factor structure of the four motor-free scales of the ... the dtvp–2 manual recommends that ......

12
502 September/October 2008, Volume 62, Number 5 Factor Structure of the Four Motor-Free Scales of the Developmental Test of Visual Perception, 2nd Edition (DTVP–2) KEY WORDS • assessment • cognition • memory • pediatrics • perception • perceptual disorders • visual perception Ted Brown, PhD, MSc, MPA, BScOT(Hons), OT(C), OTR, AccOT, is Senior Lecturer, Department of Occupational Therapy, School of Primary Health Care, Faculty of Medicine, Nursing and Health Sciences, Monash University–Peninsula Campus, Building G, 4th Floor, McMahons Road, Frankston, Victoria 3163 Australia; [email protected] Sylvia Rodger, BOccThy, MEdSt, PhD, is Associate Professor and Head, Division of Occupational Therapy, School of Health and Rehabilitation Sciences, The University of Queensland, Brisbane, Queensland 4072 Australia. Aileen Davis, PhD, MSc, BSc(PT), is Senior Scientist, Division of Outcomes and Population Health, Toronto Western Research Institute, Toronto Western Hospital, Main Pavilion, 11th Floor, Room 322, 399 Bathurst Street, Toronto, Ontario M5T 2S8 Canada. INTRODUCTION. Visual–perceptual skills of children are often assessed using the Developmental Test of Visual Perceptual Skills–2, 2nd Edition (DTVP–2). PURPOSE. The factor structure of the four motor-free DTVP–2 subscales was examined. METHOD. The scores from a sample of 356 healthy children (171 boys and 185 girls) ages 5 to 11 years were used to complete a principal components factor analysis of the 4 subscales. RESULTS. The position-in-space subscale had items load on six factors. The figure ground subscale had items load on five factors. The visual closure scale and form constancy subscales both had four factors. When the four DTVP–2 subscales were combined to form one overall motor-free visual perceptual scale, the items loaded on 21 factors. CONCLUSION. The DTVP–2 and its four motor-free subscales exhibited multidimensionality instead of the expected unidimensional visual–perceptual constructs. Brown, T., Rodger, S., & Davis, A. (2008). Factor structure of the four motor-free scales of the Developmental Test of Visual Perception, 2nd Edition (DTVP–2). American Journal of Occupational Therapy, 62, 502–513. Ted Brown, Sylvia Rodger, Aileen Davis V isual perception is an important area in occupational therapy, psychology, neurology,optometry,andeducation(Gentile,1997;Grieve,2000;Hellerstein &Fishman,1999;Kalb&Warshowsky,1991;Scheiman,1997b).Therapistsand educatorsneedtousevalidandreliablevisual–perceptualinstrumentswhenassess- ingclients(Burtneretal.,1997;Groffman&Solan,1994;Schneck,2005).Several authorshaveraisedconcernsintheprofessionalliteratureregardingthemeasure- mentpropertiesofvisual–perceptualtestscurrentlybeingused.Hammill,Pearson, andVoress(1993)stated,“[T]hetestsofvisualperceptionthatareavailabletoday areallseriouslyflawed”(p.4).SalviaandYsseldyke(1991)alsocommentedonthe currentstatusofvisual-perceptualinstruments: [W]hatthemajorityoftheresearchhasshownisthatmostperceptual–motortests areunreliable.Wedonotknowwhattheymeasure,becausetheydonotmeasure anythingconsistently...thetestsusedtoassessperceptual–motorskillsinchil- drenaretechnicallyinadequate.Andforthemostpart,theyareneithertheoreti- callynorpsychometricallysound.(p.305) Thelackoftechnicallysoundvisual-perceptualinstrumentsinhibitsclinicians andresearchersalike,aproblemcommentedonbyHammilletal.(1993),whosaid, Existing tests are so poorly constructed that their results cannot be used with confidence to identify perceptually impaired children for remedial work, to test theeffectivenessofanytreatmentprogramme,ortoserveasvariablesinresearch attemptingtostudyperception.(p.2) Downloaded From: http://ajot.aota.org/pdfaccess.ashx?url=/data/journals/ajot/930099/ on 05/01/2018 Terms of Use: http://AOTA.org/terms

Upload: phungdang

Post on 11-Feb-2018

247 views

Category:

Documents


8 download

TRANSCRIPT

Page 1: Factor Structure of the Four Motor-Free Scales of the ... The DTVP–2 manual recommends that ... The DTVP–2 = Developmental Test of Visual Perception, 2nd Edition . DTVP–2 = Developmental

502� September/October 2008, Volume 62, Number 5

Factor Structure of the Four Motor-Free Scales of the Developmental Test of Visual Perception, 2nd Edition (DTVP–2)

KEY WORDS• assessment• cognition• memory• pediatrics• perception• perceptual disorders• visual perception

Ted Brown, PhD, MSc, MPA, BScOT(Hons), OT(C), OTR, AccOT, is Senior Lecturer, Department of Occupational Therapy, School of Primary Health Care, Faculty of Medicine, Nursing and Health Sciences, Monash University–Peninsula Campus, Building G, 4th Floor, McMahons Road, Frankston, Victoria 3163 Australia; [email protected]

Sylvia Rodger, BOccThy, MEdSt, PhD, is Associate Professor and Head, Division of Occupational Therapy, School of Health and Rehabilitation Sciences, The University of Queensland, Brisbane, Queensland 4072 Australia.

Aileen Davis, PhD, MSc, BSc(PT), is Senior Scientist, Division of Outcomes and Population Health, Toronto Western Research Institute, Toronto Western Hospital, Main Pavilion, 11th Floor, Room 322, 399 Bathurst Street, Toronto, Ontario M5T 2S8 Canada.

INTRODUCTION. Visual–perceptual skills of children are often assessed using the Developmental Test of Visual Perceptual Skills–2, 2nd Edition (DTVP–2).

PURPOSE. The factor structure of the four motor-free DTVP–2 subscales was examined.

METHOD. The scores from a sample of 356 healthy children (171 boys and 185 girls) ages 5 to 11 years were used to complete a principal components factor analysis of the 4 subscales.

RESULTS. The position-in-space subscale had items load on six factors. The figure ground subscale had items load on five factors. The visual closure scale and form constancy subscales both had four factors. When the four DTVP–2 subscales were combined to form one overall motor-free visual perceptual scale, the items loaded on 21 factors.

CONCLUSION. The DTVP–2 and its four motor-free subscales exhibited multidimensionality instead of the expected unidimensional visual–perceptual constructs.

Brown, T., Rodger, S., & Davis, A. (2008). Factor structure of the four motor-free scales of the Developmental Test of Visual Perception, 2nd Edition (DTVP–2). American Journal of Occupational Therapy, 62, 502–513.

Ted Brown, Sylvia Rodger, Aileen Davis

Visual�perception� is� an� important� area� in�occupational� therapy,�psychology,�neurology,�optometry,�and�education�(Gentile,�1997;�Grieve,�2000;�Hellerstein�

&�Fishman,�1999;�Kalb�&�Warshowsky,�1991;�Scheiman,�1997b).�Therapists�and�educators�need�to�use�valid�and�reliable�visual–perceptual�instruments�when�assess-ing�clients�(Burtner�et�al.,�1997;�Groffman�&�Solan,�1994;�Schneck,�2005).�Several�authors�have�raised�concerns�in�the�professional�literature�regarding�the�measure-ment�properties�of�visual–perceptual�tests�currently�being�used.�Hammill,�Pearson,�and�Voress�(1993)�stated,�“[T]he�tests�of�visual�perception�that�are�available�today�are�all�seriously�flawed”�(p.�4).�Salvia�and�Ysseldyke�(1991)�also�commented�on�the�current�status�of�visual-perceptual�instruments:

[W]hat�the�majority�of�the�research�has�shown�is�that�most�perceptual–motor�tests�are�unreliable.�We�do�not�know�what�they�measure,�because�they�do�not�measure�anything�consistently�.�.�.�the�tests�used�to�assess�perceptual–motor�skills�in�chil-dren�are�technically�inadequate.�And�for�the�most�part,�they�are�neither�theoreti-cally�nor�psychometrically�sound.�(p.�305)The�lack�of�technically�sound�visual-perceptual�instruments�inhibits�clinicians�

and�researchers�alike,�a�problem�commented�on�by�Hammill�et�al.�(1993),�who�said,Existing� tests� are� so� poorly� constructed� that� their� results� cannot� be� used� with�confidence�to� identify�perceptually� impaired�children�for�remedial�work,� to� test�the�effectiveness�of�any�treatment�programme,�or�to�serve�as�variables�in�research�attempting�to�study�perception.�(p.�2)

Downloaded From: http://ajot.aota.org/pdfaccess.ashx?url=/data/journals/ajot/930099/ on 05/01/2018 Terms of Use: http://AOTA.org/terms

Page 2: Factor Structure of the Four Motor-Free Scales of the ... The DTVP–2 manual recommends that ... The DTVP–2 = Developmental Test of Visual Perception, 2nd Edition . DTVP–2 = Developmental

The American Journal of Occupational Therapy� 503

We�addressed�the�issue�of�the�adequacy�of�a�test’s�mea-surement�properties�by�evaluating�the�construct�validity�of�the� four� motor-free� subscales� of� the� Developmental Test of Visual Perception, 2nd Edition (DTVP–2;�Hammill�et�al.,�1993).

Literature Review

Construct Validity

In�the�past,�validity�was�defined�as�three�separate�types:�con-tent,�criterion�related,�and�construct;�criterion-related�valid-ity�was� further� subdivided� into�concurrent�and�predictive�validity�(Anastasi,�1988;�Nunnally�&�Bernstein,�1994).�With�the� publication� of� the� Standards for Educational and Psychological Testing� (American� Educational� Research�Association� [AERA],�American�Psychological�Association,�&�National�Council�on�Measurement�in�Education,�1999),�validity�was�redefined�on�the�basis�of�the�work�of�Messick�(1989,�1995).�Within�this�contemporary�framework,�validity�is�now�viewed�as�a�unitary�concept�known�as�construct valid-ity. According� to� the� Standards for Educational and Psychological Testing,�construct�validity�“refers�to�the�degree�to�which�evidence�and�theory�support�the�interpretations�of�test�scores�entailed�by�proposed�uses�of�tests”�(AERA�et�al.,�1999,�p.�9).�The�Standards for Educational and Psychological Testing discusses�five�distinct� sources�of�validity� evidence:�content,�response�processes,�internal�structure,�relationship�to�other�variables,�and�consequences�of�testing.�The�internal�structure�source�of�validity�evidence�can�include�factor�ana-lytical�studies,�differential�item�functioning�studies,�and�item�analyses� to� examine� item� relationships� (Downing,� 2003;�Goodwin,�2002).�This�study�investigated�the�construct�valid-ity�evidence�about�the�internal�structure�of�the�DTVP–2.

Visual Perception

Completion�of�many�educational�tasks�and�activities�of�daily�living�(ADLs)�requires�a�combination�of�refined�abilities�that�include�vision,�visual�perception,�and�visual–motor�functions�(Chaikin�&�Downing-Baum,�1997;�Erhardt�&�Duckman,�2005;�Gentile,�1997).�Visual perception�is�understood�here�to�include�a�person’s�ability�to�interpret,�understand,�and�define�incoming�visual�information�(Scheiman,�1997a;�Werner�&�Rini,�1976).�Therefore,�visual�perception�plays�an�important�role�in�a�person’s�daily�functioning�on�many�levels.

Optometrists,� occupational� therapists,� psychologists,�and�educators�often�assess�and�treat�visual–perceptual�prob-lems� that� occur� in� school-age� children� (Todd,� 1993).�Difficulties� in�this� skill�area�can�have�a�negative�effect�on�several�occupational�performance�and�functional�skill�areas�for�children,�including�problems�in�reading,�spelling,�cursive�

and�manuscript�writing,�visual–motor�integration,�and�math�(Dankert,�Davies,�&�Gavin,�2003;�Fischer,�Hartnegg,�&�Mokler,�2000;�Schneck�&�Lemer,�1993;�Solan�&�Ciner,�1989).� In�other�words,�visual–perceptual�dysfunction�can�negatively�affect�school-age�children’s�ability�to�successfully�complete� their�ADLs,� participate� in�play� or� recreational�activities,� and� complete� schoolwork� (Cornoldi,�Venneri,�Marconato,�Molin,�&�Montinari,�2003;�Parush,�Yochman,�Cohen,�&�Gershon,�1998;�Van�Waelvelde,�De�Weerdt,�De�Cock,� &� Smits-Engelsman,� 2004;� Wright,� Bowen,� &�Zecker,�2000).�These�difficulties,�in�turn,�can�have�a�negative�effect� on� children’s� self-esteem,� self-concept,� and� accom-plishment� of� age-related� developmental� tasks� (American�Occupational�Therapy�Association,�1991).�Therefore,�thera-pists�and�educators�must�use�assessments�that�possess�sound�measurement�properties�(e.g.,�validity,�reliability,�responsive-ness,�and�clinical�utility)�to�accurately�assess�the�presence�and�impact�of�visual–perceptual�dysfunction�in�children.�One�of�the�most� commonly�used� tests� of� visual–perceptual� skills�with�school-age�children�is�the�DTVP–2;�it�consists�of�four�visual–motor�integration�subscales�and�four�motor-free�sub-scales�(Bishop�&�Curtin,�2001;�Chu�&�Hong,�1997;�Feder,�Majnemer,�&�Synnes,�2000;�Reid�&�Jutai,�1997).

DTVP–2

The�DTVP–2�is�a�revised�version�of�the�original�assessment�tool�developed�by�Marianne�Frostig�(Hammill�et�al.,�1993).�The�DTVP–2�is�composed�of�eight�separate�but�interrelated�subscales:�(1)�eye–hand�coordination,�(2)�position�in�space,�(3)�copying,�(4)�figure�ground,�(5)�spatial�relations,�(6)�visual�closure,�(7)�visual–motor�speed,�and�(8)�form�constancy.�Four�of�the�subscales�are�classified�as�motor�enhanced,�and�the�other�four,�for�which�the�items�are�scored�dichotomously,�are�clas-sified�as�motor�reduced.�The�four�motor-reduced�visual�per-ceptual�subscales�are�(1)�position�in�space,�(2)�figure�ground,�(3)�visual�closure,�and�(4)�form�constancy.�The�DTVP–2�is�designed�for�use�with�children�ages�4�to�10�years.

When�scoring�the�DTVP–2,�the�examiner�records�the�child’s�raw�score�for�the�eight�subscales.�The�eight�raw�scores�are�then�converted�into�standard�scores,�percentiles,�and�age�equivalents�using�normative�tables.�The�eight�standard�scores�are�then�assigned�to�either�the�motor-reduced�visual�percep-tion�or�visual–motor�integration�category�and�are�used�to�calculate�two�composite�quotients�(four�scales�are�classified�as�related�to�motor-reduced�integration�and�four�as�related�to� visual–motor� integration).�A�general� visual�perception�composite�quotient�is�calculated�by�combining�the�standard�scores�from�all�eight�of�the�subtests.�In�other�words,�three�composite� quotient� scores� are� calculated:�motor-reduced�visual�perception�quotient,�visual–motor�integration�percep-tion�quotient,�and�general�visual�perception�quotient.

Downloaded From: http://ajot.aota.org/pdfaccess.ashx?url=/data/journals/ajot/930099/ on 05/01/2018 Terms of Use: http://AOTA.org/terms

Page 3: Factor Structure of the Four Motor-Free Scales of the ... The DTVP–2 manual recommends that ... The DTVP–2 = Developmental Test of Visual Perception, 2nd Edition . DTVP–2 = Developmental

504� September/October 2008, Volume 62, Number 5

The�DTVP–2�manual�recommends�that�practitioners�use�the�three�composite�quotients�for�clinical�interpreta-tions,�diagnoses,� and� judgments.� “Evaluation�of� subtest�performance�is�useful�in�generating�hypotheses�or�specula-tions�about�what�a�person�did�well�or�poorly�on�a�compos-ite,�but� important�decisions�about�diagnoses�and�place-ment� should� rest� primarily� on� the� interpretation� of�composite�values”�(Hammill�et�al.,�1993,�p.�26).�Therefore,�determining�whether�the�items�of�the�four�motor-reduced�scales� load�on�a� single�motor-reduced�visual–perceptual�factor�would�provide�valuable�information�for�practitio-ners�and�further�evidence�about�the�construct�validity�of�the�DTVP–2.

The�DTVP–2�was�normed�on�a�sample�of�1,972�chil-dren�residing�in�12�U.S.�states�(Hammill�et�al.,�1993).�The�normative�sample�is�described�in�the�DTVP–2�manual�in�terms�of�race,�ethnicity,�gender,�residence,�geographic�area,�handedness,�and�age�(Hammill�et�al.,�1993).�Children�with�disabilities�were�included�in�the�normative�group�and�rep-resented�3%�of�the�total�sample.�An�equal�number�of�boys�and�girls�made�up�the�sample.�Although�the�DTVP–2�has�moderate�levels�of�reliability�and�validity�data�reported�in�its� manual� (Hammill� et� al.,� 1993;� Moryosef-Ittah� &�Hinojosa,� 1996),� it� is� still� a� relatively� new� instrument;�therefore,�limited�construct�validity�has�been�reported�in�the� research� or� professional� literature� to� date� (Chu� &�Hong,�1997).

Reliability of the DTVP–2. Three�types�of�errors�that�can�affect�the�reliability�of�almost�any�instrument,�not�just�the�DTVP–2,�are�reported�in�the�manual:�(1)�content�sampling,�(2)�time�sampling,�and�(3)�interscorer�(also�known�as�inter-rater).�Content sampling error�reflects�the�degree�of�homoge-neity�among�the� items�within�an� instrument�and�is�com-puted�by�using� the�Cronbach’s� coefficient� alpha�method.�According�to�Hammill�et�al.�(1993),�all�the�mean�alphas�for�the�DTVP–2�subscales�were�acceptable,�ranging�from�.83�to�.95�and�in�the�.90s�for�the�composite�scores.

Time sampling error� examines� the� extent� to�which� a�child’s�test�performance�is�constant�over�time�and�is�generally�measured�using� the� test–retest� technique.�A�group�of�88�children�was�tested�twice�within�a�2-week�interval�between�administrations�of�the�DTVP–2.�Accepting�.80�as�the�mini-mum�criterion� for�a� reliability�coefficient,�Hammill� et�al.�(1993)�found�that�“of�the�coefficients�for�the�eight�subtests,�two�exceed�.80,�five�‘round’�to�.80,�and�one�(for�Copying)�is�well�below�the�criterion�level�(.71)”�(p.�35).�

Interscorer reliability�refers�to�the�consistency�in�scoring�or�rating�the�same�set�of�test�booklets�between�two�separate�groups�of�raters.� In�the�case�of� the�DTVP–2,� two�people�independently�scored�88�completed�DTVP–2�worksheets.�The�coefficients�for�the�DTVP–2�subtests�ranged�from�.92�

to� .99,�whereas�coefficients� for� the� three�composite� scales�ranged�from�.95�to�.98�(Hammill�et�al.,�1993).�On�the�basis�of�the�information�presented�in�the�manual,�the�DTVP–2�appears�to�have�adequate�levels�of�reliability.�However,�pub-lishing�other�reliability�studies� in�the�research�and�profes-sional�literature�that�replicate�these�findings�would�give�pro-spective� users� of� the� DTVP–2� greater� confidence� in� its�clinical�use�or�application�in�research�studies.

Validity of the DTVP–2. Three�types�of�validity�are�often�considered�by�test�developers�and�researchers:�content,�cri-terion�related,�and�construct.�Two�types�of�content validity�are�presented�in�the�DTVP–2�manual.�First,�a�detailed�ratio-nale� for� the� subscales’� contents� and� formats� is� included.�Second,�the�validity�of�the�items�is�empirically�demonstrated�through�the�results�of�item�analysis�procedures�that�were�used�during�the�developmental�stages�of�the�DTVP–2’s�revision�and�construction.�The� three� test�developers,� all� of�whom�were�educational�psychologists,�based�their�rationale�for�the�four� motor-free� visual–perceptual� constructs� that� were�included�in�the�DTVP–2�on�their�professional�experience�and�the�findings�of�other�researchers�(Chalfant�&�Scheffelin,�1969;�Cruickshank,�Bice,�&�Wallen,�1975;�Frostig,�Lefever,�&�Whittlesey,�1966;�Gabbard,�1992;�Hammill�et�al.,�1993;�Stephens�&�Pratt,�1989;�Wedell,�1960).�Because�their�ratio-nale�appears�to�be�comprehensive�and�justified,�the�develop-ers�of�the�DTVP–2�provided�adequate�qualitative�evidence�for�its�content�validity.

The�second�type�of�quantitative�evidence�for�the�DTVP–2’s�content�validity�is�in�the�form�of�an�item�discrimination�analysis.�The�developers� of� the�DTVP–2�used� the�point�biserial�correlation�technique�(in�which�each�item�is�corre-lated�with�the�total�test�score)�to�determine�the�item�discrimi-nation.�Anastasi�(1988)�suggested�that�statistically�significant�coefficients� of� .2�or� .3� are� acceptable.�For� the�DTVP–2,�acceptable�item�discrimination�scores�ranged�from�.31�to�.73�(Hammill�et�al.,�1993).

The�concurrent�validity�of� the�DTVP–2�was� investi-gated�by�correlating�its�four�motor-free�subtests�and�com-posite�scores�with�the�total�score�of�the�Motor-Free�Visual�Perceptual�Test�(MVPT;�Colarusso�&�Hammill,�1972),�a�relatively� pure� measure� of� visual� perception,� and� the�Developmental�Test� of�Visual�Motor� Integration� (VMI;�Beery,� 1989),� a�measure�of� visual� perception� and�motor�coordination.�Because�the�VMI�and�MVPT�have�no�sub-scales,�they�yield�only�a�single�composite�score.�The�median�of�the�coefficients�for�the�DTVP–2�subscales�and�the�MVPT�and�VMI� total� scores�was� found� to�be� .65� in�both�cases,�indicating�a�“moderately�high”�relationship.�The�DTVP–2�composite�score�correlated�highly�with�the�total�scores�of�the�MVPT�(.78)�and�VMI�(.87),�respectively�(Hammill�et�al.,�1993).�According�to�the�authors,�

Downloaded From: http://ajot.aota.org/pdfaccess.ashx?url=/data/journals/ajot/930099/ on 05/01/2018 Terms of Use: http://AOTA.org/terms

Page 4: Factor Structure of the Four Motor-Free Scales of the ... The DTVP–2 manual recommends that ... The DTVP–2 = Developmental Test of Visual Perception, 2nd Edition . DTVP–2 = Developmental

The American Journal of Occupational Therapy� 505

the�fact�that�the�DTVP–2�and�the�criterion�measures�cor-relate�so�highly�and�that�they�yielded�similar�average�stan-dard�scores�on�the�test�sample�provide�strong�evidence�of�criterion-related�validity�for�the�DTVP–2�(as�well�as�for�the�MVPT�and�VMI).�(Hammill�et�al.,�1993,�p.�40)

The�third�and�final�type�of�validity,�construct validity, relates� to� the�degree� to�which� the�underlying� traits�of� an�instrument�can�be�identified�and�the�extent�to�which�these�traits�reflect�the�theoretical�model�on�which�the�test�is�based.�The�developers�of�the�DTVP–2�demonstrated�its�construct�validity�in�six�ways:�(1)�age�differentiation,�(2)�interrelation-ship� among� the�DTVP–2�values,� (3)� relationship�of� the�DTVP–2�to�tests�of�cognitive�ability,�(4)�group�differentia-tion,�(5)�factor�analysis,�and�(6)�item�validity.�

To�summarize,�the�evidence�in�terms�of�content,�crite-rion-related,� and� construct� validity�of� the� four�DTVP–2�motor-free�subscales�are�all�well�supported�by�the�informa-tion�included�in�the�manual.�Replications�of�Hammill�et�al.’s�findings�by�other� researchers� add� strength� to� the� validity�results�already�published�in�the�DTVP–2�manual.�Finally,�evaluating�the�construct�validity�of�the�DTVP–2�using�the�framework� set� out� in� the� Standards for Educational and Psychological Testing�(AERA�et�al.,�1999)�would�provide�a�contemporary�view�of�this�instrument.

PurposeThe�purpose�of�this�research�is�to�examine�the�factor�struc-ture,�a�type�of�evidence�contributing�to�construct�validity,�of�the�four�motor-free�subscales�of�the�DTVP–2�using�principal�components� analysis�with� a� sample�of� typical� school-age�children.�It�is�hypothesized�that�the�unidimensionality�of�the�motor-free�scale�of�the�DTVP–2�and�its�four�subscales�will�be�confirmed.

Method

Study Design

The� study� was� designed� as� a� prospective� cross-sectional�evaluation.

Participants

Boys�and�girls�were�eligible�for�this�study�if�(1)�they�gave�consent�to�participate�in�the�study�(by�both�the�child�and�their�parent,�guardian,�or�caregiver);�(2)�they�were�between�ages�5�and�11;�(3)�they�had�proficient�English-speaking�and�-listening�skills;�and�(4)�they�had�no�major�diagnosed�intel-lectual�or�physical�impairment(s),�as�determined�by�screening�procedures.�A�convenience�sample�of�356�children�ages�5�to�11�was�recruited;�of�those,�171�(48%)�were�boys�and�185�

(52%)�were� girls.�Participants�were� from�one�geographic�area:�the�Ottawa�metropolitan�region,�Ontario,�Canada.�The�children�came�from�junior�kindergarten�through�Grade�7.�Children�who�are�4�years�old�attend�junior�kindergarten�on�a�part-time�basis,�and�children�who�are�5�years�old�attend�senior�kindergarten�on�a�full-time�basis.�Junior�and�senior�kindergarten�are�part�of�the�primary�school�system.

Instrumentation

A�demographic�questionnaire�was�used� to�gather� relevant�background�data�about�the�children.�The�children�then�com-pleted� the� four� motor-free� visual� perceptual� DTVP–2�subscales.

Data Analysis

The�Statistical Package for the Social Sciences Version 10.0�(SPSS;�Kirkpatrick�&�Feeney,�2001)�was�used�for�data�entry,�storage,� and� retrieval.� SPSS�was�used� for� factor� analysis,�graphing,�and�calculation�of�confidence�intervals.�Descriptive�statistics,�such�as�measures�of�central�tendency�(e.g.,�mean,�median,�mode)� and�measures� of� variance� (e.g.,� standard�deviations�or�standard�error�of�the�mean),�were�calculated�as�appropriate�to�the�data�using�SPSS.

To� ensure� that� the�data�were� entered� into� the�SPSS�database�in�a�consistent�and�reliable�manner,�a�data-entry�validation� procedure� was� completed.� Sixty-seven� (19%)�randomly�chosen�cases�out�of�the�356�cases�were�selected�for�review.�Data�were�compared�on�a�variable-by-variable�basis�against�participant�case�report�forms.�This�was�accom-plished�by�double�entry�of�the�data�from�the�67�randomly�selected�participant�cases�and�comparing�the�secondary�data�entry�to�the�initial�data�entry�for�consistency�and�accuracy.�A�negligible� error� rate� of� 0.043%�was�determined.�This�procedure�confirmed�that�the�data�were�entered�in�an�accu-rate�and�reliable�way.

The�DTVP–2�unidimensionality�and�factor�structure�was�confirmed�by�principal�components�factor�analysis�with�orthogonal�Varimax�rotation�of�the�item�scores�using�SPSS�Version�10.0�(Kirkpatrick�&�Feeney,�2001).�Factor�analysis�is�a�mathematical�process�that�determines�linear�combina-tions�of�the�variables�to�explain�the�maximum�amount�of�variance� in� the�data� (Nunnally�&�Bernstein,�1994).�The�criterion�specified�for�the�minimum�factor�loading�an�item�can�have�and�still�be�considered�part�of�the�underlying�latent�trait�was�0.40�(Nunnally�&�Bernstein,�1994).

Procedures

Ethics�committee�approval�was�obtained�from�the�University�of� Queensland� Behavioural� and� Social� Sciences� Ethical�Review�Committee,�Brisbane,�Queensland,�Australia,�and�the�Children’s�Hospital�of�Eastern�Ontario�Ethical�Review�

Downloaded From: http://ajot.aota.org/pdfaccess.ashx?url=/data/journals/ajot/930099/ on 05/01/2018 Terms of Use: http://AOTA.org/terms

Page 5: Factor Structure of the Four Motor-Free Scales of the ... The DTVP–2 manual recommends that ... The DTVP–2 = Developmental Test of Visual Perception, 2nd Edition . DTVP–2 = Developmental

506� September/October 2008, Volume 62, Number 5

Committee,�Ottawa,�Ontario,�Canada.�The�four�DTVP–2�subscales� were� administered� by� a� qualified� occupational�therapist�who�had�10�years�of�professional�experience.

Because� the�purpose�of� the�study�was� to�evaluate� the�measurement�properties�of�the�four�DTVP–2�subscales,�it�was�administered�to�each�child�in�its�entirety�instead�of�being�discontinued�when�the�child’s�performance�reached�the�ceil-ing�score�outlined�in�the�test�manual.�Under�normal�circum-stances,�when�a�child�answers� three�consecutive�questions�wrong�on�the�subscales,�his�or�her�performance�on�that�sub-scale� is� terminated.�However,� it�was�necessary� to�modify�these�standard�instructions�to�evaluate�the�factor�structure�and�unidimensionality�of�the�four�DTVP–2�subscales.

Results

Participants

The�total�sample�percentage�distribution�of�children�(N�=�356)�in�each�school�grade�level�was�as�follows:�junior�kinder-garten,�3.1%;�senior�kindergarten,�14.9%;�Grade�1,�16%;�Grade�2,�13.8%;�Grade�3,�16.3%;�Grade�4,�15.7%;�Grade�5,�9.3%;�Grade�6,�8.4%;�and�Grade�7,�2.5%.�The�age�dis-tribution�for�the�sample�is�shown�in�Table�1.�Half�of�the�children�were�enrolled�in�the�public�school�system�(n�=�178),�26.7%�were�enrolled�in�the�Catholic�school�system�(n�=�95),�and�the�remainder�were�enrolled�in�the�private�school�system�(n�=�83;�23.3%).�Most�of�the�participants�(71.3%)�spoke�only�English,�whereas� the� rest� spoke�English� and�French�(25.6%);�English�and�another�language�(1.7%);�or�English,�French,�and�another�language�(1.4%).

DTVP–2 Subscale Raw Scores

The�DTVP–2�position-in-space�scale�consists�of�25�items.�For�each�position-in-space�scale�item,�children�had�a�choice�of�three�to�five�potential�response�options.�The�raw�scores�ranged�from�a�minimum�of�7�to�a�maximum�of�25.�The�mean�score�was�21.06�(SD = 3.51).�The�average�score�for�the�5-year-

old�group�of�participants�was�16.93�(SD = 3.51),�whereas�it�was�22.05�(SD = 2.33)�for�the�8-year-old�group�and�23.74�(SD = 1.63)�for�the�11-year-old�group�(see�Table�1).

The�DTVP–2�figure�ground�scale�consists�of�18�items.�For�each�figure�ground�scale�item,�children�had�a�choice�of�5�to�10�potential�response�options.�The�scores�ranged�from�a�minimum�of�7�to�a�maximum�of�18.�The�mean�raw�score�was�15.43�(SD = 2.44).�The�average�score�for�the�5-year-old�group�of�participants�was�13.40�(SD = 2.72).�The�average�score� for� the� 8-year-old� group� was� 15.74� (SD = 2.36),�whereas� the� average� score� for� the�11-year-old� group�was�17.00�(SD = 1.45;�see�Table�1).

The�DTVP–2�visual�closure�scale�consists�of�20�items.�For�each�visual�closure�scale�item,�children�had�a�choice�of�three�to�five�potential�response�options.�The�scores�ranged�from�a�minimum�of�1�to�a�maximum�of�20.�The�mean�raw�score�was�13.76�(SD = 4.52).�The�average�score�for�the�5-year-old�group�of�participants�was�9.02�(SD = 2.95);�for�the�8-year-old�group,�it�was�14.44�(SD = 3.51),�and�for�the�11-year-old�group,�it�was�18.59�(SD = 1.39;�see�Table�1).

The�DTVP–2�form�constancy�scale�consists�of�20�items.�For�each�form�constancy�scale�item,�children�had�a�choice�of�three�to�five�potential�response�options.�The�scores�ranged�from�a�minimum�of�8�to�a�maximum�of�20.�The�mean�raw�score�was�16.53�(SD = 2.94).�The�average�score�for�the�5-year-old�group�of�participants�was�13.70�(SD = 2.46).�The�average� score� for� the�8-year-old� group�was�17.32� (SD = 2.28),�and�the�average�score�for�the�11-year-old�group�was�19.31�(SD = 1.00;�see�Table�1).

The�DTVP–2�total�scale�combining�the�four�motor-free�subscales� consists� of�83� items.�The� scores� ranged� from�a�minimum�of�24�to�a�maximum�of�83.�The�mean�total�raw�score�was�66.78�(SD = 11.66).�The�average�total�score�for�the�5-year-old�group�of�participants�was�53.05�(SD = 8.98).�It�was�69.54�(SD = 8.35)�for�the�8-year-old�group�and�78.64�(SD = 3.83)�for�the�11-year-old�group�(see�Table�1).

DTVP–2 Position-in-Space Scale Factor Analysis Results. The�DTVP–2�position-in-space�scale�consists�of�25�dichoto-

Table 1. Mean DTVP–2 Scale Scores (and Standard Deviations) Based on Age of Participants (N = 356)

Age Group (Years)

DTVP–2 Position- in-Space Scale(Range 0–25)

DTVP–2 Figure Ground Scale(Range 0–18)

DTVP–2 Visual Closure Scale(Range 0–20)

DTVP–2 Form Constancy Scale

(Range 0–20)

DTVP–2 Total Scale

(Range 0–83)

5 (n = 57) 16.93 (3.51) 13.40 (2.72) 9.02 (2.95) 13.70 (2.46) 53.05 (8.98)6 (n = 56) 18.80 (3.46) 14.70 (2.57) 10.55 (3.98) 14.25 (2.60) 58.30 (10.13)7 (n = 56) 21.34 (2.38) 15.25 (2.26) 12.66 (3.58) 16.14 (2.29) 65.39 (8.01)8 (n = 57) 22.05 (2.33) 15.74 (2.36) 14.44 (3.51) 17.32 (2.28) 69.54 (8.35)9 (n = 55) 23.16 (1.62) 16.25 (1.67) 16.76 (2.65) 18.24 (2.03) 74.42 (6.30)10 (n = 36) 22.97 (2.22) 16.64 (1.15) 17.03 (3.00) 18.31 (2.18) 74.94 (6.61)11 (n = 39) 23.74 (1.63) 17.00 (1.45) 18.59 (1.39) 19.31 (1.00) 78.64 (3.83)

Note. DTVP–2 = Developmental Test of Visual Perception, 2nd Edition (Hammill et al., 1993).

Downloaded From: http://ajot.aota.org/pdfaccess.ashx?url=/data/journals/ajot/930099/ on 05/01/2018 Terms of Use: http://AOTA.org/terms

Page 6: Factor Structure of the Four Motor-Free Scales of the ... The DTVP–2 manual recommends that ... The DTVP–2 = Developmental Test of Visual Perception, 2nd Edition . DTVP–2 = Developmental

The American Journal of Occupational Therapy� 507

mously� scored� items.�All� of� the� respondents� had�perfect�scores�on�Items�1,�2,�and�4;�therefore,�they�were�excluded�from�the�initial�factor�analysis�because�of�a�lack�of�variance.�Only�Items�3�and�5�through�25�were�included�in�the�princi-pal� component� analysis� (PCA)� using� SPSS.� When� the�DTVP–2�position-in-space�scale�was�initially�factor�analyzed�using�PCA�with�Varimax�rotation,�six�factors�were�extracted�(see�Table�2).�The�DTVP–2�position-in-space�scale�exhib-ited�multidimensionality�instead�of�the�predicted�unidimen-sionality�(e.g.,�single-factor�structure).

DTVP–2� position-in-space� scale� Factor� 1� had� seven�items�load�significantly�on�it:�12,�11,�6,�7,�13,�14,�and�21.�It�had�an�eigenvalue�of�5.54�and�accounted�for�25.77%�of�the�variance.�DTVP–2�position-in-space�scale�Factor�2�had�six�items�load�significantly�on�it:�18,�17,�25,�23,�20,�and�24.�It�had�an�eigenvalue�of�1.98�and�accounted�for�9.01%�of�the�variance.�DTVP–2�position-in-space�scale�Factor�3�had�three�items�load�significantly�on�it:�21,�22,�and�19.�It�had�an�eigen-value�of�1.46�and�accounted�for�6.63%�of�the�variance.�Item�21�loaded�on�both�Factors�1�and�3.�DTVP–2�position-in-space�scale�Factor�4�had�three�items�load�significantly�on�it:�14,�8,�and�16.�Item�14�loaded�on�both�Factor�1�and�4.�It�had�

an�eigenvalue�of�1.29 and�accounted�for�5.86%�of�the�vari-ance.�DTVP–2�position-in-space�scale�Factor�5�only�had�two�items�load�significantly�on�it:�9�and�10.�It�had�an�eigenvalue�of�1.11�and�accounted�for�5.06%�of�the�variance.�DTVP–2�position-in-space�scale�Factor�6�only�had�two�items�load�sig-nificantly�on�it:�3�and�5.�It�had�an�eigenvalue�of�1.05 and�accounted�for�4.77% of�the�variance.�All�six�of�the�factors�accounted�for�56.50%�of�the�total�variance�(see�Table�2).

DTVP–2 Figure Ground Scale Factor Analysis Results. The�DTVP–2�figure�ground�scale�consists�of�18�dichotomously�scored�items.�All�respondents�had�perfect�scores�on�Items�1,�2,�and�5;�therefore,�because�of�this�lack�of�variance,�they�were�excluded�from�the�initial�factor�analysis.�Only�Items�3�and�4�and�6�through�18�were�included�in�the�PCA�using�SPSS.�When�the�DTVP–2�figure�ground�scale�was�initially�factor�analyzed�using�PCA�with�Varimax�rotation,�five�factors�were�extracted�(see�Table�3).

The�DTVP–2�figure�ground� scale� exhibited�multidi-mensionality� instead� of� the� predicted� unidimensionality�(e.g.,�single-factor�structure).�DTVP–2�figure�ground�scale�Factor�1�had�four�items�load�significantly�on�it:�14,�15,�16,�and�17.� It� had� an� eigenvalue�of� 3.06� and� accounted� for�

Table 2. DVPT–2 Position-in-Space (PS) Rotated Component Matrix (N = 356)

Component DTVP–2 PS Items 1 2 3 4 5 6 Communalities

Item 12 0.739 4.685E-02 0.191 2.763E-02 2.277E-02 6.480E-02 0.591Item 11 0.720 1.196E-02 0.246 –6.545E-02 –1.190E-02 0.180 0.616Item 6 0.683 0.130 –0.0165 0.218 7.577E-02 –5.640E-02 0.567Item 7 0.626 7.908E-02 –0.229 0.303 0.151 –0.113 0.578Item 13 0.626 0.236 1.206E-02 –9.889E-02 0.292 0.295 0.629Item 14 0.441 0.175 0.295 0.396 8.102E-02 3.531E-02 0.477Item 21 0.420 0.250 0.396 0.276 0.226 –2.171E-02 0.523Item 18 1.227E-03 0.761 –8.521E-04 –3.619E-03 8.951E-02 7.213E-02 0.593Item 17 5.494E-02 0.752 –4.870E-02 –5.335E-02 0.179 –2.598E-02 0.607Item 25 9.648E-02 0.650 0.282 0.213 –1.177E-02 0.107 0.568Item 23 9.015E-02 0.599 0.100 0.114 –-6.019E-02 1.354E-02 0.393Item 20 0.273 0.562 0.255 7.186E-02 0.117 –0.161 0.500Item 24 0.120 0.483 0.243 0.306 –8.007E-02 0.102 0.418Item 15 0.339 0.346 0.283 0.186 –9.061E-02 –0.128 0.373Item 22 2.990E-02 0.177 0.712 0.122 9.657E-02 1.866E-02 0.564Item 19 4.325E-02 0.161 0.610 0.147 0.357 5.189E-02 0.552Item 8 8.969E-02 6.054E-02 0.109 0.779 0.161 –1.311E-02 0.656Item 16 0.165 0.271 0.363 0.543 4.813E-02 0.104 0.540Item 9 2.999E-02 0.125 8.516E-02 0.233 0.776 4.828E-02 0.683Item 10 0.241 –3.421E-02 0.210 –2.017E-02 0.697 –8.558E-02 0.597Item 3 0.111 –1.350E-02 0.252 –0.161 –0.106 0.754 0.682Item 5 6.254E-02 8.429E-02 –0.239 0.347 9.679E-02 0.723 0.721Eigenvalue 5.54 1.98 1.46 1.29 1.11 1.05% of Variance 25.77 9.01 6.63 5.86 5.06 4.77 56.495

Note. DTVP–2 = Developmental Test of Visual Perception, 2nd Edition (Hammill et al., 1993); bold = significant factor. Extraction method = principal component analysis. Rotation method = Varimax with Kaiser normalization; rotation converged in 11 iterations.

Downloaded From: http://ajot.aota.org/pdfaccess.ashx?url=/data/journals/ajot/930099/ on 05/01/2018 Terms of Use: http://AOTA.org/terms

Page 7: Factor Structure of the Four Motor-Free Scales of the ... The DTVP–2 manual recommends that ... The DTVP–2 = Developmental Test of Visual Perception, 2nd Edition . DTVP–2 = Developmental

508� September/October 2008, Volume 62, Number 5

20.37%�of�the�variance.�DTVP–2�figure�ground�scale�Factor�2�had�four�items�load�significantly�on�it:�17,�9,�8,�and�10.�It�had�an�eigenvalue�of�1.45�and�accounted�for�9.69% of�the�variance.�Item�17�loaded�on�both�Factors�1�and�2.�DTVP–2�figure�ground� scale�Factor�3�had� three� items� load� signifi-cantly�on�it:�12,�13,�and�18.�It�had�an�eigenvalue�of�1.25�and�accounted�for�8.34%�of�the�variance.�DTVP–2�figure�ground�scale�Factor�4�had�two�items�load�significantly�on�it:�4�and�3.�It�had�an�eigenvalue�of�1.15�and�accounted�for�7.69% of�the�variance.�DTVP–2�figure�ground�scale�Factor�5�had�three�items�load�significantly�on�it:�7,�6,�and�11.�It�had�an�eigen-value�of�1.06 and�accounted�for�7.04%�of�the�variance.�All�five�of�the�factors�accounted�for�53.13%�of�the�total�variance�(see�Table�3).

DTVP–2 Visual Closure Scale. The�DTVP–2�visual�clo-sure�scale�consists�of�20�dichotomously�scored�items.�All�of�the�respondents�had�a�perfect�score�on�Item�1;�therefore,�the�item�was�excluded�from�the�initial�factor�analysis�(see�Table�4).�Only� Items�2� through�20�were� included� in� the�PCA�using�SPSS.�When�the�DTVP–2�visual�closure� scale�was�initially�factor�analyzed�using�PCA�with�Varimax�rotation,�four� factors�were� extracted� (see�Table�4).�The�DTVP–2�visual�closure�scale�exhibited�multidimensionality� instead�of� the� predicted� unidimensionality� (e.g.,� single-factor�structure).

DTVP–2�visual�closure�scale�Factor�1�had�eight�items�load�significantly�on�it:�8,�16,�18,�14,�20,�10,�19,�and�17.�It�had�an�eigenvalue�of�5.56�and�accounted�for�29.24%�of�the�variance.�DTVP–2�visual�closure�scale�Factor�2�had�seven�

items�load�significantly�on�it:�5,�2,�11,�15,�13,�17,�and�3.�It�had�an�eigenvalue�of�1.26�and�accounted�for�6.65%�of�the�variance.�Item�17�loaded�on�both�Factor�1�and�2.�DTVP–2�visual�closure�scale�Factor�3�had�four�items�load�significantly�on�it:�19,�12,�9,�and�6.�It�had�an�eigenvalue�of�1.09 and�accounted� for�5.75%�of� the�variance.� Item�19� loaded�on�both�Factor�1�and�3.�DTVP–2�visual�closure�scale�Factor�4�only�had�one�item�load�significantly�on�it:�4.�It�had�an�eigen-value�of�1.07 and�accounted�for�5.61%�of�the�variance.�The�four�factors�accounted�for�47.25%�of�the�total�variance�(see�Table�4).

DTVP–2 Form Constancy Scale. The�DTVP–2�form�con-stancy�scale�consists�of�20�dichotomously�scored�items.�All�respondents�had�perfect�scores�on�Items�1,�2,�3,�and�4;�there-fore,�the�items�were�not�included�in�the�initial�factor�analysis�(see�Table�5).�Only�Items�5�through�20�were�included�in�the�PCA�using�SPSS.�When�the�DTVP–2�form�constancy�scale�was�initially�factor�analysed�using�PCA�with�Varimax�rota-tion,�four�factors�were�extracted�(see�Table�5).�The�DTVP–2�form�constancy�scale�exhibited�multidimensionality�instead�of� the� predicted� unidimensionality� (e.g.,� single-factor�structure).

DTVP–2�form�constancy�scale�Factor�1�had�eight�items�load�significantly�on�it:�18,�13,�16,�14,�17,�12,�20,�and�15.�It�had�an�eigenvalue�of�4.07 and�accounted�for�25.41%�of�the�variance.�DTVP–2�form�constancy�scale�Factor�2�had�two�items�load�significantly�on�it:�7�and�6.�It�had�an�eigen-value�of� 1.40� and� accounted� for� 8.76%�of� the� variance.�DTVP–2�form�constancy�scale�Factor�3�had�three�items�load�

Table 3. DTVP–2 Figure Ground (FG) Rotated Component Matrix (N = 356)

Component

DTVP–2 FG Items 1 2 3 4 5 Communalities

Item 14 0.817 0.107 1.666E-02 7.107E-02 –9.989E-03 0.685Item 15 0.741 –2.629E-02 0.189 7.940E-02 3.074E-02 0.593Item 16 0.470 0.196 5.918E-02 –5.506E-03 0.192 0.300Item 17 0.451 0.390 0.256 0.105 –0.208 0.476Item 9 0.132 0.729 0.133 –0.104 0.106 0.588Item 8 0.140 0.719 0.156 –0.153 –1.160E-03 0.584Item 10 1.703E-02 0.614 3.990E-03 0.200 1.379E-02 0.417

Item 12 2.273E-02 0.154 0.775 0.219 –6.502E-03 0.672Item 13 9.804E-02 0.197 0.731 0.147 0.129 0.621Item 18 0.248 –6.174E-03 0.593 –0.203 –3.362E-02 0.455Item 4 3.494E-02 4.790E-02 –3.946E-02 0.792 –5.496E-03 0.632Item 3 0.105 –8.240E-02 0.185 0.712 –4.058E-02 0.560Item 7 –4.680E-03 –2.249E-02 8.549E-02 –0.112 0.729 0.552Item 6 3.294E-02 1.230E-02 –8.551E-02 3.955E-03 0.720 0.527Item 11 0.175 0.220 0.158 0.237 0.383 0.306Eigenvalue 3.06 1.45 1.25 1.15 1.06% of Variance 20.37 9.69 8.34 7.69 7.04 53.128

Note. DTVP–2 = Developmental Test of Visual Perception, 2nd Edition (Hammill et al., 1993); bold = significant factor. Extraction method = principal component analysis. Rotation method = Varimax with Kaiser normalization; rotation converged in six iterations.

Downloaded From: http://ajot.aota.org/pdfaccess.ashx?url=/data/journals/ajot/930099/ on 05/01/2018 Terms of Use: http://AOTA.org/terms

Page 8: Factor Structure of the Four Motor-Free Scales of the ... The DTVP–2 manual recommends that ... The DTVP–2 = Developmental Test of Visual Perception, 2nd Edition . DTVP–2 = Developmental

The American Journal of Occupational Therapy� 509

Table 4. DTVP–2 Visual Closure (VC) Scale Rotated Component Matrix (N = 356)

Component

DTVP–2 VC Items 1 2 3 4 Communalities

Item 8 0.650 9.281E-02 6.566E-02 –0.102 0.445Item 16 0.631 0.199 0.110 0.145 0.472Item 18 0.580 –3.990E-02 0.238 0.346 0.515Item 14 0.571 0.194 0.144 0.238 0.441Item 20 0.542 0.327 0.152 –6.962E-02 0.428Item 10 0.462 0.365 0.342 –5.920E-03 0.464Item 19 0.446 0.195 0.432 –0.263 0.493Item 7 0.312 0.310 0.214 0.201 0.280Item 5 0.303 0.697 –0.284 –0.102 0.669Item 2 –0.246 0.658 0.118 0.261 0.576Item 11 0.327 0.619 0.270 –1.291E-02 0.563Item 15 0.246 0.522 0.374 5.435E-02 0.476Item 13 0.260 0.476 0.338 7.732E-02 0.414Item 17 0.379 0.445 0.249 –0.170 0.433Item 3 0.191 0.435 0.173 0.106 0.267Item 12 0.113 0.237 0.708 –0.194 0.608Item 9 7.899E-02 0.292 0.573 0.182 0.453Item 6 0.234 –3.700E-02 0.549 0.157 0.383Item 4 9.594E-02 0.126 1.288E-02 0.756 0.597Eigenvalue 5.56 1.26 1.09 1.07% of Variance 29.24 6.65 5.75 5.61 47.25

Note. DTVP–2 = Developmental Test of Visual Perception, 2nd Edition (Hammill et al., 1993); bold = significant factor. Extraction method = principal component analysis. Rotation method = Varimax with Kaiser normalization; rotation converged in 10 iterations.

Table 5. DTVP–2 Form Constancy (FC) Scale Item Factor Analysis Rotated Component Matrix (N = 356)

ComponentDTVP–2 FC Items 1 2 3 4 Communalities

Item 18 0.714 0.115 –2.622E-02 0.125 0.540Item 13 0.682 –1.107E-02 0.143 3.558E-03 0.486Item 16 0.666 –0.130 0.153 9.015E-02 0.492Item 14 0.664 0.183 5.725E-02 –0.169 0.506Item 17 0.644 2.327E-02 0.244 0.167 0.503Item 12 0.597 0.165 8.784E-02 –2.764E-02 0.392Item 20 0.592 –0.142 9.780E-02 0.169 0.409Item 15 0.571 0.257 2.545E-02 0.324 0.497Item 19 0.362 –6.236E-04 9.548E-02 0.300 0.230Item 7 3.002E-03 0.748 6.650E-02 0.123 0.579Item 6 8.450E-02 0.727 –6.696E-02 –5.918E-02 0.544Item 8 6.694E-02 –0.135 0.804 –1.877E-02 0.670Item 11 8.456E-02 0.357 0.577 4.819E-02 0.470Item 10 0.302 –3.520E-02 0.511 3.760E-02 0.355Item 9 –9.945E-03 –0.109 –0.114 0.781 0.635Item 5 0.162 0.202 0.142 0.598 0.445Eigenvalue 4.07 1.40 1.21 1.08% of Variance 25.41 8.76 7.57 6.73 48.465

Note. DTVP–2 = Developmental Test of Visual Perception, 2nd Edition (Hammill et al., 1993); bold = significant factor. Extraction method = principal component analysis. Rotation method = Varimax with Kaiser normalization; rotation converged in six iterations.

Downloaded From: http://ajot.aota.org/pdfaccess.ashx?url=/data/journals/ajot/930099/ on 05/01/2018 Terms of Use: http://AOTA.org/terms

Page 9: Factor Structure of the Four Motor-Free Scales of the ... The DTVP–2 manual recommends that ... The DTVP–2 = Developmental Test of Visual Perception, 2nd Edition . DTVP–2 = Developmental

510� September/October 2008, Volume 62, Number 5

significantly�on�it:�8,�11,�and�10.�It�had�an�eigenvalue�of�1.21�and�accounted�for�7.57%�of�the�variance.�DTVP–2�form�constancy�scale�Factor�4�had�two�items�load�significantly�on�it:�9�and�5.�It�had�an�eigenvalue�of�1.08�and�accounted�for�6.73%�of�the�variance.�All�four�of�the�factors�accounted�for�48.47%�of�the�total�variance�(see�Table�5).

DTVP–2 Motor-Free Scale: All Four Subscales Combined—Factor Analysis Results

The�four�DTVP–2�subscales�were�combined�to�create�one�motor-free�visual–perceptual�scale:�The�position-in-space�scale�consists�of�25�items;�the�figure�ground�scale�consists�of�18�items;�and�the�visual�closure�scale�consists�of�20�items,�as�does�the�form�constancy�scale.�The�DTVP–2�manual�states�that�the�standard�scores�of�the�four�visual–perceptual�scales� can� be� summed� to� calculate� a� composite� motor-reduced�perceptual�quotient.�This�is�the�rationale�for�com-bining�the�four�visual–perceptual�subscales�together�to�see�if�the�scale�items�loaded�on�one�motor-free�visual–percep-tual�construct.

All�of�the�children�had�perfect�scores�on�the�following�scale�items:�position-in-space�Items�1,�2,�and�4;�figure�ground�Items�26,�27,�and�30�(similar�to�figure�ground�scale�Items�1,�2,�and�5);�visual�closure�Item�44�(similar�to�visual�closure�scale�Item�1);�and�form�constancy�Items�64,�65,�66,�and�67�(similar� to� form� constancy� scale� Items� 1,� 2,� 3,� and� 4).�Therefore,�these�items�were�not�included�in�the�initial�PCA.�When�the�DTVP–2�motor-free�visual–perceptual�scale�was�initially�factor�analyzed�using�PCA�with�Varimax�rotation,�21�factors�were�extracted�that�accounted�for�61.51%�of�the�total�variance.�The�DTVP–2�motor-free�visual–perceptual�scale�exhibited�multidimensionality�instead�of�the�predicted�unidimensionality.�In�other�words,�the�DTVP–2�motor-free�visual–perceptual�scale�has�a�multifactor�structure.

The�first�factor�had�23�items�load�significantly�on�it:�53,�81,�75,�54,�77,�58,�59,�63,�56,�62,�60,�79,�76,�57,�52,�80,�25,�55,�51,�78,�61,�50,�and�46.�It�had�an�eigenvalue�of�13.28�and�accounted�for�19.91%�of�the�variance.�The�second�factor�had�8�items�load�on�it:�6,�11,�45,�13,�12,�7,�21,�and�31.�It�had�an�eigenvalue�of�3.53�and�accounted�for�4.90%�of�the�variance.�The�third�factor�had�6�items�load�on�it:�25,�51,�17,�18,�20,�and�23.�It�had�an�eigenvalue�of�2.27�and�accounted�for�3.16%�of�the�variance.�The�fourth�factor�had�3�items�load�on� it:� 19,� 22,� and�21.� It� had� an� eigenvalue�of� 2.02� and�accounted�for�2.80%�of�the�variance.�The�fifth�factor�had�5�items�load�on�it:�8,�48,�16,�14,�and�9.�It�had�an�eigenvalue�of� 1.81� and� accounted� for� 2.52%� of� the� variance.� The�remaining�factors�(e.g.,�Factors�6–21)�had�between�1�and�3�items�load�on�each�and�accounted�for�the�remaining�variance�of�28.22%.

Discussion

DTVP–2 Motor-Free Subscales

Four�motor-free�visual–perceptual�subscales�are�included�in�the�DTVP–2:�the�position-in-space�scale�(25�items),�figure�ground�scale�(18�items),�visual�closure�scale�(20�items),�and�form�constancy�scale�(20�items).�According�to�the�DTVP–2�manual,� all� four� subscales� measure� discrete� subtypes� of�visual–perceptual�skills.�Hence,�the�items�for�each�subscale�should�all�group�together�to�measure�each�individual�visual–perceptual�theoretical�construct.�However,�when�the�subscale�scores�were� factor� analyzed�using�PCA,� all� four� exhibited�multidimensionality.

The�position-in-space� subscale�had� items� load�on� six�factors.�The�figure�ground�subscale�had�items�load�on�five�factors.�The�visual�closure�subscale�and�form�constancy�sub-scale�both�had�four�factors,�respectively.�This�has�implica-tions�if�a�practitioner�is�evaluating�a�child’s�true�motor-free�visual–perceptual�skills�and�the�test�scales�measure�multiple�skill�constructs�within�the�same�scale.�Multidimensionality�is�a�problem�for�the�DTVP–2�subscales.

Hammill�et�al.�(1993)�reported�details�of�the�construct�validity�of�the�DTVP–2�in�its�manual�in�six�ways:�(1)�age�differentiation,�(2)�interrelationship�among�the�DTVP–2�values,�(3)�relationship�of�the�DTVP–2�to�tests�of�cognitive�ability,� (4)�group�differentiation,�(5)� factor�analysis,�and�(6)�item�validity.�The�factor�analysis�results�are�most�related�to�the�findings�of�this�study.�The�eight�DTVP–2�subscale�performance�scores�of�the�respondents�in�the�standardiza-tion�sample�were�factor�analyzed�using�the�principal�com-ponents�method.�The�results�of�this�analysis�yielded�a�single�factor� with� an� eigenvalue� >� 1.� Because� all� the� subtests�loaded�on�a�single�factor,�it�was�presumed�that�the�factor�measured�visual�perception.�A�second�factor�analysis�was�performed�using�the�Promax�rotation�method.�This�analy-sis�generated�two�factors�with�eigenvalues�greater�than�one,�which�were�labeled�motor-reduced�visual�perception�and�visual–motor�integration.�According�to�Hammill�et�al.,�the�results� of� the� factor� analyses� again� strongly� support� the�construct� validity� of� the� DTVP–2,� including� the� four�motor-free�subscales.

DTVP–2 Motor-Free Composite Scale

The�four�DTVP–2�subscales�were�also�combined�to�create�one�motor-free�visual–perceptual�scale�made�up�of�83�items�(e.g.,�the�25�position-in-space�items,�18�figure�ground�items,�20�visual�closure�items,�and�20�form�constancy�items).�The�DTVP–2�manual�states�that�the�standard�scores�of�the�four�motor-free�visual–perceptual�scales�can�be�summed�together�

Downloaded From: http://ajot.aota.org/pdfaccess.ashx?url=/data/journals/ajot/930099/ on 05/01/2018 Terms of Use: http://AOTA.org/terms

Page 10: Factor Structure of the Four Motor-Free Scales of the ... The DTVP–2 manual recommends that ... The DTVP–2 = Developmental Test of Visual Perception, 2nd Edition . DTVP–2 = Developmental

The American Journal of Occupational Therapy� 511

to� calculate� a� composite� Motor-Reduced� Perception�Quotient�(MRPQ).�This�was�the�rationale�for�combining�the�four�visual–perceptual�subscales�together�to�see�whether�the�scale�items�loaded�on�one�motor-free�visual–perceptual�construct.�Because�respondents�achieved�perfect�scores�on�Items�1,�2,�4,�26,�27,�30,�44,�64,�65,�66,�and�67,�these�items�were�excluded�from�the�factor�analysis.

The�DTVP–2�visual–perceptual�composite�scale�(made�up� of� the� 25� position-in-space� items,� 18� figure� ground�items,�20�visual�closure�items,�and�20�form�constancy�items)�should�theoretically�exhibit�unidimensionality�if�it�is�truly�measuring�a�single�visual–perceptual�construct.�According�the�DTVP–2�manual,�“of�all�the�DTVP–2�quotients,�the�MRPQ� is� the� ‘purest’� and�most�direct�measure�of� visual�perception�in�that�only�minimal�motor�skills�(e.g.,�pointing)�are�required�to�show�perceptual�competence”�(Hammill�et�al.,�1993,�p.�25).

On�the�basis�of�the�principal�components�factor�analysis�results,�the�DTVP–2�composite�scale�exhibited�multidimen-sionality.�The�scale�items�loaded�on�21�different�factors.�This�has� implications� for� practitioners�who�use� the�DTVP–2�composite�scale�to�obtain�a�score�of�a�child’s�visual–percep-tual�skills.�According�to�the�DTVP–2�manual,�however,�the�performance�scores�of�the�four�motor-reduced�subscales�are�combined�along�with�four�other�visual–motor� integration�subscales� to� calculate� a� child’s� visual–perceptual� skills.�However,�because�of�the�MRPQ�composite�scale’s�multidi-mensionality,�this�is�not�recommended.

The�clinical,�practical,�and�theoretical� implications�of�this�process�of�combining�scale�scores�appear�to�be�question-able.�Administering�each�of�the�four�subscales�separately�and�just�using�the�individual�scale�scores�is�more�viable�and�useful�for�diagnosing�and�detecting�any�difficulties�in�motor-free�visual–perceptual�skills.�This�information�could�then�be�used�to�establish�a�profile�of�a�child’s�visual–perceptual�skills.�Such�a�profile�would� indicate� that�visual�perception� is�a�multi-dimensional�construct,�not�one�distinct,�unitary�construct.�Only�two�critiques�of�the�DTVP–2�(Bologna,�1995;�Tindal,�1995)�and�no�empirical�studies�addressing�its�construct�valid-ity�have�been�published�to�date.

Study Limitations and Recommendations for Future Research

This�study�had�several�limitations.�First,�only�the�motor-free�visual� perception� theoretical� construct� was� considered.�Visual–motor�integration�as�a�component�of�visual�percep-tion�was�not�addressed.�Second,�the�DTVP–2�was�devel-oped�by�a�researcher�in�the�United�States.�As�a�result,�the�normative�data�for�the�DTVP–2�were�based�only�on�U.S.�respondents.�Third,�only�children�presenting�with�normal�

profiles�were�included�in�this�study.�Children�with�either�an�intellectual�or�physical�impairment�(including�developmen-tal�delays�or�learning�disabilities)�or�not�possessing�a�work-ing� knowledge� of� the� English� language� were� excluded.�Fourth,�when�recruiting�children�as�participants,�only�those�who,�along�with�their�parents,�consented�to�participate�in�the�study�were�included.�There�is�always�the�possibility�of�some�bias�related�to�parental�consent.�Children�whose�par-ents� did� not� provide� consent� may� possess� some� unique�characteristics�or�score�profiles.�Because�informed�consent�is�an�ethical�requirement,�including�children�who�did�not�have�permission�from�their�parents�to�participate�was�not�a�viable�option.

It�would�be�worthwhile�to�evaluate�the�discriminant�and�diagnostic�validity�of�the�DTVP–2�subscales,�determining�their�ability�to�differentiate�between�a�group�of�respondents�who�have�a�clinical�diagnosis�(such�as�cerebral�palsy�or�atten-tion�deficit�disorder)�with�a�group�of�respondents�who�are�typically�developing.�One�final�suggestion�for�future�study�is� to�evaluate�the�predictive�validity�of�the�DTVP–2�sub-scales.�For�example,�are�the�DTVP–2�subscales�able�to�pre-dict�future�academic�ability�of�children?

ConclusionWhen�the�four�individual�motor-free�DTVP–2�scales�(posi-tion�in�space,�figure�ground,�visual�closure,�and�form�con-stancy)�were�collapsed�together�to�form�a�scale�of�motor-free�visual–perceptual�skills,�the�items�failed�to�group�together�to�measure� a�unidimensional� construct.� In�other�words,� the�four�motor-free�DTVP–2�subscales�exhibited�a�multifactorial�structure.�For�practitioners,�this�means�that�the�four�motor-free�DTVP–2�scales�can�be�used�on�an�individual�basis�with�clients�to�generate�a�profile�of�their�visual–perceptual�skills,�but�the�scale�scores�should�be�interpreted�with�caution.�In�addition,� it� is� recommended� that� the� composite� scale�scores�not� be� used� to� calculate� summary� of� motor-free�visual–perceptual�score�or�perceptual�quotient.�From�a�mea-surement�perspective,�the�findings�of�this�analysis�provide�information�that�fits�under�the�internal structure�evidence�category�of�construct�validity�of�the�DTVP–2�and�its�four�subscales.� s

AcknowledgmentsAcknowledgments�are�extended�to�three�organizations�who�funded�grants�to�make�this�study�possible:�(1)�the�Children’s�Hospital� of�Eastern�Ontario�Research� Institute,�Ottawa,�Ontario,�Canada;� (2)� the�Bloorview�Children’s�Hospital�Foundation,� Toronto,� Ontario,� Canada;� and� (3)� the�

Downloaded From: http://ajot.aota.org/pdfaccess.ashx?url=/data/journals/ajot/930099/ on 05/01/2018 Terms of Use: http://AOTA.org/terms

Page 11: Factor Structure of the Four Motor-Free Scales of the ... The DTVP–2 manual recommends that ... The DTVP–2 = Developmental Test of Visual Perception, 2nd Edition . DTVP–2 = Developmental

512� September/October 2008, Volume 62, Number 5

Canadian� Occupational� Therapy� Foundation,� Ottawa,�Ontario,�Canada.�Thanks�are�also�extended�to�the�children�who�volunteered�to�take�part�in�the�study�by�completing�the�visual–perceptual�instruments.

ReferencesAmerican� Educational� Research� Association,� American�

Psychological� Association,� &� National� Council� on�Measurement�in�Education.�(1999).�Standards for educational and psychological testing.�Washington,�DC:�Authors.

American�Occupational�Therapy�Association.�(1991).�Statement:�Occupational� therapy�provision� for� children�with� learning�disabilities�and/or�mild� to�moderate�perceptual�and�motor�deficits.� American Journal of Occupational Therapy, 45,�1069–1073.

Anastasi,�A.�(1988).�Psychological testing.�New�York:�Macmillan.Beery,�K.�(1989).�Developmental Test of Visual–Motor Integration.�

Cleveland,�OH:�Modern�Curriculum�Press.Bishop,�K.,�&�Curtin,�M.�(2001).�The�TVPS,�MVPT�and�VMI:�

What�influences�a�therapist’s�choice?�National Association of Paediatric Occupational Therapy Journal,�5,�8–11.

Bologna,� N.� B.� (1995).� Review� of� the� Developmental Test of Visual Perception, Second Edition.�In�J.�A.�Conoley�&�J.�C.�Impara� (Eds.),� The twelfth mental measurements yearbook�(pp.� 289–290).� Lincoln,� NE:� Buros� Institute� of� Mental�Measurements.

Burtner,�P.,�Whilhite,�C.,�Bordegaray,�J.,�Moedl,�D.,�Roe,�R.,�&�Savage,�A.�(1997).�Critical�review�of�visual�perceptual�tests�frequently�administered�by�pediatric�therapists.�Physical and Occupational Therapy in Pediatrics, 17,�39–61.

Chaikin,�L.�E.,�&�Downing-Baum,�S.�(1997).�Functional�visual�skills.� In� M.� Gentile� (Ed.),� Functional visual behavior: A therapist’s guide to evaluation and treatment options (pp.�105–132).�Rockville,�MD:�American�Occupational�Therapy�Association.

Chalfant,� J.� C.,� &� Scheffelin,� M.� A.� (1969).� Task force III. Central processing dysfunctions in children: A review of research.�Bethesda,�MD:�U.S.�Department�of�Health,�Education,�and�Welfare.

Chu,�S.,�&�Hong,�S.�C.�(1997).�A�review�of�assessments�used�in�paediatric�occupational�therapy.�British Journal of Therapy and Rehabilitation,�4,�228–233.

Colarusso,�R.�P.,�&�Hammill,�D.�D.�(1972).�Motor-Free Visual Perception Test.�Novato,�CA:�Academic�Therapy.�

Cornoldi,�C.,�Venneri,�A.,�Marconato,�F.,�Molin,�A.,�&�Montinari,�C.�(2003).�A�rapid�screening�measure�for�the�identification�of�visuospatial�learning�disabilities�in�schools.�Journal of Learning Disabilities, 36,�299–306.

Cruickshank,� W.� M.,� Bice,� H.� V.,� &� Wallen,� N.� E.� (1975).�Perception and cerebral palsy.� Syracuse,� NY:� Syracuse�University�Press.

Dankert,�H.�L.,�Davies,�P.�L.,�&�Gavin,�W.�J.�(2003).�Occupational�therapy�effects�on�visual–motor�skills�in�preschool�children.�American Journal of Occupational Therapy, 57,�542–549.

Downing,�S.�M.�(2003).�Validity:�On�the�meaningful�interpreta-tion�of�assessment�data.�Medical Education, 37,�830–837.

Erhardt,�R.�P.,�&�Duckman,�R.�H.�(2005).�Visual–perceptual–motor�dysfunction�and�its�effects�on�eye–hand�coordination�and�skill�development.�In�M.�Gentile�(Ed.),�Functional visual behavior in children: An occupational therapy guide to evalu-ation and treatment options� (pp.�171–228).�Bethesda,�MD:�AOTA�Press.

Feder,�K.�P.,�Majnemer,�A.,�&�Synnes,�A.�(2000).�Handwriting:�Current�trends� in�occupational� therapy�practice.�Canadian Journal of Occupational Therapy,�67,�197–204.

Fischer,�B.,�Hartnegg,�K.,�&�Mokler,�A.�(2000).�Dynamic�visual�perception�of�dyslexic�children.�Perception, 29,�523–530.

Frostig,� M.,� Lefever,� D.� W.,� &� Whittlesey,� J.� R.� B.� (1966).�Administration and scoring manual for the Marianne Frostig Developmental Test of Visual Perception.� Palo� Alto,� CA:�Consulting�Psychologists�Press.

Gabbard,�C.�(1992).�Lifelong motor development.�Dubuque,�IA:�William�C.�Brown.

Gentile,�M.�(1997).�Functional visual behavior: A therapist’s guide to evaluation and treatment options.�Rockville,�MD:�American�Occupational�Therapy�Association.

Goodwin,�L.�D.�(2002).�Changing�conceptions�of�measurement�validity:�An�update�on�the�new�standards.�Journal of Nursing Education, 41,�100–106.

Grieve,� J.� (2000).� Neuropsychology for occupational therapists: Assessment of perception and cognition.�Malden,�MA:�Blackwell�Science.

Groffman,�S.,�&�Solan,�H.�(1994).�Developmental and perceptual assessment of learning-disabled children: Theoretical concepts and diagnostic testing.�Santa�Ana,�CA:�Optometric�Extension�Program�Foundation.

Hammill,� D.� D.,� Pearson,� N.� A.,� &� Voress,� J.� K.� (1993).�Developmental test of visual perception�(2nd�ed.).�Austin,�TX:�Pro-Ed.

Hellerstein,�L.,�&�Fishman,�B.� (1999).�Collaboration�between�occupational�therapists�and�optometrists.�Journal of Behavioral Optometry, 10(6),�147–152.�

Kalb,�L.,�&�Warshowsky,�J.� (1991).�Occupational� therapy�and�optometry:�Principles� of�diagnosis� and� collaborative� treat-ment�of�learning�disabilities�in�children.�Occupational Therapy Practice, 3,�77–87.

Kirkpatrick,�L.�A.,�&�Feeney,�B.�C.�(2001).�A simple guide to SPSS for Windows for versions 8.0, 9.0, and 10.0.�Scarborough,�ON,�Canada:�Nelson/Thomson�Learning.�

Messick,� S.� (1989).�Validity.� In�R.�L.�Linn� (Ed.),�Educational measurement (pp.�13–104).�New�York:�American�Council�on�Education�&�Macmillan.

Messick,�S.�(1995).�Validity�of�psychological�assessment:�Validation�of� inferences� from�persons’� responses� and�performances� as�scientific�inquiry�into�score�meaning.�American Psychologist, 50,�741–749.

Moryosef-Ittah,�S.,�&�Hinojosa,�J.�(1996).�Discriminant�validity�of�the�Developmental�Test�of�Visual�Perception–2�for�children�with�learning�disabilities.�Occupational Therapy International,�3,�204–211.

Nunnally,� J.,�&�Bernstein,� I.� (1994).�Psychometric theory.�New�York:�McGraw-Hill.

Parush,� S.,�Yochman,�A.,�Cohen,�D.,�&�Gershon,�E.� (1998).�Relation�of�visual�perception�and�visual–motor�integration�for�clumsy�children.�Perceptual and Motor Skills, 86,�291–295.

Downloaded From: http://ajot.aota.org/pdfaccess.ashx?url=/data/journals/ajot/930099/ on 05/01/2018 Terms of Use: http://AOTA.org/terms

Page 12: Factor Structure of the Four Motor-Free Scales of the ... The DTVP–2 manual recommends that ... The DTVP–2 = Developmental Test of Visual Perception, 2nd Edition . DTVP–2 = Developmental

The American Journal of Occupational Therapy� 513

Reid,�D.,�&�Jutai,�J.�(1997).�A�pilot�study�of�perceived�clinical�use-fulness�of�a�new�computer-based�tool�for�assessment�of�visual�perception� in�occupational� therapy�practice.�Occupational Therapy International,�4,�81–89.

Salvia,� J.,� &� Ysseldyke,� J.� E.� (1991).� Assessment.� Boston:�Houghton-Mifflin.

Scheiman,�M.�(1997a).�Review�of�basic�anatomy,�physiology,�and�development� of� the� visual� system.� In� M.� Scheiman� (Ed.),�Understanding and managing visual deficits: A guide for occupa-tional therapists (pp.�13–22).�Thorofare,�NJ:�Slack.

Scheiman,�M.�(1997b).�Understanding and managing visual deficits: A guide for occupational therapists.�Thorofare,�NJ:�Slack.

Schneck,�C.�M.�(2005).�Visual�perception.�In�J.�Case-Smith�(Ed.),�Occupational therapy for children� (pp.�412–448).�St.�Louis,�MO:�Elsevier/Mosby.

Schneck,�C.�M.,�&�Lemer,�P.�S.�(1993).�Reading�and�visual�percep-tion.�In�C.�B.�Royeen�(Ed.),�AOTA Self-Study Series: Classroom applications for school-based practice (pp.� 1–48).�Rockville,�MD:�American�Occupational�Therapy�Association.

Solan,�H.�A.,�&�Ciner,�E.�B.�(1989).�Visual�perception�and�learn-ing:�Issues�and�answers.�Journal of the American Optometric Association,�60,�457–460.

Stephens,�L.�C.,�&�Pratt,�P.�N.�(1989).�School�work�tasks�and�vocational� readiness.� In�P.�N.�Pratt�&�A.�S.�Allen� (Eds.),�

Occupational therapy for children (pp.�311–324).�St.�Louis,�MO:�Mosby.

Tindal,�G.� (1995).�Review�of� the�Developmental Test of Visual Perception, Second Edition.� In� J.� A.� Conoley� &� J.� C.�Impara� (Eds.),� The twelfth mental measurements yearbook�(pp.� 290–292).� Lincoln,� NE:� Buros� Institute� of� Mental�Measurements.

Todd,�V.�R.� (1993).�Visual� perceptual� frame�of� reference:�An�information�processing�approach.�In�P.�Kramer�&�J.�Hinojosa�(Eds.),�Frames of reference for pediatric occupational therapy (pp.�177–232).�Baltimore:�Williams�&�Wilkins.

Van�Waelvelde,�H.,�De�Weerdt,�W.,�De�Cock,�P.,�&�Smits-Engelsman,�B.�C.�(2004).�Association�between�visual�percep-tual�deficits�and�motor�deficits�in�children�with�developmental�coordination�disorder.�Developmental Medicine and Child Neurology,�46,�661–666.

Wedell,�K.�(1960).�Variations�in�perceptual�ability�among�types�of�cerebral�palsy.�Cerebral Palsy Bulletin,�2,�149–157.

Werner,� P.,� &� Rini,� L.� (1976).� Perceptual–motor development equipment.�New�York:�Wiley.

Wright,�B.�A.,�Bowen,�R.�W.,�&�Zecker,�S.�G.�(2000).�Non-linguistic� perceptual� deficits� associated� with� reading� and�language� disorders.� Current Opinion in Neurobiology,� 10,�482–486.�

Downloaded From: http://ajot.aota.org/pdfaccess.ashx?url=/data/journals/ajot/930099/ on 05/01/2018 Terms of Use: http://AOTA.org/terms