View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by OTHES Dissertation Handedness: Shortcomings of Previous Research, an Alternative Model and a New Experimental Approach Verfasser: Dipl.-Volkswirt Univ. Dr. Lothar Rup1 angestrebter akademischer Grad: Doktor der Philosophie (Dr. phil.) Wien, im April 2008 Studienkennzahl: A 092 298 Dissertationsgebiet: Psychologie Betreuer: Prof. Dr. Gerhard Benetka 1I thank all who supported this work with comments and advice, especially Gerhard Benetka. I thank Annemarie Kellner, Heidi Wurm, and Sophie Le Good for revising the English. Never- theless, I take responsibility for all remaining errors. Abstract An overview of previous handedness research and a critical assessment of methods, re- sults, and theories of this research are presented. The results of this assessment challenge the current experimental and theoretical approaches. Subsequently a new model of hand- edness is presented. This model is made up of four elements: (a) Handedness is associated with innate and genetically coded brain asymmetry. (b) The functional representation of handedness of left- and right-handers is mirror reversed. (c) The actual specication of handedness is determined in a random process. (d) The distribution is U-shaped with approximately 50% left-handers and 50% right-handers. The innate disposition of a ma- jority of left-handers is changed by environmental inuence, by practicing right hand writing, and by right hand tool use. Switching handedness causes dierences between switched and nonswitched left- and right-handers or between left and right hand writers regarding psychological characteristics and related neuronal and physiological features. It is argued that the existence of such dierences indirectly supports the new model. The alternative handedness model explains and integrates results of previous research, which do not correspond to current models and theories. Finally, ideas and considerations for an alternative approach of testing handedness are presented. Key Phrases: innate and genetically coded brain asymmetry determination of handedness in a random process 50% left- and right-handers switching handedness and consequences psychological dierences between left and right hand writers 1 Contents Summary 3 Zusammenfassung 5 1Introduction 7 2 Previous Research: Methods, Results, Theories, and Discussion 11 2.1PreviousMethods,Results,andTheories.................. 11 2.2DiscussionofMethodsandResultsofTesting............... 15 2.2.1 Questionnaire Activities are Socially Inuenced .......... 16 2.2.2 Questionnaire Items are not Dissimilar Enough . ......... 19 2.2.3 Results from Performance Tests and Questionnaires are Similar . 21 2.2.4 TheCurrentConceptofHandednessisRestricted......... 22 2.2.5 WhatQuestionnairesReallyMeasure................ 23 2.2.6 BetterItemsforTestingHandedness................ 25 2.2.7 AlternativeMethodologyofTesting................. 26 2.2.8 Assessment of Measuring of Handedness .............. 28 2.3DiscussionofHandednessTheories..................... 29 3 Alternative Handedness Model 31 3.1WhatisInnateonIndividualandSpeciesLevel?.............. 32 3.1.1 ModelofAsymmetryandDirectionofAsymmetry......... 33 3.1.2 SitusInversusinMice–AnAnalogy................ 35 3.1.3 InheritanceoftheDegreeofLateralization............. 37 3.1.4 Handedness in Animals: Innate Preference, Distribution, and Non- inheritance.............................. 38 3.1.5 HumanHandednessandLateralizationofSpeech......... 45 3.1.6 Sidedness: An Extended Concept of Handedness . ......... 52 3.2 Switching Handedness, Dierent Degrees of Inuence, and Consequences 53 3.2.1 InuencingHandednessofAnimals................. 54 3.2.2 Inuencing Human Handedness and Consequences for the Distri- bution................................. 58 3.2.3 PrevalenceofLeft-HandednessinClinicalPatients......... 67 3.2.4 PsychologicalConsequencesofSwitchingLeft-Handers...... 69 3.3 Dierences in Left-Handers, Switched Left-Handers, and Right-Handers . 71 Handedness: Alternative Model 2 3.3.1 Motor Skills .............................. 73 3.3.2 Intellectual Performance and Spatial Ability . ......... 75 3.3.3 SpeechImpairment.......................... 83 3.3.4 PersonalityTraits........................... 88 3.3.5 Scanning Direction in Visual Perception and Drawing Direction . 89 3.3.6 HemisphericAsymmetryofNeuronalActivity........... 91 3.3.7 PhysiologicalMeasures........................ 92 4 Alternative Approach of Testing Handedness 95 5 Final Remarks 103 References 107 Handedness: Alternative Model 3 Summary The aim of this thesis is to give an overview on the research of handedness and to present a critical assessment of methods, results, and theories of this research. The results of this assessment challenge the current experimental and theoretical approaches. A new model of handedness and a new experimental approach will be proposed. Previous methods of testing handedness (questionnaires and tests) and their results, and some theories on human (right-) handedness and on its origin will be presented. The discussion will also focus on what questionnaires and performance tests really measure (and what they do not) and whether the items and tasks can be regarded as appropriate to achieve the aimed objective. It will be argued that the current methods of mea- suring handedness are questionable because the questionnaire items and test tasks are selected in a particular way and the results may therefore be biased. Right-handedness, as determined by means of the traditional questionnaire or test approach, seems to be a sociocultural phenomenon. This means that the preponderance of right-handedness is a consequence of learning and instruction by the social environment and does not reect innate handedness. Research demonstrates moreover that predominant right-handedness is limited to tool use operations. Based on this critical review a new alternative model of handedness is suggested. This model is made up of four elements: (a) Handedness is associated with innate and genetically coded brain asymmetry. (b) The functional representation of handedness of left- and right-handers is mirror reversed. (c) The actual specication of handedness is determined in a random process. (d) The distribution is U-shaped with approximately 50% left-handers and 50% right-handers. Further features of innate handedness are the degree of handedness and the connection between handedness and lateralization of speech. Inuencing and switching handedness and its consequences will also be discussed. The aptitude of humans and animals of being instructed and inuenced in their handedness diers on an individual and on a species level. The innate disposition of a majority of left-handers is changed by environmental inuence, by practicing right hand writing, and by right hand tool use. Switching handedness causes dierences between switched and nonswitched left- and right-handers or between left and right hand writers regarding psychological character- istics and related neuronal and physiological features. The reported eects of shifting on motor skills, intellectual performance, spatial ability, speech impairment, personality traits, scanning direction in visual perception, drawing direction, hemispheric asymme- Handedness: Alternative Model 4 try of neuronal activity, and physiological measures indirectly support the new model of handedness. Finally, ideas and considerations for an alternative approach of testing handedness will be presented. The framework of testing (items and participants) will be discussed and six classes of test items (e.g., motor asymmetry items and coordinative tasks) will be proposed. The new approach shall indicate how it can be ensured by means of dierent methods of testing, item selection, and test design that testing is valid and reliable. This alternative handedness model explains and integrates many results of previous research, which contradict one another and do not correspond to current models and the- ories. Further research is absolutely necessary and a new approach of testing handedness is particularly required. Handedness: Alternative Model 5 Zusammenfassung Ziel dieser Arbeit ist es einen Überblick über die bisherige Händigkeitsforschung zu geben und eine kritische Bewertung der Methoden, Ergebnisse und Theorien dieser Forschung zu präsentieren. Die Ergebnisse dieser Bewertung stellen die derzeitigen experimentellen und theoretischen Ansätze in Frage. Ein neues Händigkeitsmodell und ein neuer experi- menteller Ansatz werden vorgeschlagen. Die bisherigen Methoden der Händigkeitstestung (Fragebögen und Tests) und ihre Resultate und einige Theorien zur menschlichen (Rechts-) Händigkeit und zu ihrem Ur- sprung werden vorgestellt. Es wird diskutiert, was Fragebögen und Performancetests wirklich messen (und was nicht), und ob die Items und Aufgaben zur Erreichung des angestrebten Ziel geeignet erscheinen. Es wird argumentiert, dass die derzeitigen Metho- den Händigkeit zu messen, fragwürdig sind, weil die Fragebogen-Items und Testaufgaben in einer bestimmten Weise selektiert sind und die Ergebnisse deshalb verzerrt sein kön- nen. Rechtshändigkeit scheint, so wie sie mit dem traditionellen Ansatz mittels Frage- bögen und Tests festgestellt wird, ein soziokulturelles Phänomen zu sein. Dies bedeutet, dass das Überwiegen von Rechtshändigkeit eine Folge von Lernen und Instruktion durch das soziale Umfeld ist und daher nicht die angeborene Händigkeit widerspiegelt. Die Forschung zeigt ferner, dass überwiegende