Libet's Experiment, Its Replicability, Validity and Clinical Potential
Total Page：16
File Type：pdf, Size：1020Kb
Palacký University Olomouc Faculty of Arts Department of Psychology Libet's experiment, its replicability, validity and clinical potential Libetův experiment, jeho replikabilita, validita a klinický potenciál Dissertation thesis Author: Mgr. Tomáš Dominik Supervisor: PhDr. Mgr. Roman Procházka, Ph.D. Olomouc 2019 Words of thanks Within the circles of experimental and cognitive psychologists, Libet’s experiment is sometimes dubbed “the experiment which started a thousand careers”. I sincerely hope that this thesis will add one more to that thousand. Present dissertation thesis reflects more than three years of research I, together with my colleagues, have conducted in this field. Since the beginning of my undergraduate studies, I was intrigued by the question of free will, but it took me four years to take the courage to tackle Libet’s experiment because I viewed it as something far beyond my capabilities. Nonetheless, thanks to encouragement of my supervisors and thanks to my luck of meeting the right researchers sharing my interests, I can now address some questions persisting in the “libetian” discussions to this day. I would like to express my gratitude to all the people who allowed me to conduct this research, namely: • Roman Procházka for his willingness to supervise this thesis, to share his clinical expertise with me and to read the manuscript of this thesis. • Martin Zielina for his supervision of my previous master thesis, for the stimulating discussions we had throughout my Ph.D. studies and for reading the manuscript of this thesis. • Daniel Dostál for mental stimulation, his inspiring zeal for cognitive psychology and data science, for help with data analyses and for reading the manuscript of this thesis. • Daniel Dostál, Martin Zielina, Roman Procházka, Jan Šmahaj and Zuzana Vaculčíková Sedláčková for cooperating on our projects and papers. • Barbora Sedláková, Markéta Zajícová and others who allowed me to collect data within their institutions. • Michal Kluka for language help with Studies 1 and 2. • Miroslav Kuba and Jan Kremláček for consultations pertaining the ERP analyses. • Patrick Haggard, Axel Cleeremans and all the members of their labs for hosting me and encouraging me to join the flow of current neuroscience and cognitive sciences. • The Department of Psychology, Faculty of Arts at Palacký University Olomouc, and especially its head Matúš Šucha, for creating an ideal academical working environment. • My family and especially my girlfriend, Jana Mišelnická, for much needed support. Acknowledgment This thesis was supported by Palacký University Olomouc, Czech Republic [IGA FF_2015_022, IGA FF_2017_021]. I hereby proclaim that I have written this dissertation thesis named “Libet's experiment, its replicability, validity and clinical potential” by myself, under the supervision of PhDr. Mgr. Roman Procházka, Ph.D. and using only cited literature. Studies 1 and 2 presented in this thesis were published and are used with consent of all co-authors (see Appendix 3). Místopřísežně prohlašuji, že jsem dizertační práci na téma: „Libetův experiment, jeho replikabilita, validita a klinický potenciál“ vypracoval samostatně pod odborným dohledem PhDr. Mgr. Romana Procházky, Ph.D., a uvedl jsem všechny použité podklady a literaturu. Studie 1 a 2 prezentované v této práci byly již publikovány a jsou použity se souhlasem všech spoluautorů (viz Appendix 3). In Olomouc on the 18th June 2019 Signature ................................ Table of contents Introduction ............................................................................................................................ 6 Theoretical part: History of Libet’s experiment, its methods and discussions ...................... 8 1 Historical background ..................................................................................................... 8 2 Methods and results of Libet’s experiment ................................................................... 10 2.1 Libet’s sample ........................................................................................................ 12 2.2 Libet’s equipment .................................................................................................. 13 2.2.1 Electroencephalographic recordings (EEG) .................................................... 13 2.2.2 Electromyographic recordings (EMG) ............................................................ 14 2.2.3 Experimental clock ......................................................................................... 15 2.2.4 Skin stimulation .............................................................................................. 16 2.3 Tasks in Libet’s experiment ................................................................................... 16 2.3.1 Self-initiated voluntary acts (M and W series) ............................................... 17 2.3.2 Pre-set motor acts (P and Pv series) ................................................................ 18 2.3.3 Skin stimuli at unknown times (S series) ........................................................ 19 2.3.4 Skin stimuli at pre-set times (Sp series) .......................................................... 19 2.4 Libet’s results ......................................................................................................... 20 2.4.1 Results of neural data analyses ....................................................................... 21 2.4.2 Results of introspective reports analyses ........................................................ 24 2.5 Libet’s conclusions ................................................................................................ 25 3 Critique and discussions of Libet’s experiment ............................................................ 29 3.1 Discussions of the intention to move (W reports) .................................................. 29 3.2 Discussions of the reports of the movement onset (M reports) ............................. 34 3.3 Discussions of the reports of skin stimulus (S reports) .......................................... 36 3.4 Discussions of the readiness potential (RP) ........................................................... 38 3.5 Sense of agency concept ........................................................................................ 47 Empirical part: Libet’s experiment validity, replicability and clinical potential ................. 51 4 Study 1: Validity of measuring the urge to move ......................................................... 51 4.1 Introduction ............................................................................................................ 51 4.2 Materials and methods ........................................................................................... 53 4.2.1 Participants ...................................................................................................... 53 4.2.2 Technical equipment ....................................................................................... 54 4.2.3 Experimental procedure and design ................................................................ 55 4.2.4 Variables ......................................................................................................... 56 4.2.5 Data analysis ................................................................................................... 56 4.3 Results .................................................................................................................... 59 4.4 Discussion .............................................................................................................. 60 4.5 Limitations and Recommendations ....................................................................... 64 4.6 Conclusions ............................................................................................................ 65 5 Study 2: A complex replication of Libet’s experiment ................................................. 66 5.1 Introduction ............................................................................................................ 66 5.2 Materials and methods ........................................................................................... 68 5.2.1 Participants ...................................................................................................... 68 5.2.2 Introspective data measurements .................................................................... 68 5.2.3 Recordings and skin stimulation ..................................................................... 70 5.2.4 Types of the experimental tasks ...................................................................... 72 5.2.5 Progression of the experiment ........................................................................ 75 5.2.6 Data analyses .................................................................................................. 80 5.3 Results .................................................................................................................... 84 5.3.1 EMG onset timing ........................................................................................... 84 5.3.2 Introspective impressions timing .................................................................... 86 5.3.3 Event-related potentials occurrence and timing .............................................. 91 5.3.4 Interindividual differences ............................................................................ 100 5.3.5 Series-specific effects