Research in environmental psychology has sought to identify the characteristics of environments which best support human wellbeing, including those environmental attributes which help to restore fatigued attention, providing relief from cognitive stress. While the experience of natural landscapes is known to be restorative, certain types of imagery have a similar effect on the viewer : these include nature images, including landscape scenes, and fractal patterns. Previous research has demonstrated that such types of image have an immediate and measurable de-stressing effect, but there has been little or no research in relation to the possibility of extending this effect by creating suitably structured time-based visual content. AMbiARt is a mixed-reality ambient multimedia/intermedia application, designed with the specific intention of providing restorative experiences, in the spatial context of quiet rooms in Special Educational Needs Schools for children with Autism Spectrum Disorders (ASDs). The structure and content are based in large part on Kaplan's Attentional Restoration Theory, (ART), consciously emulating the restorative characteristics of natural environments, and creating a sense of temporarily ‘being away’, as an accessible alternative to other means of relaxation and attentional restoration. AMbiARt is structured so as to produce non-repeating interactive natural and fractal imagery and sound, using generative algorithms. The content affords ‘soft fascination’, engaging and holding the viewer's attention without drawing on already-fatigued attention. Interaction is simple and intuitive, and relates visually and aurally to the screen content. As a response to sensory-perceptual sensitivity and fluctuation, controllability of all aspects of the environment is a critical element of the design. This facilitates ‘extreme personalisation’, adjustable to suit each user's sensory profile, or to accommodate fluctuating sensory perception.