Mathias Dekeyser

Bistability and biasing effects in the perception of ambiguous point-light walkers

The perceptually bistable character of point-light walkers has been examined in three experiments. A point-light figure without explicit depth cues constitutes a perfectly ambiguous stimulus: from all viewpoints, multiple interpretations are possible concerning the depth orientation of the figure. In the first experiment, it is shown that non-lateral views of the walker are indeed interpreted in two orientations, either as facing towards the viewer or as facing away from the viewer, but that the interpretation in which the walker is oriented towards the viewer is reported more frequently. In the second experiment the point-light figure was walking backwards, making the global orientation of the point-light figure opposite to the direction of global motion. The interpretation in which the walker was facing the viewer was again reported more frequently. The robustness of these findings was examined in the final experiment, in which the effects of disambiguating the stimulus by introducing a local depth cue (occlusion) or a more global depth cue (applying perspective projection) were explored.

Creating stimuli for the study of biological-motion perception

In the perception of biological motion, the stimulus information is confined to a small number of lights attached to the major joints of a moving person. Despite this drastic degradation of the stimulus information, the human visual apparatus organizes the swarm of moving dots into a vivid percept of a moving biological creature. Several techniques have been proposed to create point-light stimuli: placing dots at strategic locations on photographs or films, video recording a person with markers attached to the body, computer animation based on artificial synthesis, and computer animation based on motion-capture data. A description is given of the technique we are currently using in our laboratory to produce animated point-light figures. The technique is based on a combination of motion capture and three-dimensional animation software (Character Studio, Autodesk, Inc., 1998). Some of the advantages of our approach are that the same actions can be shown from any viewpoint, that point-light versions, as well as versions with a full-fleshed character, can be created of the same actions, and that point lights can indicate the center of a joint (thereby eliminating several disadvantages associated with other techniques).

Living with voices: 50 stories of recovery

For over 25 years, the work of Marius Romme and Sandra Escher has inspired numerous academics, practitioners, voice hearers and their families, and brought together voice hearers and professionals from all over the world in an international network. This book is yet another valuable step in a long range of efforts to understand (theoretically and phenomenologically) the experiences of voice hearers, to promote acceptance of these experiences, and to support distressed voice hearers in every possible way. In their first book, Accepting Voices (Romme & Escher, 1993), the authors advocate regarding voices as a meaningful reality for the hearer, outside the medical model. Voices should not be considered the symptom of a medical condition, but rather a meaningful reaction to life events or to the personal situation of the voice hearer. Their second book, Making Sense of Voices (Romme & Escher, 2000), is aimed at the mental health professional, offering both theoretical perspectives and practical tools in supporting the recovery of distressed voice hearers. In this third book, Living with Voices, the authors returned to their initial plea for the acceptance of voices as a normal phenomenon, backed up by 50 stories of recovered psychiatric (ex-) patients. The title of the book can be somewhat misleading as it does not just present 50 striking personal stories, but it also presents a thorough analysis of these stories and discusses several key topics of these recovery processes. These topics include steps in the recovery process, causes of hearing voices, hindering effects of the disease concept of voice hearing, effects of medication, ways of accepting and making sense of voices, peer support, and the experience of psychotherapy. The first part of the book presents the results of this analysis organized in nine chapters. The second part of the book offers edited versions of all these 50 stories. The authors have put great effort into presenting their analysis in a concise and accessible manner, as they wish to address voice hearers as well as mental health professionals. The actual stories of voice hearers are put at the center of attention in every chapter, with ample use of quotes. The stories usually encompass the writer’s whole life, but all discuss the same topics – as requested in the story guidelines (included as an appendix in the book). Thus both the stories written up by voice hearers themselves (n1⁄4 11) as well as the stories written up by or with the help of an interviewer (n1⁄4 39), are highly similar in tone and topic. Further edition of these stories were undertaken at a later stage, when many stories were abbreviated to a maximum of four pages (editing guidelines are described in the introduction section to the stories). As a result, almost every story offers evidence for the final analysis. Person-Centered & Experiential Psychotherapies Vol. 11, No. 4, December 2012, 335–339