Plan de Implementación

a surface as fingertip movement that can be characterized as approximating a single path of movement, at right angles with a surface, and extending across at most a few centimeters. To be comprehensive, computed fingertip touch should also support the forms of fingertip instrumental control where this particular type of movement occurs.

Moreover, realizing this support has some priority over realizing support for other possible forms of fingertip instrumental control: unidirectional fingertip movement orthogonal to a surface has both a prevalence in, and specific advantages for fingertip instrumental control (see Section 1.2.5).

Concretely, this implies a need for such transducer technology as can monitor aspects of motor activity, and induce aspects of somatosensory perception, that are involved in this type of movement.

1.6.2.1 Consequent choice: the human fingerpad as transducer source and target

During unidirectional fingertip movement orthogonal to a surface, the fingerpad, or pulp of the fingertip (see Section 1.3.1.4) typically is the area making mechanical surface contact. Via this contact, changes are made to sound-generating processes during instrumental control. Therefore, we will pursue transducer technology which follows the same principle, with transducer causations having the fingerpad as their anatomical source and target location.

1.6.2.2 Consequent choice: transducers based on flat, closed, rigid contact surfaces

During the mechanical contact just mentioned, the fingerpad often has an approximately flat, closed, and rigid surface as its immediate counterpart outside the human body. Surely, this is not always the case: for example, the fingertip may open and close holes on aerophones, or press strings against instrument bodies. However, many existing forms of instrumental control do occur via this type of surface: for example, the fingertip may open and close valves on aerophones; strike pads and membranes; tap and press sensor surfaces; and perform press/release cycles on push- buttons, computer keys, and the keys of piano-type keyboards (see Section 1.2.5).

These existing forms of instrumental control can be grouped together as based on unidirectional fingertip movement orthogonal to flat, closed, rigid surfaces. Then,

having the same type of surface making contact with the fingerpad could also be a useful principle for implementing transducer technology: this may allow support for many of the aspects of motor activity and somatosensory perception that are involved in these forms of instrumental control. Also, obtaining such support has some priority: because of the existing prevalence of this subtype of instrumental control, realizing support for it represents an important part of realizing support for unidirectional fingertip movement orthogonal to a surface, in general.

1.6.2.3 Consequent choice:orthogonalaswellasparallelforceoutputtothefingerpad

The above transducers will be used to implement forms of instrumental control based on dynamic mechanical contact between the surface of the transducer and that of the human fingerpad. This will involve a mutual application of forces, where mandatory transducer output (see Section 1.5.2.1) produces forces applied to the fingerpad surface. Since the wider context here is providing support for unidirectional fingertip movement orthogonal to a surface, such force output at least must include forces orthogonal to the fingerpad surface.

These forces may then be resisted mechanically by the palmar side of the fingertip, causing the somatosensory perception of fingertip touch. However, as discussed in Section 1.3.1.4, via its skin, the fingerpad also offers another main type of mechanical resistance resulting in the perception of fingertip touch: the resistance against relative movements parallel to the fingerpad surface. To also cover this other main type of sensory transduction, force output parallel to the fingerpad surface is needed, too. 1.6.3 The need for physical units in algorithms The previous discussion already points to the development of rather specific transducer technology. It is important to emphasize that any such development, even when completed, will provide only a starting point for further implementation. A general issue here is that even if a Turing- complete automaton and a concrete set of transducers have been obtained – which together enable computational liberation – this does not also imply the simultaneous realization of any direct correspondences between automaton states on the one hand, and aspects of human action and perception on the other. On the contrary: such correspondences quite probably will have to be built and discovered.

For example, in computed sound, the combination of digital wave table and electric loudspeaker has enabled computational liberation. But clearly, the first historical implementations of this combination only provided the starting points for a long and still ongoing process of further implementation, covering ever more aspects of heard musical sound (see Section 1.4). Here, not only have obstacles been overcome so as to match known aspects of heard musical sound with known automaton states. Continuing implementation has also reflected a process of more fundamental discovery: Transducer technology enabled the development and implementation of precisely defined and executed algorithmic relationships between measurable physical properties such as time and air pressure. This was then used to induce various aspects of heard musical sound in a reproducible manner. Based on this, a greater understanding has been obtained also of the very nature of aspects of heard musical sound. This increased fundamental understanding includes conceptual as well as

experiential knowledge. A seminal example of this has been the generation of heard stable sine waves, made possible by the use of digital wave tables [Mathews et al. 1969].

In computed fingertip touch, we might expect an analogous process of construction and discovery. In any case, after initial transducer implementation, there will be a need for further implementation, so as to match automaton states to those aspects of motor activity and somatosensory perception deemed relevant to the further development of instrumental control of musical sound. To facilitate this, it is important to ensure from the outset that transducer state is algorithmically represented in terms of physical units. After all, any and all matching will be based, in the first place, on the specific changes over time in the physical state of the individual output or input transducers used. Therefore, these physical changes should be transparently accessible to someone writing algorithms for the transducer technology.

1.6.4 The need for support of passive touch, active touch, and manipulation In