Methods for the characterization of motor control development and its adaptation to visual biofeedback in upright stance

Abstract

This PhD project deals with the study of the mechanisms underlying the development of motor control for upright stance. In particular, the contribution of vision on this development has been observed by proposing novel methods for the analysis of the phenomenon and by designing systems, based on the administration of particular visual inputs – i.e. Visual Biofeedback –, devoted to manipulate the physiological answer for enhancing the adaptation mechanisms of the motor control system. The development of postural control in children and the role of vision in this development have been studied through the analysis of the predictive measures extracted from a mathematical function called Time-to Boundary. This approach has permitted to assess several aspects of the postural control in children that traditional postural parameters do not show. In particular, some experiments based on protocols considering both static and dynamic conditions have been designed, implemented and administered to children with congenital blindness that have been compared to healthy ones. The outcomes of these experiments have highlighted some interesting results. Among the latter: i) at 11 years the healthy children show an adult-like postural control system with an effective integration of the vision input in postural control schemes; ii) in dynamic tasks the absence of vision leads the healthy children to loss the perception of the temporal limit of ii stability; iii) the predictive function supports the theory that excludes balance deficit in children with blindness. The vision has then been used to manipulate the response of the postural control system and to study whether proper visual stimuli could enhance the adaptation mechanisms of that system. In fact, the possibility of stimulating the adaptation processes opens interesting scenarios in the framework of the maintenance and recovery of the motor abilities. Following this rationale, different visual stimuli for biofeedback have been designed and implemented looking at the improvement of postural performance that is to the effectiveness of the Visual Biofeedback systems. In particular, the influence, which different modalities of presenting and elaborating data inside the Visual Biofeedback systems could exert on the motor performance, has been observed. Three different Visual Biofeedbacks have been designed based respectively on: i) a continuous and direct presentation of the information, ii) a discretized and indirect presentation of the information, iii) an elaboration of the centre of pressure coordinates giving raise to a predictive information. The validation of the systems, through different experimental protocols, has showed that the use of an indirect and discretized modality of presentation improves postural performance and at the same time favours a more natural postural control strategy as compared to the classical continuous Centre of Pressure presentation; moreover the Visual Biofeedback based on the predictive data elaboration improves postural performance more than the presentation of a Visual Biofeedback based on a real-time elaboration of the Centre of Pressure coordinates. By these outcomes it has been highlighted how these aspects influence in different way the postural control strategies and consequently the postural performance. All these results extend and enhance the actual knowledge about the postural control development, with special reference to the role of vision in children and to the factors that could influence the iii Visual Biofeedback effectiveness, giving important suggestions for the design of tools to be spent in training and rehabilitation.