use qualities relative to the participant's interactive experience [2]; transparency, social-action space, user control/ autonomy, pliability, playability and seductivity [11]. Interaction should be designed to enhance a participant's control and, thereby facilitating interest and motivation. Action cycles inherent in the interaction create a process of enticement by attracting the participant's attention, ability to make progress and experiencing fulfilment by ending the experience in a positive way. Thus, the person is seduced by the system's playability offering surprise and prompting emotional responses through interactional beauty [11] of auditory qualities. 3. MUSICAL TOPOLOGY OF THE 'INSTRUMENT' Realisation of therapeutic benefits outlined above requires innovative installations with potential for meaningful music making within constraints imposed by the music maker's disabilities. Critical issues are respectively discussed in this and section 4, i.e., the design of the 'keyboard' of an 'instrument' and the means of 'playing' it. Here we discuss the concept musical topology, as has emerged through the work of Rolf Gehlhaar on his SOUND=SPACE installation [8]. A musical topology results from analysis and processing of information gathered from movement of bodies in a space equipped with sensors. The information is fed as control variables to compositional algorithms, and via synthesis routines, produces sounds. Thus, the audience becomes the performers. These topologies are passive, active, or hybrid. An example passive topography is simple triggering of a sound(s) with specified duration(s) by a person stepping into the area to which the sound(s) is assigned; like walking on imaginary keyboards that span the space. The 'instrument' is deterministic, playing only when someone triggers it, sounds 'mapped' onto the space by the program. Each 'keyboard' can be structured independently or assigned to a group of keyboards in a specific region, each with different pitches, durations and sounds assigned to the 'keys'. An active topology comprises an algorithmic realtime composition by the computer, influenced by presence and movement of persons in the space. Movements are converted into control parameters of the composing algorithm. The effect is like conducting an ensemble of musicians: usually, greater activity results in more animated and complex music. The algorithm employs interlinked chains of probability matrices, which can be programmed to produce generic musical styles. The hybrid topology combines both of the above into a space that reacts not only to movement but also to position. The effect can be like controlling tempo or direction of a musical flow by moving about the space and, at the same time, triggering specific events by stepping into specific places. SOUND=SPACE implements the above topologies as a musical 'instrument' 'played', usually by several persons in an empty space surveyed by an ultrasonic echolocation system that detects positions and movement of people. These measurements are sent to a computer that converts them into sounds. Normally, the space is square (up to 10m x 10m) sufficient for 8-15 people. Sensors on two contiguous sides look inwards across the space, creating a 'grid'. Thus, SOUND=SPACE is a complex, sophisticated multifunctional, multi-user system; but its environment is uncomplicated, friendly and non-intimidating. When invaded, it responds immediately with sound. No expertise is required to create generally exciting, engaging and pleasant sounds and musical sequences. Since moving in space is key to playing this musical instrument, users improve their perception of space, and, consequently their capabilities of movement. Accuracy only becomes a requirement when an intentional (musical) gesture is desired. Thus, SOUND=SPACE allows musical expression with no special skills while promoting development and improvement of new skills. Potential for benefiting people with disabilities emerged during an installation at the Gulbenkian Foundation, Lisbon in 1986. A visit by disabled children from special schools was such a success that it catalysed Gehlhaar's intensive involvement with SOUND=SPACE in the world of disability. He came to understand that technology no longer allows us simply to make art for a public; it demands that we create opportunities for the public to make art. It is about creating situations that encourage active, creative response common to all humans, able or disabled. Accordingly, he redesigned SOUND-SPACE to tailor the interactive aspects more towards the highly varied skill sets of disabled users. A further dimension emerged during recent SOUND=SPACE workshops run by Luis Miguel Girao in Oporto, Portugal, as part of "Ao Alcance de Todos". The system was set-up for participants suffering from brain paralysis, educators and music students, in a public space that also allowed interaction with passersby. This highlighted SOUND=SPACE as a social environment also including, perhaps more importantly, interaction between person and person (disabled or nondisabled) while 'playing' in the environment. Thus, it was evident that non-disabled people had much to learn from disabled people about awareness and sensitivity to the musical environment. Finally, we note that environments, such as SOUND=SPACE, have an educational role. Techniques of progressive exploration of the instrument reveal basic principles of playing music, such as: sound/silence, musical phrase and musical dialog. A deeper approach brings up the learning of harmony and rhythm. Gehlhaar has developed different versions of the topographies, each with its own characteristic mood and nature - calming, exciting, sustained, rhythmical, percussive, and so forth. It is possible, within a workshop, to move rapidly from one mood to another, with few words spoken, to encourage participation, to support the mood and activity of the moment, to focus attention or to shift the concentration of the participants, to calm them down when they get too excited. 78
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