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Visual-Sequential and Visuo-SpatialSkills in Dyslexia: Variations Accordingto Language Comprehension andMathematics SkillsTurid Helland & Arve Asbj⊘rnsenPublished online: 09 Aug 2010.

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Child Neuropsychology 0929-7049/03/0903-208$16.002003, Vol. 9, No. 3, pp. 208–220 # Swets & Zeitlinger

Visual-Sequential and Visuo-Spatial Skills in Dyslexia:Variations According to Language Comprehension

and Mathematics Skills

Turid Helland1,3 and Arve Asbjørnsen2,3

1Institute of Special Education, University of Oslo, Norway, 2Institute of Psychosocial Science,University of Bergen, Norway, and 3Centre for Logopedics, Eikelund Resource Centre, Bergen, Norway

ABSTRACT

This study focused on visual-sequential and visuo-spatial functions in a group of 39 heavily dyslexic children,compared to a Control group. Mean age was 12.72 (SD 1.71). The dyslexia group was divided into threesubgroups by language comprehension and mathematics skills. Only on a visual-sequential task was nodifference seen between the groups. The main differences occurred between the two dyslexic subgroups with nolanguage comprehension impairment, but with varying mathematics skills. Whereas the subgroup with goodmathematics skills scored within the upper ranges, the mathematics-impaired subgroup showed significantlylower scores. The third dyslexic subgroup, with both language comprehension and mathematics impairments,performed within the norm. The study indicates a dissociation between language comprehension and visuo-spatial skills in dyslexia, which has implications for how variations in dyslexia should be understood. The resultsalso show that the visuo-spatial impairments seen in one of the dyslexia subgroups lead to two ways ofunderstanding mathematics impairment when it co-occurs with dyslexia: (1) as a visuo-spatial problem; (2) as alinguistic problem. These distinctions should imply different intervention strategies in dyslexia.

This study focused on visual-sequential and visuo-

spatial skills in dyslexia. According to the defini-

tion by the British Dyslexia Association (1998),

dyslexia is a constitutional, complex neurological

condition. The symptoms of dyslexia are related to

mastering of written language, but related skills

such as oral language, numeracy, notational and

organisational skills may be affected. Since oral

language and numeracy are basic to academic

performance, these two symptoms were selected as

independent variables in order to assess possible

variations in visual skills in a group of dyslexic

children.

Earlier, dyslexia was mainly considered a

visual impairment, cp. Morgan’s (1896) and

Hinshelwood’s (1917) concept ‘‘wordblindness’’,

or Orton’s concept ‘‘strephosymbolia’’ (Orton,

1937). Later, dyslexia was defined by modality

impairment as auditory, visual or a combination

of the two (Boder, 1968; Gjessing, 1986). During

the last 30 years dyslexia has typically been

defined as a phonological disorder, with reduced

emphasis on the visual aspects (see Liberman,

1973; Liberman, Shankweiler, Fischer, & Carter,

1974; Snowling, 1987, 1996; Vellutino, 1979; for

reviews). Today, there seems to be a consensus

that impaired phonological processing cannot

explain all variations in dyslexia. This has led to

an increasing interest in visual skills in dyslexia

(see i.e. Stein, 2003; Stein & Walsh, 1997). No

study to date has compared visual performance in

dyslexic children with and without language

Address correspondence to: Turid Helland, Centre for Logopedics, Eikelund Resource Centre, Postboks 6039,Postterminalen, 5892 Bergen, Norway. E-mail: turid.helland@statped.noAccepted for publication: March 1, 2003.

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impairment and with and without mathematics

impairment.

Pre-school speech or language impairment has

been reported in dyslexic subjects (Snowling,

1996). According to Bishop (1997), Specific

Language Impairment (SLI) is diagnosed ‘‘where

there is a failure of normal language development

that cannot be explained in terms of mental or

physical handicap, hearing loss, emotional disor-

der or environmental deprivation’’ (p. 23). The

language difficulties interfere with academic or

occupational achievement or with social com-

munication, as described in diagnostic features

of developmental Mixed Receptive-Expressive

Language Disorder (DSM-IV, 1994). Korkman and

Hakkinen-Rihu (1994) found that among children

with developmental language disorders, deficits in

receptive and naming functions and impairment

in comprehension of complex verbal instructions

were valid predictors of spelling problems.

Bishop (1997) refers to several studies of

inattentiveness to phonology, morphology, syntax,

and semantics in children with SLI, transcending

into subtle and not easily detectable pragmatic and

discursive deficits in some older SLI children. As

many as 53% of reading-retarded children and of

SLI children could be equally classified as being

reading-retarded or having an SLI (McArthur,

Hogben, Edwards, Heath, & Mengler, 2000).

The incidence of Mixed Receptive-Expressive

Language Disorders in school-age children is

estimated at 3% (DSM-IV, 1994). The diagnostic

features of this disorder should be comparable to

the subtypes at risk for developmental dyslexia, as

described by Korkman and Hakkinen-Rihu

(1994). In brief, milder language comprehension

impairment should be seen in some older dyslexic

children, indicating unresolved language impair-

ment and a variation of aetiologies and outcomes

of dyslexia.

Mathematics is often called the ‘‘silent’’ sub-

ject, meaning that classroom activities are fre-

quently left to individual work. The subject’s

building-block structure makes the distinction

between success and failure dramatic compared

to other school subjects (Miller & Mercer, 1997).

A number of different realms are potential areas of

difficulty in mathematics: directional confusion,

sequencing problems, visual perceptual problems,

spatial awareness, short term or working memory

problems, long-term memory, linguistic abilities,

conceptual ability and cognitive style (Chinn &

Ashcroft, 1993; Miles & Miles, 1992).

‘‘Impairment of mathematical skills’’ refers to

a wide range of skills essential to mathematics,

such as linguistic skills, while ‘‘dyscalculia’’,

means ‘‘difficulty with calculation’’ (Miles,

1992). Malmer (2000) found that frequency esti-

mates of dyscalculia in the population vary from

a few percent up to 15%, reflecting a lack of

definitional agreement. In the present study, the

term ‘‘mathematics impairment’’ was used, and

defined in accordance with the DSM-IV (1994,

Mathematics Disorder) if (a) mathematics ability,

as measured by individually administered

standardised tests, is substantially below that

expected, given the person’s chronological age,

measured intelligence, and age-appropriate

education; (b) the disturbance in criterion (a) sig-

nificantly interferes with academic achievement

or activities of daily living that require mathe-

matics ability. Comorbidity of dyslexia and

mathematics impairment is described in sev-

eral studies, with reported frequencies of

mathematics-impaired pupils in dyslexic samples

varying from 30% to 50% (Macaruso & Sokol,

1998; Ostad, 1998).

The very nature of mathematics, as an abstract,

accurate and exact science, puts high demands on

a child’s attention, working memory and execu-

tive functions. Verbal working memory plays a

crucial role in supporting children’s mental arith-

metic (Adams & Hitch, 1998), and deficiencies in

working memory are seen in mathematics learn-

ing disabled individuals (Macaruso & Sokol,

1998). Components of Baddeley’s working mem-

ory model of the ‘‘Central Executive’’ and its

two slave systems, the ‘‘Phonological Loop’’ and

the visual ‘‘Sketchpad’’, may be employed in

mental arithmetic (Ashcraft, 1995). The ‘‘Central

Executive’’ is responsible for the retrieval of basic

fact knowledge and executing retrieved proce-

dural knowledge, while the actual calculation is

carried out by the ‘‘Phonological Loop’’. This

indicates a close relationship between mental

arithmetic and language processing, which is in

accordance with the original model of working

memory, claiming that speed of articulation is

VISUAL SKILLS IN DYSLEXIA 209

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related to memory span (Baddeley & Hitch,

1974).

Research on the role of the ‘‘Sketchpad’’ in

mathematics skills is essentially non-existent

(Ashcraft, Kirk, & Hopko, 1998). However, one

may speculate on how visual-sequential and

visuo-spatial assets and deficits affect the perfor-

mance of paper-and-pencil calculation and geo-

metry tasks. Also, one may wonder what role

the ‘‘Sketchpad’’ may play if the ‘‘Phonological

Loop’’ is impaired; or, conversely, what role the

‘‘Phonological Loop’’ may play if the ‘‘Sketch-

pad’’ is impaired. The two slave systems are by

definition mutually independent, but they interact

through the ‘‘Central Executive’’. In concordance

with the more general view of dyslexia as an

automatisation deficit disorder (Nicolson &

Fawcett, 1993, 1994; Tallal, Galaburda, Llinas,

& von Euler, 1993), both components may be

impaired, leaving the total resources of the

‘‘Central Executive’’ low. This may explain

the variations found in dyslexic children,

where impaired language comprehension skills

accounted for low scores on executive functions

(Helland & Asbjørnsen, 2000), and impaired

mathematics skills were associated with impaired

verbal working memory (Helland & Asbjørnsen,

in press).

However, the impact of visual working

memory in language processing (Gathercole &

Baddeley, 1993) and mathematics skills (Ashcraft

et al., 1998) remains unclear. Farah (2000) refers

to several functional imaging studies (ERP, PET,

fMRI) showing dominant left temporo-occipital

activation in letter and word imagery tasks, indi-

cating a close link between visual perception,

visual cognition, and visual imagery. Impairment

within any of these visual functions should affect

reading and writing performance. Hence, ortho-

graphic visual retention, or imagery, needed for

spelling should be disturbed accordingly, espe-

cially in words with little grapheme/phoneme

correspondence. In sorting out the different

spellings of the phoneme /k/ in ‘‘ski’’, ‘‘school’’,

‘‘cake’’, ‘‘Cox’’, ‘‘square’’, phonemic awareness

is a necessary, but not sufficient, prerequisite.

Correct spelling of these words should claim

either stable visual imagery for orthography, or

sophisticated meta-knowledge of orthography.

Impaired temporo-occipital activation could there-

fore lead to, for example, spelling impairments.

The line of argumentation in this study is that

visual functions in dyslexia should be assessed in

connection with language comprehension and

mathematics skills. Although it is not clear what

the different components of visual-sequential and

visuo-spatial abilities are, their processing must

include encoding, storage and retrieval (Baddeley,

1986), and one can mainly infer processes

of encoding and storage from how a subject

retrieves. The visual tasks most often applied

demand retrieval (immediate or delayed) and/or

organising of either visual sequences (figures

or pictures) or visuo-spatial figures (concrete or

abstract). In this study visual tasks used in estab-

lished clinical tests were applied.

The dyslexia group was divided into subgroups

by language comprehension skills and mathe-

matics skills. No differences were expected

between the dyslexic subgroups as to visuo-

sequential tasks. However, subgroup differences

were expected in the visuo-spatial tasks, with (1)

normal performance where no language compre-

hension or mathematical impairment was seen;

(2) impaired performance where normal language

comprehension skills, but mathematics impair-

ment was seen; (3) normal performance where

impaired language comprehension, but no mathe-

matics impairment was seen; (4) impaired perfor-

mance where both language comprehension and

mathematics impairment were seen. However, if

no visual impairments were seen in conditions (3)

and (4), the mathematics impairment scores in (4)

should be explained by language impairment,

rather than by a visual deficit.

METHOD

ParticipantsThe dyslexia group consisted of 39 dyslexic subjectsfrom 39 different Norwegian schools. The subjects hadoriginally been referred to their local school psychol-ogy agencies for assessment and counselling. Thosewith very low skills in reading and/or writing, or witha lack of response to remediation, were subsequentlyreferred to a regional logopedic clinic, where thepresent study was conducted. The subjects includedin the study were those diagnosed with ‘‘dyslexia’’ in

210 TURID HELLAND & ARVE ASBJØRNSEN

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Table 1. Baseline Data.

Group One-way ANOVA

(C) Control,(n¼ 20)

(1) Lþ(n¼ 13)

(2) Lþ/M�(n¼ 10)

(3) L�(n¼ 16)

F, p Follow up test

Ratio, M/F 13/7 9/4 8/2 16/0Writing hand, right/left 19/1 10/3 8/2 13/3Pre-school LI; no/yes 20/0 10/3 4/6 5/11Age (SD) 12.2 (0.4) 13.1 (1.5) 13.2 (1.7) 12.1 (1.8) 2.610, n.s. –Single word reading (SD) n.a. �2.9 (1.9) �2.7 (2.1) �3.2 (2.0) 0.197, n.s. –Single word spelling (SD) n.a. �1.7 (1.3) �2.9 (1.4) �3.1 (1.8) 3.328, p¼ .05 (1) vs. (3)�Silent reading (SD) 160.40 (23.94) 58.23 (21.43) 68.67 (44.65) 46.80 (36.95) 51.050, p< .001 (C) vs. (1)–(3)���Spelling errors (SD) 2.25 (2.83) 13.18 (4.26) 15.75 (4.17) 15.00 (4.54) 41.224, p< .001 (C) vs. (1)–(3)���Colour naming (SD) 34.36 (4.90) 40.58 (8.00) 44.06 (8.39) 63.02 (32.66) 7.424, p¼ .001 (C), (1) vs. (3)��VIQ (SD) 109.90 (11.96) 89.92 (11.88) 85.90 (14.54) 82.81 (14.04) 15.677, p< .001 (C) vs. (1)–(3)���PIQ (SD) 111.37 (13.13) 105.54 (15.08) 85.50 (16.91) 93.75 (12.09) 9.621, p< .001 (C) vs. (2), (3)� (1) vs. (2)��

Note. LI: language impairment. Single word reading, Single word spelling, from Aston Index (Newton & Thomson, 1976): grade score below attended grade. Silentreading (Carlsten, 1982); words per minute. Spelling errors on sentence dictation (Carlsten, 1982): number of errors in five sentences; Colour naming; secondsused on 48 items, from Stroop Colour Word Test (Lund Johansen, Hugdahl, & Wester, 1996); Dyslexia subgroups: see text. F and p values for one-wayANOVA with group (4: C, Lþ, Lþ/M�, L�) by tasks; p for follow up test (Tukey’s HSD): �p< .05; ��p< .01; ���p< .001.

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accordance with the definition provided by the BritishDyslexia Association (1998). All dyslexic participantshad received all of their schooling in Norway. Subjectsshowing signs of any other impairments (ADHD,various syndromes, neurological impairment, impairedsight or hearing) were excluded. In addition, thedyslexic subjects were required to be within the normalrange of intelligence as defined by full scale IQ> 70(DSM-IV, 1994), with either VIQ> 80 or PIQ> 80,and reading or writing skills at least 2 years belowactual grade (for a discussion of IQ discrepancies indyslexia, see Fletcher, Shaywitz, Shankweiler, Katz, &et al., 1994; Miles, 1995; Siegel, 1992; Stanovich,1991; Tønnesen, 1995, 1997). Left-handers and chil-dren with a pre-school history of language impairmentwere over-represented in the dyslexia sample.

Information on language development was given byparents and/or in professional reports. Usually suchinformation is imprecise as to the nature of thelanguage problem, but terms such as ‘‘language delay’’,‘‘poor vocabulary’’ or ‘‘poor understanding’’ were fre-quently used, along with information stating that thechildren had been given or should have been givensome pre-school training. Half of the dyslexic subjectshad a history of language impairment in pre-schoolaccording to this information (see Table 1). Minorarticulation problems of high frequency in the Norwe-gian language (such as the phonemes /s/ or /r/), wereclassified as non-language impaired.

The Control group consisted of 20 pupils who hadnot received any special need education or been definedas needing such help. They came from six differentclasses in a rural area surrounding a major city, and allhad received all of their schooling in Norway. Half ofthem had just entered middle school/junior high school.Thus, few of these children had a shared educationalhistory. They were all volunteers by parental consent.

It should be noted that the Norwegian school systemis a public, unitary system, based on an ideology ofinclusion. There are legal consequences for failure toreport pupils with special needs. In contrast to majorlanguages, minority languages like Norwegian sufferfrom a lack of standardised tests.

AssessmentsTable 1 offers baseline statistics for the different groups(see description of dyslexia subgroups below). Forassessment of single word reading and spelling, theAston Index (Newton & Thomson, 1976) was used(dyslexia group only). Silent text reading and sentencedictation were assessed through a commonly usedscreening test in Norwegian schools, that is, theCarlsten test (Carlsten, 1982). The silent reading testcomprises an age-adjusted story with multiple choiceclosure tasks to check for comprehension. The subjects

are instructed to read as fast as they can for a maximumof 10 min, or report immediately if they complete aheadof the time limit. Words read per minute is thencalculated. The dictation test is made up of five sentencesto be read out to the subjects. The number of wordserratically spelled, is noted. Norm data matched for ageand gender on reading and writing were provided fromour data pool covering Norwegian pupils with no needfor special education. Naming speed was assessed by theStroop Colour Naming subtask of the Stroop ColourWord Test (Lund Johansen, Hugdahl, & Wester, 1996).All participants were subjected to testing of full scaleWISC–R (Wechsler, 1974). No effects of age or genderwere seen in the baseline data, but an effect of hand wasseen in PIQ in the dyslexia group, with a significanthigher score in right-handers as compared to left-handers(98.68 and 83.50, respectively, p< .02) (see Helland &Asbjørnsen (2001) for an overview and discussion oflaterality in dyslexia).

Language comprehension was assessed using theReceptive Language Test (Maul, 1989) containing 24sentences read out by the tester along with matchingpictures for the subjects to select. One point was givenfor each correct sentence response and 1/2 point foreach partly correct response (i.e. wrong sequencing) onthe picture marking task. The maximum score was 24points, with a clinical cut-off at 22 points. Due to thelevelling out of language development in early schoolyears, the expected ceiling effect occurred (median¼22.5 points). Significant correlations (Pearson) werefound between the Receptive Language Test and VIQof the WISC–R (Wechsler, 1974; r¼ .530, p< .000)and the Stroop Colour Naming Task (r¼ .552,p< .000), using both the Control group and the dyslexiagroup. The diagnostic features of subjects with scoresbelow the cut-off should be compatible with ‘‘mildcases’’ of the Mixed Receptive-Expressive LanguageDisorder (DSM-IV), where there ‘‘may be difficultiesonly in understanding particular types of words (e.g.,spatial terms) or statements (e.g., complex ‘‘if–then’’sentences)’’.

Mathematics abilities were assessed in the dyslexiagroup only. Mathematics impairment was defined if thepupil was registered by the school as in need of aspecial mathematics teaching programme. This wasreported in 22 (56.4%) of the dyslexic subjects. Furtherassessments were administered at the clinic. A key aimwas to see how each individual would perform onnumber calculation, managing carriers and remainders,and dealing with the combinations and changes ofhorizontal and vertical directions in paper and penciltasks. No standardised tests were available for thesejoint purposes (see Miller & Mercer, 1997). Sinceclinical experience supports the reports of mathematicsanxiety (Ashcraft et al., 1998) in many children withdyslexia, assessment was carried out on the basis of

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what each individual, as a starting point, was willing toshow or do. Thus, assessment was done in the followingmanner: After having read out loud selected numbersfrom 1 to 100, the subjects were to perform pencil taskson a blank sheet of paper, starting out with each subjectshowing algorithms which s/he mastered. Some of thesubjects did this with ease, starting with division.Others started out with very elementary tasks (i.e. with4þ 2¼ 6), in which case the test leader carefullyincreased the task demands, writing the tasks horizon-tally, leaving the subject to perform the needed row andcolumn operations with carriers and remainders. Toequalise classroom settings, there was as little oralcommunication as possible. The operations were scoredby levels as follows:

Level 1: uncertain as to the reading of numbers up to100.

Level 2: reads numbers up to 100.Level 3: masters addition with 2-digit numbers and

carriers.Level 4: masters subtraction with 2-digit numbers and

carriers.Level 5: masters multiplication with 2-digit numbers

and carriers.Level 6: masters division of 2-digit numbers by 1-digit

numbers, with carriers and remainders.

A subject attaining Level 3 should then have masteredaddition, but not subtraction, having erred as to the rowand column operation, the carrying or the calculations, orcombinations of these. The subject performances werecompatible with the school reports, since subjects with noreports of mathematics impairment had no problems withCalculation Levels 1–6, while none of the subjects withreported mathematics impairments reached CalculationLevel 6. Thus, this non-standardised procedure andtesting showed an expected ceiling effect. The perfor-mances of the subjects with reported mathematicsimpairments should be compatible with the DSM-IVcriteria of Mathematics Disorder.

SubgroupingThe dyslexia group was split by language comprehen-sion (L) and mathematics abilities (M) into foursubgroups. Language comprehension was defined byscores on the Receptive Language Test (Maul, 1989).Mathematics abilities were defined by school reports ofthe subject’s having received extra help in mathematicsor not. Plus (þ) meant normal performance, minus (�)meant impairment. These distinctions resulted in foursubgroups (see Table 2):

1. Lþ (n¼ 13): norm score (�22 points) on the Re-ceptive Language Test, no extra help in mathematics.

2. Lþ/M� (n¼ 10): norm score (�22 points) on theReceptive Language Test, extra help in mathematics.

3. L�/Mþ (n¼ 4): under norm score (<22 points) onthe Receptive Language Test, no extra help inmathematics.

4. L�/M� (n¼ 12): under norm score (<22 points)on the Receptive Language Test, extra help inmathematics.

Subgroup L�/Mþ was very small, leaving littlestatistical power. Preliminary analyses were carriedout on baseline data and experimental data, firstincluding all four subgroups, then excluding L�/Mþ,then on L�/Mþ versus L�/M�, and finally with the twosubgroups collapsed into one subgroup. This yielded nodifferences between L�/Mþ and L�/M� in baselinedata (i.e. VIQ: L�/Mþ¼ 86.50 (14.93) vs.L�/M�¼ 81.58 (14.19); PIQ: L�/Mþ¼ 93.75(18.39) vs. L�/M�¼ 93.75 (10.35); n.s. on two-tailed t-test, separate for both measures) or in theexperimental data. Hence, these two subgroups werecollapsed into one subgroup, L� (n¼ 16). See furthercomments in Data Analyses section. The scores on theReceptive Language Test and Calculation Level foreach subgroup with one-way ANOVAs are shown inTable 2.

As can be seen from Table 1, the dyslexia subgroupsscored significantly lower than the Control group on thereading and writing tasks and on the VIQ. Subgroupdifferences were seen in the Stroop Colour Naming Taskand PIQ, with Lþ showing little difference compared toControl, L� falling behind on the Stroop Colour NamingTask, and Lþ/M� falling behind on the PIQ.

Dependent VariablesAll applied visual tests are standardised with normativedata from Norwegian samples. For visual-sequentialmemory the ‘‘Visual-sequential Memory for Pictures’’(VSMP) and the ‘‘Visual-sequential Memory forSymbols’’ (VSMS) from the Aston Index (Newton &Thomson, 1976) were used. Both tasks contain 10 cardswith an increasing number of symbols/pictures shown tothe subjects in sequence for 5 s. Next, the subjects are topick out correct subset cards from a stack, and place themin correct order, that is, in accordance with the sequenceof symbols/pictures previously shown to them.

For visuo-spatial tasks, ‘‘Picture Completion’’,‘‘Picture Arrangement’’, ‘‘Block Design’’ and ‘‘ObjectAssembly’’ from the WISC–R (Wechsler, 1974) and theRey-Osterieth (RO) Complex Figures Test with theCopy (‘‘RO copy’’) and Recall (‘‘RO recall’’) condi-tions (Spreen & Strauss, 1991) were used.

ProcedureThe dyslexic subjects were tested individually as part ofclinical assessment. The Control subjects were testedindividually at their respective schools in undisturbed

VISUAL SKILLS IN DYSLEXIA 213

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Table 2. Scores on the Receptive Language Test and Calculation Level.

Group One-way ANOVA

(C) Control(n¼ 20)

(1) Lþ(n¼ 13)

(2) Lþ/M�(n¼ 10)

(3) L�(n¼ 16)

F, p Follow up test

Receptive Language Test (SD) 23.14 (0.74) 23.19 (0.75) 22.95 (0.64) 19.59 (1.63) 47.205, p< .001 (C), (1), (2) vs. (3)���Calculation Level (SD) n.a. 6.00 (0.00) 3.30 (1.16) 4.13 (1.50) 17.997, p< .001 (1) vs. (2), (3)���

Note. Receptive Language Test (Maul, 1989), max. score 24 points. Calculation Level: max. score 6 points. Dyslexia subgroups: see text. F and p values for one-wayANOVA with group (4: C, Lþ, Lþ/M�, L�) by tasks; p for follow up test (Tukey’s HSD): �p< .05; ��p< .01; ���p< .001.

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settings. Test procedures on the Aston Index andWISC–R subtests were according to test instructions.The RO was administered according to instructionsgiven in Spreen and Strauss (1991, pp. 341–363), butwith no shift of pencils. A small pilot study showed thatthis caused a distraction. To limit possible effects ofslow processing or motor impairments, no time limitwas set. However, no one exceeded the limits describedin the instructions. After a 30-min delay, spent pursuingother unrelated activities, the subjects were asked toredraw the figure from memory.

Data ScoringThe tasks were scored according to their instructions.Maximum score for the two sequential tasks from theAston Index was 10 points. For the WISC–R tasksscaled scores (ss) were used. Maximum score for thetwo RO tasks was 36 points. For a 30-min delayedrecall effect, a ‘‘Memory Index’’ was calculated by theformula (Copy�Recall/CopyþRecall)�100. Since asignificant difference was found in the PIQ betweenright-handers and left-handers, all the visual tasks wereanalysed for similar effects. No significant effects were

found (by correlation and t-test). Hence, hand pre-ference was not included as a co-variant.

Data AnalysesIn the initial analyses, the original L�/Mþ was treatedas a separate subgroup. It was then excluded from theanalyses, then analysed versus L�/M� only, and finallywith the two subgroups collapsed into L�. Thisprocedure did not yield any clarification as to anypossible difference between the two language impairedsubgroups. Hence only the analyses with the collapsedsubgroup L� are reported. For the dyslexia group, theReceptive Language Test scores and the CalculationLevel scores were inter-correlated and correlated to thevisual tests using Pearson Product Moment Correlation.There was no correlation between the ReceptiveLanguage Test and Calculation Level. As can be seenfrom Table 3, significant correlations were seenbetween Calculation Level and the visuo-spatial tasks.

For initial over all analyses, a two-way ANOVAwith repeated measures was used, with the basic designgroup (4: Control, Lþ, Lþ/M�, L�) by task. Forbetween-group analyses of all groups, one-wayANOVAs were executed with the basic design group(4: Control, Lþ, Lþ/M�, L�) by task. An alpha levelwas set to .05. Significant effects were followed up byPost Hoc Test (Tukey’s HSD). Since the subgroupswere small, the results of the analyses should beconsidered tentative.

RESULTS

As can be seen from Table 3, there was a

significant correlation between the Receptive

Language Test scores and VIQ and between

Calculation Level and PIQ. There was no cor-

relation between the Receptive Language Test

and any of the other separate visual tests. The

Calculation Level scores correlated significantly

with ‘‘Picture Completion’’, ‘‘Block Design’’,

‘‘Object Assembly’’ and the three RO scores,

indicating a dissociation between the linguistic

and visuo-spatial skills in the dyslexia group. The

VSMS, VSMP, and ‘‘Picture Arrangement’’

scores correlated with neither the Receptive

Language Test nor Calculation Level.

The visual test scores are shown in Table 4. A

two-way ANOVA with group (4: Control, Lþ,

Lþ/M�, L�) by task (2: VSMP, VSMP) showed

an effect of group: F(3, 55)¼ 2.875, p¼ .05, but

not of task or interaction. Tukey’s HSD test

Table 3. Correlations Between Test Scores in the Dys-lexia Group.

ReceptiveLanguage

Test

CalculationLevel

Receptive Language Test 1.00 .17Calculation Level .17 1.00

VIQ .42�� .06PIQ .06 .34�

VSMP .12 �.03VSMS �.22 �.08

Picture Completion .04 .50���Picture Arrangement .09 �.08Block Design �.01 .57���Object Assembly �.08 .33�

RO copy �.04 .47��RO recall .06 .51���Memory Index .03 �.45��

Note. VSMP: visual-sequential memory with pictures;VSMS: visual-sequential memory with symbols(Aston Index); Picture Completion; PictureAssembly; Block Design; Object Assembly(WISC–R); RO copy, RO recall, MI: MemoryIndex (Rey-Osterieth Complex Figure Test).Correlations (Pearson Product Moment Correla-tion): �p< .05; ��p< .01; ���p< .001.

VISUAL SKILLS IN DYSLEXIA 215

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Table 4. Visual-Sequential and Visuo-Spatial Tasks.

Group F, p Follow up test

(C) Control(n¼ 20)

(1) Lþ(n¼ 13)

(2) Lþ/M�(n¼ 10)

(3) L�(n¼ 16)

Aston IndexVSMP (SD) 8.68 (1.28) 8.40 (1.20) 8.40 (0.66) 8.30 (1.03) .373, n.s. –VSMS (SD) 9.40 (0.50) 8.25 (1.00) 8.56 (0.30) 8.79 (0.92) 7.064, p< .001 (C) vs. (1), (2)���

WISC–RPicture Completion (SD) 10.60 (2.68) 12.38 (2.36) 8.30 (2.36) 10.33 (2.61) 4.739, p< .005 (1) vs. (2)��Picture Arrangement (SD) 13.30 (3.02) 10.00 (3.22) 9.50 (3.14) 9.47 (2.23) 6.683, p< .001 (C) vs. (1)–(3)��Block Design (SD) 10.75 (3.42) 11.38 (2.50) 7.10 (3.11) 9.47 (2.64) 4.570, p< .01 (C), (1) vs. (2)��Object Assembly (SD) 11.55 (1.96) 11.38 (2.79) 8.40 (3.78) 10.47 (2.33) 3.479, p< .02 (C), (1) vs. (2)�

ROCopy (SD) 31.15 (2.84) 31.95 (2.95) 25.55 (8.44) 28.76 (4.80) 4.342, p< .01 (C), (1) vs. (2)�Recall (SD) 21.48 (6.76) 25.31 (5.67) 15.05 (9.76) 18.42 (8.17) 3.838, p< .01 (1) vs. (2)�Memory Index (SD) 20.06 (13.84) 12.20 (7.80) 34.51 (29.69) 25.12 (18.93) 3.161, p< .05 (1) vs. (2)�

Note. VSMP and VSMS: max. score¼ 10; Picture Completion; Picture Assembly; Block Design; Object Assembly: scaled scores; RO copy, RO recall: max.score¼ 36. Other abbreviations as in Tables 1–3. F and p values for one-way ANOVA with group (4: C, Lþ, Lþ/M�, L�) by tasks; p for follow up test(Tukey’s HSD): �p< .05; ��p< .01; ���p< .001.

21

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showed that the group effect was due to signifi-

cantly lower scores in Lþ versus Control

(p¼ .05).

A two-way ANOVA with group (4: Control,

Lþ, Lþ/M�, L�) by task (4: ‘‘Picture Comple-

tion’’, ‘‘Picture Arrangement’’, ‘‘Block Design’’,

‘‘Object Assembly’’) showed an effect of group:

F(3, 54)¼ 6.382, p< .000; no effect of task and a

significant effect of interaction: F(9, 162)¼3.236, p¼ .001. Tukey’s HSD test showed that

the group effect was due to significantly lower

scores in Lþ/M� versus Control and Lþ(p< .01), with no difference to L�. Tukey’s

HSD test showed that the effect of interaction

was mainly due to ‘‘Block Design’’ in Lþ/M�being significantly lower than all scores in Con-

trol and Lþ (p< .005), with the exception of

‘‘Picture Arrangement’’ in Lþ. ‘‘Block Design’’

in Lþ/M� was also significantly lower than

‘‘Picture Completion’’ and ‘‘Object Assembly’’ in

L� (p< .03) Further, ‘‘Picture Arrangement’’ in

Control was significantly higher than all scores

in Lþ/M� and L� (p< .01), and ‘‘Picture

Arrangement’’ in Lþ.

A two-way ANOVA with group (4: Control,

Lþ, Lþ/M�, L�) by task (2: ‘‘RO copy’’, ‘‘RO

recall’’) showed an effect of group: F(3, 55)¼4.765, p< .005, and task: F(1, 55)¼ 137.511,

p< .000, but not of interaction. Tukey’s HSD

test showed that the group effect was due to

significantly lower scores in Lþ/M� versus Con-

trol (p< . 05) and Lþ (p< .01), with no differ-

ence to L�. The effect of task showed, as

expected, that the ‘‘RO copy’’ scores were over

all significantly higher than the ‘‘RO recall’’

scores (p< .001). The data were further explored

using a test of interaction, which showed that the

‘‘RO recall’’ score in Lþ was significantly higher

(p< .001) than the ‘‘RO recall’’ scores of the

other two subgroups, with no difference to Con-

trol. Also, the ‘‘RO recall’’ score in Lþ/M� was

significantly lower (p< .01) than all other RO

scores, with the exception of the ‘‘RO recall’’

score of L�. The ‘‘RO copy’’ score in Lþ/M�was as low as the ‘‘RO recall’’ scores in Control

and Lþ.

The one-way ANOVAs are shown in Table 4.

There are four main features to be noted from the

table. First, the VSMP yielded no between-group

differences. Second, the VSMS showed a signifi-

cant difference in Control versus Lþ and Lþ/M�,

but no differences between the dyslexia sub-

groups. Third, ‘‘Picture Arrangement’’ yielded

significant differences between Control and each

of the dyslexia subgroups, but with no differences

between the subgroups. Fourth, subgroup Lþ/M�diverged significantly, with low scores on all the

other six tasks versus Lþ, and on four tasks versus

Control, but with no difference compared to

Control as to ‘‘RO recall’’ and ‘‘Memory Index’’.

DISCUSSION

The aim of this study was to assess visual-

sequential and visuo-spatial skills in dyslexia. A

group of dyslexic children were subgrouped by

language comprehension and mathematics skills,

in accordance with the definition by the British

Dyslexia Association (1998). It was hypothesised

that visual skills within dyslexia would vary

according to this subgrouping. The main findings

confirmed the hypothesis. Tests of correlation

indicated a dissociation between language com-

prehension skills and visuo-spatial skills. This

was also reflected in the between-group analyses.

Significant subgroup differences were seen in all

visuo-spatial tasks. The between-group differ-

ences increased with degree of task complexity

and abstraction, on the one hand, and with recall

load, on the other. These effects were especially

due to the fact that the subgroup with no language

comprehension impairment but with mathematics

impairment (Lþ/M�) gradually fell behind. The

group differences were minor on the visual-

sequential tasks, which is in accordance with the

studies by Vellutino (1978). Differences emerged

in the visuo-spatial tasks, however, by increasing

degree of abstraction and memory demands.

The main differences were found between the

two subgroups with no language comprehension

impairment, yet distinguished by mathematics

skills. The third subgroup, with combined lan-

guage comprehension and mathematics impair-

ment, did not differ significantly from either the

Control group or the other two dyslexia sub-

groups. Language comprehension skills did not

correlate with any of the visual tasks, whereas

VISUAL SKILLS IN DYSLEXIA 217

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mathematics skills did. This indicate that lan-

guage comprehension and visuo-spatial skills

affect dyslexia in different ways, as shown by

subgroup differences.

The subgroup with no language comprehension

or mathematics impairment (Lþ) scored in the

upper range of the norm on the visuo-spatial

tasks, showing the typical dyslexia profile

VIQ< PIQ. This may support the views of talented

visual skills in dyslexia (Wolff & Lundberg, 2002),

and of a strong ‘‘Sketchpad’’ within the Multi-

Component Model (Baddeley, 1986; Baddeley &

Hitch, 1974). As a consequence, the dyslexic

problems in this subgroup should be explained

by typical phonological problems within the

‘‘Phonological Loop’’ that do not affect language

comprehension or mathematics skills.

The subgroup with no language comprehen-

sion impairment, but with mathematics impair-

ment (Lþ/M�), deviated from the other two

subgroups according to the WISC–R profile

VIQ¼ PIQ. The subgroup did not differ from

the other subgroups as to the visual-sequential

tasks, but deviated significantly from both the

Control group and the Lþ subgroup on ‘‘Block

Design’’, ‘‘Object Assembly’’, and ‘‘RO copy’’.

In addition, the difference to Lþ alone was sig-

nificant on ‘‘Picture Completion’’, ‘‘RO recall’’

and ‘‘Memory Index’’. The low ‘‘RO copy’’ score

and the high ‘‘Memory Index’’ score indicate an

on-line visuo-spatial problem as well as a retrieval

problem in this subgroup. From the perspective of

the Multi-Component Model, the ‘‘Sketchpad’’

should be impaired. Since subgroup Lþ and

subgroup Lþ/M� both showed good language

comprehension abilities, the mathematics impair-

ment in Lþ/M� should be related to the low

visuo-spatial scores. This, in combination with

the phonological problems typical of dyslexia,

points to rather massive obstacles in reading,

writing and arithmetics.

The main feature of the collapsed subgroup

with language comprehension impairment (L�),

was that it, like subgroup Lþ, showed the WISC–

R profile typical of dyslexia, VIQ< PIQ, with

scores in a middle position between subgroups

Lþ and Lþ/M�. In contrast to subgroup Lþ/M�,

this subgroup did not show on-line visuo-spatial

problems, which leads to the tentative conclusion

that mathematics impairment for this subgroup

may primarily be linguistically based. This should

also explain the lack of variation in visuo-spatial

skills originally seen between the two collapsed

language impaired subgroups. According to this

interpretation, the good mathematics skills seen in

the four subjects of the collapsed subgroup could

then be explained by pedagogically well-adjusted

language in mathematics teaching. However, the

results of this subgroup should be interpreted with

caution, and the possibility that mathematics

impairment also in this subgroup may be asso-

ciated with visuo-spatial impairments should be

kept open.

In sum, the three dyslexic subgroups in this study

yielded differences as to visuo-spatial skills. The

results indicate that dyslexia should not be seen as

a typical phonological impairment only, but as a

phonological impairment that may or may not co-

occur with other cognitive factors such as language

comprehension impairment and visuo-spatial

impairment. Still, one cannot hold that visuo-spatial

impairment is an underlying cause of dyslexia, but

merely hypothesise that also visuo-spatial impair-

ments, when seen, affect the encoding, retrieval and

organising of symbols to create meaning.

Our main conclusion is that linguistic and

visuo-spatial impairments seem to exist more or

less independently in dyslexia, and therefore may

or may not co-occur. No ‘‘pure’’ visually impaired

subgroup was seen in this study. This supports the

view that processing impairment in dyslexia can

affect both visual and auditory functions (Stein,

in press). In dyslexia assessment, however, visuo-

spatial skills should be evaluated as a separate

indicator of dyslexia, along with an evaluation of

language comprehension and mathematics skills.

In this respect, this study adds new knowledge to

the current body of knowledge on dyslexia.

ACKNOWLEDGEMENTS

This research was funded by the Department of SpecialEducation, University of Oslo, for the first author, byEikelund Resource Centre, Bergen, for both authors,and by the Department of Psychosocial Science,University of Bergen, Norway and a grant from theMeltzer Foundation, for the second author.

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