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the pitch or the speech rate) are manipulated to indicate the hierarchical position of
items in the menu.
In an initial experiment, a small hierarchy is studied, and three parameters of
vocal synthesis are manipulated: the average pitch of the voice (
Average pitch
, AP);
the pitch range of the voice (
Pitch range
, PR); and the rate of speech (
Speech rate
,
SR). On the basis of these parameters, two sets of sounds were tested:
- set 1: depth is given by the average pitch (AP) and the pitch range (PR);
horizontal scrolling is given by the pitch rate (SR);
- set 2: depth is shown by the speech rate (SR), and horizontal scrolling by the
average pitch (AP).
Results show a marked decrease in the number of navigation errors when this
type of sound is used, compared to simple vocal synthesis without a parameter
variation. This example thus shows that we can efficiently combine a representation
of semantic content of menu items (here by vocal synthesis) with a representation of
hierarchical relationships within that menu.
8.3.4.
Discussion
A bibliographical review of the methods employed for the sonification of
hierarchical menus has been presented. The challenge consisted of associating a
sound with each item in order to represent both the position of the item in the
hierarchical structure of the menu; and the semantic content of this item or the
family of items to which it belongs.
The presented works propose the representation of the hierarchical level using
earcons, i.e. abstract sound signals constructed so as to conduct the desired
information. These earcons are built on the basis of sound parameters (e.g. tone,
pitch, rhythm or duration), which enables the hierarchical relationships that exist
between the menu items to be represented. These prove to be very efficient in
representing the position of the item in the hierarchy as it enables us to map
hierarchical relationships on the different sound parameters [BRE 98a], [LEP 00],
[LEP 02]. Earcons prove to be inefficient, however, when it is a matter of
representing the semantic content of an item or family of items. Two other methods
are then presented to compensate for this limitation:
spearcons
[WAL 06] and
auditory icons
[GAV 86]. In this case, the sound signals are more efficient and
intuitive as they represent the semantic content either directly in the case of
spearcons or metaphorically for auditory icons. A “mixed” approach that combines
earcons with the hierarchical representation and vocal synthesis or sound icons for
the semantic representation should enable us to obtain the best results by benefiting
