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Date of Award

9-1995

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Psychology

Supervisor

Dr. Harvey P. Weingarten

Abstract

Most research done on taste and smell has examined the two systems in isolation. This is unfortunate since it is the combination of taste and smell that determines flavor, perhaps the most salient characteristic of food for humans. Furthermore, assessment of flavor pleasantness is integral to food choice and intake. Yet, despite the importance of the hedonic dimension of flavor, most empirical studies of flavor have focused on the intensity of taste-odor mixtures, not their hedonic value. Thus, the experiments that comprise this dissertation focused on the pleasantness of taste-odor mixtures.

Three food odors (chocolate, raspberry, and popcorn) at five concentrations were utilized as stimuli. Experiment 1 replicated the psychophysical functions that have been reported in the literature relating stimulus strength, perceived intensity, and perceived pleasantness with these three odors. Experiments 2 and 3 demonstrated that a negative taste experienced concomitantly with odor reduces odor pleasantness ratings. Experiment 4 established that it is unlikely that this effect results from a general negative affective state since an aversive non-gustatory stimulus did not produce a similar reduction in odor pleasantness.

Subjects in Experiments 1 through 4 were required to report odor pleasantness. However, in these studies it was not clear whether subjects were reporting a downward shift in odor hedonics, a negative hedonic response to taste, or their hedonic response to the taste-odor mixture. Experiment 5 required subjects to be analytical about their hedonic response to taste-odor mixtures. They were instructed to report their independent hedonic response to the odor, taste, and overall sensation. Experiment 5 demonstrated that when subjects are explicitly required to be analytical about the hedonic experience of flavor, they can differentiate between a taste they do not like an odor that is neutral or pleasant to them. However, when not instructed to be analytical, subjects tend to fuse the components into a whole percept or "gestalt."

Metabolic changes modulate the pleasantness of sensation, a phenomenon known as alliesthesia. It is clear that hunger increases the pleasantness of sweet taste relative to the sated state, but the effect of metabolic state on odor hedonics is unclear. Thus, in Experiment 6, I first replicated alliesthesia for sweet taste and demonstrated that aversive tastes are not made more pleasant by hunger. More importantly, though, Experiment 6 showed a clear odor alliesthesia effect; that is, a reduction of odor pleasantness when subjects are full relative to hungry.

It has been suggested that odor hedonics are more labile than taste hedonics. Since no studies have empirically compared the modulation of taste-odor mixtures by hunger and satiety, it is not known whether alliesthesia is greater for the taste or odor component of flavor. Experiment 7 required subjects to be analytical about their hedonic experience of taste-odor mixtures when hungry and full. General alliesthesia was observed, that is, hedonic ratings of all stimuli were lower in the hungry state relative to the sated state. The alliesthesia effect did not depend on whether subjects rated odor alone, taste alone, or a taste-odor mixture. Thus. no distinction could be made between taste or smell in terms of degree of hedonic modulation by metabolic state.

The main goal of these experiments was to explore the hedonics of taste-odor mixtures in humans. These examinations increase our understanding of the chemical senses in general and may be particularly pertinent to understanding the relationship between food hedonics and ingestive behavior. Future work should concentrate on whether food hedonics as studied psychophysically in the manner of the experiments comprising this dissertation predict food preferences or intake. Additionally, the influence of cognitive factors (e.g. identification of the odor as food related) on the hedonics of taste-odor mixtures should be determined.

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