Assessment of the taste interaction between two qualitatively similar-tasting substances: a comparison between comparison rules

The taste interaction between sucrose and fructose was assessed by using three different comparison procedures: the summated response comparison, the factorial plot comparison, and the equimolar comparison rule. The perceived sweetness intensities were obtained on a ratio scale by using a functional measurement approach in combination with a two-stimulus procedure. The conclusions obtained from each of the three comparison rules were identical. The taste interaction between sucrose and fructose could be explained to a large extent, but not completely, by the apparent taste "interactions" within sucrose and fructose as single substances. It is argued that the apparent taste interaction within a large number of single sugars and between two of these sugars in a mixture is somewhat synergistic at low sweetness levels, additive at intermediate sweetness levels, and suppressive at high sweetness levels.     

How Sweetness Plays Sweetly in Persuasion

Three experiments explored how sweetness metaphors affect individuals’ attitudes. The results indicated that sweetness metaphors led to positive responses to the target advertisement and the advertised product, both when the sweetness was actually experienced (Experiment 1) and when the sweetness experience was imagined (Experiment 2 and 3). In Experiment 1, participants who directly experienced a sweet taste evaluated a mineral water advertisement more positively than those who did not experience a sweet taste. Experiment 2 showed that an imagined sweet taste generated favorable attitudes toward the same targets as in Experiment 1. Results of Experiment 3, which used advertisements of various product categories, were similar to those of the previous two experiments, where both direct experience and mental imagination of sweetness were advantageous for forming favorable attitudes.     

Sweetness and intensity of artificial sweeteners

In four experiments, groups of Os judged either the sweetness or the entire taste intensity of solutions of sucrose, cyclamate salts, cyclamate-saccharin mixtures, and sodium saccharin. The sensory functions obtained by magnitude estimation suggest that over the middle range of concentration the sweetness and intensity of the foregoing substances grow as power functions of concentration. As a first approximation, the exponents for sweetness and intensity are, respectively, 1.6 to 1.4 for sucrose, 1.0 to 0.8 for cyclamate salts, 0.6 to 0.85 for cyclamate-saccharin mixtures, and 0.3 to 0.6 for sodium saccharin.     

SALTNESS, SWEETNESS, AND PREFERENCE: A study of quantitative relations in individual subjects

Individual scales were constructed for saltness and preference in an experiment with eight subjects and for sweetness and preference in a second experiment with seven of these subjects. It was found (1) that power functions described the individual relations between sodium chloride and sucrose concentration, on the one hand, and the subjective variables of saltness and sweetness, on the other hand, (2) that the exponents exceeded 1 but varied greatly between subjects, and (3) that there was a great variation over individuals with regard to the form of the saltness/preference and the sweetness/preference relations.     

Sex differences in preferences for coffee sweetness among Japanese students

The purpose of the present study was to examine sex differences in preferences for coffee sweetness. The participants were 59 Japanese undergraduate students. Men preferred sweeter coffee than women, while both men and women showed almost the same preference for acidic beverage sweetness. The sex difference in preferences for coffee sweetness may be related to coffee-drinking habits.     

Sweet odours and sweet tastes are conflated in memory

Certain odours and certain tastes appear to share common perceptual properties. One example is sweetness, a perceptual experience that results from stimulation of taste receptors on the tongue typically by sugars. The experiment here examined for evidence of this perceptual similarity using a novel and indirect test. Participants were exposed six times each, to three odours (strawberry, caramel, and oregano) and three tastes (sucrose, saline, and citric acid). Following a 10-min interval, participants were given a surprise frequency estimation task, in which they had to judge how often each stimulus had occurred. If sweet-smelling strawberry and caramel odours really do share this perceptual characteristic in common with sweet tasting sucrose, then frequency estimates for sucrose should be overestimated relative to non-sweet tastes. Not only was this observed, but frequency estimates for sweet tastes were also found to correlate with (1) evaluations from a later test of similarity between these sweet smells and sucrose, and (2) the degree to which these odours smelled sweet. These findings suggest a shared perceptual feature between such odours and sucrose - sweetness - under conditions where no judgment of perceptual quality was required.     

Both perceptual and conceptual factors influence taste-odor and taste-taste interactions

Observers are often asked to make intensity judgments for a sensory attribute of a stimulus that is embedded in a background of “irrelevant” stimulusdimensions. Under some circumstances, these background dimensions of the stimulus can influence intensity judgments for the target attribute. For example, judgments of sweetness can be influenced by the other taste or-odor qualities of a solution (Frank & Byram, 1988; Kamen et al., 1961). Experiments 1 and 2 assessed the influence of stimulus context, instructional set, and reference stimuli on cross-quality interactions in mixtures of chemosensory stimuli. Experiment 1 demonstrated that odor-induced changes in sweetness judgments were dramatically influenced when subjects rated multiple attributes of the stimulus as compared with when they judged sweetness alone. Several odorants enhanced sweetness when sweetness alone was judged, while sweetness was suppressed for these same stimuli when total-intensity ratings were broken down into ratings for the sweetness, saltiness, sourness, bitterness, and fruitiness of each solution. Experiment 2 demonstrated a similar pattern of results when bitterness was the target taste. In addition, Experiment 2 showed that the instructional effects applied to both taste-odorand taste-taste mixtures. It was concluded that the taste enhancement and suppression observed for taste-odor and taste-taste mixtures are influenced by (1) instructional sets which influence subjects’ concepts of attribute categories, and (2) the perceptual similarities among the quality dimensions of the stimulus.     

Learned liking versus inborn delight: can sweetness give sensual pleasure or is it just motivating?

In this study, we separated for the first time the learned liking for a particular level of sweetness in a familiar drink from the infantile delight in sweetness as such ("the sweeter, the better"). It is widely assumed that sensing a liked food or drink evokes a pleasurable experience, but the only psychological evidence for this assumption has been tongue movements that are elicited specifically by sweet taste in animals and human neonates. We found that adults felt such movements in response to drinking juice at both their personally preferred level of sweetness and levels they deemed so sweet as to be undrinkable. Yet only the intolerably strong level of sweetness elicited enjoyment of the experienced movements, elevation of mood, and a sense of smiling. Hence, the pleasure that adults experience during ingestion could be exclusively linked with the congenital sweetness reflex that sends mother's milk down an infant's throat.     

Qualitative identification of the taste of weak sucrose-sodium chloride mixture stimuli

Near-threshold mixtures of sucrose and sodium chloride were shown to elicit acidic or bitter sensations as well as, or instead of, sweetness and saltiness. The probability of a bitter response was relatively stable and consistent with error due to residual noise in the identification task. The acidic response varied in probability with the sodium chloride concentration, and was generally substitutive for a sweet response.     

Perception of sweetness and bitterness in different vehicles

In the present study, we investigated taste-taste, taste-vehicle, and simultaneous taste-vehicle-taste mixtures. Subjects made estimates of the sweetness and bitterness of 27 stimuli. Sucrose (292, 585, and 1170 mM), caffeine (13, 26, and 52 mM), and binary mixtures of low (292-13 mM), middle (585-26 mM), and high (1170-52 mM) levels of both components were dispersed in water, carboxymethylcellulose (CMC) 1% w/v, and gelatin 6% w/v. The sweetness and bitterness of the sucrose-vehicle-caffeine combinations were significantly weaker than the respective sucrose-vehicle and caffeine-vehicle combinations. The emerged mutual suppressive effects were asymmetrical and persisted when both tastants were presented in CMC and gelatin. Moreover, the increase in vehicle consistency and the simultaneous addition of another taste reduced the perceived intensity of a taste either presented alone or dissolved in water. For both sweetness and bitterness, the total taste suppression observed was always significant.     

Evidence for neural inhibition in bittersweet taste mixtures.

Three lines of evidence from psychophysical experiments implied that mutual suppression of bitter and sweet tastes is due to neural inhibition rather than chemical interactions in solution or competition of molecules for common receptor sites. Removal of sweetness from bittersweet mixtures caused the bitterness to increase. This was accomplished by adaptation to sucrose or by treatment with Gymnema sylvestre, neither of which affect the concentration of sucrose on the tongue. Such increases in the bitterness of mixtures, independent of the concentration of the sweet masking substance, are difficult to reconcile with suppression by means of chemical interactions. Similar dependence of suppression on perceived intensity (and independence from concentration) was observed with mixtures of phyenylthiocarbamide and sucrose. Tasters of phenylthiocarbamide showed stronger suppression of sweetness than nontasters. This result was also inconsistent with molecular interactions causing suppression, which would have resulted in the same degree of suppression for the two groups. Instead, these findings support neural explanations of mixture suppression, such as antidromic inhibition or occlusion.     

Interactions between CO2 oral pungency and taste

Two experiments are reported in which the perceptual interactions between oral pungency, evoked by CO2, and the taste of each of four tastants--sucrose (sweet), quinine sulfate (bitter), sodium chloride (salty), and tartaric acid (sour)--were explored. In experiment 1 the effect of three concentrations of each tastant on the stimulus-response function for perceived oral pungency, in terms of both rate of change (slope) and relative position along the perceived pungency axis, was determined. In experiment 2 the effect of three concentrations of CO2 on the stimulus-response function for the perceived taste intensity of each tastant was examined. Results show that the characteristics of the mutual effects of tastant and pungent stimulus depend on the particular tastant employed. Sucrose sweetness and CO2 oral pungency have no mutual effect; sodium chloride saltiness or tartaric acid sourness and CO2 oral pungency show mutual enhancement; and quinine sulfate bitterness abates CO2 oral pungency, whereas CO2 has a double and opposite effect on quinine sulfate bitterness--at low concentrations of bitter tastant CO2 enhances bitterness, and at high concentrations of bitter tastant CO2 abates bitterness. It is suggested that the perceptual attributes of saltiness and sourness are closer, from a qualitative point of view, to oral pungency than are the attributes of bitterness and sweetness.     

Perceptual changes in taste mixtures

Three studies were conducted to quantify perceptual changes that occur when sapid chemicals are tasted in mixture solutions. The primary effect when mixing sweetness (glucose or fructose) with salt (NaCl), sour (citric acid), or bitter (quinine sulfate) was to reduce the intensity of each taste in the mixture. The reduction was not equal for the two components, although the overall (total) taste intensity of the mixture appeared to be approximately 50% of the sum of the intensities of the unmixed components. Mixtures of sweet and salt developed an “unblended” or “clashing” taste, in which the components alternated in attempting to dominate the taste percept. Sweet mixed with either sour or bitter blended in almost all proportions. The “flavor” of sweetness in mixtures differed from that of simple sugar sweetness, suggesting that the presence of a second taste modified the qualitative aspect of sweetness. The magnitude of change in sweetness quality depended upon the sugar being rated, and upon the quality and intensity of the second, or modifying, taste.     

Hedonic and sensory characteristics of odors conditioned by pairing with tastants in humans

Animals readily acquire positive odor-taste hedonic associations, but evidence for this in humans remains weak and was explored further. Retronasal pairing of odors with sucrose or salty stimuli (Experiment 1) increased the rated sweetness of sucrose-paired odors without altering liking, although changes in odor pleasantness correlated with sucrose liking. Experience of odors with sucrose or quinine by sweet likers (Experiment 2) found increased pleasantness and sweetness for sucrose-paired odors, whereas quinine-paired odors became less liked and more bitter. Odor-sucrose pairings in sweet likers and dislikers (Experiment 3) found increased sweetness in both groups but increased odor liking only in likers. These data suggest that evaluative and sensory learning are dissociable and that evaluative changes are sensitive to individual differences in sweet liking.     

“Ratios” and “differences” in perceived sweetness intensity

For a number of perceptual continua, it has been shown in previous studies that subjects use only one quantitative comparison between two sensory impressions of a pair of stimuli, irrespective of whether they are instructed to judge “ratios” or “differences”. This comparison can be described by algebraic subtraction. The present study was designed to investigate whether this one-operation theory for psychophysical judgment also applied to the sensory continuum of sweetness. Subjects were presented with pairs of fructose solutions, and judged “ratios” of, or “differences" in, perceived sweetness intensities. The pairs were constructed on the basis of a factorial judgment design. The results showed that the reported “differences” could be adequately described by a difference response model, and that the reported “ratios” could be adequately described by a ratio response model. However, the reported “ratios” and reported “differences” were monotonically related, and the marginal means of the log-transformed response matrix of “ratios” were a linear function of the marginal means of the response matrix of “differences”. These results are incompatible with the notion that subjects judged differences when instructed to judge “differences”, but ratios when instructed to judge “ratios”. The consistency of the ratio response model with “ratio” judgments is probably caused by a comparative operation based on “differences” in combination with an exponential response output function. It may be concluded that subjects judge only “differences”, and not “ratios”, between perceived sweetness intensities.     

Acquired hedonic and sensory characteristics of odours: Influence of sweet liker and propylthiouracil taster status

Repeated pairings of novel food-related odours with sweet tastes can result in enduring changes in sweetness of the odour alone, but have less consistent effects on odour liking. Variation in ability to taste propylthiouracil (PROP) might account for this, since PROP supertasters (ST) have been reported both to experience stronger sweetness intensity and to be more likely to dislike sweetness than do PROP nontasters (NT). Alternatively, individual differences in liking for sweetness may transfer to sweet-paired odours independently of PROP sensitivity. To explore this, evaluations of sucrose, saccharin, and PROP solutions were used to classify 92 volunteers as either sweet likers or dislikers and as PROP ST, NT, or medium tasters (MT). Changes in pleasantness of odours that had been paired with the taste of saccharin increased in sweet likers but decreased in dislikers. Odour sweetness increased regardless of PROP taster or sweet liker status. PROP ST rated saccharin as more bitter than did other taster groups and also showed greater increases in acquired bitterness of the saccharin-paired odour. Overall, these data suggest that individual differences in evaluation of saccharin reliably predict subsequent changes in evaluation of saccharin-paired odours, with hedonic changes corresponding with liking for sweet tastes and sensory changes reflecting differences in sensory quality between PROP taster groups.     

Monogeusia for fructose,glucose, sucrose,and maltose

We investigated the ability of subjects to discriminate sugars with a whole-mouth forced-choice paradigm, in which a standard solution was compared with a test solution of varied concentration. Discrimination probabilities were U-shaped functions of test concentration: for 6 subjects and pairwise combinations of fructose, glucose, and sucrose, discriminability always declined to chance over a narrow range of test concentrations. At concentrations ≦ 100 mM, maltose was indiscriminable from fructose but discriminable at higher concentrations for 4 subjects. By analogy with themonochromacy of night vision, whereby any two lights are indiscriminable when their relative intensities are suitably adjusted, we call the gustatory indiscriminability of these sugarsmonogeusia. The simplest account of monogeusia is that all information about the indiscriminable sugars is represented by a single neural signal that varies only in magnitude. The discriminability of maltose from the other sugars at higher concentrations is consistent with the hypothesis that maltose also activates a second gustatory code.     

Perceptual integration of tertiary taste mixtures

Integration psychophysics was used to explore the taste perception of mixtures of sucrose, fructose, and citric acid. Three levels of each stimulus were varied in a 3 x 3 x 3 factorial design. Subjects rated total intensity, sweetness, and acidity of the 27 mixtures on graphic rating scales. Consistent with earlier work, the perceived total intensity of the tertiary mixtures was found to be dictated by the intensity of the (subjectively) stronger component alone (i.e., either the integrated sweetness or the acidity, whichever was the more intense). In contrast, the sweetness and acidity of the mixture were susceptible to mutual suppression: Sweetness suppressed acidity, acidity suppressed sweetness. There was, however, a difference between sucrose and fructose in their interactions with citric acid, fructose being the more susceptible to suppression. This selectivity of suppression indicates that the two sweetnesses could not have been inextricably integrated. Implications for taste coding are discussed, and the findings are reconciled in terms of two separate coding mechanisms: one for taste intensity, another for taste quality.     

The effects of viscosity upon perceived sweetness

U.S. Army Natick Laboratories, Natick, Massachusetts 01760 Six concentrations of sucrose and six concentrations of sodium saccharin were presented as stimuli to 30 Ss. The concentrations were equally spaced logarithmically, covering a 32: I range for each solute. The 12 aqueous solutions were presented at four levels of viscosity, ranging approximately from I to 10,000 centipoises, with sodium carboxymethylcellulose (cellulose gum) as the thickening agent. Magnitude estimates indicate that perceived sweetness decreases with viscosity. In log-log coordinates the Viscosity-sweetness relation is roughly linear with a negative slope, suggesting that sweetness of both sodium saccharin and sucrose varies as a power function of viscosity, with an exponent between ?.20 and ?.25.     

Effects of context in judgments of sweetness and pleasantness

Dramatic effects of the immediate stimulus context were demonstrated for ratings of sweetness and also for ratings of pleasantness of soft drinks containing different concentrations of sucrose. The same drinks were rated sweeter when the lower concentrations were presented more frequently, less sweet when the higher concentrations were presented more frequently. A quasi-normal distribution of frequencies yielded ratings falling between the two skewed distributions. Ratings of sweetness were accurately predicted by Parducci’s (1974) range-frequency model of judgment, which was originally developed to explain contextual effects in other psychophysical dimensions. Ratings of pleasantness were also affected by context; the highest ratings were assigned to concentrations of intermediate sweetness in their respective contexts.