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Wolff, PeterMirror Image Confusability in Adults.Wisconsin Univ., Madison. Research and DevelopmentCenter for Cognitive Learning.Office of Education (DHEW), Washington, D.C.TR-203BR-5-0216Jan 72OEC-5-10-15415p.

MF-$0.65 HC-$3.29Information Processing; Neurological Organization;Phyiology; *Response Mode; *Sensory Integration;*Stimuli; Vision; *Visual Discrimination; *VisualStimuli

ABSTRACTSeveral studies have indicated that children have

difficulty differentiating mirror-image stimuli. In the present studyadults were required to classify pairs of horseshoe stimuli as sameor different. Response times were compared for stimulus pairs thatvaried in orientation (left-right vs up-down) and spatial plane ofthe pair (horizontal vs. vertical). Stimulus pairs in which theorientation matched the spatial plane of the pair (i.e., horizontaland left-right or vertical and up-down) took longer to classify thanstimulus pairs in which these two variables were crossed. Theseresults are interpreted as reflecting the necessity of synthesizingtwo sources of information in order to compare the former pairtypestemporally encoded visual infornation and directionalinformation from the motor scanning process. Implication for thesource of children's difficulty with mirror-image stimuli of thistype are discussed. (Author)

MIRROR-1MAGE CONFUSABILITYIN ADULTS

WISCONSIN RESEARCH AND DEVELOPMENT

Technical Report No. 203

MIRROR-IMAGE CONFUSABILITY IN ADULTS

By Peter Wolff

Report from the Project on theRole of Stimulus-Correlated

Motor Behavior in Children's Perception

Peter Wolff, Principal Investigator

Wisconsin Research and DevelopmentCenter for Cognitive LearningThe University of Wisconsin

Madison, Wisconsin

January, 197 2

Published by the Wisconsin Research and Development Center for Cognitive Learning, supportedin part as a research and development center by funds from the United States Office of Education,Department of Health, Education, and Welfare. The opinions expressed herein do not necessarilyreflect the position or policy of the Office of Education and no official endorsement by the Officeof Education should be inferred.

Center No. C-03 / Contract OE 5-10-154

Statement of Focus

The Wisconsin Research and Development Center for Cognitive Learningfocuses on contributing to a better understanding of cognitive learning by chil-dren and youth and to the improvement of related educational practices. Thestrategy for research and development is comprehensive. It includes basic re-search to generate new knowledge about the conditions and processes of learn-ing and about the processes of instruction, and the subsequent development ofresearch-based instructional materials, many of which are designed for use byteachers and others for use by students. These materials are tested and refinedin school settings. Throughout these operations behavioral scientists, curricu-lum experts, academic scholarz-, and school people interact, insuring that theresults of Center activities are based soundly on knowledge of subject matterand cognitive learning and that they are applied to the improvement of educa-tional practice.

This Technical '.ieport is from the Project on Variables and Processes inCognitive Learning in Program 1, Conditions and Processes of Learning.General objectives of the Program are to generate knowledge and developgeneral taxonomies, models, or thew ies of cognitive learning, and to utilizethe knowledge in th c! development of curriculum materials and procedures.Contributing to these Program objectives, this project has these objectives:to ascertain the imp jrtant variables in cognitive learning and to apply rele-vant knowledge to the development of instructional materials and to the pro-gramming of instruction for individual students; to clarify the basic processesand abilities involved in concept learning; and to develop a system of indi-vidually guided motivation for use in the elementary school.

Ili

Contents

Page

List of Tables vii

Abstract ix

I. Introduction 1

II. Method 3Subjects 3

Materials and Apparatus 3

Procedure 3

III. Results 5

IV. Discuscion 7

References 9

List of Tables

TablePage

1 Mean RT in Msec. (and Total Errors) for Aligned andMirror-Image Stimulus Pairs in the Horizontal andVertical Plane

5

Abstract

Several studies have indicated that children have difficulty differen-tiating mirror-image stimuli. In the present study adults were required toclassify pairs of horseshoe stimuli as same or different. Response timeswere compared for stimulus pairs that varied in orientation (left-right vs.up-down) and spatial plane of the pair (horizontal vs. vertical). Stimuluspairs it- which the orientation matched the spatial plane of the pair (i.e.,horizontal and left-right or vertical and up-down) took longer to classifythan stimulus pairs in which these two variables were crossed. Theseresults are interpreted as reflecting the necessity of synthesizing twosources of information in order to compare the former pair types--tempor-ally encoded visual information and directional information from the motorscanning process. Implications for the source of children's difficultywith mirror-image stimuli of this type are discussed.

ix

Introduction

The discrimination of mirror-image stimuliis known to be uniquely difficult for children(Huttenlocher, 1967a, 1967b; Rudel & Teuber,1963; Sekuler & Rosenblith, 1964), as well asmany species of lower animals (Sutherland,1957; Mackintosh & Sutherland, 1963; Riopelle,Itoigawa, Rahm, & Draper, 1964). Usingthree-sided horseshoe-shaped stimuli in ahorizontal plane, Rudel and Teuber (1963)found that children confused left-right orientedhorseshoes (i.e.,C ), but not up-down3oriented ones (i.e., U). While these find-ings led investigators to believe that the phe-nomenon of mirror-image confusability wasspecific to left-right criented stimuli, subse-quent research demonstrated that the relativeposition of the pair of mirror-image stimuliis important in determining their discriminabil-ity. When the stimuli were in the horizontalplane, left-right oriented horseshoes wereconfused more often than up-down pairs, asprevious studies had shown. However, whenthe irs were in the vertical plane (i.e., Hor ) the reverse was trueconfusabilit§swas greater for up-down than left-right orientedstimuli (Huttenlocher, 1967a, 1967b; Sekuler& Rosenblith, 1964).

Huttenlocher (1967b) suggested that theimportant factor in mirror-image confusabilityis the orientation of the stimulus pair in rela-tion to their axis of separation. In her studynursery school children were required to matchthe orientation of a standard horseshoe. Eachchild's horseshoe was to be placed either be-side or below the standard. She found thatchildren made errors in their placement onlywhen rotation of a covertly placed test horse-shoe around the axis separating the pair wouldchange its orientation relative to the standard.In other words, errors were made on this t ._13.eof configuration, CI x , but not on this, nix ,

where "x" denotes title position of the testhorseshoe and the dotted line represents the

axis of separation of the pair. She called theformer pair-type "mirror-image," and the lat-ter pair-type "aligned." Her data also indi-cate that more errors were made on left-rightthan up-down oriented stimuli, and amongmirror-image stimuli, there were more errorson pairs in the horizontal plane than in thevertical plane.

While the existence of mirror-image con-fusability in children and animals is unques-tioned, there is little agreement about a suit-able explanation for the phenomenon. Caldwelland Hall (1969, 1970) have recently claimedthat the child's difficulty with mirror-imagestimulus pairs in a matching-to-sample taskresults from the child's inadequate definitionof the concepts "same" and "different" asapplied to mirror images. Since prereadingchildren have always regarded mirror imagesof an object as the same object, this habitis carried over to the judgment of mirror-imageletter pairs. These authors demonstratedsignificant improvement in discrimination ofthese pairs after a training task which theyfelt defined mirror-image stimuli as different.Gibson, Gibson, Pick, and Osser (1962) offera similar explanation for the tendency ofchildren in their study to confuse mirror-imageletter-like pairs.

Corballis and Beale (1970), on the otherhand, have proposed that mirror-image con-fusion arises from the bilaterally symmetricalorganization of the organism's nervous system.They demonstrate that a perfectly bilaterallysymmetrical system would be unable to distin-guish left from right, and hypothesize thatleft-right confusability disappears in thechild when handedness or consistent left-right scanning habits, made possible by thedeveloping asymmetry of the brain, becomeestablished.

While Caldwell and Hall's (1969) explana-tion has the advantage of simplicity, it violates

1

the fact that adults are known to confuse mir-ror-image stimuli, as, for example, in writingd for b or d for g, and direction, as in thecase of a driver who signals a left turn andthen turns right. There is, however, almostno empirical evidence concerning the discrim-ination of mirror-image stimuli for adults.

The present study examined the relativedifficulty of mirror-image and aligned-stimuluspairs, using adult Ss but following as closelyas possible the stimulus material and proce-dures used by Huttenlocher (1967b) with chil-dren. Time to respond "same" or "different"to a pair of horseshoe stimuli was used as ameasure of difficulty since performance byadults in Huttenlocher's task presumablywould be error frec. Applying Huttenlocher'sterminology, a mirror-image pair is one forwhich the rotation of one of the horseshoesaround the axis of separation of the pairchanges the identity status of the pair from

2

either same to different (i.e. ,C C ) or dif-ferent to same (i.e. ,C An aligned pairis one for which this rotation does not changethe identity status of the pair (i.e.,ULjorUn).

If, as Caldwell and Hall (1969) propose,children's mirror-image confusions simplyreflect a definitional pmblem arising from thetendency of the child to call different orienta-tions of a figure the same figure, then adultswho fhoroughly understand the requirementsof the task should compare mirror-imagestimulus pairs as quickly as aligned pairs.

If the bilateral symmetry explanation ofCorballis and Beale (1970) is a sufficientexplanation of the phenomenon, any superi-ority of aligned over mirror-image pairs shouldbe restricted to pairs located in the horizontalplane, since the human organism does notPossess symmetry around the horizontal medianplane,

Subjects

Twenty-four undergraduates with normalor corrected-to-normal vision served indivi-dually as subjects.

Materials and Apparatus

Stimuli were 16figures. The hofollowing pairs:30 ,UU, n.

IIMethod

pairs of horseshoe-shapedtaLeet consisted of the

, and Lin.Pairs one, two, six, and seven are mirror-

image pairs. The remaining pairs are aligned.The vertical set consisted of 900 rotations ofeach of these pairs. The horseshoe pairs weredrawn with black India ink and the final stim-uli were duplicated from these drawings byphoto offset onto heavy white stock. Each ofthe three sides of the horseshoes was 3.2 cm.long (subtending 4.20 of visual angle) and1.2 mm. wide (.30° of visual angle). The twohorseshoes making up a stimulus pair wereseparated by 1.3 cm. (1.7° of visual angle).

Stimuli were presented in a Polymetric2-channel tachistoscope (Model V-0959) witha blank fixation field. The tachistoscope waswired with a Hunter "Klockcounter" and a re-sponse panel containing two buttons, one fora "same" response and the other for a "differ-ent" response. Exposure of a stimulus startedthe clock, and depression of one of the re-sponse buttons stoliped the clock and turned

off the stimulus.

Procedure

Before responding in the reaction time(RT) task, S was shown each of the stimuluspairs and required to say whether their orienta-tion was the same or different. He was toldthat when a stimulus pair appeared in thetachistoscope he was to respond "same" or"different" by pressing the appropriate re-sponse button. Subjects were instructed torespond as quickly as possible but to avoidmaking errors.

Each session was divided into two parts,separated by a 5-min. rest period, with thehorizontal pairs presented in one part and thevertical pairs in the other. Subjects respondedto 11 replications of each series of 8 stimuli.The first presentation of each stimulus servedas a practice or warm-up trial and was not in-cluded in the analysis. Each replication waspresented in a dtherent random order. Presen-tation of each stimulus wr;s preceded approx-imately 1 sec, by a "ready" signal. Half theSr- received the horizontal pairs in the firstpart, while the remaining half received thevertical pairs. For half of each order groupthe "same" response was made with the pre-ferred hand, while the remaining half used thenonpreferred hand. The correctness and laten-cy of each response were recorded.

3

Results

Mean RTs for the various pair types areshown in Table 1. Aligned stimulus pairs wereresponded to 57 msec. faster than mirror-imagepairs: F (1,20) = 49.23, p < .001. This differ-ence is less pronounced for same pairs (39msec.) than for different pairs (75 msec.):F (1, 20) = 15.21, 2 < .001, but is highly sig-nificant for both (F = 29.39 and 43.68, respec-tively, 2< . 001) .

For stimuli in the horizontal plane, alignedpairs were responded to 51 msec. faster thanmirror-image pairs. For vertically alignedpairs this difference was 6 2 msec. Separateanalyses showed each of these differences tobe highly significant: t(23) = 5.45 and 5.27,respectively, < .001. The difference be-tween these two values, which is equivalentin this stimulus set to the difference betweenup-down and left-right orientation, does not

approach significance (F < 1).1 While therewas no difference in RT to up-down and left-right orientat1o:1, up-down stimuli were re-sponded to slightly faster than left-right stim-uli when the stimuli were the same. For dif-ferent pairs, the reverse was true. This inter-action is significant: F (1, 20) = 7,21, 2 < .01.

1Within the constraints of this stimulusset, the alignment factor (mirror-image vs.aligned) is actually the interaction of relativeplacement of the pair (horizontal vs. vertical)and orientation of the stimuli (up-down vs.left-right) . Its "main effect" status is thustheoretical and not statistical,

Table 1. Mean RT in Msec. (and Total Errors) for Aligned andMirror. Image Stimulus Pairs in the Horizontal and Vertical Plane

Same

Horizontal Different

Mean

Same

Vertical Different

Mean

10

Aligned Mirror-Image

554 (18) 598 (22)

573 (1 6) 631 (22)

564 (17) 615 (22)

583 (14) 615 (15)

577 (1 6) 668 (19)

580 (15) 642 (17)

5

Responses to same pairs were 25 msec.!cister than thos, .i'.iferent pairs: F (1,20) =17.35, a< .0i this effect mustbc evaluated wItn ;he significant interactionbetween response and pair type reported above.For mirror-image pairs, same responses weremade 42 msec. faster than different responses.For aligned pairs, this difference was only 7msec.

A significant interaction between the

6

plane of the stimulus pair and the order ofpresentation of the two planes was found:F (1,20) = 27.14, < .001, reflecting thefact that RT decreased from the first to thesecond half of the session.

While the error rate was only 3.7%, andthe differences among conditions small, moreerrors were made on mirror-image than onaligned pairs and more on horizontal than onvertical pairs (see Table 1).

IVDiscussion

The results of this study demonctrateconclusively that adults have difficulty com-paring mirror-image stimulus pairs when "mir-ror-image" is defined in terms of the axis ofseparation of the pair. Furthermore this dif-ficulty is found rqually for pairs in the verti-cal and horizontal planes.

One atudy with adult Ss using a same-different RT task and stimuli of this type hasbeen reported by Sekuler and Houlihan (1968).Translating their results into the language ofthis paper, the differences between mirror-image and aligned stimuli were significantfor horizontal but not for vertical pairs.These results must be interpreted with cautionhowever, since these differences were numer-ically almost identical, 42 and 38 msec. forhorizontal and vertical pairs, respectively.Their failure to find significant differencesbetween mirror-image and aligned pairs in thevertical plane is probably due to several fac-tors contributing to instability in their data.Ss were uncertain as to the plane in whichthe pairs would appear since presentation ofhorizontal and vertical pairs was intermixed.In addition, Ss responded by moving a toggleswitch to the right or left. A directional re-sponse of this type may be incompatible witha task requiring comparison of stimulus direc-tionality. These factors, as well as theiruse of median values of only six responsesto each stimulus, may explain the fact thattheir median RI's were almost 200 msec. longerthan the mean RTs found in the present study.

;lie fact that aduli. response times areio jer for mirror-image stimuli argues againstth.3 claim by Caldwell and Hall (1969, 1:370)that children's errors are caused merely bytheir misunderstanding of the definition ofidentity applied to mirror-image pairs. Inthe present study Ss clearly understood therelevant distinction to be made before starting

in the RT task. Also, since mirror-imagedifficulty was no greater for horizontal thanfor vertical pairs, and RT was the same forup-down and left-rigia stimuli, the bilaterallysymmetrical nervous system of human adultscannot explain their performance on this task.

A plausible explanation of these findings,based on a suggestion by Deutsch (1955), de-pends on the fact that for mirror-image pairsthe orientation of the individual stimuli (right-left or up-down) always matches the plane ofthe pair (horizontal or vertical). For alignedpairs the opposite is trueup-down stimuliare in the horizontal plane, while left-rightstimuli are in the vertical plane. If it isassumed that the subject either explicitlyor implicitly scans the pair of stimuli, eitherfrom the center outward in each direction orstarting at one end of the array, then in orderfor S to determine the orientation of a mirror-image stimulus he must integrate temporally-organized sensory information with motor in-formation about the direction of his scan.This point is most clearly seen in the exampleol_a pair of horizontal mirror-image horseshoes,

x with "x" representing the subject'sinitial point of fixation. A scan to either theleft or the right would result in exactly thesame pattern of stimulation over time. Thistemporal equivalence is suggested by Deutsch(1955) as a possible explanation for the con-fusability of mirror-image stimulus pairs. Inorder for the two horseshoes to be distinguishedspatially, additional information, provided bythe g! s knowledge of his direction of scan,would have to be integrated with this temporal-ly-organized stimulation. This analysis ap-plies in the same way to mirror-image pairs inthe vertical plane. For aligned pairs, however,no integration of motor scan knowledge is neces-sary since the directionality of these stimuliremains the same regardless of direction of

7

scan. 2 If it is assumed that this integrationof information from more than one source re-quires time, comparison of both horizontalind vertical mirror-image pairs should takelonger than comparison of aligned pairs asfound in the present study.

The difficulty young children have withmirror-image stimuli may be due in part tothe requirement of integrating these sourcesof information. In addition, the fact thatKindergarten children have unusual difficulty

2The integration of visual with motor scaninformation has also been used by Ghent(1961) to explain children's choices of "rightside up" and "upside down" stimuli, and byvon Hoist (1954) to account for the fact thatthe environment remains stationary during avoluntary eye movement.

6

with horizontal compared with vertical mirror-image pairs and with left-right stimuli com-pared with up-down stimuli (Huttenlocher,1967b) suggests that at this age they cannotderive the necessary directional informationfrom their movements in the horizontal plane.This lack of leftright response differentiationmay well be, as Corballis and Beale (1970)have suggested, a function of the bilaterallysymmetrical organization of the child's ner-vous system.

Gesell and Ames (1947) report that handed-ness does not become definitely established irthe child until the age of five. The successof Caldwell and Hall's (1969) training proce-dures in decreasing confusion between mirror-image letter pairs possibly is explained bythe fact that their kindergarten Ss have justreached the age where directional differences,especially left-right discriminations, car besuccessfully processed when a training taskrelevant to these differences is used.

GPO +9215-509

References

Caldwell, E. C., & Hall, V. C. The influ-ence of concept training on letter discrim-ination. Child Development, 1969, 40,63-71.

Caldwell, E. C., & Hall, V. C. Distinctive-features versus prototype learning reexam-ined. Journal of Experimental Psychology,1970, 83, 7-12.

Corballis, M. C., & Beale, I. L. Bilateralsymmetry and behavior. PsychologicalReview, 1970, 77, 451-464.

Deutsch, J. A. A theory of shape recognition.British Journal of Psychology, 1955, 46,30-37.

Gesell, A., & Ames, L. B. The developmentof handedness. Journal of Genetic Psychol-ogy, 1947, 70, 155-175.

Ghent, L. Form and its orientation: A child'seye view. American Journal of Psychology,1961, 74, 177-190.

Gibson, E. J., Gibson, J. J., Pick, A. D., &Osser, J. A developmental study of thediscrimination of letter-like forms. Journalof Comparative & Physiological Psychology,1962, 56, 892-898.

Huttenlocher, J. Discrimination of figureorientation: Effects of relative position.Journal of Comparative & PhysiologicalPsychology, 1967, 63, 359-361. (a)

Huttenlocher, J. Children's ability to order

GPO 826-501;

and orient objects. Child Development,1967, 38, 1169-1176. (b)

Mackintosh, J., & Sutherland, N. S. Visualdiscrimination by the goldfish: The orien-tation of rectangles. Animal Behavior,1963, 11, 135-141.

Riopelle, A. J., Itoigawa, H., Rahm, V., &Draper, W. A. Discrimination of mirror-image patterns by rhesus monkeys. Percep-tual & Motor Skills, 1964, 19, 383-389.

Rudel, R. G., & Teuber, H. Discriminationof direction of line in children. journal ofComparative & Physiological Psychology,1963, 56, 892-898.

Sekuler, R. W., & Houlihan, K. Discrimina-tion of mirror-images: Choice time analy-sis of human adult performance. QuarterlyJournal of Experimental Psychology, 1968,20, 204-207.

Sekuler, R. W., & Rosenblith, J. F. Dis-crimination of direction of line and theeffect of stimulus alignment. PsychonornicScience, 1964, 1, 143-144.

Sutherland, N. S. Visual discrimination oforientation and shape by octopus. Nature,1957, 179, 11-13.

von Hoist, E. Relations between the cent.ralnervous system and the peripheral organs.British Journal of Animal Behavior, 1954,2, 89-94.

149

National Evaluation Committee

Helen BainImmediate Past PresidentNational Education Association

Lyle E. Bourne, Jr.Institute for the Study of Intellectual BehaviorUniversiy of Colorado

Jeanne S. ChallGraduate School of EducationHarvard University

Francis S. ChaseDepartment of EducationUniversity of Chicago

George E. DicksonCollege of EducationUniversity of Toledo

Hugh J. ScottSuperintendent of Public SchoolsDistrict of Columbia

H. Craig SipeDepartment of InstructionState University of New York

G. Wesley SowardsDean of EducationFlorida International University

Benton J. UnderwoodDepartment of PsychologyNorthwestern University

Robert J. WisnerMathematics DepartmentNew Mexico State University

Executive Committee

William R. BushDirector of Program Planning and Managementand Deputy Director, R & D Center

Herbert J. Klausmeier, Committee ChairmanDirector, R & D Center

Wayne OttoPrincipal InvestigatorR & D Center

Robert G. PetzoldProfessor of MusicUniversity of Wisconsin

Richard A. RossmillerProfessor of Educational AdministrationUniversity of Wisconsin

James E. WalterCoordinator of Program PlanningR & D Center

Russell S. Way, ex officioProgram Administrator, Title ILL ESEAWisconsin Department of Public Instruction

Faculty of Principal Investigators

Vernon L. AllenProfessor of Psychology

Frank H. FarleyAssociate ProfessorEducational Psychology

Marvin J. FruthAssociate ProfessorEducational Administration

John G. HarveyAssociate ProfessorMathematics

Frank H. HooperAssociate ProfessorChild Development

Herbert J. KlausmeierCenter DirectorV. A. C. Henmon ProfessorEducational Psychology

Stephen J. KnezevichProfessorEducational Administration

Joel R. LevinAssociate ProfessorEducational Psychology

L. Joseph LinsProfessorInstitutional Studies

Wayne OttoProfessorCurriculum and Instruction

Thomas A. RombergAssociate ProfessorCurriculum and Instruction

Peter A. SchreiberAssistant ProfessorEnglish

Richard L. VenezkyAssociate ProfessorComputer Science

Alan M. VoelkerAssistant ProfessorCurriculum and Instruction

Larry M. WilderAssistant ProfessorCommunication Arta