We tested four normosmics and four anosmics in detection thresholds
for six terpenes commonly found indoors: cumene,
p-cymene, delta-3-carene,
linalool, 1,8-cineole and geraniol. Normosmics provided odor
thresholds and anosmics provided nasal pungency thresholds.
All subjects provided nasal localization (
i.e., right/left nostril)
and eye irritation thresholds. Each type of threshold was measured
eight times per subject-stimulus combination. Stimuli were presented
from squeeze bottles in a two-alternative forced-choice procedure
via an ascending method of limits. Odor thresholds ranged between
0.1 and 1.0 parts per million (ppm, by volume). Nasal pungency
thresholds lay about three orders of magnitude above odor thresholds.
Nasal localization and eye irritation thresholds did not differ
between normosmics and anosmics, and fell close to nasal pungency
thresholds. Olfactory thresholds could be obtained for all stimuli
in all repetitions using the criterion of five correct choices
in a row. Trigeminal thresholds (
i.e., pungency, localization
and eye irritation) could be obtained on all repetitions only
for some terpenes using that same criterion. Carene and cineol
produced nasal pungency and eye irritation on all repetitions.
None of the terpenes could be localized on all repetitions,
but cineol was localized a higher percentage of instances than
were the other stimuli. At the other extreme, geraniol failed
to evoke any of the three trigeminal responses in most instances.
Overall, the results indicate that the three trigeminal thresholds
produce a uniform view of the potency of these terpenes, with
nasal pungency and eye irritation being slightly more sensitive
than nasal localization. Furthermore, application of a previously
derived linear solvation energy relationship to the results
reinforced the view that physico-chemical properties can predict
the chemesthetic impact of volatile organic compounds.
