The Role of Odor and Sensory Irritation in Human Chemical Sensitivity

Abstract: The main objective of this thesis is to apply complimentary psychophysical theories and methods to investigate human perception of odor and sensory irritation of chemical compounds present in indoor air. Three psychophysical theories: Signal Detection Theory (SDT), Threshold Theory and Luce’s Choice Theory (CT) were applied to measure detection and recognition of odor and sensory irritation of two odorous irritants (pyridine and formaldehyde) by using the method of constant stimuli. Participants exhibited a superior perceptual ability for odor detection than sensory-irritation detection. Substance recognition was more associated with odor detection than sensory-irritation detection. Individual differences in sensory sensitivity and response bias were larger for sensory-irritation than for odor. Luce’s CT fits well the simultaneous detection and recognition data. Perceived intensity was used for determining the near-threshold psychophysical function and for revealing how concentrations at preceding trials and the inter-presentation intervals affect odor and sensory irritation for a subsequent stimulus. As a new candidate of odorous irritants, hexanal was used as stimulus. Significant effects of concentration and interaction of concentration and time intervals were observed for odor but not for sensory irritation. However for the same sniff, the duration of sensory irritation was experienced to last longer than that of an odor. A further experiment was conducted on "chemically-sensitive" persons (CS), stringently selected from a population-based questionnaire. The results confirmed that CS-persons had tendencies of heightened odor sensitivity as compared with non-CS persons. Although the difference was not statistically significant, the sensitivity indices of odor indicated that CS-persons are a homogenous group, with a high precision in odor detection.