Enhancement of food aversion by exposure to a poisoned conspecific in Norway rats (Rattus norvegicus)

Two experiments were conducted to determine whether exposure to a poisoned conspecific enhances prior food aversion in rats. In Experiment 1, subjects were serially exposed to two foods, cocoa‐flavored and cinnamon‐flavored ones, and were then poisoned 1 h later. On the next day, they were exposed to a poisoned conspecific that had eaten a cocoa‐flavored food. On the subsequent choice test, subjects had an enhanced aversion to cocoa‐flavored food. The result was replicated in Experiment 2, in which a cinnamon‐flavored food was assigned as a target. The results are discussed in relation to previous findings.     

Responses of observer rats (Rattus norvegicus) to complex, diet-related signals emitted by demonstrator rats

We explored the effects of complex, food-identifying signals emitted by demonstrator Long-Evans rats (Rattus norvegicus) on food preferences of their observers. In Experiments 1 and 2, observers identified each of 2 or 3 foods their demonstrators had eaten before interacting with observers. In Experiment 3, individual observers interacted with groups of demonstrators. Some of these demonstrators had eaten one food, some another. Observers then chose between the two foods. The greater the proportion of demonstrators in a group that had eaten a diet, the greater the proportion of that diet the observers ate. In Experiment 4, each observer interacted over several weeks with a series of demonstrators and preferred each of the foods its demonstrators had eaten. In sum, the food preferences of observers were affected by several different types of complex, food-identifying signals like those one might expect rats to encounter outside the laboratory.     

The Effects of Vocalisation on Situational Frequency Estimation

Two experiments are reported that studied the effects of vocalisation on situational frequency judgment. Subjects saw lists of words and were later asked to judge frequency of occurrence on the list. In Experiment 1, the word list was learned incidentally, and frequency estimates were higher for words that subjects had read aloud during study than for those that had been read silently. In Experiment 2, an intentional-learning procedure was used; higher estimates for words read aloud than for those read silently were found when pronunciation was manipulated within subjects but not when it was manipulated between subjects. In all cases, pronunciation had no effect on estimates for words that had only been presented once on the study list. These results suggest that multiple processes may underlie frequency estimation.     

Food choice in rats (Rattus norvegicus): the effect of exposure to a poisoned conspecific

Three experiments were conducted to examine the effects of exposure to a poisoned conspecific on subsequent food aversion in rats. In Experiment 1A, rats that had been aversively conditioned to a cocoa-flavored food were exposed to a poisoned conspecific that had eaten the same food. On the subsequent choice test, the animals increased their aversion to that food. These results were reconfirmed in Experiment 1B, in which a cinnamon-flavored food was used as the stimulus. In Experiment 2, subjects were first exposed to a poisoned conspecific and then conditioned to the food which the conspecific had eaten. On the test, they showed no sign of increased aversion to that food.     

Lack of interference in long-term memory for socially learned food preferences in rats (Rattus norvegicus)

Outside the laboratory, rats (Rattus norvegicus) are likely both to interact with several conspecifics that have eaten various foods and to eat a variety of foods themselves before they encounter any particular food for which they have a socially enhanced preference. Here the authors examine the stability of rats' socially learned food preferences following 6 days of potentially disruptive ingestive experiences. The authors found that 6 days of (a) eating unfamiliar foods, (b) interacting with demonstrators that had eaten unfamiliar foods, or (c) both eating unfamiliar foods and interacting with demonstrators that had eaten those foods had no measurable effect on rats' socially learned food preferences. The stability of socially enhanced food preferences over time and despite potentially disruptive experiences is consistent with the view that social learning about foods is an important determinant of the food choices of free-living Norway rats.     

Rats (Rattus norvegicus) do not prefer salted solid food

Many studies have demonstrated that when sodium-replete rats are given a choice between water and isotonic saline, they consume more of the isotonic saline. Their ingestive responses to a choice between salted and unsalted food, however, have not been studied in the same detail. Because humans consume salt in or on food rather than in pure water, this lack of information calls into question the use of the rat as the animal model for human excess salt consumption. In Experiment 1, 16 Sprague-Dawley rats were given 1-hr access to salted and unsalted foods (potato chips, peanuts, soup) commonly consumed by humans in the salted form. In each choice situation, rats consumed more of the unsalted variety of solid food. In Experiment 2, the concentration of salt in a wider variety of foods was varied. Fifteen rats were allowed a choice of a given salt concentration or the unsalted food. In no case was the salted solid food eaten in excess of the unsalted solid food, and in general, more of the unsalted solid food was eaten. In a third experiment, two groups of 8 rats were given exposure from weaning to either salted or unsalted potato chips. Three-months of exposure to salted chips or unsalted chips did not alter the rats' relative intake of salted chips. When given a choice, more unsalted chips were consumed by both groups. These experiments indicate that sodium-replete Sprague-Dawley rats generally prefer unsalted solid foods to salted ones.     

Social interaction modifies learned aversions, sodium appetite, and both palatability and handling-time induced dietary preference in rats (Rattus norvegicus)

In a series of four experiments, I examined the extent to which socially transmitted diet preference could counteract the effects of a learned aversion (Experiment 1), a palatability-based diet preference (Experiment 2), a polyethylene glycol 20,000-induced sodium appetite (Experiment 3), and a handling-time induced dietary preference (Experiment 4). I found that rats poisoned after eating a novel diet ate very substantial amounts of the averted diet following interaction with conspecifics that had eaten the averted diet. Following interaction with conspecifics that had eaten an unpalatable diet, rats offered a choice between palatable and unpalatable diets ate more than twice as much unpalatable diet as did controls lacking social experience. Sodium-deficient rats offered a choice between sodium-enriched and sodium-adequate diets ate less than half as much sodium-enriched diet, following interaction with conspecifics that had eaten sodium-adequate diet as did control rats lacking social experience. Rats offered a choice between isocaloric, roughly equipalatable foods with long and short handling times (e.g., sunflower seeds with and without shells) chose the food having the longer handling time after interacting with conspecifics eating that food. These findings suggest that social influence is a major factor in guiding diet selection by rats.     

Social transmission of food preferences in Japanese monkeys (Macaca fuscata) after mere exposure or aversion training

In Experiment 1, 3 mother-child pairs of Japanese monkeys (Macaca fuscata) were given simultaneous choice tests between raisins and popcorn. The mothers and offspring showed different choice patterns. Cofeeding opportunities were then alternated with individual choice tests. In Experiment 2,2 other pairs were added. Each animal was again offered simultaneous choice tests between marshmallows and almonds. Food aversion conditioning was used to create different choice patterns for mothers and offspring. After cofeeding and choice tests, the differences in choice patterns disappeared in both experiments. The changes after contact with the other's eating pattern during cofeeding was as follows: foods consumed by either came to be eaten by both; foods consumed by both continued to be eaten by both; and foods consumed by neither continued to be ignored. The results provide evidence for social transmission of food preferences in this species.     

Mere social knowledge impacts children's consumption and categorization of foods

How does social information affect the perception of taste early in life? Does mere knowledge of other people's food preferences impact children's own experience when eating? In Experiment 1, 5‐ and 6‐year‐old children consumed more of a food described as popular with other children than a food that was described as unpopular with other children, even though the two foods were identical. In Experiment 2, children ate more of a food described as popular with children than a food described as popular with adults. Experiment 3 tested whether different perceptual experiences of otherwise identical foods contributed to the mechanisms underlying children's consumption. After sampling both endpoints of a sweet‐to‐sour range (applesauce with 0 mL or 5mL of lemon juice added), children were asked to taste and categorize applesauce samples with varying amounts of lemon juice added. When classifying ambiguous samples that were near the midpoint of the range (2 mL and 3 mL), children were more likely to categorize popular foods as sweet as compared to unpopular foods. Together, these findings provide evidence that social information plays a powerful role in guiding children's consumption and perception of foods. Broader links to the sociality of food selection are discussed.     

Predicting compliance behavior from moral judgment scales

Two experiments with college males examined the relationship between moral judgment and compliance in a modified Asch paradigm. In Experiment 1 moral judgment was assessed with the written form of Kohlberg's dilemmas. Stage of moral judgment interacted with type of compliance, with Stage 4 subjects showing a compromise response between their own perceptions and the responses of others. In Experiment 2 moral judgment was assessed with Rest's Defining Issues Test. Compliance was found to be negatively related to level of moral judgment. The relationship found between moral judgment and compliance in the two experiments was interpreted in terms of a trend away from external standards and toward internal standards with higher levels of moral judgment.     

The effect of exogenous spatial attention on auditory information processing

This study investigated the effect of exogenous spatial attention on auditory information processing. In Experiments 1, 2 and 3, temporal order judgment tasks were performed to examine the effect. In Experiment 1 and 2, a cue tone was presented to either the left or right ear, followed by sequential presentation of two target tones. The subjects judged the order of presentation of the target tones. The results showed that subjects heard both tones simultaneously when the target tone, which was presented on the same side as the cue tone, was presented after the target tone on the opposite side. This indicates that spatial exogenous attention was aroused by the cue tone, and facilitated subsequent auditory information processing. Experiment 3 examined whether both cue position and frequency influence the resulting information processing. The same effect of spatial attention was observed, but the effect of attention to a certain frequency was only partially observed. In Experiment 4, a tone fusion judgment task was performed to examine whether the effect of spatial attention occurred in the initial stages of hearing. The result suggests that the effect occurred in the later stages of hearing.     

Social identification of toxic diets by Norway rats (Rattus norvegicus)

In the present experiment, a naive rat (an observer) interacted with two conspecifics (demonstrators) that had recently eaten a diet unfamiliar to the observer, ate two unfamiliar foods in succession, one of which was the food its demonstrators had eaten, suffered toxicosis, and finally, was offered a simultaneous choice between the two diets it had eaten prior to toxicosis induction. During the choice test, observers exhibited an aversion to that diet their respective demonstrators had not eaten. This result indicates that exposure of a rat to conspecifics that have eaten a diet can act, as does actual ingestion of a diet, to reduce that diet's subsequent associability with toxicosis. I discuss this finding as suggesting that interaction with conspecifics may provide an alternative to individual trial and error learning in identification of toxic foods by rats that ingest a number of novel foods in succession before becoming ill.     

Blocking between occasion setters and contextual stimuli

Two appetitive conditioning experiments with rats used a blocking procedure to compare the mechanisms through which contexts and positive occasion setters control responding to conditioned stimuli (CSs) in discrimination learning. In Experiment 1, a light (L) initially set the occasion for food reinforcement of a tone CS (T). Then a compound of L and a novel context signaled reinforcement of T. Previous learning about L blocked contextual control of responding to T. Blocking was not due to simple excitation conditioned to L during discrimination training; comparable excitation to L in a control group did not result in blocking. Conversely, in Experiment 2, initial learning about the context blocked the acquisition of occasion setting to L. Excitation conditioned to the context could not account for the blocking. In general, the results suggest that contexts and occasion setters may control responding to CSs through similar mechanisms.     

Hash browns for breakfast,baked potatoes for dinner: Changes in food attitudes as a function of motivation and context

Two studies investigated whether participants' motivational state and the context in which attitude reports are made influence food attitudes. Specifically, these studies examined whether hunger and the time‐typicality of foods (i.e. match or mismatch between the time when a food is typically eaten and the time the attitude is reported) interact to influence reported attitudes. Study 1 suggests that hunger leads to more positive attitudes toward foods that are typically eaten at the time the attitude report is made (e.g. breakfast foods in morning) compared to foods not typically eaten at the time the attitude report is made (e.g. breakfast foods in evening). Study 2 replicates this time‐typical effect of hunger and suggests that time‐typical experience rather than general experience with foods is important for hunger induced attitude change. By demonstrating that food attitudes are influenced by motivational states and the match between when the attitude is reported and when it is typically encountered, the present studies extend previous attitude theory and research that has identified other contextual factors that influence attitude reports. Copyright © 2004 John Wiley & Sons, Ltd.     

Food pleasantness affects visual selective attention

Fundamental to adaptive behaviour is the ability to select environmental objects that best satisfy current needs and preferences. Here we investigated whether temporary changes in food preference influence visual selective attention. To this end, we exploited the fact that when a food is eaten to satiety its motivational value and perceived pleasantness decrease relative to other foods not eaten in the meal, an effect termed sensory-specific satiety. A total of 26 hungry participants were fed until sated with one of two palatable foods. Before and after selective satiation, participants rated the pleasantness of the two foods and then viewed the same as stimuli on a computer screen while attention was assessed by a visual probe task. Results showed that the attentional bias for the food eaten decreased markedly from pre- to postsatiety, along with the subjective pleasantness for that food. By contrast, subjective pleasantness and attentional bias for the food not eaten did not show any such decrease. These findings suggest that the allocation of visual selective attention is flexibly and rapidly adjusted to reflect temporary shift in relative preference for different foods.     

Learning and transfer of calorie information

This study compared generating information about food to viewing and verbally producing that information for learning and transfer. Specifically, during training, a list of food items was shown, and some participants generated either real calories (Experiment 1) or fabricated prices (Experiment 2) associated with those foods with feedback provided (seeding), some viewed and read aloud values provided (viewing), and others read aloud the names of the items with no values provided (control). All participants were tested immediately and 1 week later on both old and new foods. In both experiments, the seeding and viewing conditions showed more learning than the control condition, and only the experimental conditions showed transfer of learning from old to new foods, with advantages found for seeding over viewing only in some cases. The results are discussed in terms of the seeding, testing, generation, and production effects, as well as their applications to health and policy.     

Social facilitation of eating novel food in tufted capuchin monkeys (Cebus apella): input provided by group members and responses affected in the observer

Learning about food palatability from watching what conspecifics eat might be one of the advantages of group living. A previous study investigated whether group members' presence or eating activity account for social facilitation of eating of foods never previously tasted. Capuchins encountered novel colored foods when (1) alone (Alone condition) or (2) with group members visible in the nearby cage (Group-present condition) or (3) with group members present and eating a familiar food that had not been colored (Group+food condition). Social facilitation of eating occurred when group members were eating, despite the difference in color between the familiar food eaten by them and the novel food presented to the experimental subject. To clarify what subjects learnt from group members when social facilitation occurred, we further analyze here the data from the previous study. The number of visual exposures to the colored novel food (as a group member) correlated with increased consumption of that novel food when encountered later (as experimental subject). In contrast, the number of times that an individual fed on the familiar food (as a group member) did not decrease its consumption of novel food (as experimental subject). Therefore, capuchins (1) habituated to the colors of the novel foods, and (2) did not take into account that seeing group members eating a food does not provide information about the palatability of a differently colored food. Since social facilitation of eating occurs when foods do not match in color, at least in capuchins, social facilitation of eating should not be considered as a way of learning about a safe diet, but rather as a way of overcoming neophobia. Accepted after revision: 18 August 2001 Electronic Publication     

The role of prior knowledge in explaining hypothetical events

Having subjects explain a hypothetical future event biases their subjective likelihood estimates for that event. However, Sherman, Zehner, Johnson, and Hirt (1983, Journal of Personality and Social Psychology, 44, 1127–1143) found that the biasing effects of an explanation task were reduced when subjects formed an initial impression based on the information (prior to the explanation task). Nonetheless, there are no doubt many factors that may influence subjects' ability to form strong initial impressions. The present studies address two of these factors. Experiment 1 used both subjects who were knowledgeable and unknowledgeable (naive) about a stimulus domain (football). Experiment 2 used only knowledgeable subjects, but gave these subjects information about unfamiliar teams and players. Subjects first read information about teams in an upcoming game and were then asked to explain a hypothetical victory by one team. They then made judgments about the actual future game and recalled the information. Only knowledgeable subjects given an initial impression set and given information that was easily integrated with past knowledge were able to resist the explanation bias. All other subjects demonstrated judgments that were strongly biased in the direction of the outcome explained. An examination of the relation between judgment and recall implied that knowledgeable and naive individuals differed in the ways they made judgments.