Classification of the Tools ​

Classification According to ISO 9999 ​

Based on the “Nordic Classification System for Aids for Disabled Persons”, a comprehensive internationally valid classification system for technical aids for disabled persons was created by the standard ISO $9999$ “Technical aids for disabled persons – Classification” (adopted into the European body of standards under EN ISO $9999$). The ISO $9999$ standard divides aids into three hierarchical levels: Classes, Subclasses and Divisions. On the top hierarchy, $10$ classes (Classes) are distinguished and assigned to a code. To have space for later additions, so far only every third code was assigned (Table 1).

Example of classification of a telephone hearing amplifier coded $21$ $36$ $21$ (Table 2).

For our considerations, the class $21$ is of particular importance. It is described in more detail in Table 3 by means of some examples.

Classification According to the Mode of Action ​

Augmentative (Enhancing) Aids ​

By this we mean aids that enhance a stimulus (an action) in such a way that it can also be perceived (performed) by an organ whose performance is reduced. Figure 1 clarifies the mode of operation with an example. The incoming sensory stimulus can be perceived by the disabled person only in an attenuated form because of damage to the sensory organ in question. The task of the aid marked A is to amplify the incoming stimulus in a suitable way so that it can be perceived with the same intensity as a non-disabled person would have perceived it. Examples of augmentative aids are hearing aids and eyeglasses.

Substituting (Replacing) Aids ​

Substituting means aids with which a stimulus is diverted to another than the usual sensory organ. The same applies when an action (movement or triggering of a movement) is obtained from another than the usual actuatory organ. In this case, a substitution = vicariate occurs. Figure 2 shows a person in whom the perception of optical stimuli is not possible due to blindness. The aid A shown in the middle diagram suitably converts the optical stimulus into an acoustic stimulus and directs it to the hearing of the blind person. Similarly, the right plot of Figure 2 shows the conversion to a tactile stimulus. Examples of substituting aids include the use of Braille, which is read with the fingertips instead of the eyes, and lip-reading, in which the eyes perform tasks that are usually performed by the ears.

Bypassing (Bridging) Tools ​

By this we mean aids that replace or bridge an interrupted part of a functional chain, but return the stimulus (action) to the original organ or its neural pathways. The graphic in Figure 3 represents a person who, because of a complete functional failure of the sensory organ in question, is unable to perceive a stimulus, whether it is offered in the usual way or in an amplified way. The function of the aid A is to guide the stimulus around the defective area in such a way that, by stimulating the nerve pathways lying later, an impression is produced which is as close as possible to the effects of the original stimulus. Examples of bypassing aids are cochlear implants and functional electrical stimulation.

The Vicariate ​

By a vicariate (substitution, proxy) we mean all measures in which a function that has failed due to damage is replaced by another. In this case, the tool has the task of executing the appropriate transformation as an interface to the environment.

Sensory Vicariate ​

Sensory vicariance is the replacement of one failed sensory organ by another. Figure 4 illustrates this by means of damage to the eyes, as a result of which visual stimuli can no longer be perceived. The aid marked “A” in the picture has the task of converting the visual stimulus (the optical signal from the environment) into a tactile stimulus (accessible to the sense of touch).

Since the performance of the individual sensory organs (the bandwidth in the broadest sense) and also the type of perception that takes place via them varies greatly, the tool (aid) must attempt to convey as much relevant information as possible. Table 4 shows a comparison of the “bandwidths” of the individual sensory organs. From this it can be seen what limitations must be expected in the use of vicariates. Smell and taste are, therefore, not considered for vicariates. Thermal stimuli also provide only small bandwidths.

Actuatory Vicariate ​

An actuatory vicariate is effective in the opposite direction, i.e. from the person to the environment. Figure 5 shows this on the basis of damage (absence) of the upper extremities, according to which the person is not able to lift the weight. In this example, the assumed assistive device (aid) A receives voice commands and controls a lifting device.

Attribution/Citation ​

Would you like to cite, share or edit this book? This book is licensed under Creative Commons Attribution-NonCommericial-ShareAlike 4.0.

Third party intellectual property is appropriately marked or cited and is not part of this book. All attribution and citation information applies only to the contents of this book, which are not derived from third party sources.

Attribution ​

If you wish to publish or distribute this book in print, edited or unedited, the following attribution must be included on each physical page:

Available for free at .

If you wish to publish or distribute this book edited or unedited in digital form, the following attribution must be included on each digital page:

Available for free at .

Citation ​

Use the following information to cite this book.

• Author: Dr. Wolfgang L. Zagler
• Title: Rehabilitationstechnik
• Date: March 1, 2008
• Location: Vienna, Austria
• Book URL:
• Chapter URL:

List of Abbreviations ​

EN

European Standard (Europäische Norm)

ISO

International Organization for Standardization

List of Figures ​

• Figure 1: Functionality of an augmentative (enhancing) aid [3].

• Figure 2: Mode of operation of a substituting (replacement) aid [3].

• Figure 3: Functionality of an inserting aid [3].

• Figure 4: Mode of action of a sensory vicariate (substitution of vision by the sense of touch) [3].

• Figure 5: Mode of action of an actuatory vicarage (replacement of lifting by speaking) [3].

List of Tables ​

• Table 1: Classes of ISO $9999$

• Table 2: Example of classification according to ISO $9999$.

• Table 3: Examples of classification of technical aids according to ISO $9999$ (EN ISO $9999$).

• Table 4: Bandwidths of the human sensory organs [1, 2].

List of Sources ​

• [1]: The Information Capacity of the Human Fingertip (Kenneth Kokjer, DOI: 10.1109/tsmc.1987.289337)

• [2]: Automatic visual to tactile translation. I. Human factors, access methods and image manipulation (T.P. Way, K.E. Barner, DOI: 10.1109/86.559353)

• [3]: Rehabilitationstechnik (Wolfgang L. Zagler - CC-NC-SA 4.0)