Editing Stimulus modality (section)

==Smell modality==

===Sensation===

The sense of smell is called [[olfaction]].  All materials constantly shed molecules, which float into the nose or are sucked in through breathing.  Inside the nasal chambers is the [[neuroepithelium]], a lining deep within the nostrils that contains the receptors responsible for detecting molecules that are small enough to smell.  These receptor neurons then synapse at the olfactory cranial nerve (CN I), which sends the information to the olfactory bulbs in the brain for initial processing.  The signal is then sent to the remaining olfactory cortex for more complex processing.<ref>{{cite journal | author = Doty R | year = 2001 | title = Olfaction | journal = Annual Review of Psychology | volume = 52 | issue = 1| pages = 423–452 | doi = 10.1146/annurev.psych.52.1.423 | pmid=11148312}}</ref>

===Odors===
An olfactory sensation is called an [[odor]].  For a molecule to trigger [[olfactory receptor neuron]]s, it must have specific properties.  The molecule must be:
# volatile (able to float through the air)
# small (less than 5.8 x 10-22&nbsp;grams)
# [[hydrophobic]] (repellant to water)

However, humans do not detect or process the smell of various common molecules such as [[nitrogen]] or [[water vapor]].

Olfactory ability can vary due to different conditions.  For example, olfactory detection thresholds can change due to molecules with differing lengths of carbon chains.  A molecule with a longer carbon chain is easier to detect, and has a lower detection threshold.  Additionally, women generally have lower olfactory thresholds than men, and this effect is magnified during a woman's [[ovulatory period]].<ref name="Wolfe" /> People can sometimes experience a hallucination of smell, as in the case of [[phantosmia]].

===Interaction with other modalities===
Olfaction interacts with other sensory modalities in significant ways.  The strongest interaction is that of olfaction with taste.  Studies have shown that an odor coupled with a taste increases the perceived intensity of the taste, and that an absence of a corresponding smell decreases the perceived intensity of a taste.  The olfactory stimulation can occur before or during the episode of taste stimulation.  The dual perception of the stimulus produces an interaction that facilitates association of the experience through an additive neural response and memorization of the stimulus.  This association can also be made between olfactory and tactile stimuli during the act of swallowing.  In each case, temporal synchrony is important.<ref>{{cite journal |author1=Labbe D. |author2=Gilbert F. |author3=Martin N. | year = 2008 | title = Impact of olfaction on taste, trigeminal, and texture perceptions | journal = Chemosensory Perception | volume = 1 | issue = 4| pages = 217–226 | doi = 10.1007/s12078-008-9029-x |s2cid=144260061 }}</ref>

===Tests===
A common [[psychophysics|psychophysical]] test of olfactory ability is the triangle test.  In this test, the participant is given three odors to smell.  Of these three odors, two are the same and one is different, and the participant must choose which odor is the unique one.  To test the sensitivity of olfaction, the staircase method is often used.  In this method, the odor's concentration is increased until the participant is able to sense it, and subsequently decreased until the participant reports no sensation.<ref name="Wolfe" />