The effect of adaptation on odor detection

The sensitivity of human Ss to a weak odor (hydrogen sulphide) following prior exposure to it varying in both duration (0–5 min) and concentration (4.05 × 10^?7 to 24.40 × 10^?7 mg/liter) was studied with a yes-no detection method and a specially designed olfactometer. The effect of adaptation was demonstrated, because the proportion of hits was lower the higher the concentration of the adaptation stimulus, when the response criterion, as measured by the proportion of false alarms, was fairly constant. By contrast, the proportion of hits was apparently independent of the duration of the exposure to the adaptation concentration. This finding suggests that the sense of smell is more stable than is usually believed. The paper ends with a discussion of the importance of considering adaptation in contemporary detection theory.     

On the consistency of intramodal intensity matching in olfaction

Magnitude matchings of odor intensity were obtained for three chemical compounds (hydrogen sulfide, pyridine, and dimethyl disulfide) in four experiments. An equal-sensation function in the form of a power function described the data well. This equation can be written neglecting the multiplicative constant, Ф_i = Ф_k ^b _ik, where i and k represent two different odorants. The exponent b_ik, where the first index stands for matching continuum and the second index for reference continuum, was fairly well predicted according to the formulae, (ie, 264, 2) where i, j, and k are three different odorants. The results validate the equal-sensation function and indicate implicitly that intensity matchings between different intramodal continua are approximately transitive and symmetric with respect to odor.     

Separate and joint scaling of perceived odor intensity ofn-butanol and hydrogen sulfide

To determine which combination of scaling method and experimental procedure is optimal for measuring perceived odor intensity, the intensity perception of one odorous substance was scaled both separately and together with a second odorous substance in the same session. The methods used were magnitude estimation with and without a standard reference and cross-modal matching with finger span. The results show that separate and joint scalings ofn-butanol and H₂S give identical scales, regardless of scaling method. Different results are obtained in magnitude estimations with a homoquality, a heteroquality, and no standard. From these results, one would not expect to find a single true power function independent of method. Cross-modal matching with finger span may be the best choice for odor intensity scaling, since it results in the widest response range, thereby giving the best resolution.     

PERCEIVED INTENSITY OF ODOR AS A FUNCTION OF TIME OF ADAPTATION

The perceived intensity of odor under conditions of constant stimulation with hydrogen sulphide was investigated in two experiments. A two-step scaling method, involving cross-modality matching and numerical scaling of the matching continuum, was used for measuring intensity of odor. Perceptual intensity was found to decrease exponentially with increase of time of stimulation. Preliminary data concerning the subsequent recovery phase were also obtained.