Proposal summary: The present project will investigate the main principles of development and neuroplasticity in humans in the domain of multisensory processes (the interplay between sensory systems). It will be tested how learning plasticity of the human brain changes from childhood to adulthood and how early experience constraints neuroplasticity at later developmental stages as well as in adults. The project is based upon animal findings in sensory development and plasticity. Both a prospective (studies in children) and a retrospective (studies in people with a history of visual or auditory deprivation) approach are employed. Behavioural paradigms from experimental psychology addressing multisensory processes are combined with electroencephalographic recordings (EEG). First, we investigate the functional principles and neural correlates of multisensory development. Second, we investigate multisensory processes in people who suffered from a transient phase of sensory deprivation after birth: (a) in people who were born with bilateral dense cataracts that were removed later, and (b) in congenitally deaf individuals, who were equipped with a cochlear implant to restore hearing. This line of research will reveal the critical contribution of single sensory systems as well as the synchronized input across modalities with regard to the emergence of successful multisensory binding. Third, we will investigate whether it is possible to alleviate neural changes demarcating the end of sensitive phases or critical periods by implementing an incremental training procedure. Last, we will look at whether experimentally induced transient sensory deprivation increases neuroplasticity loss during a sensitive phase or critical period. We are convinced that basic research, such as the present, will reveal important principles of development and neuroplasticity which will be useful in applied setting to improve education, the rehabilitation of individuals with sensory defects and the treatment of developmental disorders.