Perception of the direction of articulatory motion of point-light figures

Observing and interpreting the direction of human movements and actions are necessary to interact effectively and efficiently with other human beings. For instance, predicting the speed with which an elder steps back from an angry dog may increase her/his safety because we would be able to intervene and prevent an attack. From an experimental perspective, the study of the perception of the direction of articulatory human motion may be traced back to the original theoretical perspective and procedures introduced by Johansson (1973) to study perceptual organization. Remarkably, the author was able to create a stimulus consisting of a number of point-lights that represent some of the joints of a person to elicit perception of human motion in laboratory contexts very similar to our perception in daily life: the biological motion stimulus. As the present dissertation deals with a study of the perception of the direction of articulatory motion of human actions depicted as point-light displays, it seems reasonable to follow Johansson’s ideas about the way to analyze the stimulus –using physical concepts- and the kind of research he expected to have as a logical development of his program. Following this vein, studies on effects of geometric properties of human relative motion using point-light displays have explored a diversity of effects on the perception of aspects such as depth (Schouten, Troje, & Verfaillie, 2011; Vanrie, Dekeyser, & Verfaillie, 2004; Vanrie & Verfaillie, 2006), viewpoint (Jokisch, Daum, & Troje, 2006), and inversion (Troje & Westhoff, 2006, Sumi, 1984), among others. The first chapter introduces the theoretical framework and specific paradigms that have been applied to study the perception of the direction of articulatory motion of human actions depicted as point-light displays. It comprises general considerations which consist of a brief review of theoretical approaches and definitions that have shaped the topic, brief descriptions of the theoretical and experimental paradigms used in the study of biological motion perception, the statement of research questions and methodology we have used in our studies, and an overview of the dissertation. The purpose of Chapter 2 is to investigate perception of articulatory motion in point-light figures using the simultaneous-masking paradigm with a masked (forward or backward moving) walker (signal) or a scrambled (forward or backward moving) walker (noise). We analyze sensitivity (d’) as well as response bias (c). In Chapter 3 we investigate perception of articulatory motion in different point-light actions (walking, crawling, hand walking, and rowing) presenting a forward or backward moving person to decide on the direction of articulatory motion of the person. We analyze sensitivity (d’) as well as response bias (c). In addition to the type of action, the diagnosticity of the available information was manipulated by varying the visibility of the body parts (full body, only upper limbs, or only lower limbs) and the viewpoint from which the action was seen (from frontal view to sagittal view). The goal of Chapter 4 is the introduction of a novel technique to explain sensitivity responses in psychophysical experiments as reported in Chapter 3. We summarize the main findings of our research reported in Chapter 3 and explain the need for a technique to measure the amount of asymmetry in the horizontal direction of motion of animated actions. Then we deduce four indices to measure symmetry/asymmetry of the direction of its motion and the phase portrait representation and use them to analyze asymmetry of motion of individual joints clustered by body parts and varying for orientations from profile to frontal view, for the point-light actions studied in Chapter 3. In Chapter 5 we compare perception of forward and backward point-light walkers versus their reversed displays. We analyze sensitivity (d’) measures derived from response to signal (forward/backward moving walker) and noise (reversed versions) stimuli as well as response bias (c). Finally, in Chapter 6 we summarize empirical findings, methodological novelties, sketch future research, and make concluding remarks stressing strengths and limitations of the work.Contents CHAPTER 1 INTRODUCTION 1 GENERAL CONSIDERATIONS 3 DEFINITIONS 4 Biological motion 4 Perception of biological motion 5 Perception of the direction of articulatory motion 5 THEORETICAL AND EXPERIMENTAL PARADIGMS 5 Psychophysics 5 Perception 6 Perception and action 7 Movement science 8 Cognitive neuroscience 8 RESEARCH QUESTIONS AND METHODOLOGY 10 OVERVIEW OF THE DISSERTATION 11 CHAPTER 2 PERCEPTION OF THE DIRECTION OF ARTICULATION OF WALKING: THE SIMULTANEOUS MASKING-PARADIGM 13 INTRODUCTION 15 EXPERIMENT 17 METHOD 17 Participants 17 Stimulus 17 Procedure ……………. 18 RESULTS 18 DISCUSSION 20 CHAPTER 3 PERCEPTION OF THE DIRECTION OF ARTICULATORY MOTION OF POINT-LIGHT FIGURES 21 INTRODUCTION 23 EXPERIMENT 1 27 METHOD 27 Participants 27 Stimulus 28 Procedure and design 28 RESULTS AND DISCUSSION 29 EXPERIMENT 2 30 METHOD 31 Participants 31 Stimuli 31 Procedure and design 31 RESULTS AND DISCUSSION 31 EXPERIMENT 3 33 METHOD 34 Participants 34 Stimuli 34 Procedure and design 34 RESULTS AND DISCUSSION 34 EXPERIMENT 4 36 METHOD 36 Participants 36 Stimuli 36 Procedure and design 37 RESULTS AND DISCUSSION 37 EXPERIMENT 5 38 METHOD 39 Participants 39 Stimuli 39 Procedure and design 39 RESULTS AND DISCUSSION 39 GENERAL DISCUSSION 41 CHAPTER 4 PHASE PORTRAIT ANALYSIS OF ACTIONS 45 INTRODUCTION 47 ANALYSIS OF PHYSICAL ASYMMETRIES OF THE DIRECTION OF HORIZONTAL MOTION OF POINT-LIGHT ANIMATIONS 49 TEMPORAL INDEX OF ASYMMETRY (TIA) 50 VELOCITY INDEX OF ASYMMETRY (VIA) 53 ACCELERATION INDEX OF ASYMMETRY (AIA) 55 PHASE PORTRAIT INDEX OF ASYMMETRY (PPIA) 57 APPLICATION OF THE PHASE PORTRAIT TECHNIQUES TO THE ANALYSIS OF THE DIRECTION OF HORIZONTAL MOTION IN HUMAN ACTIONS 60 PHASE PORTRAIT ANALYSIS OF INDIVIDUAL JOINTS IN THE ANIMATED HUMAN WALKER 60 PHASE PORTRAIT ANALYSIS OF THE ANIMATED HUMAN CRAWLER 71 PHASE PORTRAIT ANALYSIS OF THE ANIMATED HUMAN HAND WALKER 77 PHASE PORTRAIT ANALYSIS OF THE ANIMATED HUMAN ROWER 82 PHASE PORTRAIT ANALYSIS OF GROUPS OF JOINTS 87 DISCUSSION 97 CHAPTER 5 PERCEPTION OF THE DIRECTION OF ARTICULATION OF MOTION OF ANIMATIONS DERIVED FROM A SINGLE WALKER DATA 101 INTRODUCTION 103 EXPERIMENT 105 METHOD 105 Participants 105 Stimulus 105 Procedure and design……………. 106 RESULTS 106 DISCUSSION 108 CHAPTER 6 GENERAL CONCLUSIONS 113 EMPIRICAL FINDINGS 115 PERCEPTION OF THE DIRECTION OF ARTICULATION OF WALKING: THE SIMULTANEOUS MASKING-PARADIGM 115 PERCEPTION OF THE DIRECTION OF ARTICULATORY MOTION OF POINT-LIGHT FIGURES INVOLVED IN DIFFERENT ACTIONS 115 PHASE PORTRAIT ANALYSIS OF ACTIONS 116 PERCEPTION OF REAL FORWARD AND BACKWARD MOTION IN POINT-LIGHT WALKERS 116 METHODOLOGICAL NOVELTIES 116 KINEMATIC INDEXES AND PHASE PORTRAIT 116 CONCLUDING REMARKS 117 OPEN QUESTIONS 120 POSSIBLE FUTURE RESEARCH 121 REFERENCES 125 APPENDICES 139 APPENDIX A VIEWING POINT-LIGHT ANIMATIONS FROM DIFFERENT VIEWPOINT ANGLES 141 APPENDIX B MATLAB CODE TO GENERATE POINT-LIGHT ANIMATIONS FROM DIFFERENT VIEWPOINT ANGLES 142 APPENDIX C LOOPABILTY OF ACTIONS 143 APPENDIX D MOTION CAPTURE AND 3D ANIMATION TECHNIQUE ADAPTATION 144nrpages: 144status: publishe