Orientation in space using the sense of smell

Several studies reported that respiration interacts with olfactory
perception. Therefore, in the pilot study of this experiment series
human breathing was investigated during an olfactory experiment.
Breathing parameters (respiratory minute volume, respiratory
amplitude, and breathing rate) were quantified in response to odor
stimulation and olfactory imagery. We provide evidence that
respiration changed during smelling and during olfactory imagery in
comparison to the baseline condition. In conclusion, olfactory
perception and olfactory imagery both have an impact on the human
respiratory profile, which is hypothesized to be based on a common
underlying mechanism named sniffing. Our findings underline that
for certain aspects of olfactory research it may be necessary to
control and/or monitor respiration during olfactory stimulation.
The human ability to localize odors has been investigated in a
limited number of studies, but the findings are contradictory. We
hypothesized that this was mainly due to differential effects of
olfactory and trigeminal stimulation. Only few substances excite
selectively the olfactory system. One of them is hydrogen sulphide
(H2S). In contrast, most odorants stimulate both olfactory and
trigeminal receptors of the nasal mucosa. The main goal of this
study was to test the human ability to localize substances, which
excite the olfactory system selectively. For this purpose we
performed localization experiment using low and high concentrations
of the pure odorant H2S, the olfactory-trigeminal substance isoamyl
acetate (IAA), and the trigeminal substance carbon dioxide (CO2).
In preparation for the localization study a detection experiment
was carried out to ensure that subjects perceived the applied
stimuli consciously. The aim of the detection study was to quantify
the human sensitivity in response to stimulation with H2S, IAA, and
CO2. We tested healthy subjects using an event-related experimental
design. The olfactory stimulation was performed using an
olfactometer. The results showed that humans are able to detect H2S
in low concentration (2 ppm) with moderate sensitivity, and possess
a high sensitivity in response to stimulation with 8ppm H2S, 50%
v/v CO2, and 17.5% v/v IAA. The localization experiment revealed
that subjects can localize H2S neither in low nor in high
concentrations. In contrast to that, subjects possess an ability to
localize both IAA and CO2 stimuli. These results clearly
demonstrate that humans are able to localize odorants which excite
the trigeminal system, but they are not able to localize odors that
stimulate the olfactory system exclusively, in spite of consciously
perceiving the stimuli.