Measurement of Specific Anosmia

Abstract

This paper describes the first quantitative investigation of specific anosmia or “odor blindness.” Certain Ss with an otherwise normal sense of smell are unable to perceive the sweaty odor of isobutyric acid. Their olfactory detection threshold for this compound is 50 times the normal threshold concentration of 8.5 ppm in water. The chemical extent of this olfactory defect was studied by measuring the thresholds for 18 compounds related to isobutyric acid. The maximum deficiency was observed with isovaleric acid, for which the mean threshold of the specifically anosmic Ss was 95 times the normal. The paper is principally devoted to a detailed consideration of the experimental methods required for measuring specific anosmia. These include rigorous purification of the odorants, procedure for individual threshold measurement, and statistical evaluation of the results. Experimental test criteria are given for eliminating nonspecific partial anosmics and for selecting Ss exhibiting specific anosmia to isobutyric acid. The tests were applied to a mixed population of 420 persons, which yielded 10 specific anosmics to isobutyric acid. The objective of this work was to measure the quantitative deficiency of the specific anosmics, in comparison with normal Ss with respect to each odorant. These data were required for the definition of what is believed to be one of the “primary odors” of the sense of smell, the “sweaty” primary epitomized by isovaleric acid.