UC San Diego

Section I of this Thesis presents the stimulus-response (i.e., psychophysical) functions for the total nasal perceived intensity of two pungent odorants, formaldehyde and ammonia, presented either alone or mixed with varying concentrations of the other irritant. Stimuli comprised formaldehyde at 1.0, 3.5, 6.9, and 16.7 ppm; ammonia at 210, 776, 1,172, and 1,716 ppm; and their 16 binary mixtures. At low, medium, and high concentrations within the ranges selected, the total perceived intensity of the mixtures was, respectively, significantly lower than (hypoadditivity), equal to (simple additivity), and greater than (hyperadditivity) the sum of the intensities of its individual components. In Section II, subjects were again asked to rate the total nasal perceived intensity of the previous stimuli, but now they also rated the olfactory (i.e., odor) and the trigeminal (i.e., pungency or irritation) attributes of the evoked sensations. Psychophysical functions for pungency were steeper than those for odor. Furthermore, odor was always hypoadditive in mixtures, whereas pungency was, mainly, additive, and even reached hyperadditivity. Total nasal perceived intensity of the stimuli, singly and in mixtures, followed the stimulus-response patterns for pungency, which, therefore, emerged as the dominating attribute used by the subjects to rate the explored range of concentrations. In turn, the relationship between total nasal perceived intensity of the mixtures and the sum of the intensities of their components reflected hypoadditivity, resembling the outcome for the odor attribute.