Odor - The Electronic Nose Artificial Olfaction Technology - page 93

4.5.4 Hedonic Tone

Hedonic tone is a measure of the pleasantness or unpleasantness of an odor. It is
the degree to which an odor is perceived as pleasant or unpleasant. Such per-
ceptions differ widely from person-to-person, and are strongly influenced, inter
alia, by previous experience and emotions at the time of odor perception.
An evaluator uses her/his personal experience and memories of odors as a
hedonic tone referencing scale. During training, evaluator becomes aware of their
individual odor experience and memory referencing. The reported hedonic tone
value by an odor testing laboratory is an average of individual hedonic tone values
assigned by each evaluator [ 15 ]. The members of a panel of evaluators are asked to
indicate perceived hedonic tone at each presentation as a value from the nine-point
hedonic tone scale:
+4

very pleasant

+3 pleasant

+2 moderately pleasant

+1 mildly pleasant

0 neutral odor/no odor

-1 mildly unpleasant

-2 moderately unpleasant

-3 unpleasant

-4 offensive.

Subjective: relying upon ones personal feelings or beliefs; relating to or arising
within one's self or mind in contrast to what is outside.
Objective: treating or dealing with facts without distortion by personal feelings
or prejudices; dealing with things external to the mind rather than with thoughts or
feelings.
The assigning of a hedonic tone value to an odor by an evaluator is ''sub-
jective'' to the evaluator [ 16 ]. The evaluator's experiences and memories force
their personal feelings and beliefs into the decision-making process. Through
training, evaluators assign a hedonic tone and then set aside their personal feelings
and make objective decisions regarding detection and recognition thresholds,
intensity referencing using a butanol scale, and character identification using a
category reference [ 8 ].

4.5.5 Odor Character

It is basically what the odor smells like. It allows differentiating between various
types of odors. For example, Nitrogen dioxide (NO 2 ) gas has a biting and irritating
odor and it is an air pollutant. The character of an odor can change with intensity.
The quality or character of an odor is difficult to evaluate. Main difficulty is that