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USAARL Report No. 98-04

The Practical Effect of Routine DataTransformations on Absolute

EEG Power Derived fromSpectral Analysis

John A. Caldwell, Jr.and

Kristi A. Roberts

Aircrew Health and Performance Division

November 1997

Approved for public releeee, diitribution unlimited.

U.S. Army Aeromedical Research LaboratoryFort Rucker, Alabama 3636200577


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UnclassifiedSECURITY CLASSIFICATION OF THIS PAGE

REPORT DOCUMENTATION PAGE OMB No. 0704-0188la. REPORT SECURITY CLASSIFICATION lb. RESTRlCTlVE MARKING SUnclassified2a. SECURITY CLASSlFlCATlON AUTHORITY 3. DlSTRlBUTlON /AVAILABILITY OF REPORTApproved for public release, distribution26. DEClASSlFlCATlON / DOWNGR ADING SCHEDULE unlimited4. PERFORMING ORGANIZAT ION REPORT NUMBER(S)USAARL Report No. 98-04

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6a. NAME OF PERFORM ING ORGANIZATION 6b. OFFICE SYMBOL 7a. NAME OF MONITORING ORGANIZATIONU.S. Army Aeromedical (If applicable) U.S. Army Medical Research and MaterielResearch Laboratory MCMR-UAC Command6~.ADDRE SS (City, State, and ZIP code) 7b. ADDRESS (City, State, andZiP Code)P.O. Box 620577 Fort DetrickFort Rucker, AL 36362-0577 Frederick, MD 21702-50128a. NAME OF FUNDING SPONSORINGORGANlZATlON 6b. OFFICE SYMBOL(/f applicable) 9. PROCUREMENT INSTRUMENT IDENTIFICATION NUMBER

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10. SOURCE OF FUNDING NUMBERSPROGRAM PROJECTELEMENT NO. NO.0602787A 3M162787A879

TASK WORK UNlTNO. ACCESSION

OD 175(U) The practical effect of routine data transformations on absolute EEG power derivedfrom spectral analysis

12. PERSONAL AUTHOR(S)John A. Caldwell, Jr. and Kristi A. Roberts13a. TYPE OF REPORT 13b. TIME COVEREDFinal 14. DATE OF REPORT r/ear, Month, Day) 15. PAGE COUNT1997 November16. SUPPLEMENTAL NOTATION

7. COSATI CODES 16. SUBJEC T TE RMS (Continue on reverse ifnecessary and identify by block number)FIELD GROUP SUB-GROUP EEG, data transformations, log-natural, relative power,06 05 and Gaussian properties.'19 A?

19. ABST RACT (Continue on reverse if necessary and idenm by block number)This investigation was conducted to evaluate the effects of selected EEG datatransformations on analysis of variance (ANOVA) results in a repeated measures design.Eighteen subjects were given resting EEG evaluations at 8 different times during a perioof continuous wakefulness. Following spectral analysis, the data were either analyzed untransformed absolute EEG power, log-natural transformed power, or 2-arcsine-square rotransformed relative power. Results indicated that while the relative powertransformation lead to a more sensitive statistical analysis, it concurrently introduceddata interpretation problems. In contrast, the results with both untransformed andtransformed absolute power were quite similar. Overall, it was concluded that althoughtransformations improve the Gaussian properties of the data, they do not appear tosubstantially impact the conclusions that will be drawn from a repeated measures ANOVA.

20. DlSTRlBUTlON /AVAlLABlLllY OF ABSTRACT[? UNClASSlFlEDlUNLlMlTED q SAME AS RPT. 21. ABSTRACT SECURllY CLASSlFlCATlON0 DTICUSERS Unclassified

22a. NAME OF RESPONSIBLE INDIVIDUAL 22b. TELEPHONE (Include Area Code) 22~.OFFICE SYMBOLChief, Science Support Center (334) 255-6907 MCMR-UAX-SIDD Form 1473, JUN 88 Previous editions are obsolete. SECURITY CLASSIFICATION OF THIS PA

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Table of contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..lMethods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .._....._._............. 1Res ults .......................................Delta activity .............................Absolute ower .....................Log NaturalTransformed ower ........Transformed elativePower ...........ThetaActivity ............................Absolute ower .....................Log NaturalTransformed ower ........Transformed elativePower ...........AlphaActivity ............................Absolute ower .....................Log NaturalTransformed ower ........Transformed elativePower ...........

Beta Activity .............................Absolute ower .....................Log NaturalTransformed ower ........Transformed elativePower ...........TestsFor N ormality ........................

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................. 2................. 2................. 2................. 2................. 3................. 5

................. 5................. 5................. 7

................. 9................. 9................ 10

................ 13

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................ 13................ 14................ 16................ 16

Discussion..............................................._...._...........17References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...20

List of tables1. Meandeltaactivityateachtestingtime ....................................... .42. Meanthetaactivityateachtestingtime ........................................ .3. Meanalphaactivityateachtestingtime ....................................... 144. Mean betaactivityat each esting ime ........................................ 175. Skewnessndkurtosis alues or the datarecorded rom eachelectrode .............. 18

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Table of contents continued)List of figures

1. Effectsof testing ime andeye closure n untransformedbsolute eltaactivityat02 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...22. Effectsof testing ime and eye closure n log-natural ransformed bsolute eltaactivityatFzand02 _. . . ,. . ._. . . . . . ._. . . . . . . . . . . . . . . . . . . . . . ._. . . . . .._. .33. Effectsof testing ime and eye closure n transformedelativedelta activityatOlandO2........................~..................................44. Effectsof testing ime and eye closure n untransformedbsolute hetapowerat Cz,Fz,an d02...........................................................65. Effectsof time of testingand eye closure n log-natural ransformedheta activityatCzand0 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...76. Effectsof testing ime and eye closure n transformedelative heta powe rat C3, Cz,Fz,an d02...........................................................87. The effectsof testing ime and eye closure n untransformedbsolute lphaactivity a t

several lectrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ . _ . . . _ . . . . . , . . . . . _ 118. Effectsof testing ime andeye closure n log-natural ransformed lphaactivityatseveral lectrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . 129. Effectsof testing im e and eye closure n relativealphaactivity at several lectrodes . . . 1510. Effectsof testing ime andeye closure n transformedelativebetapowerat 01and02.............................................................16

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IntroductionAlthough esearchndicateshe humanEEG possessesaussian ropertiesBenderet al.,1992 ), he results f spectral nalysis f thesedataoften are not norm allydistributed.This hasled to the recommendationhat log or other ransform ationse applied Gasser, &her, andMoths, 1982) sincemanystatisticalechniquesncluding nalysis f variance AN OV A) rely on

normaldistributionsHayes,1973). Gass er, &her, andMoths (1982) reported hat broadbandspectral EG parametersrom healthy olunteers ften departsubstantiallyrom normality. Theyrecommendedhat ap propriateransformationsanminimizeproblems ssociated ith the scaleof measurem entnd he underlyingmechanismsesponsibleor the EEG. Specifically,heseauthors eported he application f log transformationsubstantiallyeduced eparturesornnormality n abso lute o werdata except n the betaband)and arc&e-square-roottransformationsi@cantly improved he behaviorof relativepower data although log(x/( -x)) transformation as evenbetter). However,although he authors horoughly ddressedheissue f the effectsof transformationsn normalityversus on-normality,hey did not indicate heextent o which he transformations ould ead o d ivergent onclusionsbout he effectsofindependentariables fter statistical nalysis.SinceANO VA is known o be robust o violationsof the normalityassumptionKirk, 1968 ), a determination f the impactof two of therecommendedransformationsn the numberof statistically-significantffects esulting rom a 2-way ANO VA of the samedata transformed ersus on-transformed) asof interest.

MethodsEighteenmalesubjects etween he agesof 22 and3 1 (m ean=24.4)were ested o examinethe differencen EEG as-a unctionof sleepdeprivation.Sub jects ere continuously eprived fsleep or 38 hours. EEG data rom 7 electrode ites I , C3, Cz, C4 , Pz, 01, and 02) werecollected singa standard adwellSpectrum 2. Subjects ere tested t 1030,1430, and 1830on pre-deprivation aysandat 0230,0630, 1030, 1430,and 1 830 on deprivation ays. DuringeachEEG session, ubjects ere asked o remainstill andquietwith eyesopen or 1.5 minutesfollowedby 1.5 minutes f eyesclosed. Spectral nalyses ere performed n threeartifact-freeepochs f eyesopenand eyesclosedEEG for eachsubject.The activitybandswere delta l.O-3.0 Hz), theta 3-O-8.0Hz), alpha 8.0-13.0 Hz), andbeta 13.0-20.0 Hz). The average bsolutepowerwithin eachof thesebandswasanalyzed eparately s: 1) untransformedbsolute owerdata,2) log-natural-transformedbsolute ower,and 3) arcsine-square-rootransformedelativepow er. Each of the activitybands or the three setsof datawas analyzedwith repeatedmeasuresANO VAS for time (1030,1430,1830,0230,0630, 1030, 1430, 1830) andeyes eyesopenandeyesclosed). Thus, herewere our analysesdelta, heta,alpha,andbeta)conducted n eachdataset untransformed,og transformed, nd arc&e-square-root ransformed). his permittedan evaluation f wh ether he num ber f significant ffectswas alteredasa functionof thetransformations.n addition, description f the skew nessndkurtosis f the transform edvariables ermitted n examination f how normalitywas affected.

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Delta activityAbsolutePower

The ANOV A on delta activity ndicated time-by-eyes ffect at 02 (F(7,119)==3.80,p=.OOO 9) hich wasdue o differencesn the amountof deltaactivityrecorded crosshe testingtimesundereyesclosed ut not eyesopen. Follow-upcontrastsndicated herewas more deltarecorded t B1030, B1430 andD1830 whencomparedo D0230, DO630andD103 0 (see igure1). Therewere main effectson the time factorat C3 (F(7,119 )=2.44, p=.O2 24)and C4 (F(7,119)=2.19,p=.O400). Theseeffectswe re primarilydue o m ore deltarecordedduring he D 1830testing ime than the B1430, B1830 , D0230, andDO630 imes. For electrodeC4, therewas moredeltaat D143 0 thanDO230 see able 1). Therewere eyesmain effects t C3 (F (1,17)=53.80,p=.OOOl),C4 (F(1,17)=33.78, p=.OOOl),Cz (F(1,17)=20.54,p=.OOO3),z (F(1,17)=27.73,p=.OOOJ),1 (F&17)=17.02, p=.OOO7),2 (F& 17)=32.95, p=.OO Ol), ndPz (F&17)=42.51,p=.OOOl).Thesewere all due o increasesn deltapowerundereyesclosedwhen comparedoeyesopen.

8 I I

1030 1430 1830 230 630 1030 1430 1830-~Predeprivation DeprivationTime

Figure 1. Effectsof testing ime andeye closureon untransformedbsolute eltaactivityat 02.Log Natural Transformed ower

The ANO VA on deltaactivity ndicated ime-by-eyes ffectsat Fz (F(7,119 )=2.06, p=.O5 30)and02 (F(7, 119)=4.01,p=.OOO6). heseeffectswere due o difherencesn the amountof delta

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activity ecorded ndereyesclosed ut not eyesopen. Contrasts howe dherewasmoredeltarecorded t D1830 thanB1030, B1430, DO230andDO 630 or electrode z. For Fz, therewasalsomore deltaat B1830 than he otherbaselineimeswhile DO 230showed decreasen deltafrom the D1030 andB 1830 imes. For electrode 2, therewasmoredeltarecorded t D1830thanD0230, D0630, or D1030. Therewas also essdelta ecorded t DO 230 han any of thebaselineimes. The B1030 testing ime for 02 show edmore delta han he D0230, D0630, andD1030 times,and herewasmoredeltaat B143 0 thanD103 0 (see igure2). Therewere imemaineffects t C3 (F(7,119)=2.49,p=.O201),C4 (F(7,119)=2.32,p=.O297),andFz(F(7,119)=2.32,p=.O299). Thesewere dueprimarily o more delta ecorded t D183 0 than heother esting imes o r eachof the electrodeshowe ver, herewere exceptions). or electrode z,therewasalso essdeltaat B1430 andDO230 hanB183 0. For C3, contrastsndicatedherewasmoredeltaat D1 030 than any of the remainingesting imes exceptD 1830). Therewas essdelta or C3 at DO 630 h anD1430. ElectrodeC4 showedessdeltaat B 1830 hanD1030 andlessdeltaat DO230 hanD143 0 (see able 1). Therewere alsoeyesmaineffects t C3(F(1,17)=95.55,p=.OO Ol), 4 (F(1,17)=57.31,p-.0001), Cz (F(1,17)=57.27,p=.OOOl), z(F&17)=92.86, p=.OOOl), 1 (F&17)=44.67, p=.OOOl), 02 (F(1,17)=63.12, p=.OOOl), and Pz(F(1,17)=62.8 1, p=.OOO). Thesewere due o increased elta activityundereyesclosedcomparedo eyesopen.

1030 1430 1830 230 630 1030 1430 1830Pre-deprivafon Deprivation

Time

_.__ 1030 1430 1830 230 630 1030 1430 1830Predeprivation Deprivation

TimeFigure2. Effectsof testing ime andeye closure n log-natural ransformed bsolute eltaactivityat Fz and02.Transformed elativePower

The ANOV A on deltaactivity nd icatedime-by-eyes ffectsat 01 @? (7,119)=3.84,=.OOO9)and02 (F(7,119)=4.87,p=.OOOl).The effects t 01 were due o morerelativedelta ecordedundereyesopen han eyesclosed, specially t D0230, although herewere no overall ime e ffectsundereithercondition. The effects t 02 were due o d ifferencesn the amountof deltaactivity

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undereyesopenbut not eyesclosed. There wasmore deltarecorded t DO2 30 han any of thebaselineimesor D1430 andD1830. Contrastsndicated herewas essdeltarecorded t B1830thanmanyof the deprivationimes or 02. In addition, essdeltawasrecorded t D1830 thanDO230or D1030 (see igure 3). There were no overall ime maineffects. However, herewereeyesmaineffectsat all electrode ites:C3 (F(1,17)=66.74, p=.OOO l), C4 (F(1,17)=64.89,p=.OO Ol), z (F&17)=68.54, p=.OO Ol), z @?(1,17)=59.68, =.OOO l), 1 (F(1,17)=83.11,2.00 2.00

6 8ii iii3 sE 1.50 ______----_----_ E 1.50 --_------_-_____..E $ii EF Et t,z 1.00 6 1.00

A?P

lfiz B0" 0.50 8 0.50Q).z

Q).z

m iGB 0.00 2 0.001030 1430 1830 230 830 1030 1430 1830 1030 1430 1830 230 830 1030 1430 1830

Pr&&priVdiOtl Deplivation Predeprivation Deprivation

1

Time TimeFigure3. Effectsof testing ime and eye closure n transformedelativedeltaactivityat01 and 02.

Table 1.Mea n d elta activityat each esting ime.DataType Electrode B1030 B1430 B1830 DO230 DO630 D1030 D1430 D1830

bsolute C3 4.12 4.11 4.21 4.01 3.83 6.35 5.41 5.45Power c4 4.45 4.28 4.13 3.78 4.74 6.63 5.63 6.01Fz 6.77 5.63 7.14 5.83 5.35 10.0 6.70 7.99Log c3 1.55 1.50 1.56 1.54 1.48 1.73 1.69 1.74Power c4 1.57 1.56 1.52 1.51 1.65 1.75 1.74 1.80Fz 1.86 1.75 1.93 1.80 1.74 2.04 1.88 2.04Relative c3 0.69 0.65 0.69 0.71 0.68 0.74 0.71 0.74Power c4 0.70 0.71 0.67 0.71 0.73 0.77 0.72 0.75Fz 0.77 0.70 0.78 0.76 0.71 0.82 0.73 0.78p=.OOOl), 2 (F&17)=69.78, p=.OOOl), ndPz (F&17)=117 .37, p-.0001). Theseeffectsweredue o more delta activityundereyesopen han eyesclosed.

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Theta A ctivityAbsolutePower

The ANO VA on thetapower ndicatedime-by-eyes ffectsat Cz (F(7,119)=2.20,p=.O393),Fz (F(7,119)=2.44,p=.O224), nd02 (F(7,119)=2.08,p=.O503),due o differencesn the amountof theta activityundereyesclosed ut not eyesopen. Contrasts howe d herewasmore hetarecorded t D1830 thanat B 1830 or DO230 or Cz. Cz alsoshowedmore hetaat B1030 thanDO230andsubstantially ore hetaat D1030 than B1830 or D0230. At F z, contrastsndicatedmore heta ecorded t D1030 than several f the other esting imes. At 02, therewasmorethetaat D1030 thanBl830 or D023 0. Therewasalsomore hetaat DO630 hanD0230. Inaddition, herewasmore hetaat B1030 thanB 1430 (see igure4). Time main effectswereobserved t Cz (F(7,119)=2.4 , p=.O24), F z (F(7,119)=3.12,p=.OO 47), nd 02 (F(7,119)=2.19,p=.O3 98). The effects t Cz w ere due o less heta activityat DO230 hanany of the rema iningdeprivationimes. Therewas also ess heta at B18 30 thanD103 0 or D1830 for Cz. The timeeffectsat Fz weremainlydue o m ore hetarecorded t D 1030 andD 1830 han he remainingtesting imes, hou gh herewasalso ess heta at DO23 0 hanD0630, D1030, or D1830. Theeffects t 02 were due o less heta ecorded t DO2 30 han he remaining eprivationestingtimesandB1030 (see able2). Therewere eyesmaineffects t C3 (F(1,17)=45.22,p=.OOOl), 4(F(1,17)=37.78,p=.OO Ol), z (F(1,17)=49.95,p=.OOOl), z (F&17)=32.69, p=.OOOl), 1(F&17)=22.92, p=.OO O2),2 (F(1,17)=15.55,p=.OOlO), ndPz 0;(1,17)=27.69, p=.OO Ol).Thesewere due o increasesn thetaactivityduringeyesclosedn comparisono eyesopen.Log NaturalTransformed ower

The ANO VA on thetaactivity nd icatedime-by-eyes ffectsat Cz (F(7,119)=2.09,p-.0495)and02 (F(7,119)-2.49, p=.O19 9) ue o differencesn thetaduringeyesclosed ut not eyesopen. The effects t Cz werebecause f more hetaat D1830 thanB1030, B1830, andD0230.The effects t Cz alsowere attributableo less heta at DO23 0 han at mostof the remainingdeprivationimes. In addition, herewas ess heta at B1830 thanD103 0 or D183 0 (see igure 5).The effects t 02 weremainlydue o less heta recorded t DO 230 han he remaining eprivationtimes,andat B1030 andB1430 . The presence f more hetawasdetected t B1030 thanB1830or DO 230 or 02. Contrastsor 02 alsoshowed herewasmore heta at D1030 thanB 1830 orD0230. Therewere ime maineffects t C3 (F(7,119)=3.96,p-.0006), C4 (F(7,119)=3.63,p-.0014),Cz~(7,119)=3.09,p-.0050),Fz(F(7,119)=4.78,p=.0001),andPz(F(7,119)=2.47,p=.O211). Theseeffectswere mainlydue o more hetarecorded t D1830 than he majorityofthe remainingesting imesat C3, C4, andFz. Cz showedmore heta at D1830 thanB1030,B1830, andDO 230. Contrasts t C3 indicated herewasmore hetaat D1030 thanmostof theremainingesting imes see able2). Less hetawasdetected t DO230when comparedo theother imes or eachelectrode. At electrodes 4 andCz, therewas ess hetaat DO230 han heremaining eprivationimesandat B1430 . Cz alsohad ess hetaat DO230 hanB1030.ElectrodeFz showedmore hetabeing e corded t D1030 than he majorityof the testing imes.Generally, or Fz therealsowasmore hetarecorded t DO63 0 han he other esting imes

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0.00 1030 1430 1830 230 630 1030 1430 1830Pre-deprivation Deprivation

Time

m Eyesdosed8

0.00 1030 1430 1830 230 630 1030 1430 1830Pre-deprivation Deprivation

Time

Figure5. Effectsof time of testing ndeye closure n log-natural ransformedhetaactivityatCz and02.Transformed elativePower

The ANO VA on theta activity ndicatedime-by-eyes ffectsat C3 (F(7,119)=2.44,p=.O224),Cz (F(7,119)=2.18,p=.O402), z (F(7,119)=2.41,p=.O242),01 (F(7,119)=2.57,p=.O170), nd02 (F(7,119)=4.07,p=.OOOS)hichwere due o differencesn the amountof thetaactivity ecorded t various imesof dayundereyesclosed ut not eyesopen. Contrasts howedtheseeffectswere predominantly ue o m ore hetarecorded t D183 0 for C3, Cz, andFz, andmore hetaat D1030 at eachelectrode.01,02, andFz showedmore hetaat D1830 thanD0230. 02 and 01 also showedmore heta at D1830 thanB1830. 01 hadmore hetaat D1830thanB 1030. Therewas ess hetarecorded t DO230 hanmostof the other esting imes,and,generally,more hetawas recorded t DO63 0 han at DO2 30 or eachelectrode.Electrode z hadmore heta at DO63 0 han B 1830 andB 1030. At electrodes 3 , Cz, and02 therewasmore hetaat D1030 than at D1430 (see igure6). Therewere ime main effects t C3 (F(7,119)=3.96,p=.OOO 6), 4 (F(7,119)=3.30,p=.OO31), z (F(7,119)=3.28,p=.O O32), z (F(7,119)=6.62,p=.OOO),1 (F(7,119)=3.08,p=.OO 51), 2 (F(7,119)=2.42,p=.O235), ndPz (F(7,119)=3.04,p-.0056). Foilow-upcontrastsndicatedmore hetaat D 1830 han he majorityof the other imesfor C3, C4, andFz. Cz and 01 hadmore heta at D1830 than B1030, B1830, or D0230. Therewasmore hetaat D1030 than he majorityof the times or C3, Cz, Fz, 01,02, andPz. C4 hadmore hetaat D1030 than B1830 or DO230 see able2). In addition, herewas ess hetaatDO2 30 han mostof the other esting imes for eachelectrode.At several lectrodes, ontrastsshowedmore hetaat D103 0 thanD1430. Therewere eyesmain effects t C3 (F& 17)=7.22,p=.O156),C4 (F&17)=5.02, p=.O387),Cz (F(1,17)=11.76,p=.OO 32), z (F(1,17)=7.70,

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1030 1430 1830 230 630 I030 I430 1830Pre-ckprivation Deprivation

Time

5z 1.50 --------EEt;k 1.0032mTiiF 0.509-iiiB 0.00

1030 1430 1830 230 630 1030 1430 1830Predephation Deprivation

Time

1030 1430 1830 230 630 1030 1430 1830Predeprivation Deprivation

Time

-------------- --I

1030 1430 1830 230 630 1030 1430 1830Predeprivation DeprivaUon

Time

Figure 6. Effects of testing ime and eye closureon transformedelative hetapower at C3, Cz,Fz, and 02.

p=.O130),01 (F(1,17)=38.12, p=.OO Ol), 2 (F (1,17)=31.27,p=.OOOl), ndPz (F&17)=14.47,p=.OO14).Theseeffectswere due o differencesn the amountof theta activitybetweeneyesopenand eyesclosed greater elative hetaundereyesopen).


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Alpha ActivityAbsolute ower

The ANO VA on alphapower ndicated ime-by-eyes ffectsat C3 (F(7,119)=3.25, p=.OO34),C4 (F(7,119)=2.16, p=.O421), Cz (F(7,119)=2.23, p=.O364), Fz (F(7,119)=2.05, p=.O546), 01(F(7,119)=3.68, p=.OO12), 02 (F(7,119)=2.87, p=.OO83),andPz (F-(7,119)=2.64, p= .OWI).These effectswere due o d ifferencesn the amountof alphaactivity or eyesclosed t C3, C4,Cz, 01,02, andPz (the effect or Fz w asmarginal t p-.0654). Electrode 2 also showeddifferences nder eyes open. Contrasts or the effectsat eyes closedshowe d a trend for lessalphaat DO630 than many of the other times at C3, C4, Cz, 02, and Pz, and contrastsat 01 showedlessalpha at DO630 co mpared o D0230 . Also, at 01 and 02, alpha tended to be lower at D1830than elsewhere. At C3, C z, 02, and Pz, alpha was greater at DO230 than D1830. At 02, therewas a decrease rom DO630 to D1830, and at 01, alpha was lower at D1030 than most other

2.ableMean theta activity at eac h esting time.

LogPower

Data type Electrode B1030 B1430 B1830 DO230 DO630 D1030 D1430 D1830AbsolutePower

Fz 17.33 17.60 17.15 15.09 26.68 28.92 23.60 29.86c3 12.94 14.78 12.48 9.03 17.50 18.20 15.70 17.33c4 14.31 14.70 12.95 9.91 17.82 19.24 14.91 19.89cz 20.46 21.92 18.23 14.71 23.31 30.87 22.72 29.65Pz 19.67 20.94 14.72 12.15 18.33 23.12 17.59 21.7901 10.56 10.73 8.38 8.29 10.89 13.06 9.60 13.1002 12.36 10.45 7.98 7.18 11.20 12.21 9.33 13.44Fz 2.67 2.71 2.66 2.60 2.91 2.97 2.85 3.05c3 2.38 2.48 2.37 2.18 2.48 2.61 2.56 2.61c4 2.42 2.45 2.37 2.24 2.53 2.62 2.52 2.70cz 2.79 2.84 2.75 2.62 2.84 3.01 2.90 3.04Pz 2.60 2.69 2.52 2.41 2.58 2.74 2.65 2.7501 2.11 2.14 2.03 1.98 2.05 2.20 2.13 2.2102 2.20 2.14 2.04 1.91 2.07 2.17 2.05 2.18

RelativePower

Fz 1.23 1.26 1.22 1.19 1.41 1.41 1.29 1.43c3 1.13 1.17 1.15 1.03 1.26 1.28 1.19 1.27c4 1.18 1.22 1.14 1.10 1.24 1.30 1.14 1.30cz 1.25 1.26 1.23 1.17 1.33 1.38 1.24 1.37Pz 1.06 1.06 1.03 0.97 1.13 1.21 1.04 1.1401 0.93 0.95 0.91 0.89 1.03 1.14 0.94 1.0702 0.98 0.95 0.91 0.90 1.02 1.11 0.93 1.00

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times. C3, Cz, 02, andPz showed decreasen alpha i-omDO230 o D1030. 02 also showedmore alphaat B183 0 than D10 30. At C 3, therewasan increaserom B1830 to D0230. At C4,alphawasgreaterat D1430 than DO630or D103 0. At Cz , therewasmore alphaat D1430 thanD103 0. 01 indicated n increase t DO 230 rom the B183 0 testing ime. The eyesopeneffect at02 was due o lessalphaat DO 230 han he baselineimes se e igure 7). Therewere time maineffectsat C4 (F(7,119)=2.07,p=.O517),Cz (F(7,119)=2.29,p=.O321),01 (F(7,119)=3.00,p=.OO62), ndPz (F(7,119)=2.35,p=.O2 76). At C4, therewasmore alphaat B1830 than DO630andD1030, andmore alphaat D143 0 than D103 0. At C z, therealsowasmore alphaat B1830than at DO6 30andmorealphaat DO230 han at DO630or D103 0. Alpha end ed o increaseromD103 0 to D14 30 for Cz. At 01, therewas essalphaat D1830 than at B1030, B1830, andD0230. D1030 showed trend or lessalphaat 0 1 while DO 230 ndicatedmore alphacomparedto the other es ting imes. At Pz, alphawas ower at DO63 0comparedo the other imes,while itwas higherat DO 230 see able 3). Therewere eyesmaineffects t C3 (F( 1,17)=40.18,p.=.OOOl),C4 (F(1,17)=45.91,p=.OOOl),Cz (F(1,17)=39.01,p=.OO Ol), z (F(1,17)=41.30,p=.OOOl), 1 (F(1,17)=41.06,p=.OOOl), 2 (F(1,17)=50.81,p=.OOOl), ndPz (F(1,17)=47.33,p=.OOOl).Thesewere due o substantialncreasesn alphaactivityat eyesclosed n com parisonto eyesopen.Log Natural Transformed ower

The ANOV A on alphaactivity ndicated ime-by-eyes ffects t C3 (F(7,119)=2.28,p=.O328),01 (F(7,119)=4.73,p=.OOOl), 2 (F(7,119)=4.85,p=.OO Ol), z (F(7,119)=2.36,p=.O271),andFz (F(7,119)=2.84,p=.OO 90). he effectswere due o differencesn the amountofalpha ecorded crosshe different esting imesundereyesclosed or eac helectrode.Also, atelectrodes 1 and 02, therewere differences nd ereyesopen. Contrastsndicated trend orlessalphaat DO630comparedo the other imesundereyesclosed t every electrode xcept02,which showedessalphaat DO630comparedo D0230. At C3,01,02, andFz, therewas atrend owards essalphaat D1030 than at m ostof the other imes. At Pz, therewas essalphaatD1030 comparedo DO230andB143 0. For C3, therewas essalphaat D1030 than D1830, andat 01 the comp arison etweenD1830 andDO230wa s significantlessalphaat D183 0). Forelectrodes 3 and01, therewasmore alphaat DO230 hanB 1830. 01 also showedmore alphaat DO230 hanB1430 undereyesclosed. At C3,01, andFz, morealphawas detected t D1430comparedo D103 0 (see igure 8). The contrastsor eyesopenat 01 and 02 showedessalphaat DO230andDO 630 han at the other esting imes. At 02 therealsowasmore alphaat D1830and D1430 comparedo DO230andD0630. 02 alsoshowedmorealphaat B1430 than mostdeprivationimes. Therewere time m ain effectsat Fz (F(7,119)=2.03,p=.O573), 01(F(7,119)=2.50, p=.O198),and02 (F(7,119)=2.06,p=.O526). Theseeffectswere due o a trendtowardsdecreasedlphaat D103 0 in com parisono the other imes or Fz and 01. At 02, therewas essalphaat D1030 thanB1830 andB143 0. Also, at 01 and 02, therewas a trend owardslessalphaat DO630 han mostof the other imes, There was alsoan increase t D1430 whencomparedo D1030 at Fz and01 (see able 3). Eyesmain effectswere ocatedat C3(F(1,17)=146.30,p=.OOOl), 4 (F(1,17)=133.31,p=.OOOl),Cz (F(1,17)=130.41,p=.OOOl), z(F(1,17)=121.60,p=.OO Ol), 1 (F &17)=2 79.74, p =.OOO l), 2 (F(1,17)=23 9.22,p=.OOOl), nd

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80.00

c3?ii 80.00bBn2 40.00_na

2o.w

0.00 1030 1430 1830 230 630 1030 1430 1830Predeprivation Deprivation

Time


Time

0.00 1030 1430 1830 230 630 1030 1430 1830

Figure7.

Predeprivation DeprivationTime

tzn2 40.waa225: 20.009

0.00 1030 1430 1830 230 630 1030 1430 1830Pm-deprivation Deprivation

Time150.00,

90.00

60.00

30.W


Time

0.00 1030 1430 1830 230 630 1030 1430 1830Predepfivation DeprivationTime

The effectsof testing ime andeye closure n untransformedbsolute lphaactivityatseveral lectrodes.

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6.CC

1030 1430 1830 230 630 1030 1430 1830Pmdephvation Deprdticil

Time1030 1430 1830 230 630 1030 1430 1830

Pmdeprivation DeprivdonTime

1030 1430 1830 230 630 1030 1430 1830Predepdvation Deprivation

Time


Time

Figure8. Efkcts of testing ime andeye closure n log-natural ransformed lphaactivity atseveral lectrodes.

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Pz (F(1,17)=204.78, p=.OOOl).Thesewere due o increasesn alphaactivityduringeyesclosedin comparisono eyesopen.Transformed elativePower

The ANOVA on alphaactivity ndicated ime-by-eyes ffects t C3 (F(7,119)=3.09,p=.OO49), z (F(7,119)=2.97, p=.OO66),Fz (F(7,119)=4.27, p=.OOO3),01 (F(7,119)=4.63,p=.OOOl), 2 (F(7,119)=5.51, p=.OOOl),andPz (F(7,119)=2.90,p=.OO78).Theseeffectsweredue o differencesn the amountof alphaactivityat eyesclosed or all electrodes.At electrode02, therewere difkrencesundereyesopenaswell. Contrastsor eyesclosed ffectsshowedtrend oward essalphaat D10 30 than elsewhe re.At C3 andFz, therewas essalphaat D1830thanat other ime s. At Cz, therewas essalphaat D1830 thanat B1030, B1830, or D0230. At01, therewas essalphaat D1830 thanDO230or B1030. 02 showedessalphaat D1830 thanatB1430, B1830 or D0230. Therewasan ncreasen alphaat DO23 0 or mostelectrodes.Atelectrodes 3 andFz, therewasa tendencyowards essalphaat DO630and essalphaat D1030thanD1430. At 01 and02, therewasmore alphaat D1430 thanD1030. At 02, for eyesopen,therewasa decreasen alphaat DO230when comparedo the baselineimes.Therewas anincreasen alpha or 02 at B1830 comparedo DO230andDO63 0 or eyesopen. In addition,therewasmorealphaat D1430 thanDO230or D1030 (see igure9). Therewere ime maineffects t C3 0;(7,119)=2.33,p=.O287),C4 (F(7,119)=2.62,p=.O149),Cz (F(7,119)=2.46,p=.O2 18), z (F(7,119)=4.44,p=.OOO2),1 (F(7,119)=2.24,p=.O356), nd02 (F(7,119)=2.05,p-.0542). Foilow-up contrasts howed trend oward ess lphaactivityat D1030 whencom pared ith the other esting imes, h ough02 showedessalphaat only D10 30 com paredoB1830 andB1430. For C3 andFz, therewasa decreasen alphaat the D18 30 testing ime. ForFz, therewasa trend or lessalphaat DO630 han elsewhere.C3 and C4 showedessalphaatDO630comparedo D0230. C4 and02 alsoshowedess lphaat DO63 0 hanat B1830. C4 andCz showedessalphaat D18 30 thanB1830. C4 indicatedessalphaat D1830 thanB143 0 whileCz showedessalphaat D1830 thanD0230. Generally, herewasmorealphaat DO230 hanatthe other imes or m ostof the electrodesested, houghat 01, the only significant om parisonwasbetween O230andD1030. At every electrode ,herewasan ncreasen alphaat D1430whencompared ith D1030 (see able3). Therewere eyesmaineffects t C3 (F( 1,17)=41.37,p=.OO Ol), 4 (F&17)=2 8.95, p=.OO Ol), z (F(1,17)=41.34,p=.OO Ol), z (F(1,17)=34.37,p=.OO Ol), 1 (F(1,17)=112.97,p-.0001), 02 (F&17)=79.22, p=.OOOl), ndPz (F&17)=58.85,p=.OOOl).Thesewere due o increasesn alphaactivityundereyesclosedwhencomparedoeyesopen.

Beta ActivityAbsolute o wer

The ANOV A on betapow er ndicated herewasa time maineffectat 01 (F(7,119)=3.25,p=.OO34) ue o morebetaactivityat B1430 andB183 0 than at the other esting imes. Therealsowasan increase n beta at DO230 when comparedwith DO630 (see table 4). There were eyes

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main effects at C3 (F(1,17)=51.60, p=.OOO l), C4 (F(1,17)=58.17, p=.OOO l), Cz (F& 17)=52.29,p=.OOO l), Fz (F&17)=43.78, p=.OOO l), 01 (F(1,17)=57.10, p=.OOO l), 02 (F(1,17)=57.20,p=.OOO l), and Pz (F(1,17)=59.78, p-.0001). These were due to increasedbeta activity undereyes closed n comparison o eyes open.

Data Type Electrode B1030 B1430 B1830 DO230 DO630 D1030 D1430 D1830AbsolutePower

Fz 28.05 26.79 28.22 31.23 22.85 22.02 29.87 22.59c3 25.90 27.60 24.98 30.53 19.69 22.63 26.83 22.66c4 23.57 23.15 27.11 25.74 20.51 21.65 29.49 21.36cz 32.82 34.40 36.36 40.04 27.09 29.48 40.21 29.10Pz 49.53 58.71 52.23 61.44 38.29 46.95 57.42 45.3901 47.88 44.33 45.10 52.38 35.17 30.80 42.67 32.1702 40.05 39.44 40.25 46.69 33.68 29.95 36.21 29.87

LogPowerFz 2.85 2.87 2.85 2.84 2.68 2.58 2.93 2.74c3 2.86 2.89 2.81 2.85 2.65 2.64 2.86 2.71c4 2.76 2.72 2.85 2.74 2.71 2.59 2.94 2.73cz 2.96 3.01 2.99 2.95 2.84 2.75 3.11 2.92Pz 3.34 3.44 3.33 3.31 3.10 3.06 3.41 3.2401 3.13 3.11 3.13 3.06 2.79 2.69 3.12 2.8602 3.09 3.13 3.14 2.97 2.80 2.70 3.05 2.90

RelativePower

Fz 1.38 1.40 1.37 1.39 1.24 1.15 1.36 1.20c3 1.53 1.51 1.51 1.56 1.39 1.34 1.45 1.37c4 1.46 1.44 1.53 1.50 1.39 1.30 1.49 1.34cz 1.39 1.41 1.42 1.44 1.33 1.22 1.43 1.28Pz 1.64 1.66 1.67 1.68 1.55 1.48 1.65 1.5501 1.75 1.71 1.78 1.75 1.64 1.52 1.75 1.6302 1.70 1.74 1.78 1.72 1.63 1.54 1.76 1.64

Table 3.Mea n alpha activity at each testing time.

LOP Natural TransformedPowerThere was a single ime main effect at 01 (F(7,119)=3.33, p==.OO 29) hich was due to m orebeta activity at B1430 and B1830 than at the other testing times. This was followed by a decrease

in beta activity from D O230 to DO63 0 (see table 4). There were eyes main effects at C3(F(1,17)=55.73, p=.OOO l), C4 (F&17)=74.35, p=.OOO l), Cz (F&17)=70.53, p=.OOO l), Fz(F(1,17)=52.84, p=.OOO l), 01 (F&17)=123.22, p=.OOO l), 02 (F(1,17)=116.82, p=.OOO l), andPz (F( 1,17)=1Oi. 75, p=.OOO ). These were d ue to increasedbeta activity under eyes closed ncomparison o eyes open.

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5t83I? 1.002_na9-iiixi 0.WK 1030 1430 1830 230 830 1030 1430 1830Predeprivation Deprivation

:

I2 3.00iio^EgE 2.00gz38z

1.00SaP).Lii5 0.00K

N

Time


z;E 2.00tiiz2 1.002sa$.-?iiI$ 0.00 1030 1430 1830 230 630 1030 1430 1830Predeprivation Deprivation

Time

ieE 2.w c -------------t3B 1.002_nasz_md 0.00 1030 1430 1830 230 630 1030 1430 1830

Predeprivation Deprivation

Pm-deprivation DeprivationTime

1030 1430 1830 230 630 1030 1430 1830Predeprivation DeprivationTime

Figure 9. Effects of testing time and eye closure on relative alpha activity at several electrodes.

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Transformed elativePowerThe ANO VA indicated ime-by-eyes ffects t 01 (F(7,119)=3.79, p=.OO O9)nd 02(F(7,119)=2.45, p=.O222). Theseeffectswere due o dif&rencesn the amountof beta activityrecorded t eyesopenacrosshe different esting imes or both electrodes.Therewas essbetarecorded t D1830 than mostof the remaining imes,while therewasan increasen beta at B1430

comparedwith D1030 (see igure 10). Therewasa tim e main effectat Pz (F(7,119)=2.05,p=.O541)due o m orebetarecorded t DO 630 hanB1430 or D0230. Lessbetawas detected tD1030 when comparedo B 1830 and D0630. Also, there wasmorebeta recorded t DO6 30 hanD1030 or D1430 . Therewere eyesmain effects t C3 (F(1,17)=119.06, p=.OO Ol),C4(F&17)=136.14, p=.OO Ol), z (F(1,17)=159.68, p=.OO Ol), z (F(1,17)=86.60,p=.OOOl), 1(F(1,17)=114.65, p=.OO Ol), 2 (F&17)=65.07, p=.OO Ol), ndPz (F(1,17)=255.99,p=.OOOl).Theseeffectswere due o m orebeta activity recorded ndereyesopen han at eyesclosed.TestsFor Normality

Normality was estedby examining kew nessndkurtosis or eachof the diierenttransformations. aluesof skewnessnd kurtosiswhichwere greater han 1 were nterpreted sindicating hat the distributions ad heavier ails han he normaldistribution.Table 5 shows heskewness ndkurtosis alues or eachof the electrodesested. For absolute ower,41 out of 56valuesof skewnessailed h e test or normality,while 39 failed for kurtosis. The log naturaltransformationndicated failedvalues or skewnessnd 4 for kurtosis.Relativepower showed10 values ailingnormality or skew ness nd 12 for kurtosis.

I-

,-

b- 1030 1430 1830 230 630 1030 1430 1830Predeprivation Deprivation

Time

Figure 10.

1030 1430 1830 230 630 1030 1430 1830Predeptivation Deprivation

Time

Effectsof testing ime and eye closure n transform edelativebetapower at 01and02.

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Table4.Mean betaactivityat each esting ime.DataType Electrode B1030 B1430 B 1830 DO230 DO63 0 D1030 D1430 D1830Absolute Pz 4.64 5.02 4.70 4.65 4.83 3.97 4.80 5.08Power 01 3.82 4.45 4.36 3.83 3.41 3.43 3.62 3.40Loi3 Pz 1.64 1.67 1.64 1.59 1.64 1.49 1.65 1.66Power 01 1.45 1.55 1.55 1.46 1.35 1.37 1.41 1.33Relative Pz 0.58 0.57 0.59 0.57 0.62 0.54 0.56 0.57Power 01 0.62 0.65 0.65 0.63 0.63 0.64 0.59 0.58

DiscussionAs wasexpected ased n the findings f Gasser, &her, andMoths (1982), the log naturaland arcsine ransformationslearly mproved he normalityof the data. As a result, hereweredifferencesn the num ber nd ocationof statistically ignifkanteffects. Of 36 significantimeeffects,10 were oundon the absolute owerdata, 12 were foundon transformed bsolutepower, and 14 were foundon transformedelativepowe r. O f the instancesn which significancewas obtained n eitherof the absolute owermeasures,herewasagreemen t cross oth only 40percentof the time. Agreem ent cross ll threemea sures ccurred nly 16 percentof the time.Thus, data ransformationsill have some m pacton conclusionsegardinghe presence rabsence f effects n a givendataset. In addition, he choiceof a specific ata epresentation

(relativeversus bsolute ower), egardless f whetheror not it is transform ed, ay affect heinterpretation f the sign&ant findings.Wh ereas nterpretationsf absolute ow erversus ransformed bsolute owerwere quitesimilar, he sam e annot e said or relativepower. A reviewof the results ased n absolutepower showedhat when herewere significant ffectson transformed nduntransformedabsolute ower, he form of the relationship as consistent.Where herewere nteractionsbetween he time andeyes actors, nalysis f simple ffects ndicatedhe time effectoccurredbecause f differencesn the eyescloseddata egardless f whetheror not the dataweretransformed.Also, whencontrasts ere performedo pinpoint he precise atureof the effect,

the conclusionsrawn rom hesecontrasts ere consistent espitehe data ransformations. orinstance,n the caseof thetaactivity, t wasoften ound hat thetawas ower at 0230 on thedeprivation ay han t wasat manyof the other imes undereyesclosed).This was rueregardless f wh ether he datawere analyzed s absolute oweror log-natural-transformedabsolute ow er although ifkent electrodes ere affecteddifferently). Furthe rmo re, h endifferencesn activitybetween yesopenandeyesclosedwere ound,visual nspection f theresults lways evealed reaterpowerundereyesclosed elative o eyesopen. Thus, egardless

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Table 5.Skew ness nd kurtosis alues or the datarecorded rom eachelectrode.Location Absolute pcwer Log Natural Power Relative Power

band Skewness Kurtosis Skewness Kurtosis Skewness KuriosisODen Fz delta 2.33 a.86 0.43 0.63 0.13 -0.36theta 1.76 4.11 0.35 0.06 -0.28 0.31

alpha 1.24 1.59 0.09 -0.47 -0.14 0.11beta 0.74 -0.11 0.13 -0.92 -0.01 -0.98c3 deltatheta

alphabata

0.75 0.84 -0.10 -0.66 0.15 0.211.05 1.12 0.16 -0.43 -0.02 0.302.21 9.86 on6 -0.15 -0.01 -0.200.91 0.81 0.08 -0.12 -0.11 -0.10Cz delta 0.75 0.49 Q.11 -0.40 0.23 4.07theta 1.29 2.01 0.34 -0.13 0.03 5.12alpha 1.54 4.28 0.00 6.37 -0.18 0.50bata 0.84 0.33 0.14 -0.65 -0.01 -0.67C4 delta 1.37 2.87 0.16 0.02 0.44 5.17theta I .76 5.28 0.43 -0.03 0.06 5.3oalpha 0.90 0.31 -0.18 -oso -0.37 0.11beta 1.23 2.12 0.30 -0.29 0.11 5.43Pz delta 1.29 2.12 0.18 -0.06 0.25 0.03

theta 2.32 8.65 0.57 0.95 0.24 0.18alpha 1.70 4.94 -0.03 -0.40 -0.36 5.45beta 0.88 0.99 0.08 -0.09 -0.09 5.2301 delia 2.02 6.30 0.30 0.86 0.04 5.57theta 1.96 4.86 0.59 0.48 0.35 0.07alpha 3.92 23.57 0.39 0.20 -0.10 -0.56bata 0.68 0.26 0.w -0.75 -0.15 5.8802 delta 3.47 16.74 0.95 1.70 0.46 -0.13theta 2.02 5.15 0.52 0.17 0.44 0.02alpha 2.17 6.24 0.07 -0.48 -0.27 5.91beta 1.29 2.16 0.23 0.21 0.05 0.20

M Fz delta 4.61 28.79 I.04 1.65 I.04 1.03theta 2.64 8.66 0.56 -0.35 0.61 5.32alpha 1.16 1.52 -0.59 -0.22 -0.73 0.16beta 0.91 0.69 4.19 -0.27 -0.54 0.02C3 delta 3.46 16.89 0.92 I .oa 1.02 1.47theta 2.61 9.60 0.46 -0.24 0.92 0.42alpha 1.15 1.16 -0.62 0.19 -0.91 0.92beta 0.83 0.87 -0.38 0.06 -0.68 OXICz delta 6.61 57.33 1.10 2.42 1.19 2.31ttteta 2.08 4.28 0.55 -0.36 0.71 5.13alpha 1 Ol 0.55 6.51 -0.28 -on 0.09beta 0.63 0.67 -0.41 0.15 -0.73 0.48C4 della 4.94 3a.59 0.54 0.63 1.14 2.98theta 2.68 9.17 0.49 0.22 0.86 0.13alpha 0.90 0.41 -0.72 0.16 -0.90 0.41beta 0.77 0.71 -0.42 0.1 I 0.73 0.50h delta 2.00 6.65 0.32 -0.28 1.11 2.01thala 2.56 7.12 0.54 -0.01 1.W 0.70alpha 1 Ol 0.57 -0.95 0.96 -1.70 3.31beta 1.07 1.97 -0.31 0.15 -0.59 0.3001 delta 3.43 20.08 0.36 0.18 1.10 1.70thata 2.36 6.47 0.19 -0.15 1.49 2.12alpha 1.37 2.21 -0.94 0.50 -1.84 3.75b&a 0.79 0.67 0.44 0.02 -0.76 0.3002 della 2.36 9.40 0.20 -0.20 1.33 2.59theta 3.28 12.9 0.35 0.42 1.36 1.51alpha 1.25 1.63 -0.98 0.59 -1.74 2.82beta 0.85 0.79 -0.39 003 -0.63 0.16

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of whetherabsolute oweror transformed bsolute owe rwas analyzed,he findingswere quitesimilar o one anothe r.Transforminghe data nto relativepower,howeve r, eads o different nterpretationsf theresults.This wasparticularly oticeablen everybandwith the exception f alphaactivity. Fo rinstance , lthough he significantnteractionsn relative hetawere found o be a resultof

differences mong esting imesat eyesclosed a fIndingsimilar o the oneobserved ith absolutepow er), he overall rendwas or more elative hetapower o haveoccurred ndereyesopenthan eyesclosed the opposite f what was observed ith absolute ower). The apparentinconsistencyas attributableo the fact that alphawas substantiallyncreased hensubjectsclosed heir eyesand,since he other ypesof activity delta, h eta,andbeta)changedittle incomparison,he relativepower n eachof the otherband s p peared reater rather han ess)undereyesopen han eyesclosed.Thus, n the abse nce f information bout he otherEEGbands, nemighthaveassumedhat the actualmag nitude f thetadecreaseds a functionof eyeclosurewhen in fact, the oppositewas rue. B ecaus e f this, caution hould e exercised he nattemptingo interpret elativepowerbecause hangesn the variousband s re not mutuallyexclusivesince elativepowe r eflects he amountof activity n eachband n comparisono theamountof activity n all others).This cautionaside, t seem shat relativepoweranalysesmay be slightlymore sensitiveotreatment ffects haneither ype of absolute o weranalysis. n the present tudy,14 of the 36time maineffectswere oundon relativepowerasopposedo 12 on transformedbsolute ower,and 10 on untransformedbsolute ower. The totals or time-by-eyesnteractionsor each ypeof datawere 15,9, and 11, respectively. his mproved ensitivity robably esults rom slightdecreasesn the errorvariancen the relativemeasuresince hey tend o show essseverefluctuationsrom onecondition o the next or from one subjecto the next. Ho wever,aswasstated bove, his slight mprovementn sens itivity om eswith the associatedostof more

difhcult nterpre tations f the data .In conclusion,he presentindings uggesthat, while ANO VA is rather obustwith regardto violations f the normalityassumption,t is not robus t o the extent hat the datadistributionswill not exertsome mpacton the overall es ults.Howe ver, he practicalmpactappearso berathersmallwhen com paringhe changesn normality o the obs erved hangesn the numberofstatistically ignificantindiis. Therecertainly s not a one-to-one mprovem ent etween hequalityof the outcomemeasuresnd he degree o which he dataare normallydistributed.Thiswas evidentCorn he fact that transforming bsolute ower nto its log natural educ ed roblemswith skewn ess9 percen t from 73 percent o 4 percent), ut increasedhe num ber f statisticallysignificant ffectsonly 6 percent Corn27 pe rcent o 3 3 p ercent).A similar elationship as

observedn the relativepowerdata i.e., the transformationmproved ormalitybut did notsubstantiallyhange ensitivity).Thus, h e smallchanges s a functionof data ransformationsmay not be worth the required omputational verhead, t least n a repea ted-meas uresesign.

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ReferencesBender,R, Schultz,B., Sch ultz,A., andPichhnayr,. 1992. Testing he gaussianity f thehumanEEG duringanesthesia.Methodsof Information n Med icine. 3 1: 56-59.Gas ser, ., B&h er, P., andMock s, J. 1982. T ransformationsowards he normaldistribution f

broadbandspectral aram eters f the EEG . Electroencephalogranhynd ClinicalNeuroDhvsiolog;v.3: 119-124.Hayes,W. L. 1973. Statisticsor the socialsciences.New York: Holt, RinehartandWinston,

Inc.

Kirk, R. E. 1968. Exnerimental esimx Procedu resor the behavioral ciences.Belmont:Brooks/ColePublishing ompany.

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