The link between odors and illness : how health cognitions affect odor perception

Some people report health effects after exposure to relatively low levels of odorous chemicals, levels which are often well tolerated by the majority of the population. The research in this thesis was aimed at investigating the role of cognitive influences in this phenomenon. Could it be possible that ideas, beliefs and expectations about odors and health have such an impact that the perception of odor changes, possibly resulting in ‘corresponding’ health effects? To learn more about odor and health cognitions that could influence perception, implicit odor attitudes were studied. Participants completed an odor-version of the Implicit Association Test during which they were asked to associate words belonging to the concept odor with words that belonged either to the concept illness or to the concept healthy. A robust implicit association between the concepts odor and illness was found, an association that was not found when this relation between odor and illness was studied in an explicit manner. This implicates that implicit and explicit odor associations are different. Moreover, it suggests that odors belong to a group of stimuli that have a certain biological preparedness, i.e. a strong innate association with possible danger, even in the absence of actual threat. From an evolutionary perspective, this leads to a well-adapted perceptual strategy. Scanning the environment for possible danger in an automatic manner is more efficient than relying on a system which needs cognitive capacity to make such evaluations. However, an automatically operating system increases the chances on false alarms: harmless odors that become classified as dangerous toxicological chemicals. In the second part of this thesis, the impact of cognitive influences on odor perception was studied. Participants learned to associate an odor with a painful sting in the nose (induced by a short CO2 pulse), through instructional learning and classical conditioning. Brain potentials (Olfactory Event Related Potentials; OERPs) while participants smelled the odor were recorded. This technique enabled us to study whether cognitive influences had an impact on the relatively ‘late’ stages of stimulus processing (reflected by the P2 peak of the OERP signal), or whether cognitions would already penetrate ‘early’ phases of information processing during which very basic stimulus information is encoded, like stimulus intensity (reflected by the N1 peak of the signal). Both amplitudes and latencies were investigated, which gave an indication of the depth and the speed of stimulus processing. It turned out that the perception of an odor changed after associating it with pain: Processing speed and intensity of the early encoding phases increased, especially in case of an unpleasant odor. This implicates that health-related cognitions do not only affect the more interpretational stages of information processing, but specifically affect those stages associated with early perception (encoding of basic stimulus characteristics). In a final experiment, it was demonstrated that expecting negative health consequences had an impact on olfactory sampling behaviour: Participants who believed that they were being exposed to a dangerous chemical, inhaled less vigorously. This suggests that cognitions already affect the way an odor enters the body, which could have implications for further processing. In conclusion, odor and health cognitions affect (early) odor perception. An altered perception might play an important role in odor-associated health effects.