UC San Diego

The present investigation explores the stimulus-response (psychophysical) functions for total nasal perceived intensity for two pungent odorants, formaldehyde and ammonia, presented either alone or with different backgrounds of the other irritant. Stimuli were comprised of four formaldehyde concentrations (1.0, 3.5, 6.9 and 16.7 p.p.m.); four ammonia concentrations (210, 776, 1172 and 1716 p.p.m.); and their 16 binary mixtures. Ammonia functions showed a consistent upward concavity. At low, medium and high concentrations, the total perceived intensity of the mixtures showed hypoadditivity, simple additivity and hyperadditivity, respectively. That is, the intensity of the corresponding mixtures was significantly lower than, equal to, or greater than the sum of its components. The progressive involvement of pungency, aroused by common chemical sense stimulation, may be responsible for the increasing additivity observed. Simple additivity, and even hyperadditivity, may characterize mixtures involving common chemical stimulation.