Body representation and motor imagery : effects of adaptability
Corinne Jola, Marie‐Claude Hepp‐Reymond · Zurich Open Repository and Archive (University of Zurich) · 2009
We are occupants of a body that receives diverse sensory input via our visual and somatosensory system. Furthermore, as we are the agent of our own body, the brain must also deal with both the afferent and efferent signals that occur with movement, namely the motor system. How do we perceive our stationary or moving body as well as the world around us as a coherent whole? Mental representations are assumed to support and modify our perception, as well as the resulting behaviour, the action. In this thesis, representational processes in the perception of the body and its movements are discussed in relation to the particular systems: vision, somatosensory, and motor. In chapter 1, the general introduction, the terms „representation‟ and „images‟, as well as „body representation‟ and „movement representation‟ are described along the lines of previous research and defined for their appropriate use within this thesis. Specific background literature and concepts with respect to the experiments are discussed in the introductory sections within each individual chapter. Chapters 2 and 3 explore representations of the stationary body by the sensory modalities vision, proprioception, and touch, whilst chapter 4 deals with mental representation in movement. Overall, the results of these investigations exemplify the adaptability of representational processes based on different sensory systems in the stationary and the moving body (see chapter 5). The three experiments combined in chapter 2 investigated body representations based on the visual sensory system. The question was, to what extent does the form of what we visually perceive influence our mental transformation processes? All three experiments gave evidence that different 3 forms of body representations in response to vision are behaviourally not as disparate as suggested by previous investigations. For example, participants needed more time to mentally transform visually presented stimuli with increasing angular disparity between them. This was the case for abstract objects as well as for bodies when no rotation in depth was necessary (Experiment 1). The response pattern for identifying the outstretched arm in a body figure was thus comparable to that when identifying abstract objects. Hence without depth rotation, egocentric body transformation is akin to mental object rotation. In contrast to the hypothesis on effects of expertise, however, no effect could be observed between subjects: The reaction times between dancers, who are experienced in mentally transforming bodies, and novices did not differ significantly (Experiment 2). Surprisingly, when body postures were presented in the abstract dance notation of Laban (Experiment 3), no mental rotation costs were measured. These three experiments showed that mental transformations were available in different prospects, of which one is perspective-independent. Consequently, in certain conditions the mental presentations seem to switch quickly from a perspective dependent to an independent form. Accordingly, mental representations are not singularly dependent on the presentation form. Cognitive processing of either visually perceived abstract objects, body drawings, or body-related symbols were comparable, whereas the spatial frame of reference, the orientation between the observer and the perceived orientation of the stimuli, was of primary relevance. The type of visual presentation only defines the form of mental representation used for the transformation when a mental rotation in depth is needed. 4 The experiments in chapter 3 looked at how we sense the body in egocentric space based on somatosensory perception. In particular, the first of these psychophysical investigations was concerned with the perception of body limbs in space, that is, proprioceptive sensory mode (Experiment 4). The second was an experiment on tactile perception on the body surface, that is, tactile sensory mode (Experiment 5). Proprioception is the sense which is thought to give us the experience of our own body posture. The tactile sensory mode consists of two distinct perceptual processes: the tactile experience itself (tactile recognition) and the localisation on our body surface (tactile localisation). Both proprioception and tactile localisation revealed effects of adaptability on body reference points. The experiment on proprioception showed that actively pointing to a location in egocentric space is biased by two reference centres of the body located at each shoulder in all but the visual condition. Dancers showed a smaller bias of the two reference centres; but interestingly, they also showed it in the visual task. Therefore, the perception of the self in egocentric space referred to different functional body references according to both the sensory modality used and the individual‟s motor expertise. Moreover, the modality can be substituted with simulation, such as simulated proprioception in the dancers‟ group. The experiment on tactile localisation showed that the point of sensations of touch was located closer to the body centre than the original stimulation. This was the case in both sensory modes that were available to localise a point of touch: vision (by visual estimation) and motor (by pointing). Thus, the body centre acts as a reference point independent of the response mode. Interestingly, additional tactile information from the tip of the finger caused a switch in the direction of the mislocalisation from the body centre to the periphery. Consequently, 5 representations of the egocentric space are adaptable in both the short- and long-term, and this adaptability is dependent on both sensory input and expertise, respectively. Further, tactile perception is immediately integrated in the perception of the body space and has a dramatic effect on spatial localisation on the body surface. Chapter 4 discusses how movement representations can evolve by motor imagery training compared to common execution training. Mentally rehearsing the abduction of the big toe, a movement without established motor command, caused a reduction in the time taken to move whereas exertion force was most increased by execution training (Experiment 6). This finding shows conceptually different training effects between imagery and execution. It goes beyond previous behavioural studies that have shown differences between imagery training and execution training in the level of performance increase alone. In addition, a representation of the movement goal (anticipation) surprisingly improved participants‟ movement abilities, as could be observed by a performance increase in the movement range of the abduction. Thus along with representations of the stationary body, mental representations can be consciously instrumentalised in the moving body, such as motor imagery or anticipation; they can also show short- and long-term performance adaptations, respectively. Chapter 5 is a general discussion of the experimental results. The data from this thesis supports the existence of a nonmodular adaptable body representation that can accommodate long-term changes (through experience) as well as rapid switches (from different sensory feedback information). Representations are hypothesised to be the effect of adaptability processes. In addition, the importance of differential observation is highlighted. Der Körper ist unser Instrument, mit dem wir uns in der Welt zurechtfinden. Űber die verschiedenen Sinnessysteme des Körpers können wir unsere Umwelt sowie die ‚Körperinnenwelt‟ erfahren. Das visuelle System ermöglicht ein Abbild der Aussenwelt. Das somatosensorische System, bestehend aus der Propriozeption und der Berührungsempfindung ist wichtig, um die Position unseres Körpers im Raum sowie die Gestalt unseres Körpers wahrzunehmen. Nebst diesen im passiven Körper vorhandenen Sinneseindrücken haben wir aber auch Bewegungsempfindung: Wir sind nicht nur Empfänger von Sinneseindrücken, wir agieren aktiv mit unserem Körper in der Umwelt. Im Gehirn findet ein Zusammenspiel sowohl von solchen afferenten als auch efferenten Signalen statt. Wie aber ist es möglich, dass wir trotz der Information von verschiedenen Sinnessystemen unseren passiv oder aktiv (bewegten) Körper sowie die Welt um uns herum als eine zusammenhängende kohärente Entität wahrnehmen? Mentale Repräsentationen sind ein zentrales Element in diesem Integrationsprozess: Sie spielen eine wichtige Rolle in dem Zusammenspiel von Wahrnehmung und resultierendem Verhalten (die Handlung). In dieser Arbeit werden mentale Repräsentationen der Wahrnehmung des Körpers und seiner Bewegungen in Bezug auf die besonderen Sinnessysteme besprochen: visuelle, somatosensorische und motorische Sinneswahrnehmung. Das erste Kapitel gibt eine Einführung in die Begriffe Repräsentation und mentale Bilder, sowie Körperrepräsentation und Bewegungsrepräsentationen. Insbesondere wird der spezifische Gebrauch der Begriffe innerhalb dieser Arbeit 7 definiert. Weitergehende Einführungen sind in den Einleitungen der jeweiligen experimentellen Kapitel zwei bis vier zu finden. Die mentale Körpertransformation basierend auf dem visuellen System wird in Kapitel zwei besprochen. In Experiment 1 wurden die Prozesse in der mentalen Rotation von Objekten und Körpern untersucht. Dabeit hat sich gezeigt, dass insbesondere die Rotation in der Tiefe das Verhalten der Versuchspersonen beeinflusst. Versuchspersonen benötigen für die Diskriminierung zweier abstrakter Objekte in der Regel länger, je grösser die Diskrepanz in der Ausrichtung der zu beurteilenden Objekte ist. Dieser Rotationseffekt konnte auch bei der Identifizierung von Körperstimuli nachgewiesen werden, jedoch nur wenn die Ausrichtung der Stimuli mit der egozentrischen Perspektive der Versuchsperson übereinstimmte, das heisst, wenn keine Rotation in der Tiefe notwendig war. In Experiment 2 wurde der Einfluss der generellen Bewegungsexpertise von Tänzern auf die mentale Transformation von Körpe