Temporal integration of pungency

Four experiments explored possible temporal summation in olfactionand the common chemical sense. In one experiment, participantsjudged the perceived magnitude of various concentrations anddurations (1.25–3.75 s) of the pungent odorant ammoniaand the nonpungent odorant isoamyl butyrate. The perceived magnitudeof ammonia increased during an inhalation whereas the magnitudeof isoamyl butyrate did not. Time-intensity trading relationsfor ammonia indicated nearly perfect temporal summation. Inanother experiment, modulation of the concentration of ammoniaduring an inhalation led to assessments of perceived magnitudethat confirmed the high degree of temporal summation seen inthe first experiment. That is, approximately equal time-integratedmass of inhaled ammonia led to approximately equal perceivedintensity. A third experiment indicated that temporal summationfor ammonia arose from its pungency rather than from its odor,a fourth that trigeminally-mediated reflex apnea in responseto ammonia also exhibits temporal summation. The degree of temporalsummation measured with the reflex came very close to that assessedpsychophysically. When stimulated with ammonia, the common chemicalsense behaves more like a totalmass detector than a concentrationdetector. The investigation raises the possibility that theshortterm sensory reaction to most pungent stimuli may followthis simple rule.     

Odor, taste, and flavor perception of some flavoring agents

Psychophysical functions for the odor, taste, and flavor offive common flavorings were obtained by the method of magnitudeestimation. The stimuli included three simple compounds (vanillin,piperonal, and benzaldehyde) and two complex ones (natural vanillaextract and artificial almond essence). The odor intensity ofall the flavorings grew much less rapidly with concentrationthan did taste intensity. The growth of flavor for the complexsubstances and piperonal behaved very much like taste. For vanillinand benzaldehyde, the flavor functions resembled taste functionsat high concentrations but showed a tendency to flatten at lowerconcentrations. These findings implied that, at least for someflavorings, the growth of flavor reflects the most salient featureon the particular concentration range studied. At low concentrationsodor seems to be the most important feature and so flavor functionsare generally flat, but at high concentrations taste becomesthe salient feature and so flavor functions steepen.     

A model for odour thresholds

Odour detection thresholds, that we have previously obtained, have been analysed by a general equation for selective transport. It is shown that such selective transport can account for some 77% of the total effect. The remainder is due to a specific size effect, that might involve odour-binding proteins, and a specific effect for aldehydes and carboxylic acids. Our analysis raises the question of whether selective transport is physically separable from the specific effects of receptor activation. The model predicts a chemical cut-off in odour detection along any homologous series.     

Detection thresholds for an olfactory mixture and its three constituent compounds

Single sub-threshold odorants can, according to a few reports,become perceptible in concert. That is, they can exhibit mixtureadditivity. The present study measured thresholds for mixtureof 1-butanol, 2-pentanone, and n-butyl acetate, and for eachof these separately. ‘Complete’ additivity resulted,in that the threshold concentration of each compound in themixture (measured by gas chromatography) turned out to be one-thirdof each component separately. Earlier threshold studies alsoclaimed complete additivity and even hyper-additivity (synergism);in this regard they, like this study, differ from the more numerousstudies of suprathreshold mixtures, which yield imperfect additivity(hypo-additivity). Mixtures not only enhance sensitivity, butthey may also promote stability; intersubject variability wassmaller for the mixture than for the components. Subjects were20 young (18–26 years) and 20 elderly (69–91 years)persons, who gave two sets of thresholds on 2 days. Concordantwith earlier findings, the elderly's thresholds averaged higher(     

Perception of pungent odorants alone and in binary mixtures

The present investigation explores the stimulus–response(psychophysical) functions for total nasal perceived intensityfor two pungent odorants, formaldehyde and ammonia, presentedeither 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. Ammoniafunctions showed a consistent upward concavity. At low, mediumand high concentrations, the total perceived intensity of themixtures showed hypoadditivity, simple additivity and hyperadditivity,respectively. That is, the intensity of the corresponding mixtureswas significantly lower than, equal to, or greater than thesum of its components. The progressive involvement of pungency,aroused by common chemical sense stimulation, may be responsiblefor the increasing additivity observed. Simple additivity, andeven hyperadditivity, may characterize mixtures involving commonchemical stimulation.     

Interactions in caffeine-sucrose and coffee-sucrose mixtures: evidence of taste and flavor suppression

Taste–taste and flavor–taste interactions (suppression)in caffeine–sucrose and coffee–sucrose mixtureswere determined. Similar interactions for both types of mixturesshowed an extended hypoadditivity effect for overall taste orflavor intensity (percentage of suppression about 30–40%).Futhermore, mutual suppression among the components has beendetermined. Firstly, the physical intensity of the suppressivecomponent controls the amount of suppression of the other component.Thus, the suppression of bitterness and coffee flavor qualitiesincrease when sucrose levels increase, and similarly, the suppressionof sweetness increases when caffeine or coffee levels rise.Secondly, the magnitude of suppression depends upon the qualityof the suppressive component. Comparisons of the reciprocalactions were made at similar subjective intensities of the mixture'sconstituents in isolation. The results showed that, at similarperceived intensities, caffeine bitterness or coffee flavorwere suppressed by sucrose but sweetness was not affected bycaffeine or coffee.