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Department of Psychology (W.W., S.D., I.V.D., P.E., O.V.D.B.), and Faculty of Medicine (B.N., H.V., K.V.D.W.), University of Leuven, Leuven, Belgium.
Address reprints requests to: Omer Van den Bergh, PhD, Department of Psychology, Tiensestraat 102, B-3000 Leuven, Belgium. Email: omer.vandenbergh{at}psy.kuleuven.ac.be
OBJECTIVE: Previous studies showed that somatic symptoms can be acquired in response to chemical substances using an associative learning paradigm, but only when the substance was foul smelling and not when it smelled pleasant. In this study, we investigated whether warnings about environmental pollution would facilitate acquiring symptoms, regardless of the pleasantness of the smell.
METHOD: One group received prior information framing the study in the context of the rapidly increasing chemical pollution of our environment. Another group received no prior information. Conditional odor stimuli (CS) were diluted ammonia (foul-smelling) and niaouli (neutral-positive smelling); the unconditional stimulus (UCS) was 10% CO2-enriched air. Each subject breathed one odor mixed with CO2 and a control odor mixed with air in 80-sec breathing trials. The type of odor mixed with CO2 was counterbalanced across participants. Next, the same breathing trials were administered without CO2. Breathing behavior was measured during each trial; subjective symptoms were assessed after each trial.
RESULTS: Only participants who had been given warnings about environmental pollution reported more symptoms to the odor that had previously been associated with CO2, compared with the control odor. This was so for both the foul- and the pleasant-smelling odor. Symptom learning did not occur in the group that did not receive warnings. The elevated symptom level could not be accounted for by altered respiratory behavior, nor by experimental demand effects.
CONCLUSIONS: Raising environmental awareness through warnings about chemical pollution facilitates learning of subjective health symptoms in response to chemical substances.
Key Words: associative learning, • odors, • subjective symptoms, • multiple chemical sensitivity, • environmental pollution, • psychosomatic medicine.
Abbreviations: AN(C)OVA = analysis of (co)variance;; CO2 = carbon dioxide;; CS = conditioned stimulus;; CR = conditioned response;; ES = effect size;; f = breathing frequency;; FETCO2 = end-tidal fractional concentration of CO2;; M = mean;; MCS = multiple chemical sensitivity;; NA = negative affectivity;; PANAS = positive and negative affect scale;; SD = standard deviation;; TI = inspiratory time;; TE = expiratory time;; UCR = unconditioned response;; UCS = unconditioned stimulus;; VE = minute ventilation;; VT = tidal volume;
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