Characterisation of human behaviour during odour perception.

Factors which govern the optimum perception of odours have not yet been defined. This has hindered the development of standard methods and instruments for measuring olfactory responses. As an initial step towards defining these conditions, inhalation rates and volumes, number of sniffs, and sniff duration were measured for twenty-three humans in odour-threshold and odour-intensity tests with pentyl acetate, 1-butanol, and diethylamine. Measurements were made with the aid of a hot-wire anemometer concealed within the outlet of an air-dilution olfactometer. Individuals varied markedly in their sampling techniques but maintained their characteristic sniffing patterns with different odours and olfactory tasks. Only three parameters consistently varied with odour concentration: total volume of odour sampled, total sampling time, and number of sniffs. Maximum inhalation rate was remarkably stable and was independent of the type, concentration, and pleasantness of odour. Values recorded for sniff volumes and inhalation rates indicate that most olfactometers in use do not accommodate human inhalation requirements during a sniffing episode. The many common characteristics in the varied sampling techniques of different subjects suggest that the techniques are close to those providing optimum odour perception. Whether these are inherited or developed through habit or experience is not known.