Deprivation, expectation and threat: Effects on salivation in the obese and nonobese

Physiology & Behavior, Vol. 17, pp. 187--193. Pergamon Press and Brain Research Publ., 1976. Printed in the U.S.A.

Deprivation, Expectation and Threat: Effects on Salivation in the Obese and Nonobese' O R L A N D W. WOOLEY, SUSAN C. WOOLEY AND R A N D A L L B. DUNHAM 2

Psychiatry Department, University o f Cincinnati, College o f Medicine Cincinnati, OH 45267

(Received 7 January 1975) WOOLEY, O. W., S. C. WOOLEY AND R. B. DUNHAM. Deprivation, expectation and threat: effects on salivation in the obese and nonobese. PHYSIOL. BEHAV. 17(2) 187-193, 1976. - Eight obese and 8 nonobese male subjects' salivation was measured before and after presentation of a food stimulus (pizza) on four different days at 8:00 p.m. Half the time subjects had skipped supper (deprivation condition); half the time they were not allowed to eat the pizza after salivation measurement (expectation condition). Deprivation and expectation conditions were crossed and counterbalanced. Subjects salivated more in response to the food when they expected to eat it than when it was prohibited. The nonobese subjects salivated more if they were deprived, especially before the food was present. The obese were unaffected by deprivation. These findings are interpreted in terms of the classical conditioning concepts, negative conditioned stimulus and differentiation. The obese subjects salivated less under conditions of threat (high deprivation-negative expectation) than under conditions of nonthreat (low deprivation-positive expectation); the nonobese salivated more when threatened than when not. These findings support a hypothesis that the obese tend to conserve energy in the face of threats associated with eating and the nonobese tend to expend it. Conditioned appetitive salivation

Energy utilization

Obesity

SALIVATION has been shown to be a sensitive index of the effects of at least 4 different factors which are known or hypothesized to be related to appetite in humans. These 4 factors are caloric intake [14], d-amphetamine [13], length of deprivation [ 16], and rate of food consumption [12]. Wooley, Wooley and Woods [14] found that subjects of normal body weight salivated less in the presence of a palatable food stimulus 1 hr after a 900 calorie liquid meal than after an identically tasting 450 calorie meal of equal volume; the amount of salivation elicited by the presentation of the food stimulus was greater than when no food was present following the 450 calorie meal only. For obese subjects the effect of caloric intake was less than for the nonobese; they salivated more when the palatable food stimulus was present than when it was absent after both the 900 and the 450 calorie meal. Wooley, Wooley and Williams [ 13 ] found the amount of salivation elicited by the presence of a palatable food stimulus was less 1 hr after ingestion of I0 mg of d-amphetamine than after ingestion of a placebo. Wooley and Wooley [16] found that the amount of salivation elicited by the presentation of a palatable food stimulus was directly related to length of deprivation.

Negative conditioned stimuli

Deprivation

Wooley and Wooley and Turner [12] found that the amount of salivation elicited by the presentation of a palatable dessert food (chocolate cake ala mode or banana split) 1 hr after a meal (hamburger) eaten slowly was less than after an identical meal eaten quickly; these results were interpreted as validating the behavioral treatment technique of encouraging obese patients to eat more slowly in order to "achieve a normal state of satiation with less food intake" (p. 361 of [10] ). Salivation has also been shown to reflect differences in the way individuals respond to threatening situations. Bogdonoff, Bogdonoff, and Wolf [ 1 ] reported that subjects rated as "aggressive" - by a "b l i n d " interviewer - salivated more during the presence of a dentist's drill ("The drill was started and brought toward the mouth, but no actual drilling was conducted") than in its absence. Subjects rated as defensive salivated less in the presence of the drill than in its absence. They conclude: "The potential biologic purpose of increased salivation is not clear; but as part of an aggressive approach to a threat the increase may relate to the general increased mobilization of energy that characterizes the aggressive type of behavioral response. The decrease in flow may be viewed as part of the relative immobility

t This research was supported in part by United States Public Health Grant - 1 R0I MH 22319-01. 2Now at University of Illinois, Psychology Department, Urbana, IL 61801. 187

188

WOOLEY, WOOLEY AND DUNHAM

and restraint of energy release of the defensive reaction" (p. 173). Bogdonoff et al. [1] do not report the body weightsof their subjects. However, Nisbett [5] has reported a study in which an interpretation of aggressive approach by nonobese, but not obese subjects is tenable. He showed that the likelihood of nonobese subjects crossing a room for more food is a function of their prior caloric intake, and that obese subjects are unlikely to go for more food regardless of prior intake. The present study includes a test of the hypothesis that the obese respond defensively and the nonobese aggressively to threat. In previous studies by the present investigators [12, 13, 14, 16] subjects were required to eat the experimental food stimuli after salivation measures were completed. The present study was designed to determine the effect on salivation of obese and nonobese subjects expecting and not expecting to eat the food stimuli presented to them. In the study of the effect of length of deprivation on salivation [16] the number of subjects was too small to draw any conclusions about possible obese-nonobese differences. The present study was designed to determine if any such differences exist. The experimental procedure of the present study differs from the previous studies in two ways: (1) the subjects of the present study were college students; the subjects of the previous studies were prison inmates. (2) the subjects of the present study were more naive than those of prior studies in that they were not given any practice sessions. In prior experiments subjects were given 2 or 3 preexperimental trails on which salivation was measured before and during presentation of palatable food stimuli. The present subjects' first experience with the salivation measurement technique was on the first experimental day. The effect of this difference in procedure was assessed by analyzing the salivation data (not previously published) from the preexperimental trials of 2 prior studies [ 13,14]. The design of the present study is similar to that of the previous studies in that all 3 studied conditions of high satiety - 900 calorie meal [14], amphetamine [13], and low deprivation (present study) - and conditions of low satiety - 450 calorie meal [14], placebo [13], and high deprivation (present study). As will be shown, obese-nonobese differences which appeared only as trends in the previous studies reached statistical significance in the present study. METHOD

Experimental Overview Eight obese and 8 nonobese subjects participated in 4 experimental sessions a week apart. Sessions were held at 8 p.m. and consisted of salivation measures when no food was present followed by measures of salivation while looking at a pizza. Two variables were manipulated in a 2 x 2 design: (1) deprivation: In the deprived condition, subjects had skipped the evening meal; in the nondeprived condition they had eaten their regular evening meal. (2) expectation of eating: In the positive expectation condition, subjects were notified upon arrival that they would be permitted to eat the test food (pizza) after the saliva measures were collected; in the negative condition they were told they could not eat it.

Subjects Eight obese and 8 nonobese male subjects were selected from a larger random sample of freshmen contacted by mail. To be selected for the study, prospective subjects had to rate their liking for pizza at 6 or better on a seven- point scale, and meet the height-weight criteria. Obese subjects were required to be at least 15% above ideal weight for height, or 30% above ideal weight if varsity athletes or weight lifters. Nonobese subjects were required to be within 10% of ideal weight for height (Metropolitan Life Insurance Tables, 1959). Obese subjects ranged from 18% to 60% above average for their age and height and were a mean 34% above average; the median weight was 25% above average. All subjects were paid $10 for participation.

Experimental Foods The food stimuli used for salivary tests were pizzas purchased from a local student restaurant. During screening subjects were asked what type of pizza they liked best, and at all sessions each individual's specified favorite was provided for him.

Salivary Measures Saliva was collected with cotton dental rolls (Johnson & Johnson No. 2 1 - 1 / 2 in. dental rolls available from dental supply companies) weighed to the nearest 0.001 g before and within 1 hr after use. Three rolls were inserted in the mouth, 2 bilaterally and 1 sublingually, and left in place for three 2-min collection periods separated by 2 min rest intervals. During salivary collection, subjects were instructed not to move their mouths. The average weight of saliva obtained in the 3 collections constituted the measure. (See reference [16] for more information on measurement procedures.)

Procedure Subjects participated in the 4 experimental conditions in 1 of 4 counterbalanced orders. On the morning of each experimental day subjects were notified whether or not to eat dinner that day. Upon arrival they were told whether or not they would be permitted to eat the pizza that night. In the one condition in which subjects missed dinner and were not allowed to eat during the experimental session, they were given money to purchase a meal at 10 p.m. Obese subjects were tested on 4 consecutive Wednesdays at 8 p.m.; nonobese subjects on consecutive Thursdays at 8 p.m. During experimental sessions, activities of the subjects were cued by an instructional videotape. First, subjects rated their hunger on a seven-point scale. Next, salivary collections were taken with no food stimuli present; this measurement will be referred to as prefood salivation. Following the measurement of prefood salivation, the foods (pizzas) were placed before the subjects. A second set of hunger ratings were made, and subjects rated how appetizing the food looked. Salivation, while looking at the pizza, was measured as described above; this measurement will be referred to as salivary response. At the end, subjects who had been told they could eat the pizza were allowed to do so, and the rest were dismissed.

DEPRIVATION, EXPECTATION AND THREAT

189 TABLE1

SALIVARY RESPONSE TO THE PRESENTATIONOF FOOD STIMULI AND PREFOOD SALIVATION(g/2 MIN.) BY OBESE AND NON-OBESE SUBJECTS IN FOUR CONDITIONS: 1. DEPRIVED, EXPECT TO EAT; 2. NONDEPRIVED, EXPECTTO EAT; 3. DEPRIVED, EXPECT NOT TO EAT; 4. NONDEPRIVED, EXPECT NOT TO EAT Condition I. Deprived Expect to Eat Column

Obese (n=8) X S.D. Nonobese (n=8) X S.D.

II. Nondeprived Expect to Eat

III. Deprived Expect Not to Eat

IV. Nondeprived Expect Not to Eat

1

2

3

4

5

6

7

8

Prefood Salivation

Salivary Response

Prefood Salivation

Salivary Response

Prefood Salivation

Salivary Response

Prefood Salivation

Salivary Response

1.36 0.64

1.69 1.00

1.62 0.72

2.07 1.16

1.35 0.56

1.48 0.81

1.12 0.33

1.44 0.78

1.65 0.68

1.83 0.85

1.20 0.56

1.35 0.80

1.83 0.98

1.47 0.83

1.43 0.60

1.28 0.44

Effect o f food presentation during practice trials in two prior experiments. To determine if the obese respond to food more readily than the nonobese - i.e., if they need fewer practice sessions before their salivary responses stabilize - data from practice sessions in 2 prior studies [13,14] were analyzed. These 2 studies were selected because each involved a direct manipulation of satiety; a manipulation of caloric intake in one case [14], the administration of amphetamine in the other [ 13 ]. Responses to threat. In order to determine whether or not the obese responded "defensively", in Bogdonoff et ars [1] terms, and the nonobese "aggressively", a separate analysis of a selected subset of the total data was performed. It was assumed that (1) high deprivation is more "threatening" - to again use Bogdonoff et ars term - than low deprivation, and (2) not being allowed to eat food (negative expectation) is more threatening than being allowed to eat it (positive expectation). On these assumptions, the high deprivation-negative expectation condition (i.e., the day that subjects both skipped supper and were not allowed to eat the pizza) should represent the greatest threat. The low deprivation-positive expectation condition (i.e., subjects had supper and were allowed to eat the pizza) should be the least threatening. The other 2 conditions - high deprivation-positive expectation and low deprivation-negative expectation - are "mixed" and of intermediate threat, between the 2 "pure" conditions. The "pure" conditions - called "threat" and "no threat" for present purposes - were analyzed separately to test the hypothesis based on the Bogdonoff et al. concept, with special attention to the interaction between body weight and degree of threat. RESULTS Prefood salivation and salivary responses by the obese and nonobese subjects in the 4 conditions of this experiment are presented in Table 1. The effects of food presentation, deprivation, expectation, and "threat" on the 2 weight groups were determined by analysis of these data.

Effect o f Food Presentation Obese subjects salivated more (1.67 g/2 min; mean of Columns 2, 4, 6, and 8 of Table 1)during the presentation

of the food stimuli (pizza) than when no food was present (prefood salivation), 1.36 g/2 min. (mean of Columns 1, 3, 5, and 7 of Table 1), but the nonobese subjects did not: 1.48 g/2 min. when food was present, 1.53 g/2 min. when no food was present. The statistical significance of the differential effect of food presentation on the obese and nonobese was confirmed by the following results of analysis of variance: (1) A nonsignificant main effect of the presence of food (i.e., food present vs. food not present); (2) a significant interaction between the presence of food and body weight, F(1,14) = 4.6, p< 0.05; (3) a significant t test for correlated means (mean prefood salivation vs. mean salivary response), t(7) = 2.15, p<0.05, one-tailed, for the obese and a nonsignificant t for the nonobese; and (4) the obese salivated more when food was present than not on all 4 experimental days, the nonobese on only the 2 days when they were allowed to eat the food.

Food presentation during practice trials in two prior experiments. During the first 2 practice sessions in 2 prior experiments [13,14] there was a tendency for the obese subjects to be more responsive to the presentation of food than were the nonobese subjects. Table 2, Columns 1 and 2, presents prefood salivation and salivary response on the first practice sessions of all subjects in these prior experiments. On the first day the obese, on the average, salivated .83 g/2 min. more when food was present than when it was not; the nonobese salivated only .35 g/2 min. more when food was present. On the second day the values were .91 g/2 min. for the obese, and .44 g/2 min. for the nonobese. The difference between the second day values approaches significance, t(29) = 1.81, p<0.08, two-tailed. However, even though the nonobese subjects tended to be less responsive than the obese, they did salivate significantly more in the presence of food than when no food was present, on the first day salivation was measured, t(16) = 1.79, p<0.05, and on the second day, t(16) = 2.53, p<0.01. The t values for the obese subjects: t(13) = 2.87, p<0.007 for the first day and t(13) = 4.67, p<0.0002 for the second day. (All 4 probability values are one-tailed.) In summary, the hypothesis that the nonobese subjects in the present study did not salivate more when food was presented because there was no practice session is not confirmed.

190

WOOLEY, WOOLEY AND DUNHAM TABLE2 SALIVARY RESPONSE TO THE PRESENTATION OF FOOD STIMULI AND PREFOOD SALIVATION (g/2 MIN) ON FIRST TWO DAYS OF PREEXPERIMENTAL PRACTICE TRIALS AND PREFOOD SALIVATION UNDER CONDITIONS OF HIGH SATIETY (900 CALORIE MEAL OR 10 mg AMPHETAMINE) AND LOW SATIETY (450 CALORIE MEAL OR PLACEBO) FOR OBESE AND NONOBESE SUBJECTS IN TWO PRIOR EXPERIMENTS [13, 14]

Obese (n=14) X S.D Nonobese (n= 17) X S.D.

1

2

3

4

First Practice Day Prefood Salivary Salivation Response

Second Practice Day Prefood Salivary Salivation Response

High Satiety Prefood Salivation

Low Satiety Prefood Salivation

1.74 0.70

2.57t 1.05

1.59 0.69

2.50~ 1.09

1.20 0.50

1.23 0.50

2.11 1.16

2.46" 1.15

1.77 1.02

2.21 t 0.98

1.24 0.40

1.50t 0.49

Note: Values marked with asterisks are significantly greater than the value to the immediate left: *p 0.05. tp 0.01. Sp 0.0002.

The Effect of Deprivation Only the nonobese subjects' salivation was affected by deprivation. As can be seen in Fig. 1, the nonobese salivated less under conditions of low deprivation than under conditions of high deprivation. Deprivation affected salivation in the nonobese when food was present and when it was not, but especially when it was not. The statistical significance of this finding is shown by (1) the significant interaction (deprivation level x body weight group), F(1,14) = 4.53, p<0.051; (2) significant ts (for correlated means) when comparing the nonobese subjects mean salivation values under conditions of high and low deprivation but not when comparing the corresponding values for the obese; (3) a significant interaction between deprivation and weight group, F(1,14) = 4.88, p<0.05 in a separate analysis of variance of just the prefood salivation (Columns 1, 3, 5, and 7, Table 1 ; no other significant F's in the analysis). Mean nonobese prefood salivation under high deprivation was 1.74 g (mean of Columns 1 and 5, Table 1) under low, 1.32 g (Columns 3 and 7, Table 1), t(7) = 4.18, p<0.004, two-tailed; mean nonobese salivary response under high deprivation was 1.65 g (Columns 2 and 6, Table 1), under low, 1.32 g (Columns 4 and 8, Table 1), t(7) = 2.015, p<0.04, one-tailed. However, it is only when they expect to eat the food that nonobese subjects' salivary response is increased by deprivation: salivary response, deprived, positive expectation, is 1.83 g/2 min (Column 2, Table 1) not deprived, 1.35 g/2 min (Column 4, Table 1), t(7) = 2.15, p<0.03, one-tailed. Mean prefood salivation values for the obese were 1.35 g (high deprivation) and 1.37 g (low deprivation); mean salivary response values were 1.59 g and 1.75 g; t(7)< 1 in both cases. Level of deprivation in two prior experiments. To determine the stability of the finding that nonobese subjects salivate more when deprived than when not, especially when no food is present, prefood salivation data from 2 previous experiments [13,14] were analyzed. In each of these experiments obese and nonobese subjects' salivation was measured under conditions of high satiety i.e., 900 calorie liquid meal [ 14], amphetamine [ 13], -

NO Food Present ~Food

Present

2.00

~

k

1.00

~,

,~

High

Low

High

Low

Deprivation

Deprivation

Deprivation

Deprivation

OBESE (N=B)

NON-OBESE (N=8)

FIG. 1. Prefood salivation and salivary response (g/2 min.) by obese and nonobese to a palatable food stimulus under conditions of high deprivation and low deprivation. and of low satiety - i.e., 450 calorie meal [ 14], placebo [13]. For each weight group the prefood salivation data from the high satiety conditions were combined and compared with the combined prefood salivation data from the low satiety conditions. Table 2, Columns 3 and 4, present mean prefood salivation values for obese and nonobese subjects under conditions of high and low satiety; these data are from the same subjects as those in Columns 1 and 2 of Table 2. Prefood salivation under conditions of low satiety (or high deprivation) is greater than under conditions of high satiety (or low deprivation) among the nonobese subjects but not among obese subjects. The nonobese salivated 1.50 g/2 min when relatively deprived and 1.24 g/2 min when relatively satiated, t(16) = 2.41, p<0.03, two-tailed. The obese salivated about 1.20 g/2 min at both levels of deprivation.

DEPRIVATION, EXPECTATION AND THREAT

191

"M

"-,I

m

No Food Present F o ~ Present

No/rood Present Food Present

2.00

2.00

9~

~1.oo

1.00

k.

Positive Expectation

Negative Expectation

OBESE (N=8)

Positive Expectation

Negative Expectation

NON-OBESE (N=B)

Threat

No Threat

OBESE(N=8)

Threat

No Threat

NON-OBESE (N=8)

FIG. 2. Prefood salivation and salivary response (g/2 min.) by obese and nonobese to a palatable food stimulus under conditions of positive expectation (subjects expect to eat the stimulus) and negative expectation.

FIG. 3. Prefood salivation and salivary response (g/2 min.) by obese and nonobese to a palatable food stimulus under conditions of threat (high deprivation-negative expectation) and non-threat (low deprivation-positiveexpectation).

Effect of Expectation

g/2 min; Column 7, Table 1), t(7) = 2.36, p<0.05, two-tailed. An analysis of variance of just the salivary responses revealed that expectation was the only significant main effect, F(1,14) = 14.7, p<0.002, and that no interactions were significant. In summary, when they knew they could eat the food stimuli, subjects salivated more than when they knew they could not, but only when the food was actually present and attended to. Thirteen of the 16 subjects showed a larger increase (or a smaller decrease) in salivation when the food was present (vs. their own prefood salivation) in the positive condition than in the negative expectation condition. For the nonobese, there was a tendency for salivation to decrease when the prohibited food to which they were asked to attend was presented, especially when they had skipped supper (high deprivation).

Subjects salivated more in the presence of food when they expected to eat it than when they expected not to eat it. Figure 2 presents prefood salivation and salivary responses under conditions of positive and negative expectation for the obese and nonobese subjects. Analysis of variance revealed that expectation was nearly significant F ( I , 1 4 ) = 4.4, p < 0 . 0 5 5 , and that the interaction between expectation and the presence of food (food present vs. food not present or salivary response vs. prefood salivation) was significant, F(1,14) = 5.56, p<0.03. As shown in Fig. 2, when food was present, obese and nonobese subjects salivated more when they knew they could eat the food (1.88 g/2 min for the obese, 1.59 g/2 min for the nonobese; mean of Columns 2 and 4, Table 1) than when they knew they could not (1.46 g/2 min for the obese, 1.38 g/2 min for the nonobese; mean of Columns 6 a n d 8 , Table 1). When food was not present, the nonobese subjects salivated more in the negative condition than in the positive condition (Fig. 2). In fact, when they could not eat the food they salivated more when food was not present than when it was, t(7) = 2.24, p<0.06, two-tailed. However, this effect approached significance only when the nonobese subjects were deprived. Prefood salivation in the negative expectation-high deprivation condition was 1.83 g/2 min (Column 5, Table 1), salivary responses was 1.47 g/2 min. (Column 6, Table 1), t(7) = 2.12, p<0.07, two-tailed; the values for the negative expectation-low deprivation condition were 1.43 g/2 min (prefood salivation; Column 7, Table 1), and 1.28 g/2 min (salivary response; Column 8, Table 1), t(7) = 1.32, p<0.23, two-tailed. As was described above, the nonobese subjects' prefood salivation was elevated in the high deprivation conditions. Within the negative expectation condition, prefood salivation was greater when nonobese subjects were deprived (1.83 g/2 min; Column 5, Table I ) than when they were not (1.43

Responses to Threat Obese subjects salivated less in the threatening condition (high deprivation-negative expectation, Columns 5 and 6, Table 1) than in the nonthreatening condition (low deprivation-positive expectation, Columns 3 and 4, Table 1). The nonobese subjects showed the opposite pattern; threat increased their salivation. Figure 3 presents prefood salivation and salivary response of both groups in the 2 conditions. The analysis of variance revealed a highly significant, F(1,14) = 9.75, p<0.007, body weight by degree of threat interaction. T-tests for correlated means revealed that the obese subjects mean total salivation (prefood salivation + salivary response + 2; Columns 5 and 6, Table 1) in the threatening condition, 1.41 g, was significantly less than in the nonthreatening situation (Columns 3 and 4, Table I), 1.84 g, t(7) = 2.35, p<0.05, two-tailed. The nonobese subjects mean total salivation was less in the nonthreatening

192

WOOLEY, WOOLEY AND DUNHAM

situation, 1.28 g, than in the threatening situation, 1.65 g, t(7) = 2.06, p<.07, two-tailed. Further comparisons showed that it is when food is present that the obese show the greatest effect of threat; their salivary response to the pizza was 1.48 g in the threat condition (Column 6, Table I), 2.07 g in the nonthreat condition (Column 4, Table 1), t(7) = 2.60, p<0.035, two-tailed; their prefood salivation was 1.35 (Column 5) and 1.62 (Column 3), t(7) = 1.50, p<0.18, two-tailed, in the threat and nonthreat conditions, respectively. For 7 out of 8 obese subjects, salivary response was greater in the no-threat than in the threat condition. The nonobese subjects are more affected by threat when food is not present; their prefood salivation was 1.83 g in the threat (Column 5), and 1.20 g in the nonthreat condition (Column 3), t(7) = 2.95, p<0.02, two-tailed; their salivary response was 1.47 g (Column 6), and 1.35 g (Column 4) in the threat and nonthreat conditions, respectively, t ( 7 ) < l . For 6 out of 8 nonobese subjects, prefood salivation was greater in threat than in the nonthreat condition. The analysis of variance also revealed a highly significant, F(1,14) = 11.33, p<0.005, interaction between degree of theat and presence of food. T-tests for correlated means showed that only in the nonthreat condition did the presentation of food elicit a salivary response greater than prefood salivation: prefood salivation = 1.41 g (obese + nonobese + 2, Column 3), salivary response = 1.71 g (obese + nonobese - 2, Column 4), t(15) = 2.30, p<0.02, one-tailed; in the threat condition the values were: prefood salivation = 1.59 g (Column 5) salivary response = 1.47 g (Column 6). An analysis of variance of the remaining data - i.e., high deprivation-positive expectation and low deprivation-negative expectation (Columns 1, 2, 7, and 8, Table I) revealed no significant factors or interactions. In summary, the obese subjects' defensive response to threat showed up especially in their salivary responses to food; the nonobese subjects' aggressive response to threat was most apparent in their prefood salivation before food was presented. Hunger Ratings Obese and nonobese subjects did not differ in their ratings of hunger. Both groups show a highly significant effect of deprivation, F(1,14) = 297, p<0.001. Hunger ratings of both groups increased when the food was presented, F(1,14) = 166, p<0.001. And neither group showed any effect of expectation on rated hunger. Ratings of the appeal of the food stimuli showed a similar pattern, being affected by the manipulation of deprivation, but not the manipulation of expectation. DISCUSSION When they expected to eat the experimental meal (pizza), subjects salivated more than when they did not, but only if the food was actually present. Nonobese subjects salivated more when they were deprived than when not, and the effect was stronger when food was not present. The most unexpected result given the previous findings [12, 13, 14], was the effect of deprivation on prefood salivation by the nonobese. Calories [14], amphetamine [ 13], and rate of eating [12] had no significant effect on prefood salivation when only the data of single studies were analyzed. When combined and analyzed the data yield the

same conclusions as the present study: nonobese subjects salivate more when physiologically hungry; obese subjects are unaffected by deprivation. The increased salivation by the nonobese with no food present means that what in previous studies [12, 13, 14, 16] had been called baseline salivation is not really a baseline; and thus it is unsuitable in the present study as a comparison value in determining the extent to which the nonobese subjects responded appetitively to the presentation of the food. Bogdonoff et al's [1] concept of aggressive and defensive response to threat may explain why the nonobese salivate more when they are hungry; food deprivation is threatening to life. The obese subjects' nonresponsiveness to deprivation with food present corroborates the finding [14] that recent prior caloric intake has little effect on obese individuals' appetite for palatable food. Experiments with dogs [3,9] show that satiation (i.e., food intake) normally reduces the strength of the conditioned salivary response to any given food stimulus. In humans of normal body weight, who reported having never been overweight, the strength of the salivary response to palatable food was inversely related to recent caloric intake, even though the subjects did not know how many calories they had eaten [14]. This relative lack of effect of caloric intake on the conditioned salivary responses by the obese may have etiological-therapeutic implications. To the extent that obese people eat when they are not hungry, as when highly preferred foods are available, and do not eat when they are, as when they fast, diet, and skip meals, their ingestive behavior may lead to a discontinuity between physiological hunger and appetite. In terms of classical conditioning theory, their appetitive (salivary) responses have not been differentially reinforced on the basis of hunger drive stimuli. Internal signals associated with high and low hunger levels have not acquired stimulus properties because reinforcement (i.e., food in the mouth) and nonreinforcement have not been made contingent on these signals. Current theories of obesity [2, 6, 7, 8] hold that it is because these internal signals are not perceived that they play no role in controlling intake, but the perception and discrimination of hunger and satiety signals may be possible only under the proper reinforcement ("differentiation", reference [4], p. 345) conditions. Even if perception of hunger and satiety is possible, it may not be necessary in regulating body weight; even subjects of normal body weight have been shown incapable of perceiving and discriminating the post-ingestional effects of high and low calorie meals [ 11,15]. Both the obese and the nonobese subjects salivated less in response to food which they could not eat than to food which they could eat. Prohibited food seemed to have effects similar to what Konorski [4] calls "negative conditioned stimuli", stimuli which signal that no food will be available. When a negative conditioned stimulus is paired with a positive conditioned stimulus (i.e., a signal that food will be available), the effect of the latter on salivation is decreased. Konorski's conceptualization of such effects helps explain the tendency of the nonobese subjects' salivation to decrease in response to the presentation of the prohibited food, especially when they were deprived. He postulates that, rather than there being an absence of response to the negative conditioned stimulus, a "hunger antidrive conditioned response" is learned. This response "is manifested by the striking fact that a voracious animal

DEPRIVATION, EXPECTATION AND THREAT

193

who displayed a strong m o t o r e x c i t e m e n t during the intertrial intervals due to the hunger d r i v e . . , m o m e n t a r i l y calms d o w n w h e n the . . . no-food [stimulus] is p r e s e n t e d " (p. 325). The n o n o b e s e subjects' increased p r e f o o d salivation m a y be due to " s t r o n g m o t o r e x c i t e m e n t " - a state n o t incompatible w i t h the increased energy m o b i l i z a t i o n char-

acteristic of the aggressive t y p e of response to threat [ 1 ] and their decreased salivation u p o n presentation of the f o o d may be attributable to the negative c o n d i t i o n e d stimulus (i.e., prohibited food) which elicits no salivation itself ( [ 4 ] , p. 326) but which does elicit the " h u n g e r antidrive", thus removing the cause of the increased salivation (i.e., m o t o r e x c i t e m e n t ) .

REFERENCES 1. Bogdonoff, M. D., M. M. Bogdonoff and S. G. Wolf, Jr. Studies on salivary function in man: Variation in secretory rate as part of the individual's adaptive pattern. J. Psychosom. Res. 5: 170-174, 1961. 2. Brueh, B. Eating Disorders; Obesity, Anorexia Nervosa, and the Person Within. New York: Basic Books, 1973. 3. James, W. T., L. J. Peacock, and J. B. Rollins. The effect of satiation on the value of the conditioned salivary response. Acta Biol. exp. Warsaw, 26: 245-250, 1966. 4. Konorski, J. Integrative Activity of the Brain. Chicago: University of Chicago Press, 1967. 5. Nisbett, R. Determinants of food intake in human obesity. Science 159: 1254-1255, 1968. 6. Schachter, S. Cognitive effects on bodily functioning: Studies of obesity and eating. In: Neurophysiology and Emotion, edited by D. C. Glass. New York: Rockefeller University Press and Russell Sage Foundation, 1967. 7. Schachter, S. Obesity and eating. Science 161: 751-756, 1968. 8. Schaehter, S. and J. Rodin. Obese Humans and Rats. New York: John Wiley and Sons, 1974. 9. Soltysik, S. The effect of satiation upon conditioned and unconditioned salivary responses. Acta neurobiol, exp. 31: 59-63, 1971.

10. Stuart, R. B. Behavioral control of overeating. Behav. Res. Ther. 5: 357-365, 1967. 11. Wooley, O. W., S. C. Wooley and R. B. Dunham. Can Calories be perceived and do they affect hunger in obese and nonobese humans? J. comp. physiol. Psychol. 80: 250-258, 1972. 12. Wooley, O. W., S. C. Wooley and K. Turner. The effects of rate of consumption on appetite in the obese and nonobese. In: Recent Advances in Obesity Research I: Proceedings of the First International Congress on Obesity, edited by A. Howard. London: Newman Publishing, Ltd., 1975. 13. Wooley, O. W., S. C. Wooley and B. S. Williams. Salivation as a meaure of appetite: Studies of the anorectie effects of calories and amphetamine. In: Hunger: Basic Mechanisms and Clinical Implications, edited by D. Novin, W. Wyrwicka and G. Bray, New York: Raven Press, 1976. 14. Wooley, O. W., S. C. Wooley and W. A. Woods. Effect of calories on appetite for palatable food in obese and nonobese humans. Z comp. physiol. Psychol. 89: 619-625, 1975. 15. Wooley, S. C. Physiologic versus cognitive factors in short-term food regulation in the obese and nonobese. Psychosom. Med. 34: 62-68, 1972. 16. Wooley, S. C. and O. W. Wooley. Salivation to the sight and thought of food: A new measure of appetite. Psychosom. Med. 35: 136-142, 1973.