

dexed by rapid naming tests), then sin-gle letters in a word will not be acti-vated in sufficiently close temporalproximity [italics added] to allow thechild to become sensitive to letter pat-terns that frequently co-occur in print&dquo;(p. 203).

Neurophysiological Evidence

Based on work in the cognitive neuro-sciences, Wolf (1991; Wolf & Obreg6n,1992) studied potential connections be-tween slow visual naming speed andaberrant neurological development atthe cellular level. For example, Living-stone, Rosen, Drislane, and Galaburda

(1991) found, in a small study of

dyslexic brains, aberrant developmentin the lateral geniculate nucleus (LGN),an area in the thalamus responsible forthe cortical and subcortical coordina-tion of visual information. Importantto arguments involving timing, the

specific area of aberrant developmentin the LGN was the magnocellularsystem-that is, those cells responsiblefor fast and transient processing of in-formation. Livingstone et al. found a

reduction in cell number and cell sizein the magnocellular system, as well asabnormalities in neural migration. Al-though the database was necessarilyvery limited, these data provided someof the first evidence for a neurophysio-logical basis for some naming-speeddeficits, albeit at the level of visual

input only (see visual processes in

model of visual naming in Figure 2).More recently, we (Wolf & Bowers,

1999) have begun the task of connect-ing all three areas: naming speed,neurophysiological evidence, and or-thographic recognition. For example,Chase (1996) stressed the importanceof low spatial frequency componentsin the visual analysis of the constituentfeatures of letters, words, and so forth

(see also Breitmeyer, 1993; Lovegrove& Williams, 1993). As discussed in themodel’s description under Question 3,low spatial frequency information in-volves very rapid processes that ex-tract the more global shapes of objects,letters, or words within 60 to 80 ms

(Legge, 1978). These frequencies areprocessed at the cellular level in the vi-sual areas by the magnocellular sys-tem. Chase (1996) connected the previ-ously discussed cytoarchitectonic dataon the LGN by Galaburda (Livingstoneet al., 1991) to his studies of visualflicker fusion in dyslexic children. Inthese studies, two very brief visual im-

ages are presented in rapid successionwith varying ISIs; children with read-ing disabilities require far greater timein the ISI to be able to see two imagesrather than a single fusion of the twostimuli. On the basis of his own andGalaburda’s findings at the neuronallevel, Chase argued that the speed andquality of visual information for lowspatial frequency components is weak-ened in impaired readers, preventingthem in higher level tasks from makingsufficiently rapid visual discrimina-tions and high-quality orthographicrepresentations.

Reflecting previously discussedwork and our earlier study (Bowers &

Wolf, 1993), our first hypothesis aboutthe relationship between namingspeed and reading leads to the follow-ing argument. If the speed and quality

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of visual information at the level of low

spatial frequencies are compromised(based, potentially, on underlying aber-rations at the cellular level), then letteridentification proceeds too slowly bothfor making high-quality letter repre-sentations and for forging the nec-

essary links between frequently co-

occurring letters to store them as

patterns (Seidenberg & McClelland,1989). The consequences for readingare as follows: The quality of ortho-graphic representations will be af-

fected, the number of common ortho-

graphic patterns (a key factor in fluentreading) will be restricted, and consid-erably more exposures (practice) willbe needed for word identification. Thework of Manis et al. (in this issue),Berninger (1994), and their colleaguesprovides increasing evidence suppor-tive of this connection between namingspeed and specific aspects of orthogra-phy (see, however, important contrast-ing arguments in Torgesen et al., 1997).Also supportive is the reading skill

profile of children who make up thesingle naming-speed deficit subgroup.These children are characterized byproblems with fluency, word identifi-cation, and comprehension.

Question 5

Do naming-speed deficits reflect a

larger, systemic timing deficit? Em-bedded in this question are two highlycomplex and unresolved issues. First,does naming speed represent the lin-guistic analogue of a larger, potentiallydomain-general timing deficit that

goes beyond language? Second, howwould such a broadened conceptual-ization of processing-speed deficits re-late to reading processes? These issueswill be initially decoupled in this sec-tion and then brought together in a de-scription of our second hypothesisabout the relationship of naming speedto reading failure. Three types of evi-dence will be brought to bear regard-

ing the breadth of the timing deficit: re-action time data, neurophysiologicalfindings, and developmental data.

The Nature of the Timing Deficitand the Question of DomainSpecificityReaction Time Data. In order to un-

derstand how extensive temporal-related deficits are in dyslexic pop-ulations, we examined the growingliterature on reader group differencesin timing at the behavioral level acrossvisual, auditory, and motoric areas (seereviews in Breznitz, 1996; Farmer &

Klein, 1995). In an attempt to add clar-ity to this research, we have provideda set of charts that depict examples ofthe range of behavioral findings for vi-sual, auditory, and motoric domains(see Tables 2, 3, and 4, respectively).

Several key points become apparentin this overview of the varied sensoryand motoric findings. The first in-

volves the sheer range of findings

TABLE 2

Behavioral Findings for Visual Tasks

asignificant differences favoring average readers. brequires simple judgment about presence/absence of stimulus. crequires more complex detection of 2 stimuli;e.g., flicker fusion tasks.

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across the perceptual and motoricareas and an explanation for thisbreadth. As noted by Wolff (1993) andby Nicolson and Fawcett (1994), therange of these findings invites but can-not be explained by a simple, across-the-board reaction time (RT) explana-tion. As denoted on the tables forvisual and auditory processes, no RTdifferences appear on single-task con-ditions at the most basic level of per-ceptual detection; rather, perceptualtiming differences in dyslexic readersseem to occur when some aspect ofchoice and integration of more thanone set of subprocesses are required

(see also Farmer & Klein, 1995). Thisfinding reinforces earlier conclusionsin studies by Blank, Berenzweig, andBridger (1975) and by Moore, Kagan,Sahl, and Grant (1982). Blank et al. ex-amined the effects of stimulus com-

plexity in intra- and crossmodal per-formance for dyslexic and averagereaders and found that the demands ofstimulus complexity in the visual

modality differentiated dyslexic read-ers : &dquo;Difficulties in processing com-plex, meaningful, visual information-and possibly in processing any

complex meaningful information-doseem to represent a pivotal source of

difficulty&dquo; (Blank et al., 1975, p. 139).Moore et al. investigated the differ-ences between average and dyslexicreaders on an extensive array of cogni-tive, perceptual, and motor tasks thatincluded 14 decision time tasks. Theyconcluded that &dquo;when the task is verysimple, decision times for retarded

readers and normal readers tend tobe very similar, but the differencesbetween the two groups increase

when the task is made more complex&dquo;(Moore et al., 1982, p. 91; see also lackof differentiation for reader groups ondot matrix tasks in Arnett & DiLollo,1979).. ’.

TABLE 3Behavioral Findings for Auditory Tasks

asignificant differences favoring average readers. brequires simple judgment about the presence/absence of stimulus. crequires more complex detection of2 stimuli.

TABLE 4

Behavioral Findings for Motor Tasks

asignificant differences favoring average readers.

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In the motoric area, drawing on along history of work on motoric prob-lems in dyslexia (Klicpera, Wolff, &

Drake, 1981; Wolff et al., 1990a, 1990b,1990c), Wolff (1993) asserted that mo-toric problems emerge in dyslexicreaders when they are required to &dquo;as-semble component units of behaviorinto temporally ordered larger ensem-bles&dquo; (p. 101). It would appear, there-fore, that across both sensory andmotor domains, processing-speed dif-ferences are found between reader

groups, but not at the level of basic re-action time. The elements of choice and

precise, temporal coordination-bothof which contribute to the system’scognitive &dquo;load&dquo; (J. Holmes Bernstein,personal communication, June 1997)-appear necessary for the timing def-icits to be evidenced.The second, related point involves

the combination of seriation and

speed, particularly in the visual andauditory domains. As shown in Tables2 and 3, when stimuli are presented atrelatively longer intervals, differencesbetween dyslexic and average readersdo not appear; rather, they appearwhen faster levels of speed and serialrequirements occur. Thus, it would

appear that the requirements of rapid-ity and seriation present dyslexicreaders with special difficulty. Both ofthese requirements are essential as-

pects of naming-speed tasks. (Notethat Schwartz & Regan, 1996, reacheda similar conclusion for children with

receptive language problems.)

Neurophysiological Evidence. Sev-eral bodies of research, some at the cel-lular level, have suggested specific cor-tical and subcortical mechanisms that

may underlie the varied perceptualand motoric findings. In addition tothe previously discussed magnocellu-lar anomalies in the lateral geniculatenucleus (LGN), Galaburda and his col-leagues have found similar magnocel-lular anomalies in the medial genicu-late nucleus (MGN), the thalamic arearesponsible for coordinating auditoryinformation (Galaburda, Menard, &

Rosen, 1994). Because the MGN mag-nocellular pathways are intrinsically

involved in the speed with which audi-tory information is processed, aberrantdevelopment in these auditory areascould affect a child’s early ability todiscriminate individual phonemes andto develop good quality phonemic rep-resentations. This, in turn, would po-tentially disrupt the development ofvarious phonological processes, a posi-tion incorporated in the research ofMerzenich, Tallal, and their colleagueswith children with language impair-ments (Merzenich et al., 1996; Tallalet al.,1996). The directionality of the ef-fects of cortical-subcortical anomalies,however, is not straightforward. Ani-mal models of induced cortical pathol-ogy indicate that changes in the behav-ioral speed of auditory processing canhave subcortical effects on underlyingthalamic nuclei (see Herman, Gala-burda, Fitch, Carter, & Rosen, 1997;and Sherman, reported in Galaburda,1996).

In their studies of motoric timing dif-ferences, Wolff and his colleagues(Waber, 1999; Wolff, 1993; Wolff et al.,1990a, 1990b, 1990c) found that dyslexicreaders are also affected by increasedrate requirements, but particularlyunder certain conditions (e.g., alternat-ing hand conditions that require bi-hemispheric input). Wolff et al. (1990c)included differences in the rate of in-

terhemispheric transfer as one possi-ble, more general explanation for theirfindings. In a recent MRI study of asmall sample of dyslexic readers, Hyndet al. (1995) noted some morphologicaldifferences in the anterior and poste-rior regions of the corpus callosum,areas that would affect how rapidly thetwo hemispheres transfer informationbetween homologous regions neces-sary for reading. Hynd et al. (Hynd etal., 1995; Hynd & Semrud-Clikeman,1989; Hynd, Semrud-Clikeman, Lorys,Novey, & Eliopulos, 1990) connectedtheir MRI findings to previously dem-onstrated cellular level anomalies in thefrontal areas of people with dyslexia(Galaburda, Sherman, Rosen, Aboitiz,& Geschwind, 1985; see Note 2).There has been increased attention to

the nature of timing in human behav-ior (see Rosenbaum & Collyer, 1998).

Three major types of explanations fortiming are frequently discussed (Co-hen, 1999):

1. a central time-keeping mechanism;2. multiple reference systems;3. no mechanisms or systems, but

rather the product of sequencingand memory processes.

With the first view, one central ques-tion is whether specific cortical or sub-cortical areas function as an oscillator-

clock controlling the rate of oscillationin various processes. A precursor ofthis view is found in earlier work byOjemann (1983, 1984). After demon-

strating that naming, reading, and se-quential, orofacial movements are alldisturbed when the same anterior

frontal lobe areas are blocked by elec-trical stimulation, Ojemann arguedthat the mechanism common to these

particular language and motor functionsmight be a precise timing mechanism crit-ical to both decoding and languageproduction. Attempting to understandpossible connections among naming,reading, and motoric problems, Wolf(1991) used work by Ojemann (1983,1984) and by Tzeng and Wang (1984) toargue for the existence of a common

precise timing mechanism employedin some linguistic, perceptual, andmotor functions. In this earlier work,Wolf posited that a breakdown withinsuch a mechanism could help explainboth the breadth of timing deficitsnoted among dyslexic readers and onepossible source of the connections be-tween naming speed and readingbreakdown.Another example of a more central

time-keeping explanation for percep-tual, linguistic, and motoric timingdeficits in dyslexic readers is from thework of Llinas (1993, 1996). Llinas

(1993) conceptualized dyslexia as a

syndrome in which the disruption oftemporal processes may underlie read-ing failure. Briefly, Llinas speculatedthat the intralaminar nucleus in thethalamus may function as a timingmechanism that coordinates the rate ofoscillation in various sensory and mo-toric regions. If Llinas’ hypothesis

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400

about the role of the intralaminar nu-cleus in timing is to be evaluated, onefuture direction in dyslexia researchwould be cytoarchitectonic investiga-tions in this area of the thalamus, sim-ilar to previous work with the lateraland medial geniculate nuclei.There is to date no resolution con-

cerning what causes or connects theobserved timing deficits across vari-ous linguistic, perceptual, and motoricdomains. Wolf’s earlier hypothesisabout the role of a precise timing mech-anism in reading failure (Wolf, 1991)and Llinas’ hypothesis about the time-governing role of the intralaminarnucleus are examples of more unifiedoscillator-clock explanations for tim-ing disruptions in some dyslexic read-ers. Researchers like Denckla (1998)and Wolff (1993) have eschewed thepossibility of any single mechanism ca-pable of explaining all the deficits

noted. Recent work by Wood (personalcommunication, February 7, 2000) andIvry and his colleagues (Mangels &

Ivry, 1999) has suggested explanationsthat invoke multiple reference sys-tems ; for example, findings by Man-gels and Ivry indicate that multiplepathways involving the cerebellum,prefrontal cortex, and thalamic areasare involved in various aspects of tim-ing.Another possible example of the ef-

fects of multiple reference systems in-volves a scenario where there are basic,simultaneous problems in the speedand quality of both visual and auditoryinformation, as would be the case ifboth indicated subcortical areas (LGNand MGN) are poorly developed (Gal-aburda et al., 1994) or too slowly coor-dinated in time (Llinas, 1993, 1996). Al-though either of these failures to buildhigh-quality visual and auditory rep-resentations would impede word iden-tification and word attack skills, thecombination of both would cripple thesystem by permitting no compen-satory routes from the other system.The most intractable forms of readingdisability, such as those seen in thedouble-deficit subtype, fit such a de-scription and could be explained by

either multiple system or central time-keeping explanations.

Developmental Data. A related setof scenarios about explanations for

timing has been discussed by Kail andHall with an emphasis on namingspeed (Hale, 1990; Kail, 1991; Kail &

Hall, 1994). They posited that there canbe at least three possible sources fordifferences in the normal developmentof processing rates: a global speed-of-processing factor that affects all com-ponents ; a local trends factor that is lo-calized to particular components; anda task-strategy factor (e.g., the rate forthe letter- and number-naming taskswill always be faster than the rate forcolor- or object-naming tasks, due tothe automatized properties inherent inalphanumeric stimuli). Kail and Hall(1994) provided evidence for a moregeneral or global processing-speedfactor that underlies naming-speedchanges in average-reading childrenand that is connected to the speed ofword recognition in reading.

It remains, however, unknownwhether differences in naming speedamong dyslexic readers can be as-

cribed to global, task-strategic, or localfactors. The cumulative timing deficitscovered by Hypothesis 2 cross do-mains and point toward the break-down either of multiple systems or ofa more global processing factor, at leastin many of the most impaired readers.The presence of single naming-speeddeficits in some readers with disabili-

ties, however, points to the possibilityof a more local rate factor (e.g., in an in-dividual, underlying component-likevisual processing of letters).Marcus (1997) in our lab conducted a

replication of Kail and Hall’s (1994)work and investigated some of thesecomplex issues in subgroups of im-paired readers whose reading level

was discrepant or nondiscrepant withgeneral cognitive ability. Preliminaryresults indicated that timed visual per-ceptual tasks (i.e., the visual matchingand cross-out tasks used by Kail andHall) correlated with all naming-speedmeasures, word identification, and

comprehension in the .50 to .91 rangein children whose poor reading wasdiscrepant with their high intellectualpotential. None of the timed tasks,however, correlated even moderatelywith word attack or phonologicalblending, and the significant correla-tions between the timed tasks and

reading measures were not found fornondiscrepant readers (see earlier sim-ilar findings under Question 1). Thesmall sample sizes in this study pre-vent generalization, but point to theimportance of examining the roles ofboth general and specific processingspeeds’ contributions to reading fail-ure in various reader subgroups (seenew work by Kail, Hall, & Caskey,1997). The more precise specification ofwhat constitute the underlying compo-nents of naming speed and how dis-ruption of each component in namingmight affect specific reading skills is

one of the most important future di-rections in this line of research (see on-going work by Cutting, Carlisle, &

Denckla, 1998; Marcus, 1997; Scarbor-

ough & Domgaard, 1998; also Manis &Seidenberg, personal communication,July, 1997).

In brief, far more evidence is neededbefore any conclusions can be drawn

about whether naming-speed deficitsreflect a more systematic failure in

timing processes. Our own currentemphasis has been on the multiplesources of breakdown in naming speedand reading that are possible in differ-ent readers (see also Denckla, 1998).The possibility of multiple sources,

however, does not exclude the possi-bility that one source in some dyslexicreaders could be found in an area

that functions as a more central time-

keeping mechanism for some percep-tual and motoric areas. In addition to

the need for further work on the un-

derlying neurological explanations ofnaming-speed deficits, future inves-

tigations are critical to understandwhether the range of naming-speedand timing deficits documented in Ta-bles 2 through 4 across different sam-ples can be demonstrated within thesame sample of severely impaired read-

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401

ers. A major question is whether theobserved extent of timing problemswill be found in particular subtypes ofreading disability. Ongoing researchprograms by Waber, Bernstein, Wolff,Duffy, and their colleagues (see Waber,1995, 1999) on populations of childrenreferred with general learning disabil-ities and by Morris, Lovett, and Wolf(1995) on children with defined read-ing disabilities have begun to investi-gate this issue with batteries of timedsensory and motor tasks.

The Possible Relationshipsof Naming Speed toReading FailureThere are many missing pieces in theconceptualizations concerning the va-riety of paths whereby deficits in nam-ing speed could result. As noted fre-quently here, the direct implication ofa multicomponential view of namingspeed is that multiple sources of its

breakdown are possible. Hypothesis 1emphasized what occurs when the un-derlying rate of processing in visualareas is disrupted and argued that theeffects of this disruption on formingorthographic representations are im-portant in fluency and comprehension.In our second hypothesis, we examinethe possible effects of broader, moregeneralized disruption in multipleprocesses with processing-speed re-

quirements. In this second hypothesis,the extent to which any individual

process is disrupted by processing-speed deficits is hypothesized to be de-pendent on the specific requirementsfor rapidity within that process or setof processes. For example, the sameunderlying source of processing-speedproblems might dramatically compro-mise lower level visual and auditorycomponents (that need to operatewithin a very narrow time window)but less obviously compromise articu-latory processes, because of the largertime window employed in articulationprocesses.Combining the multicomponential

depiction of naming in the third sec-tion with the notion of more systemic

or multiple timing deficits in dyslexicreaders, an alternative account of nam-

ing speed’s relationship to reading fail-ure emerges in Hypothesis 2. Withinthis hypothesized set of events, nam-ing speed is conceptualized as a multi-componential process that is itself amid-level subset of deficits within a

cascading system of malfunctioningtiming effects. In other words, if thereare more general timing problems,naming speed could represent at onceboth the combined effects of slowed,lower level visual, auditory, concep-tual, and motoric processes (any onecombination of which may slow it) anda cause itself of further disruption offluent reading. The causal effect is

based on the working assumption thatslower access to lexical and sublexical

information may impede the develop-ment of fluency in reading, which, inturn, impedes comprehension (seemodel of these influences in Marcus,1997).To summarize Questions 4 and 5,

these sections begin and end in specu-lation, evolving knowledge, and an in-tense need for further study. Our hy-potheses are set within this context andwithin a broader context for looking atmultiple etiologies of reading disabil-ity, discussed earlier by Wolf (1991). Inthis account, disruption in reading ornaming speed can be caused by

1. breakdown in any one specificcomponent (e.g., phonologicalprocessing);

2. failure to integrate informationacross subprocesses; and

3. rate deficits either in a singlecomponent (Hypothesis 1) oracross multiple components(Hypothesis 2).

The first hypothesis emphasizes theconnections between processes under-

lying naming speed and automatic or-thographic pattern recognition in wordidentification. In the second hypothe-sis, naming-speed deficits representthe potential linguistic manifestationof a broader, more extensive set of tim-

ing problems, with ramifications for

word attack, word identification, and

comprehension. These hypotheses arenonexclusive and, indeed, in conjunc-tion with the better understood phono-logical deficit hypotheses, could helpexplain more of the heterogeneity ofreading disabilities than currently pos-sible. For example, single naming-speed deficit readers, who remain theleast understood, may best be de-scribed by Hypothesis 1 or a variationof it; single phonological deficit read-ers would be aptly described by cur-rent phonological core deficit theories;and many double-deficit readers couldbe characterized by Hypothesis 2 or bya combination of these explanations.

Question 6

What are the implications from thisresearch for diagnosis and clinical

and educational practice? The first

major implication of the double-deficithypothesis for diagnosis is that naming-speed measures should be added reg-ularly to kindergarten and first-gradescreening batteries. Their inclusion

will aid the early identification pro-cess, particularly of the children whosedecoding problems are apparentlyminor but whose naming-speed prob-lems presage later delays in fluent

reading and sometimes in readingcomprehension. Biddle (1996) demon-strated that it is essential to test in both

kindergarten and first grade because ofthe large variability in young readersbefore automaticity for symbol recog-nition is complete (see Note 1).There are two other advantages re-

garding the inclusion of serial namingtests in predictive and diagnostic bat-teries. As demonstrated in a readingprediction study by Hurford et al.

(1994), phonological awareness tasksdo not consistently predict later read-ing as sufficiently as expected. Catts(1996) and Torgesen, Wagner, and theircolleagues (Wagner et al., 1994) haveconvincingly demonstrated that thecombination of serial naming tests

with phonological awareness mea-sures provides the strongest prediction

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capabilities to date. Another advantageis purely pragmatic. The administra-tion of the typical RAN and rapid al-ternating stimulus (RAS) tasks for let-ters, numbers, colors, and common

objects (see Wolf, 1986) takes 5 to 8minutes in total. The tests are simplyconstructed (see Wolf et al., 1986),quickly administered, and easily per-formed by most children.An implication for clinical practice is

that naming-speed measures make animportant contribution to a wide vari-ety of diagnostic batteries, well beyondreading prediction. This information isparticularly relevant for poor readersor other children with learning disabil-ities who appear in the normal rangefor most phonological and decodingskills (see Blachman, 1994; Felton,1993). Slow performances on continu-ous naming tasks can prompt a morein-depth examination of the under-

lying factors that may affect fluent

reading.

Question 7

What are the implications of thedouble-deficit hypothesis for educa-tional intervention? As mentioned inthe introductory article, if the principalassumptions of the double-deficit hy-pothesis are correct, two importantsubgroups of impaired readers receiveinsufficient attention to skills involved

in the development of fluency and au-tomaticity in word recognition. Al-

though Lovett, Steinbach, and Frijters(in this issue) clearly demonstrate thattreatment for children with naming-speed deficits and double deficitsshould certainly include the phonemicawareness and phonological decodingtraining currently prescribed, inter-

vention should also include explicittraining toward establishing the auto-maticity of these skills. Furthermore,compared to children with singlephonemic deficits, children with dou-ble deficits may well require extraordi-nary amounts of practice in readingand rereading text (Bowers & Ken-

nedy, 1993; Young, Bowers, & MacKin-

non, 1996). We have hypothesized thatsome of the treatment-resistant groupsdescribed by Torgesen et al. (1994) intheir phonological awareness-basedtreatments may be composed of chil-dren who fall into either the singlenaming-speed deficit subgroup or thedouble deficit subgroup.

Lovett, Steinbach, and Frijters (inthis issue) have made the first criticalforay into investigations in this area byretrospectively subtyping participantsin their intervention studies and exam-

ining the preferential response of thesegroups to their well-established, theo-retically motivated phonological andmetacognitive treatment programs. It

is essential to note that all subtypesmade substantial gains on phonologi-cal measures and word identification

accuracy with their programs. The

naming-speed deficit subtype showedno changes in RAN naming speed, butdid improve in latencies for keywords.The phonological deficit group mademost gains in nonword reading tasks.These are the first retrospective treat-ment data supporting some of thebasic assumptions of the double-deficithypothesis within existing phonologi-cal programs. However, as pointed outby Lovett et al., only when we haveprograms specifically addressing in-

creased fluency in word recognitionprocesses will we be able to test the

utility of this hypothesis with regard totreatment response.An ongoing NICHD research project

by Morris, Lovett, and Wolf (1995) isdirectly investigating, among othergoals, the preferential treatment re-

sponse of double-deficit hypothesissubtypes to Lovett et al.’s (in this issue)phonological and metacognitive pro-grams and to a new curriculum explic-itly designed to address issues of rateand automaticity. Small groups of ran-domly assigned children are given anintensive pull-out intervention basedon one of three different treatment

packages or a control (math and studyskills) program. A phonological base isessential to each treatment package.

Thus, the first half of each package in-cludes the systematic phonologicalanalysis and blending (PHAB) pro-gram, used by Lovett et al. and shownto have strong generalization andtransfer effects (Lovett et al., 1994). ThePHAB program is based on the SRA

Reading Mastery Fast Cycle program(Engelmann & Bruner, 1988). The sec-ond half of each treatment representsone of three approaches:

1. a control, study skills programthat would allow phonological-treatment-only comparisons;

2. a metacognitive strategy program(adapted by Lovett from parts ofthe Benchmark School program;see Gaskins, Downer, & Gaskins,1986); and

3. the RAVE-O (Retrieval, Automatic-ity, Vocabulary Elaboration, Or-thography) curriculum designedby Wolf and her colleagues (Wolf,Miller, & Donnelly, in this issue).

The combined emphases of theRAVE-O program embody the philo-sophical principles of a connectionistapproach to reading (see Adams, 1990;Foorman, 1994)-that is, that skillfulword reading is the consequence of therapid, &dquo;coordinated and highly inter-active processing of the orthography ofwords, their meanings and pronuncia-tions&dquo; (Adams, 1990, p. 107). As con-ceptualized here, the RAVE-O programrepresents the first comprehensive ap-proach to fluency in outcome readingbehaviors (i.e., word attack, wordidentification, and comprehension)and to automaticity in underlyingcomponent processes (e.g., visual andauditory discrimination, orthographicpattern recognition, vocabulary devel-opment, and lexical retrieval; see a re-view of fluency-related programs inMeyer & Felton, 1998). RAVE-O is thefirst of a series of efforts to addressthe implications of the double-deficithypothesis-with its explicit emphasison automaticity and fluency-in class-room intervention.

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SummaryThe research summarized in this arti-cle and special issue represents a shiftin perspective from the direction ofreading disabilities research over thelast decade and a half. The double-deficit hypothesis represents an evolv-ing conceptualization of reading dis-abilities that integrates previous workon phonological deficits with researchon naming-speed deficits. The viewthat phonological processing deficitslie at the core of reading failure hasbeen extended to incorporate a secondmajor core deficit in the processes un-derlying naming speed. Three sub-types of impaired readers are presentlycategorized under this hypothesis,characterized, respectively, by phono-logical deficits, naming-speed deficits,and a combination of both. A range ofevidence in several languages demon-strates that children with double defi-cits represent the most serious forms ofreading disability.Although naming-speed processes

clearly include aspects of phonologicalprocessing, they are not reducible to asubset of phonological processes.Rather, naming speed is conceptual-ized as a complex ensemble of atten-tional, perceptual, conceptual, memory,phonological, semantic, and motoricsubprocesses that have precise, rapidtiming requirements within and acrossall components. The structural com-plexity of the naming-speed processeswas the basis for two nonexclusive hy-potheses about the nature of the linkbetween naming speed and reading.The first hypothesis emphasized theconnections among processes under-

lying naming speed, automatic ortho-graphic pattern recognition, wordidentification, and reading fluency.The second hypothesis explored thepossibility of multiple or domain-

general timing problems and their ef-fects on naming speed and readingfailure.

In summary, the authors of this spe-cial issue believe that a more refined

understanding of the unique and com-

bined contributions of both phonolog-ical and naming-speed processes willprove essential for an ultimately moredifferentiated view of reading failureand, very important, a more compre-hensive approach to reading interven-tion. It is, in fact, the implications fordiagnosis and intervention that havepropelled this change in our perspec-tive and that demand our best effortsin future research.

ABOUT THE AUTHORS

Maryanne Wolf, PhD, is director of the Cen-ter for Reading and Language Research at TuftsUniversity and a professor in the Eliot-PearsonDepartment of Child Development. Her workfocuses on reading disabilities, reading inter-vention, and neuropsychology. Patricia G.

Bowers, PhD, is an associate professor of psy-chology at the University of Waterloo, Ontario,Canada. She is a member of the Clinical Psy-chology Division in the Psychology Depart-ment, with research interests primarily in read-ing disabilities. Kathleen Biddle, PhD, wasresearch coordinator for the Center for Readingand Language Research. Her interests includeneuropsychology and reading intervention. Ad-dress : Maryanne Wolf, Center for Reading andLanguage Research, Miller Hall, Tufts Univer-sity, Medford, MA 02155.

AUTHORS’ NOTE

We wish to thank all past and present membersof the Tufts Center for Reading and LanguageResearch, particularly Heidi Bally, Theresa

Deeney, Katharine Donnelly, Katherine Fein-berg, Alyssa Goldberg, Julie Jeffery, Terry Joffe,Cynthia Krug, Lynne Miller, Maya Misra,Tasha Moni, Mateo Obreg6n, Claudia Pfeil, andDenise Segal for work cited in this article. Wewish to thank the following colleagues at theUniversity of Waterloo for their work cited here:Elissa Newby-Clark, Jonathan Golden, RichardSteffy, Kim Sunseth, and Arlene Young. We aregrateful to Wendy Galante for technical help onthis article and to Tamar Katzir-Cohen and

Osnat Margalit for their contributions to the ta-bles. The first author wishes to acknowledge thesupport of the Stratford Foundation, Educa-tional Foundation of America, Biomedical Sup-port Grants, Fulbright Research Fellowship,and Tufts Eliot-Pearson Department of ChildDevelopment Fund for the first phases ofthis work, and NICHD Grant No. lR55HDI

OD30970-01AI to the first author and to Drs.Robin Morris and Maureen Lovett for supportduring ongoing intervention phases.

NOTES

1. Beyond the scope of this article are criticaldiscussions about the nature of automaticity(see Logan, 1988; Stanovich, 1990; Wolf,1991) and about comparisons between al-phanumeric (letters and numbers) stimulithat achieve more automatic-like rates than

colors or objects across all populations stud-ied (see Wolf, 1991; Wolf et al., 1986). Alsoof importance in this discussion is the role ofexperience and familiarity. Clearly, somechildren whose environments provided themwith less exposure to symbolic stimuli thanother children will achieve automatic rates

at later ages for reasons other than those de-scribed here for dyslexic readers (Sankarana-rayanan, personal communication, May1997).

2. It is important to note that individuals withdyslexia traditionally perform poorly onfrontal lobe tests and that RAN tasks are in-creasingly categorized in neuropsychologi-cal batteries as frontal lobe tasks. A promis-ing direction in future imaging and evokedpotential studies would be to explore the

connections between naming speed andother timed tasks and areas of morphologicaldifferences in people with dyslexia, particu-larly in frontal and prefrontal regions (seeGalaburda, 1996).

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