Optimum perception of odor intensity by humans.

The sniff duration that provides optimum perception of odor intensity was determined for 17 humans. Subjects were trained to match the duration of their sniff to the duration of a buzzer that sounded for 0.2, 0.5, 1.0 or 2.0 sec. Sniff characteristics were monitored with a hot wire anemometer and an oscilloscope. Intensity estimates were obtained at the four durations for three concentrations of phenyl ethanol, butanol and propionic acid. Optimum perception of intensity occurred between 0.39 and 0.64 sec for phenyl ethanol and propionic acid and a value of no more than 1.63 sec is proposed for butanol. The longer duration for butanol is attributed to the delayed response of nerves in the throat which appear to respond to this odorant but not to the others. The complexity of the intensity sensation and implications of the results for neurophysiological studies of intensity coding are discussed and the properties of an olfactometer for odor intensity measurements are outlined.