Interaction Model of Pen-and-Paper User Interfaces - Human-Computer Interaction - page 86

could play this music. A second example is system feedback, which can be given on
another channel, i.e. in another representation.

Appropriate Complementing Representations In case of complementary infor-
mation, which complementary modalities should be chosen? Table 3.3 provides an
overview of combinations of paper-based and digital representations and of their
properties. These can be classified by four dimensions:

1. The time needed for updating information in the complementing representation.
2. The spatial distance between paper-based and complementing representations.
Ideally, contents of the complementing representation should be made available
in-situ, directly at the location of the paper document.
3. Whether the same or a different modality is used (information that is printed on
paper has a visual representation).
4. The amount of data that can be transferred using the complementing represen-
tation. The data rate should be high to provide comprehensive information (e.g.
the contents of a document page), while representations with lower data rates can
be used for purposes such as indicating success or failure of an operation or the
current mode of the system.

Complementing information that is in situ, immediate, of the same modality and
provides high data rates can be realized by a projection that overlays information
that is printed on paper. Alternatively, a small and lightweight display can be placed
onto paper in order to display additional contents. Both approaches require a rather
complex technical setup that is not yet available as an out-of-the-box solution. A
technically less complex solution for realizing in situ and immediate information
with a high data rate consists of using an auditory channel. However, this channel
has a different modality (which is not necessarily a drawback). While it offers a
high data rate for conveying textual information, it cannot be used for transferring
visual contents. If this restriction is not acceptable, extensive visual information can
only be conveyed by accepting trade-offs with respect to distance or immediacy.

Tabl e 3. 3 Appropriate complementing representations

Representation Complementing representation

Overlaid projection ••••

Overlaid display ••••

Nearby display • - ••

Paper Visual

Re-print - •••

Pen display / LED ••• -

Auditory Speaker •• - • /-

Haptic Pen •• --