Odor - The Electronic Nose Artificial Olfaction Technology - page 85

Fig. 4.1 Henning's odor

prism

4.2 Odor Perception

The chemical senses, for smell (olfaction) and taste (gustation), are mainly mea-
sured to be the oldest ones in evolutionary development. While humans are a
comparatively recent development in evolutionary terms, the function of our sense
of smell is the same as for other type: it helps us to evaluate our environment. In
easy talking of behavior, perception of odors can lead to two basic behavioral
responses: avoidance or approach. These responses can occur for example in
judging food or water, but also in a social context.
The human sense of smell helps us to evaluate our environment in a very
straight manner. The sensor in the nose opening is a direct interface between the
brain and the environment. It is a highly sophisticated sense, which interacts with
our life and behavior on many levels. The process of odor detection, perception,
and evaluation is therefore understandably complex.
A human has an ability to sense and differentiate up to 3,000 odors. Latest
research indicates that as many as 1,000 genes out of the total of 100,000 in our
genome are dedicated to sense of smell. This significant proportion of 1 % suggests
that the sense of smell is of considerable importance in evolutionary terms [ 3 ].
The sense of smell is closely related to long-term memory. The nerves that
connect the sensor to the brain lead directly to the hippocampus, which is the part
of the brain that regulates basic functions, such as the organization of long-term
memory and emotions. It is, therefore, not surprising that smells are often highly
associative and can elicit vivid memories of experiences that occurred even in
early childhood. This associative aspect is highly relevant to environmental odors.
Once a negative association is formed, it is very difficult to change the appreciation
of that particular odor stimulus in an individual. This helps to explain why an odor
problem from the past often seems to haunt site operators, even after the odor
emissions have been significantly reduced.
Smell is confined of residual molecules in the air by receptor cells and the
resulting perceptions of 'smell' tell the living being about something that is
nearby. Smell also has an intense effect on our day-to-day experience and can
trigger memories.