Perception of odor and irritation

Abstract Compared with visual and auditory perceptions, smells, which in the colloquial sense include both odor and irritation, are often difficult to identify by name and are therefore not well processed cognitively— and yet they persist as disquieting feelings of arousal. These two factors, the persistence and poor semantic identification, form the basis for the strong impact of environmental smells associated with environmental stimulation. The literature of experimental psychology, anatomy, physiology and epidemiology relevant to perception of odor, mediated by the olfactory nerve, and irritation, mediated by the trigeminal nerve is reviewed. It is proposed that the two perceptions are higly interelated and that while anatomically different structures are involved in such environmental stimulation, perceptions are not so readily categorized. In the most simple case, whether or not odor or irritation is experienced depends on the strength of the stimulus. But it is usually more complex than that because perception is affected by the environmental context, facilitation and inhibition by other stimulation, and the state of adaptation of the perceiver. In addition, there are three important differences between odor perception and irritation. One is that the reaction time to odor is shorter than that of irritation, but this observation is perhaps of limited application to practical field research. The second is that while odors persist, they do show adaptation after prolonged exposure and, in particular, habituation. By contrast, the distinguishing characteristic of irritation is that it shows neither habituation nor adaptation. The third, partly as a consequence of these two, is that while odor perception is more sensitive and functions to arouse explorative behavior, learning, and odor memory, irritation has a general and direct effect on behavior, involving respiration, cutaneous effects, and potential pathological consequences. Odor per se does not make one sick. Evidence of effects on behaviour beyond mere perception, reinforces the need for a broader approach to problems such as mental fatigue and other performances which appear to be affected by smell.