Odor threshold

An odor threshold is the lowest concentration of an odorant detectable under specified conditions. It depends on the odorant, measurement method, and individual or population tested.

Olfactory receptor: A sensory protein in olfactory neurons that binds odorant molecules and initiates neural signaling. Receptor responses help determine how little of an odorant can trigger detection.
Odorant: A chemical substance capable of activating the olfactory system and producing an odor percept. Threshold is defined for a particular odorant rather than for smell in general.
Odor activity value: The ratio of an odorant's concentration to its odor threshold in a given medium. This ratio estimates whether a measured odorant concentration may contribute perceptibly to an odor.
Odor recognition threshold: The lowest odorant concentration at which an odor can be identified or named correctly. Recognition requires more information than the mere detection measured by odor threshold.
Olfactory transduction: The conversion of odorant binding in olfactory neurons into electrical signals sent to the brain. Detection requires odorant-driven signals to rise above neural and perceptual noise.
Olfaction: The sensory process by which organisms detect and interpret airborne chemical compounds. Odor thresholds quantify the lower limit of this sensory process.
Gas chromatography–olfactometry: An analytical method that separates volatile compounds and uses a human nose to detect odor-active fractions. It can identify compounds whose concentrations approach their sensory thresholds.
Odor discrimination threshold: The smallest concentration difference between odor stimuli that can be distinguished reliably. Discrimination compares stimuli, whereas odor threshold concerns detecting an odor at all.
Signal detection theory: A framework for distinguishing sensitivity to a signal from the decision criterion used to report it. Odor detection thresholds depend on how experiments define a detectable response.
Concentration: The amount of a substance present in a specified volume or mass of a mixture. An odor threshold is expressed as a concentration under stated measurement conditions.

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