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Effects of hunger, satiety and glucose load upon taste intensity and taste hedonics
Physiology & Behavior, Vol. 16, pp. 471-475. Pergamon Press and
Brain Research Publ., 1976. Printed in the LI.S.A.
Effects of Hunger, Satiety and Glucose Load Upon Taste Intensity and Taste Hedonics HOWARD R. MOSKOWITZ ~ , V. KUMRAIAH, KAMAL N. SHARMA, HARRY L. JACOBS AND S. DUA SHARMA
Food Science Laboratory, U. S. A r m y Natick Laboratories, Natick MA 01 760 and Department o f Physiology, St. Johns Medical College, Bangalore, India (Received 6 November 1974) MOSKOWITZ, H. R., V. KUMRAIAH, K. N. SHARMA, H. L. JACOBS AND S. D. SHARMA. Effects of hunger, satiety andglucose load upon taste intensity and taste hedonics. PHYSIOL. BEHAV. 16(4) 471-475, 1976. - Subjects rated both the taste intensity and taste pleasantness of 4 compounds representing sweet, salty, sour and bitter, respectively. The typical pleasantness ratings appeared to conform to an inverted L shaped function for sweetness (maximum pleasantness at 1.0 M glucose) and for saltiness, and conformed to a negatively sloping function for citric acid and quinine sulfate. These pleasantness functions appeared robust when testing was performed either after an overnight fast, after breakfast or after lunch, respectively. After a satiating glucose load, however, the pleasantness of glucose taste failed to exhibit a breakpoint at 1.0 M glucose, suggesting that a change occurred in hedonic perception of taste after this exceptionally satiating intake. Satiety seems to influence taste pleasantness, but only to a limited degree, and affects only sweet preferences. Taste
Taste intensity
Taste hedonics
Glucose-load
HUMAN taste preferences fall into 2 groups. Traditionally, sweet tasting stimuli have been reported to be pleasing, at least at low and moderate concentrations [3,9]. The taste of sodium chloride is ambiguous. Some individuals find salt to be increasingly pleasant at increasing concentrations, others find salt to be increasingly unpleasant, whereas still others find salt to first increase in pleasantness until a maximum point is reached, at which point the taste becomes less pleasant and finally becomes unpleasant with increasing concentrations [3,12]. For sour and bitter stimuli, human taste preferences for European subjects appear relatively unambiguous. Increasing concentrations of stimuli become increasingly unpleasant. Indian laborers from the Karnataka region of North India like increasing acid concentrations, however [ 1 1 ], and may like increasing concentrations of quinine sulfate. Biological states of satiety and hunger influence taste preferences. Blood sugar had been previously implicated in preferences for 5% vs 30% sugar solutions [8]. Individuals with high blood sugar found the very sweet and concentrated sugar solution to be less pleasant, whereas individuals with low blood sugar preferred the sweeter "solution. Cabanac's recent series of studies on the affective value of sweet (sucrose) taste and the aroma of orange oil [ 1] suggest that after a satiating load comprising glucose solution, taste and aroma preferences diminish. Similar shifts in liking to disliking occur for some food aromas as well after an appropriate satiating load [ 2]. Such shifts in the hedonic
Hunger and taste intensity
Satiety and taste intensity
tone of a stimulus after change in body state have been termed alliesthesia by Cabanac, who applied it as well to the pleasantness and unpleasantness of thermal stimulation [11. Evidence for the influence of abnormal body states on taste preference (e.g., obesity) have been adduced by other investigators [7], who have shown that obese individuals dislike increasingly sweet concentrations of sucrose. These findings were obtained in 2 ways, one by direct rating scale procedures, in which the subjects provided ratings of liking and the other by choices between all pairs of sucrose solut i o n s (paired comparisons). In this paradigm normal individuals were shown to have a maximum preference for sweetness at a sucrose level around 6.2% w/v, whereas obese individuals were shown to dislike the sweetness of sucrose to an increasing degree with increasing concentration. The present series of experiments was motivated by the hypothesis that simultaneous evaluation of taste intensity and taste preference for individuals under various hunger states can reveal systematic shifts in preference behavior. One does not know from studies such as Cabanac's whether the stimulus tastes the same to hungry vs sated individuals, or whether the stimulus possesses a different taste. Direct scaling of taste intensity can answer that question. In addition, considerable data has accrued on the relation between taste acuity and body state (satiety, hunger) and time of day [6]. Shifts of the pleasantness of a stimulus across days may be reducible to an invariant hedonic
1Send reprint requests to: H. R. Moskowitz, MPI Sensory Testing, Inc., 770 Lexington Ave., New York, NY 10021. 471
MOSKOWlTZ ET AL.
472 response to a stimulus, but a varying sensory input. Again, scaling of taste intensity can indicate whether the taste systems of all groups of individuals undergoing the same treatments have remained the same. Parameters of these functions (e.g., intercept) can be compared across groups. METHOD
Subjects The subjects were 4 different groups of male medical studenst (ages 1 8 - 2 6 ) enrolled in St. John's Medical College, Bangalore, India. The first group was tested after an overnight fast of 14 hr or so, (before breakfast group). This group comprised 16 individuals. The second, third and fourth groups were tested just after breakfast, just after lunch, and after an oral glucose load, respectively. Eight subjects participated in each of these 3 groups. The subjects were naive as to the purpose of the experiment.
Stimuli The stimuli were 7 concentrations each of glucose (starting concentration = 2.0 M, with 6 successive half dilutions), 7 of NaCI (starting at 1.0 M), 7 of citric acid (0.05 M), and 7 of quinine sulfate (0.001 M). All stimuli were Analar grade 1. The stimuli were diluted in distilled water, and presented to the subjects at room temperature, in coded paper cups, which disguised concentration and taste quality. The order of presentation was randomized, to prevent effects due to order of concentration and quality. Rinse water (tap) was used between samples to rid the mouth of the remaining stimulus. Subjects rinsed until they could not taste the previous stimulus.
Procedure The subjects were instructed to taste a series of solutions, and to rate the taste intensity on a 0 - 6 category scale (0 = no taste, 6 = extremely strong taste). For pleasantness ratings, the same subjects were provided with a 6 point category scale (I = extremely disliked, 2 = moderately disliked, 3 = slightly disliked, 4 = slightly liked, 5 = moderately liked, 6 = extremely liked). No neutral point was provided to denote indifference so that subjects were required to state whether they liked or disliked the stimulus. During any one session the subject tasted either the sweet and the salty stimuli, or the bitter and the sour stimuli, and rated either taste intensity or taste pleasanthess, by the 2 scales, respectively. The sessions were arranged so that at the end of the experiment 3 replicate judgments were collected for each stimulus on both the taste intensity and taste pleasantness, respectively. Sessions were randomized according to taste quality and judgment (intensity, affect). For the oral glucose load a 20% glucose solution was prepared with some lime juice added to improve its palatability. The subjects were provided with a solution and they ingested 1.5 g glucose/kg body weight. Testing in that condition began 5 - 2 0 rain after ingestion. RESULTS The average category estimates for all tastes and pleasantness were computed. The mean and standard deviations for glucose sweetness and pleasantness are shown in Table 1. In addition, for each quality least square estimates of the slopes and the intercepts of the following
functions were computed: (a)Taste Intensity = kl + k21og C; (b)Taste Pleasantness = k 3 + k41og C + ks(log C) 2 + k6(log C) 3. Traditionally, logarithmic functions have been fitted to category estimates of sensory magnitude for a variety of perceptual continua [ 13]. In the present study the noticeable curvilinearity in the glucose pleasantness function necessitated quadratic and cubic terms in order to correct for the curvilinearity. Measures of the goodnessof-fit of these 5 parameters for the 4 taste qualities, 2 judgment types (intensity, pleasantness), and 4 groups were computed. (Individual functions for taste intensity were also computed. Almost all Pearson r values exceeded 0.85 for individual functions. For taste pleasantness the individual r values were often considerably lower, especially for glucose and NaC1, suggesting curvilinear functions even at the individual level.) The most striking findings of this study pertain to the pleasantness function for the sweet glucose. For all groups except those subjects who were artificially sated with glucose load, the average pleasantness of glucose sweetness increases monononically with concentration, reaches a maximum point, and then diminishes. The function is shaped like an inverted L. In these 3 sets of data that point of maximum pleasantness is at 1.0 M glucose, for the averaged data, although the high variability of the pleasantness ratings at that region (Table 1) suggests that some individuals might not find sweetness to decrease in pleasantness at a higher concentration. This breakpoint region around 1.0 M glucose has been found in several other studies, including one that evaluated the sweetness and pleasantness of 32 sugars [9], and another that evaluated the sweetness and pleasantness for a variety of foods that were sweetened with sucrose [ 10]. An important finding in both those studies was that the maximum region of preference occurred at a constant sweetness level, not at a constant concentration level. That finding suggests a relatively invariant region in the taste system at which pleasantness maximizes, and implies that sweetness is encoded in absolute terms in the nervous system [10]. Otherwise, one would expect that breakpoint to vary considerably from one study to another, as a function of the different stimuli and experimental conditions. In contrast to the breakpoint at 1.0 M for the first 3 groups, the subjects who were artificially sated on glucose failed to show the expected reduction in pleasantness with increasing sweetness. Their mean pleasantness ratings increased at the same rate as the increase in pleasantness for lower concentration. In addition, an individual analysis of the ratings showed that more than half of the individuals continued to increase their ratings, so that the finding probably is not the result of averaging a few individuals with anomalously high pleasantness ratings at 2.0 M with a group of individuals that show the expected breakpoint. Finally, the variability at 1.0 M for sweetness is lower for this sated group then for the other 3 groups (Table 1). It is not clear from these data whether the breakpoint in the glucose pleasantness function is eliminated entirely, or whether the breakpoint is shifted to a higher concentration not investigated here (e.g., 3.0 M glucose). Another important finding is that the portion of the glucose pleasantness function that is negatively sloping is never steeper in absolute value than the portion of the pleasantness function that is positive sloping. If one decomposes the pleasantness function into its 2 halves, and uses terminology such as aversive limb, previously used for animal studies of preference [5], then for humans the
TASTE HEDONICS AND INTENSITY
473 TABLE 1
MEAN SWEETNESSAND PLEASANTNESSRATINGS
Condition After Breakfast
Before Breakfast
After Lunch
After Load
Glucose Molarity
Sweetness (S.D.)
Pleasantness (S.D.)
5.83 (.80) 4.71 (1.11) 4.17 (1.88) 2.96 (1.16) 2.50 (.76) 1.75 (.62) 1.71 (.38) 5.73 (.45) 4.85 (.55) 3.96 (.97) 3.16 (1.13) 2.21 (.97) 1.56 (.71) 1.44 (.59) 5.79 (.41) 5.25 (.61) 3.96 (1.45) 3.17 (1.37) 2.21 (1.21) 1.50 (.66) 1.50 (.83) 5.66 (.48) 4.75 (.98) 3.75 (1.18) 2.75 (.74) 2.00 (.93) 1.46 (.58) 1.33 (.70)
4.79 (1.95) 5.50 (1.31) 4.33 (1.49) 3.58 (1.61) 3.37 (1.64) 3.16 (2.03) 2.83 (1.78) 4.85 (2.36) 5.25 (1.69) 4.38 (1.37) 4.02 (1.25) 3.39 (1.08) 3.56 (1.12) 3.68 (1.00) 4.92 (1.35) 5.83 (1.35) 4.91 (1.21) 4.46 (1.06) 4.41 (1.34) 4.21 (1.05) 4.21 (2.43) 5.87 (.90) 5.37 (1.17) 5.08 (1.14) 4.21 (1.18) 4.00 (.98) 3.83 (1.01) 3.92 (.88)
2.0 1.0 0.5 0.25 0.125 0.06 0.03 2.0 1.0 0.5 0.25 0.125 0.06 0.03 2.0 1.0 0.5 0.25 0.125 0.06 0.03 2.0 1.0 0.5 0.25 0.125 0.06 0.03
aversive limb is governed by a function not steeper than the pleasantness limb. It should be noted, however, that in this experiment even the higher concentrations of glucose were found to be pleasant, not aversive. Further studies are needed filling in concentrations between 1.0 M and 2.0 M, and beyond, to define the exact functions operating here. The taste of NaC1 shows pleasantness functions that concur with previously published reports [3, 4, 12]. For example, the pleasantness of saltiness tends in most instances to remain constant, up to a breakpoint of 0.25 M, at which point the pleasantness begins to drop precipitously. Previous reports for saltiness suggest that its pleasantness obeys an inverted U or L shaped function, with the maximum pleasantness at a low concentration. Hunger and satiety do not appear to affect salt preference markedly. Here citric acid pleasantness is inversely proportional to citric acid sourness, in the same way that quinine sulfate pleasantness is inversely proportional to its bitterness, in contrast to data collected on the Karnataka Indian population [ 1 1 ]. DISCUSSION This study bears critically upon the recently growing evidence that internal body state modifies taste and olfactory preference. Cabanac has called the interaction alliesthesia, and suggests that the current body state can affect the hedonic tone of many different sensory stimuli
(including gustatory, olfactory, and thermal sensations). Cabanac's main finding [ 1] for normal individuals was that the ingestion of an artificially satiating load of glucose t r a n s f o r m e d t h e pleasantness functions for glucose dramatically. Concentrations that were previously preferred on a category scale of liking and disliking were no longer preferred under a satiated state. In the present experiment, which also used normal weight subjects, just the opposite was found for ratings by individuals who were artificially sated (Group 4). For those medical students who were hungry (Group 1) vs the other 2 groups that were tested after breakfast and after lunch (Group 2, 3), no effect of load could be noted. The pleasantness ratings of the glucose stimuli were approximately equal, and the intensity functions for glucose were approximately superimposable. The present study confirms previous suggestions that normal weight individuals possess a capacity [I0] to indicate to them whether a taste solution is overly sweet. In the previous study [ 10] a fixed breakpoint for the sweetness of 4 foods was noted, when subjects were instructed to reate the pleasantness of sucrose solution, cherry flavored beverage, pudding and cake that have been varied experimentally to produce different levels of perceived sweetness. In normals that fixed breakpoint occurred at a fixed sweetness level, corresponding to that sweetness produced by 1.0 M glucose (18% w/v glucose, or equally sweet 9% w/v sucrose). In this experiment normal individuals under slight
M O S K O W l T Z E T AL.
474
TABLE 2 PARAMETERS OF INTENSITY AND PLEASANTNESS FUNCTIONS* Intensity k2
k,
rt
k:~
k4
Pleasantness k.~ k6
r
Glucose Before Breakfast After Breakfast After Lunch After Load
4.78 4.80 4.92 4.62
2.49 2.34 2.60 2.51
.88 .85 .84 .87
(.99) (.98) (.98) (.98)
5.08 5.16 5.48 5.37
-0.72 +0.79 -0.03 +1.42
3.62 -4.53 -4.10
NaC I Before Breakfast After Breakfast After Lunch After Load
6.16 5.86 5.81 5.92
2.73 2.51 2.86 2.75
.91 .87 .88 .90
(.99) (.99) (.98) (.99)
1.87 1.82 1.41 1.76
-4.21 -5.72 -4.36 -3.57
-2.09 -3.35 -1.77 - 1.49
Citric Acid Before Breakfast After Breakfast After Lunch After Load
6.57 6.66 6.53 6.48
2.25 2.43 2.34 2.00
.83 .85 .83 .83
(.98) (.97) (.99) (.99)
1.82 2.12 2.93 2.62
- 1.03 -I.18 - .72 - .58
-.41 -.43 -.31 -.25
(-.97) (-.83) (-.72) (-.86)
Quinine Sulfate Before Breakfast After Breakfast After Lunch After Load
10.22 10.28 9.92 9.03
2.18 2.15 2.02 1.61
.71 .73 .69 .62
(.98) (.96) (.96) (.99)
-I.62 -1.55 -1.30 -0.77
-I.44 -1.50 -1.41 - 1.61
-.60 -.51 -.61 -.56
(-.97) (-.99) (-.96) (-.99)
-2.63 3.20 -2.69
.22 .21 .11 .44
(.97) (.93) (.82) (.95)
.28 .21 .55 .32
(.93) (.78) (.93) (.96)
* l = k , + k2(log C) P=k3 + k4(Iog C) + ks(log C) 2 + k6(Iog C):L tFirst value for r pertains to unaveraged data. Second value for r pertains to mean data.
--INTENSITY
t~---.~... •
LU ~E
°•"•
.........
"-
~
.....
PLEASANTNESS
SULFATE
.
a
---A.
CITRIC ACID
C~ "
.C~
0-.
j" - a "'0.
-o.
o
~j
~
a
o
a
o
hi o (.9
W ¢.. . . .
N
(,9
a
C
I
...............
o
'".
a
eL...0
W }-
m I
...9.
....
BEFORE BREAKFAST
..--
....
AFTER
"" ""
AFTER
B RE J~}J~EAS"i"
RELATIVE
"" "
COSE
MOLAR
LUNCH
C~_UCOSELOAD
CONCENTRATION
FIG. 1. Relation between estimated taste intensity (solid line), taste pleasantness (dashed line) and concentration of glucose, NaCI, citric acid, and quinine sulfate. On the intensity scale 6 = very strong, 0 = same as water. On the pleasantness scale 6 = like extremely, 1 = dislike extremely. The treatments are listed for each panel, and the same observers rated all 4 tastes under each treatment. The concentrations are given in relative terms (highest glucose = 2 M, NaC1 = 1 M, citric acid = 0.05 M, quinine sulfate = 0.001 M), and shown in logarithmic coordinates, in which equal ratios of concentrations appear as equal distances.
TASTE HEDONICS AND INTENSITY
475
hunger and moderate satiation after meals exhibit this maximum point whereas an artificially and extremely sated (with glucose) individual fails to show the point. It appears as if the individual when extremely sated no longer is able to differentiate clearly between affect of a solution and the sweetness of the solution. In a study of obese individuals who were instructed to rate both the degree of pleasantness or unpleasantness of sucrose solutions, and also to choose between pairs of sucrose solutions on the basis of pleasantness of taste, Grinker and Hirsch [7] presented evidence that obese individuals consistently disliked sweet solutions, and with increasing sweetness found t h e taste to be increasingly unpleasant, and less preferred. At first glance their data imply that individuals with a chronically altered body state (obesity) react in the exact opposite way to individuals in another short term alteration in body state (viz. satiety after glucose). However, it is quite possible that the same psychological mechanism applies to both instances. If there
exists a hedonic monitor, and if this hedonic monitor is eliminated when an individual is obese or satiated with glucose, then the individual can only respond to the sensory signal of the taste and not to its hedonic property (or at least he is unable to determine when the maximum hedonic point is reached). The normal individuals sated with glucose may interpret the taste to be pleasant, but lack the hedonic monitor. The obese individuals, also relying upon the taste intensity, interpret the same taste to be unpleasant. What differentiates the group is their interpretation of the sensory information into terms of a positive or negative hedonic tone. Finally, it should be noted that our discussion of load effect has been in behavioral terms, without speculation as to hormonal mechanisms (e.g., insulin, glucagon, etc.). Since our loading procedure confounded oral and gastric stimulations (via drinking) and we did not measure load intensity effects on track circulation, hormones, this must be left to other workers.
REFERENCES 1. Cabanac, M. Physiological role of pleasure. Science 173: 1103-1107, 1971. 2. Declaux, R., J. Feisthauer and M. Cabanac. Effets du repas sur l'agr6ment d'odeurs alimentaires et nonalimentaires chez l'homme. Physiol. Behav. 10: 1029-1033, 1973. 3. Ekman, G. and C. A. Akesson. Saltiness, sweetness and preference: A study of quantitative relations in individual subjects. Rep. Psychol. Lab. University of Stockholm 177: 1964. 4. Engel, R. Experimentalle Untersuchungen fiber die Abhangigkeit der Lust and Unlust yon der Reizstarke beim Geschmacksinn. Arch. Gesamte Psychol. 64: 1-36, 1928. 5. Epstein, A. N. Feeding without oropharyngeal sensations. In: Chemical Senses and Nutrition, edited by M. R. Kare and O. Mailer. Baltimore: The Johns Hopkins Press, 1967, pp. 263-280. 6. Goetzl, F. R., A. J. Ahokas and J. G. Payne. Occurrence in normal individuals of diurnal variations in acuity of the sense of taste for sucrose. J. appl. Physiol. 2: 619-626, 1950.
7. Grinker, J. and J. Hirsch. Metabolic and behavioral correlates of obesity. In: Physiology, Emotion & Psychosomatic Illness. Amsterdam, Holland: Elsevier, 1972, pp. 349-374. 8. Mayer-Gross, W. and J. W. Walker. Taste and selection of food in hypoglycaemia. Br. J. exp. Path. 27: 297-305, 1946. 9. Moskowitz, H. R. The sweetness and pleasantness of sugars. Am. J. Psychol. 84: 387-405, 1971. 10. Moskowitz, H. R., R. A. Kluter, J. Westerling and H. L. Jacobs. Sugar sweetness and preference: Evidence for different psychological laws. Science 184: 583-585, 1974. 11. Moskowitz, H. R,, K. N. Sharma, H. L. Jacobs S. D. Sharma and V. Kumraiah Cross cultural differences in simple taste preference. Science in press, 1975. 12. Pangborn, R. M. Individual variations in affective responses to taste stimuli. Psychon. Sci. 21: 125-128, 1970. 13. Stevens, S. S. and E. Galanter. Ratio scales and category scales for a dozen perceptual continua. J. Exp. Psychol. 54: 377-411, 1957.
Brain Research Publ., 1976. Printed in the LI.S.A.
Effects of Hunger, Satiety and Glucose Load Upon Taste Intensity and Taste Hedonics HOWARD R. MOSKOWITZ ~ , V. KUMRAIAH, KAMAL N. SHARMA, HARRY L. JACOBS AND S. DUA SHARMA
Food Science Laboratory, U. S. A r m y Natick Laboratories, Natick MA 01 760 and Department o f Physiology, St. Johns Medical College, Bangalore, India (Received 6 November 1974) MOSKOWITZ, H. R., V. KUMRAIAH, K. N. SHARMA, H. L. JACOBS AND S. D. SHARMA. Effects of hunger, satiety andglucose load upon taste intensity and taste hedonics. PHYSIOL. BEHAV. 16(4) 471-475, 1976. - Subjects rated both the taste intensity and taste pleasantness of 4 compounds representing sweet, salty, sour and bitter, respectively. The typical pleasantness ratings appeared to conform to an inverted L shaped function for sweetness (maximum pleasantness at 1.0 M glucose) and for saltiness, and conformed to a negatively sloping function for citric acid and quinine sulfate. These pleasantness functions appeared robust when testing was performed either after an overnight fast, after breakfast or after lunch, respectively. After a satiating glucose load, however, the pleasantness of glucose taste failed to exhibit a breakpoint at 1.0 M glucose, suggesting that a change occurred in hedonic perception of taste after this exceptionally satiating intake. Satiety seems to influence taste pleasantness, but only to a limited degree, and affects only sweet preferences. Taste
Taste intensity
Taste hedonics
Glucose-load
HUMAN taste preferences fall into 2 groups. Traditionally, sweet tasting stimuli have been reported to be pleasing, at least at low and moderate concentrations [3,9]. The taste of sodium chloride is ambiguous. Some individuals find salt to be increasingly pleasant at increasing concentrations, others find salt to be increasingly unpleasant, whereas still others find salt to first increase in pleasantness until a maximum point is reached, at which point the taste becomes less pleasant and finally becomes unpleasant with increasing concentrations [3,12]. For sour and bitter stimuli, human taste preferences for European subjects appear relatively unambiguous. Increasing concentrations of stimuli become increasingly unpleasant. Indian laborers from the Karnataka region of North India like increasing acid concentrations, however [ 1 1 ], and may like increasing concentrations of quinine sulfate. Biological states of satiety and hunger influence taste preferences. Blood sugar had been previously implicated in preferences for 5% vs 30% sugar solutions [8]. Individuals with high blood sugar found the very sweet and concentrated sugar solution to be less pleasant, whereas individuals with low blood sugar preferred the sweeter "solution. Cabanac's recent series of studies on the affective value of sweet (sucrose) taste and the aroma of orange oil [ 1] suggest that after a satiating load comprising glucose solution, taste and aroma preferences diminish. Similar shifts in liking to disliking occur for some food aromas as well after an appropriate satiating load [ 2]. Such shifts in the hedonic
Hunger and taste intensity
Satiety and taste intensity
tone of a stimulus after change in body state have been termed alliesthesia by Cabanac, who applied it as well to the pleasantness and unpleasantness of thermal stimulation [11. Evidence for the influence of abnormal body states on taste preference (e.g., obesity) have been adduced by other investigators [7], who have shown that obese individuals dislike increasingly sweet concentrations of sucrose. These findings were obtained in 2 ways, one by direct rating scale procedures, in which the subjects provided ratings of liking and the other by choices between all pairs of sucrose solut i o n s (paired comparisons). In this paradigm normal individuals were shown to have a maximum preference for sweetness at a sucrose level around 6.2% w/v, whereas obese individuals were shown to dislike the sweetness of sucrose to an increasing degree with increasing concentration. The present series of experiments was motivated by the hypothesis that simultaneous evaluation of taste intensity and taste preference for individuals under various hunger states can reveal systematic shifts in preference behavior. One does not know from studies such as Cabanac's whether the stimulus tastes the same to hungry vs sated individuals, or whether the stimulus possesses a different taste. Direct scaling of taste intensity can answer that question. In addition, considerable data has accrued on the relation between taste acuity and body state (satiety, hunger) and time of day [6]. Shifts of the pleasantness of a stimulus across days may be reducible to an invariant hedonic
1Send reprint requests to: H. R. Moskowitz, MPI Sensory Testing, Inc., 770 Lexington Ave., New York, NY 10021. 471
MOSKOWlTZ ET AL.
472 response to a stimulus, but a varying sensory input. Again, scaling of taste intensity can indicate whether the taste systems of all groups of individuals undergoing the same treatments have remained the same. Parameters of these functions (e.g., intercept) can be compared across groups. METHOD
Subjects The subjects were 4 different groups of male medical studenst (ages 1 8 - 2 6 ) enrolled in St. John's Medical College, Bangalore, India. The first group was tested after an overnight fast of 14 hr or so, (before breakfast group). This group comprised 16 individuals. The second, third and fourth groups were tested just after breakfast, just after lunch, and after an oral glucose load, respectively. Eight subjects participated in each of these 3 groups. The subjects were naive as to the purpose of the experiment.
Stimuli The stimuli were 7 concentrations each of glucose (starting concentration = 2.0 M, with 6 successive half dilutions), 7 of NaCI (starting at 1.0 M), 7 of citric acid (0.05 M), and 7 of quinine sulfate (0.001 M). All stimuli were Analar grade 1. The stimuli were diluted in distilled water, and presented to the subjects at room temperature, in coded paper cups, which disguised concentration and taste quality. The order of presentation was randomized, to prevent effects due to order of concentration and quality. Rinse water (tap) was used between samples to rid the mouth of the remaining stimulus. Subjects rinsed until they could not taste the previous stimulus.
Procedure The subjects were instructed to taste a series of solutions, and to rate the taste intensity on a 0 - 6 category scale (0 = no taste, 6 = extremely strong taste). For pleasantness ratings, the same subjects were provided with a 6 point category scale (I = extremely disliked, 2 = moderately disliked, 3 = slightly disliked, 4 = slightly liked, 5 = moderately liked, 6 = extremely liked). No neutral point was provided to denote indifference so that subjects were required to state whether they liked or disliked the stimulus. During any one session the subject tasted either the sweet and the salty stimuli, or the bitter and the sour stimuli, and rated either taste intensity or taste pleasanthess, by the 2 scales, respectively. The sessions were arranged so that at the end of the experiment 3 replicate judgments were collected for each stimulus on both the taste intensity and taste pleasantness, respectively. Sessions were randomized according to taste quality and judgment (intensity, affect). For the oral glucose load a 20% glucose solution was prepared with some lime juice added to improve its palatability. The subjects were provided with a solution and they ingested 1.5 g glucose/kg body weight. Testing in that condition began 5 - 2 0 rain after ingestion. RESULTS The average category estimates for all tastes and pleasantness were computed. The mean and standard deviations for glucose sweetness and pleasantness are shown in Table 1. In addition, for each quality least square estimates of the slopes and the intercepts of the following
functions were computed: (a)Taste Intensity = kl + k21og C; (b)Taste Pleasantness = k 3 + k41og C + ks(log C) 2 + k6(log C) 3. Traditionally, logarithmic functions have been fitted to category estimates of sensory magnitude for a variety of perceptual continua [ 13]. In the present study the noticeable curvilinearity in the glucose pleasantness function necessitated quadratic and cubic terms in order to correct for the curvilinearity. Measures of the goodnessof-fit of these 5 parameters for the 4 taste qualities, 2 judgment types (intensity, pleasantness), and 4 groups were computed. (Individual functions for taste intensity were also computed. Almost all Pearson r values exceeded 0.85 for individual functions. For taste pleasantness the individual r values were often considerably lower, especially for glucose and NaC1, suggesting curvilinear functions even at the individual level.) The most striking findings of this study pertain to the pleasantness function for the sweet glucose. For all groups except those subjects who were artificially sated with glucose load, the average pleasantness of glucose sweetness increases monononically with concentration, reaches a maximum point, and then diminishes. The function is shaped like an inverted L. In these 3 sets of data that point of maximum pleasantness is at 1.0 M glucose, for the averaged data, although the high variability of the pleasantness ratings at that region (Table 1) suggests that some individuals might not find sweetness to decrease in pleasantness at a higher concentration. This breakpoint region around 1.0 M glucose has been found in several other studies, including one that evaluated the sweetness and pleasantness of 32 sugars [9], and another that evaluated the sweetness and pleasantness for a variety of foods that were sweetened with sucrose [ 10]. An important finding in both those studies was that the maximum region of preference occurred at a constant sweetness level, not at a constant concentration level. That finding suggests a relatively invariant region in the taste system at which pleasantness maximizes, and implies that sweetness is encoded in absolute terms in the nervous system [10]. Otherwise, one would expect that breakpoint to vary considerably from one study to another, as a function of the different stimuli and experimental conditions. In contrast to the breakpoint at 1.0 M for the first 3 groups, the subjects who were artificially sated on glucose failed to show the expected reduction in pleasantness with increasing sweetness. Their mean pleasantness ratings increased at the same rate as the increase in pleasantness for lower concentration. In addition, an individual analysis of the ratings showed that more than half of the individuals continued to increase their ratings, so that the finding probably is not the result of averaging a few individuals with anomalously high pleasantness ratings at 2.0 M with a group of individuals that show the expected breakpoint. Finally, the variability at 1.0 M for sweetness is lower for this sated group then for the other 3 groups (Table 1). It is not clear from these data whether the breakpoint in the glucose pleasantness function is eliminated entirely, or whether the breakpoint is shifted to a higher concentration not investigated here (e.g., 3.0 M glucose). Another important finding is that the portion of the glucose pleasantness function that is negatively sloping is never steeper in absolute value than the portion of the pleasantness function that is positive sloping. If one decomposes the pleasantness function into its 2 halves, and uses terminology such as aversive limb, previously used for animal studies of preference [5], then for humans the
TASTE HEDONICS AND INTENSITY
473 TABLE 1
MEAN SWEETNESSAND PLEASANTNESSRATINGS
Condition After Breakfast
Before Breakfast
After Lunch
After Load
Glucose Molarity
Sweetness (S.D.)
Pleasantness (S.D.)
5.83 (.80) 4.71 (1.11) 4.17 (1.88) 2.96 (1.16) 2.50 (.76) 1.75 (.62) 1.71 (.38) 5.73 (.45) 4.85 (.55) 3.96 (.97) 3.16 (1.13) 2.21 (.97) 1.56 (.71) 1.44 (.59) 5.79 (.41) 5.25 (.61) 3.96 (1.45) 3.17 (1.37) 2.21 (1.21) 1.50 (.66) 1.50 (.83) 5.66 (.48) 4.75 (.98) 3.75 (1.18) 2.75 (.74) 2.00 (.93) 1.46 (.58) 1.33 (.70)
4.79 (1.95) 5.50 (1.31) 4.33 (1.49) 3.58 (1.61) 3.37 (1.64) 3.16 (2.03) 2.83 (1.78) 4.85 (2.36) 5.25 (1.69) 4.38 (1.37) 4.02 (1.25) 3.39 (1.08) 3.56 (1.12) 3.68 (1.00) 4.92 (1.35) 5.83 (1.35) 4.91 (1.21) 4.46 (1.06) 4.41 (1.34) 4.21 (1.05) 4.21 (2.43) 5.87 (.90) 5.37 (1.17) 5.08 (1.14) 4.21 (1.18) 4.00 (.98) 3.83 (1.01) 3.92 (.88)
2.0 1.0 0.5 0.25 0.125 0.06 0.03 2.0 1.0 0.5 0.25 0.125 0.06 0.03 2.0 1.0 0.5 0.25 0.125 0.06 0.03 2.0 1.0 0.5 0.25 0.125 0.06 0.03
aversive limb is governed by a function not steeper than the pleasantness limb. It should be noted, however, that in this experiment even the higher concentrations of glucose were found to be pleasant, not aversive. Further studies are needed filling in concentrations between 1.0 M and 2.0 M, and beyond, to define the exact functions operating here. The taste of NaC1 shows pleasantness functions that concur with previously published reports [3, 4, 12]. For example, the pleasantness of saltiness tends in most instances to remain constant, up to a breakpoint of 0.25 M, at which point the pleasantness begins to drop precipitously. Previous reports for saltiness suggest that its pleasantness obeys an inverted U or L shaped function, with the maximum pleasantness at a low concentration. Hunger and satiety do not appear to affect salt preference markedly. Here citric acid pleasantness is inversely proportional to citric acid sourness, in the same way that quinine sulfate pleasantness is inversely proportional to its bitterness, in contrast to data collected on the Karnataka Indian population [ 1 1 ]. DISCUSSION This study bears critically upon the recently growing evidence that internal body state modifies taste and olfactory preference. Cabanac has called the interaction alliesthesia, and suggests that the current body state can affect the hedonic tone of many different sensory stimuli
(including gustatory, olfactory, and thermal sensations). Cabanac's main finding [ 1] for normal individuals was that the ingestion of an artificially satiating load of glucose t r a n s f o r m e d t h e pleasantness functions for glucose dramatically. Concentrations that were previously preferred on a category scale of liking and disliking were no longer preferred under a satiated state. In the present experiment, which also used normal weight subjects, just the opposite was found for ratings by individuals who were artificially sated (Group 4). For those medical students who were hungry (Group 1) vs the other 2 groups that were tested after breakfast and after lunch (Group 2, 3), no effect of load could be noted. The pleasantness ratings of the glucose stimuli were approximately equal, and the intensity functions for glucose were approximately superimposable. The present study confirms previous suggestions that normal weight individuals possess a capacity [I0] to indicate to them whether a taste solution is overly sweet. In the previous study [ 10] a fixed breakpoint for the sweetness of 4 foods was noted, when subjects were instructed to reate the pleasantness of sucrose solution, cherry flavored beverage, pudding and cake that have been varied experimentally to produce different levels of perceived sweetness. In normals that fixed breakpoint occurred at a fixed sweetness level, corresponding to that sweetness produced by 1.0 M glucose (18% w/v glucose, or equally sweet 9% w/v sucrose). In this experiment normal individuals under slight
M O S K O W l T Z E T AL.
474
TABLE 2 PARAMETERS OF INTENSITY AND PLEASANTNESS FUNCTIONS* Intensity k2
k,
rt
k:~
k4
Pleasantness k.~ k6
r
Glucose Before Breakfast After Breakfast After Lunch After Load
4.78 4.80 4.92 4.62
2.49 2.34 2.60 2.51
.88 .85 .84 .87
(.99) (.98) (.98) (.98)
5.08 5.16 5.48 5.37
-0.72 +0.79 -0.03 +1.42
3.62 -4.53 -4.10
NaC I Before Breakfast After Breakfast After Lunch After Load
6.16 5.86 5.81 5.92
2.73 2.51 2.86 2.75
.91 .87 .88 .90
(.99) (.99) (.98) (.99)
1.87 1.82 1.41 1.76
-4.21 -5.72 -4.36 -3.57
-2.09 -3.35 -1.77 - 1.49
Citric Acid Before Breakfast After Breakfast After Lunch After Load
6.57 6.66 6.53 6.48
2.25 2.43 2.34 2.00
.83 .85 .83 .83
(.98) (.97) (.99) (.99)
1.82 2.12 2.93 2.62
- 1.03 -I.18 - .72 - .58
-.41 -.43 -.31 -.25
(-.97) (-.83) (-.72) (-.86)
Quinine Sulfate Before Breakfast After Breakfast After Lunch After Load
10.22 10.28 9.92 9.03
2.18 2.15 2.02 1.61
.71 .73 .69 .62
(.98) (.96) (.96) (.99)
-I.62 -1.55 -1.30 -0.77
-I.44 -1.50 -1.41 - 1.61
-.60 -.51 -.61 -.56
(-.97) (-.99) (-.96) (-.99)
-2.63 3.20 -2.69
.22 .21 .11 .44
(.97) (.93) (.82) (.95)
.28 .21 .55 .32
(.93) (.78) (.93) (.96)
* l = k , + k2(log C) P=k3 + k4(Iog C) + ks(log C) 2 + k6(Iog C):L tFirst value for r pertains to unaveraged data. Second value for r pertains to mean data.
--INTENSITY
t~---.~... •
LU ~E
°•"•
.........
"-
~
.....
PLEASANTNESS
SULFATE
.
a
---A.
CITRIC ACID
C~ "
.C~
0-.
j" - a "'0.
-o.
o
~j
~
a
o
a
o
hi o (.9
W ¢.. . . .
N
(,9
a
C
I
...............
o
'".
a
eL...0
W }-
m I
...9.
....
BEFORE BREAKFAST
..--
....
AFTER
"" ""
AFTER
B RE J~}J~EAS"i"
RELATIVE
"" "
COSE
MOLAR
LUNCH
C~_UCOSELOAD
CONCENTRATION
FIG. 1. Relation between estimated taste intensity (solid line), taste pleasantness (dashed line) and concentration of glucose, NaCI, citric acid, and quinine sulfate. On the intensity scale 6 = very strong, 0 = same as water. On the pleasantness scale 6 = like extremely, 1 = dislike extremely. The treatments are listed for each panel, and the same observers rated all 4 tastes under each treatment. The concentrations are given in relative terms (highest glucose = 2 M, NaC1 = 1 M, citric acid = 0.05 M, quinine sulfate = 0.001 M), and shown in logarithmic coordinates, in which equal ratios of concentrations appear as equal distances.
TASTE HEDONICS AND INTENSITY
475
hunger and moderate satiation after meals exhibit this maximum point whereas an artificially and extremely sated (with glucose) individual fails to show the point. It appears as if the individual when extremely sated no longer is able to differentiate clearly between affect of a solution and the sweetness of the solution. In a study of obese individuals who were instructed to rate both the degree of pleasantness or unpleasantness of sucrose solutions, and also to choose between pairs of sucrose solutions on the basis of pleasantness of taste, Grinker and Hirsch [7] presented evidence that obese individuals consistently disliked sweet solutions, and with increasing sweetness found t h e taste to be increasingly unpleasant, and less preferred. At first glance their data imply that individuals with a chronically altered body state (obesity) react in the exact opposite way to individuals in another short term alteration in body state (viz. satiety after glucose). However, it is quite possible that the same psychological mechanism applies to both instances. If there
exists a hedonic monitor, and if this hedonic monitor is eliminated when an individual is obese or satiated with glucose, then the individual can only respond to the sensory signal of the taste and not to its hedonic property (or at least he is unable to determine when the maximum hedonic point is reached). The normal individuals sated with glucose may interpret the taste to be pleasant, but lack the hedonic monitor. The obese individuals, also relying upon the taste intensity, interpret the same taste to be unpleasant. What differentiates the group is their interpretation of the sensory information into terms of a positive or negative hedonic tone. Finally, it should be noted that our discussion of load effect has been in behavioral terms, without speculation as to hormonal mechanisms (e.g., insulin, glucagon, etc.). Since our loading procedure confounded oral and gastric stimulations (via drinking) and we did not measure load intensity effects on track circulation, hormones, this must be left to other workers.
REFERENCES 1. Cabanac, M. Physiological role of pleasure. Science 173: 1103-1107, 1971. 2. Declaux, R., J. Feisthauer and M. Cabanac. Effets du repas sur l'agr6ment d'odeurs alimentaires et nonalimentaires chez l'homme. Physiol. Behav. 10: 1029-1033, 1973. 3. Ekman, G. and C. A. Akesson. Saltiness, sweetness and preference: A study of quantitative relations in individual subjects. Rep. Psychol. Lab. University of Stockholm 177: 1964. 4. Engel, R. Experimentalle Untersuchungen fiber die Abhangigkeit der Lust and Unlust yon der Reizstarke beim Geschmacksinn. Arch. Gesamte Psychol. 64: 1-36, 1928. 5. Epstein, A. N. Feeding without oropharyngeal sensations. In: Chemical Senses and Nutrition, edited by M. R. Kare and O. Mailer. Baltimore: The Johns Hopkins Press, 1967, pp. 263-280. 6. Goetzl, F. R., A. J. Ahokas and J. G. Payne. Occurrence in normal individuals of diurnal variations in acuity of the sense of taste for sucrose. J. appl. Physiol. 2: 619-626, 1950.
7. Grinker, J. and J. Hirsch. Metabolic and behavioral correlates of obesity. In: Physiology, Emotion & Psychosomatic Illness. Amsterdam, Holland: Elsevier, 1972, pp. 349-374. 8. Mayer-Gross, W. and J. W. Walker. Taste and selection of food in hypoglycaemia. Br. J. exp. Path. 27: 297-305, 1946. 9. Moskowitz, H. R. The sweetness and pleasantness of sugars. Am. J. Psychol. 84: 387-405, 1971. 10. Moskowitz, H. R., R. A. Kluter, J. Westerling and H. L. Jacobs. Sugar sweetness and preference: Evidence for different psychological laws. Science 184: 583-585, 1974. 11. Moskowitz, H. R,, K. N. Sharma, H. L. Jacobs S. D. Sharma and V. Kumraiah Cross cultural differences in simple taste preference. Science in press, 1975. 12. Pangborn, R. M. Individual variations in affective responses to taste stimuli. Psychon. Sci. 21: 125-128, 1970. 13. Stevens, S. S. and E. Galanter. Ratio scales and category scales for a dozen perceptual continua. J. Exp. Psychol. 54: 377-411, 1957.