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activated. When an alerting or alarming acoustic signal is perceived, the mobility of
eye movements associated with the exploration of the surroundings increases.
The internal status of a listener functions as a filter and activates the specific
sonic eco-field.
Several factors influence the assessment of sound annoyance, and this largely
depends on nonacoustical features, or the visibility of an unwanted noise source.
For example, the position in the city makes further differences: living along a pretty
street produces a reaction to noise less stressful than to live in a noisy periphery. It is
necessary to approach the soundscape using a semantic distinction of the sound
sources and of the context in which a sound is perceived and not only the noise by
using level measurements. We have to introduce the concept of meaning by using a
semiotic approach of
interpretation, as
recommended by Raimbault and
Dubois (
2005
).
When the sound and in particular noise is considered, it seems important to
distinguish between voluntary exposure to noise, as in a disco, or involuntary
exposure to a noisy ambience, such as at the side of a busy road. The social
consequences are different, and also the regulation tools are different. Probably,
however, direct consequences on human health are more severe when hearing full-
volume music than when walking in a urban park considered acoustically polluted.
5.2 Psychological Approach to Soundscape Interpretation
Soundscape evolves and develops according to the character of landscapes,
according to the time and the technology, and is strongly influenced by cultural
and political issues as well (Botteldooren et al.
2006
). Consequently, to be efficient
soundscape studies must rapidly develop toward a more integrated holistic
approach in which the visual component is blended with psychological feelings
such as the sense of safety, or with the air quality. In fact, vision and hearing are
strictly connected in human perception of the surroundings. For instance, the
presence of vegetation in a noisy ambience creates the conditions for a lower
perceived noise, although the vegetation does not function as an efficient barrier,
as argued by Anderson et al. (
1984
).
Plants along roads are regarded as true barrier to noise diffusion, and a study
conducted by Watts et al. (
1999
) has demonstrated experimentally that noise rating
was depressed in people to whom noise was supplied in concomitance with the
vision of green barriers. In other words, the noise rating was higher when the source
of noise was visually screened. This experiment demonstrates how the psychologi-
cal effect of visual cues reduces the effect of acoustic exposition. When a metal
barrier was submitted to noise rating versus a barrier of willow shrubs, no
differences were found in noise reduction between the two type of barriers. Of
course this study was not conducted to demonstrate the efficiency of green barriers,
which can be provided by direct measurements, but to indicate how the visual
source of noise affects the final results.
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