Measurement of olfactory signal detectability using an air-dilution olfactometer

The Cheesman air dilution olfactometer, although designed for group threshold measurements, was modified to allow individual testing of subjects. However, adaptation effects of olfactory stimuli precluded use of interstimulus intervals of less than 30 sec. so that 3-hr. testing sessions were necessary to obtain a single measurement of sensitivity. Four subjects were tested intensively with isopropyl alcohol (CH3CH(OH)CH3) at concentration levels determined by previous group threshold studies. In the first condition, one concentration only was presented in testing sessions, while in the second condition, six concentrations were presented and the limits of concentrations adjusted to allow subthreshold presentations. Signal detectability indices (dc') were calculated more frequently and more reliably in the second condition than in the first.