Trigeminal and olfactory sensitivity: comparison of modalities and methods of measurement

Abstract

Objective: The principal objective was to chart sensitivity for human nasal irritation by alternative psychophysical methods, a common detection procedure vs. a nasal lateralization procedure that required the subject to indicate whether a vapor had stimulated the left or right nostril. This objective relates to the broader issues: a) whether subjects with normal olfaction (normosmics) can yield, through novel methodology, an index of sensitivity to nasal irritation comparable to that obtained from subjects without olfaction (anosmics) and b) whether both types of subjects have similar irritation sensitivity in general. This study sought to gauge interconvertability both between types of subjects and between modes of stimulus presentation, for irritative and, where appropriate, olfactory stimulation.Methods: Static dilution series of four n-aliphatic alcohols, chosen to represent volatile organic compounds (VOCs), provided the source of calibrated olfactory and irritative vapors, emitted from their squeezable containers into the nose or eye by either a mechanical device or by hand.Standard psychophysical methodology (forced-choice; ascending strength of stimulation) served to chart detection thresholds for irritation and odor and an analogous procedure served to chart the threshold for localization of stimulation.Results: Within the limits of resolution, detection thresholds and nasal localization thresholds yielded comparable indices of the potency of the VOCs to evoke nasal irritation. The thresholds agreed well with those for detection of eye irritation, though only the eyes proved able to detect irritation from 1-octanol. The method of emitting the stimulus had little material effect on measures of either irritative or olfactory detection. Conclusions:The threshold for nasal localization offers a suitable way to measure nasal irritation in normosmic persons. Olfactory stimulation does not interfere with the measure since subjects cannot localize on that basis. Anosmic and normosmic persons have comparable sensitivity to nasal and ocular irritation. If anosmic persons have any lower sensitivity, as sometimes claimed, it would seem to have only trivial consequences for estimates of the irritative potency of VOCs.

Psychometric functions for the olfactory and trigeminal detectability of butyl acetate and toluene

“…This performance was considered 100 % detection. The ascending concentration order and an interstimulus interval of at least 45 sec to 1 min helped to minimize any potential changes in olfactory and/or trigeminal sensitivity 22 .…”

Concentration-detection functions for eye irritation evoked by homologous n-alcohols and acetates approaching a cut-off point

“…Perceptual differentiation between a strong smell and a weak nasal "feel" or irritation could prove difficult for a subject, and is likely to be biased by individual criterion (Cometto-Muñiz and Cain 1990). The task of nasal lateralization (or localization), whereby the subject seeks to identify the nostril (right or left) receiving the chemical stimulus when the other nostril simultaneously receives an identical puff of blank air, has proven a convenient tool to probe into detection of nasal chemesthesis unbiased by smell (Wysocki et al 1997;Cometto-Muñiz and Cain 1998;Dalton et al 2000). The approach relies on the observation that nasal lateralization is only achieved through trigeminal chemesthetic activation, not through olfactory stimulation (Schneider and Schmidt 1967;Kobal et al 1989).…”

Setting occupational exposure limits in humans: contributions from the field of experimental psychology

“…Bottles containing a blank or a chemical were consecutively presented to either the left or right eye, and the subject had to decide which bottle produced the stronger ocular sensation. Results they obtained from studies comparing eye thresholds between normosmics and anosmics show that nasal localization thresholds agree well with eye irritation thresholds (Cometto-Munˇiz and Cain 1998;ComettoMunˇiz et al 1998b). Opiekun et al (2003) applied the lateralization concept to the eyes.…”

“…Contradictory findings have been reported. In a series of studies by Cometto-Munˇiz et al (1998, 1998a no significant differences were found between anosmics and normosmics in concentrations that yielded irritancy employing forced-choice procedures using homologous alcohols as the stimuli (Cometto-Munˇiz and Cain 1998) or terpenes (Cometto-Munˇiz et al 1998a;. However, in studies by Hummel et al (1996) and Kendal-Reed et al (1998), normosmics reported chemesthetic sensations at lower concentrations than did anosmics.…”