The dynamics of experimentally induced criterion shifts

Investigations of decision making have typically assumed stationarity, even though commonly observed "context effects" are dynamic by definition. Mirror effects are an important class of context effects that can be explained by changes in participants' decision criteria. When easy and difficult conditions are blocked alternately and a mirror effect is observed, participants must repeatedly change their decision criteria. The authors investigated the time course of these criterion changes and observed the buildup of mirror effects on a trial-by-trial basis. The data are consistent with slow, systematic changes in decision criteria that lag behind stimulus changes. The length of this lag is considerable: analysis of a simple dynamic signal-detection model suggests participants take an average of around 14 trials to adjust to new decision environments. This trial-level measurement of experimentally induced changes has implications for traditional blockwise analyses of data and for models of decision making.     

The effect of feedback on luminance thresholds for peripherally presented stimuli

The effect of a central task on peripheral vision was determined by obtaining absolute luminance thresholds for peripherally presented stimuli. A competing central task was provided by interrupting the fixation light and requiring the S to reilluminate it. Data were obtained over five sessions, with feedback information provided on each trial. Thresholds were highest for the initial session and declined as a function of practice. The magnitude of the change depended upon the interruption rate. When central and peripheral stimuli compete for attention, priority is given initially to the central task, but, with practice, the differences are reduced.     

The effect of hunger on water intake in rats

Although reciprocal inhibition between eating and drinking has been postulated, the commonly observed reduction of water intake by hungry rats may not be due to any direct inhibitory mechanism. In one experiment rats deprived of food for 24 hr. and then injected with 2 ml. of NaCl drank the same as rats that had received food ad lib. In the second experiment a stomach load of 10 ml. of water 3 hr. before the salt injection was designed to abolish any water deficit that might have occurred during food deprivation had there been inhibition of drinking by hunger. Here again rats deprived of food did not drink less than undeprived animals. In fact the hungry rats drank slightly but significantly more. This phenomenon may be related to the observation confirmed here that during food deprivation rats excrete about twice as much rather dilute urine as during ad lib food intake. This seems to indicate that though in general food deprived rats drink less than normal they actually drink more than they need. Schedule induced polydipsia also occurs during food deprivation and this too makes it unlikely that water-intake is actually inhibited during hunger.     

The effect of inpatient cognitive-behavioral therapy for eating disorders on temperament and character

Personality traits seem to have an important role in the development, clinical expression, course, and treatment response in eating disorders (EDs). We investigated the effects of an inpatient cognitive-behavioral treatment (CBT) on the measures of temperament and character (Temperament and Character Inventory (TCI)) in 149 consecutive patients with EDs. Baseline assessment included anthropometry, the Eating Disorder Examination (EDE), the Beck Depression Inventory (BDI), and the TCI. Treatment was based on the transdiagnostic cognitive behavior theory and treatment of ED, adapted for an inpatient setting. Treatment effects were tested by paired ANOVA, adjusted for covariates. No effects were found on Novelty Seeking, Reward Dependence, and Cooperativeness. Harm Avoidance (F=18.17, p<0.001), Persistence (F=7.71, p=0.006), Self-Directedness (F=27.55, p<0.001), and Self Transcendence (F=16.38, p<0.001) significantly changed after treatment. Changes in TCI scores were wholly dependent on the changes in BDI and EDE, and independent of ED diagnosis and behavior and of BMI changes. We conclude that in ED, a few scales of both temperament and character are significantly modified by CBT, in relation to changes in psychopathology and depression, independently of nutrition. These results are relevant for future studies based on TCI.     

The effect of perceived distance on induced movement

The magnitude of induced movement was measured as a function of the perceived depth between the test object and the plane of the induction object, with this perceived depth produced by stereoscopic cues. Three experiments were conducted. In each experiment, the induction object (a frame of constant physical size) was positioned at one of three distances with the test object (a point of light) placed successively at each of the three distances. Predictions of the magnitude of induction as a function of the depth separation of the test and induction object were made from the subject-relative and object-relative hypotheses of induced motion. It was expected, however, that neither of these hypotheses would predict the results independently of a factor described in the adjacency principle. This principle states that the effectiveness of whatever cues or processes determine the induced movement will decrease with increased depth between the test and induction object. The data indicate that the adjacency principle must be considered in explaining the results. The subject-relative rather than object-relative hypothesis as modified by the adjacency principle was most successful in predicting the results. Control conditions in which the frame was stationary and the point of light was physically moving were also used. Despite the fact that the relative displacement of the objects on the eye in the experimental and control conditions were the same, the results indicate that O could distinguish between these two kinds of conditions. Although the apparent movement was greater in the control conditions than in the experimental conditions, the reverse is true if the total perceived movement of the test and induction object are considered together.     

The effect of social cues on the eating behavior of obese and normal subjects1

Schachter's externality hypothesis suggests that overweight individuals are more likely to be induced to eat by salient external cues than normal weight individuals. While a range of studies have demonstrated the plausibility of this hypothesis in the case of sensory stimuli (e.g., taste cues), there is little evidence that the hypothesis applies to social stimuli. The current study examines this latter proposition by exposing male and female, overweight and normal weight subjects to a same-sex or opposite-sex peer model. Under the guise of engaging in a taste experiment, the subjects were either exposed to a model who tasted experiment, the subjects were either exposed to a model who tasted no crackers (no eat), one cracker (low eat), or twenty crackers (high eat). In addition, control model-absent conditions were also run for purposes of establishing baseline eating rates. If the externality hypotheses were to prevail in social domains, one would expect overweight subjects to be more prone to model the cracker-eating behavior of the peer than normal weight individuals. However, the findings indicate that all subject groups regardless of weight evidence a rather clear modeling effect and all subjects evidence social inhibition effects on their eating behavior as well. Several intriguing interactions among subject sex, model sex, subject weight, and social condition were also found. The discussion explores the relevance of an externality model of overweight eating in social domains, and focuses upon the interesting and somewhat distinct pattern of socially mediated eating exhibited by overweight females.     

The saliva priming effect,eating speed and the measurement of hunger

Volunteers were tested under two conditions, either just before or just after a meal. The aim of the investigation was to identify subjective, behavioural and physiological correlates of hunger. Subjective measures of hunger and expected enjoyment as well as speed of eating clearly differentiated the two conditions. Although the basal level of salivation did not change significantly, there was a clear differential priming effect after consuming a small amount of chocolate. The saliva priming effect was greater when subjects were hungry. Correlations between change scores suggest that two partially independent systems are activated by food deprivation which could be labelled ‘hunger-salivation’ and ‘enjoyment-speed of eating’.     

Testing two classes of theories about group induced shifts in individual choice

One class of theories explains group induced shifts in individual choice in terms of interpersonal comparison process. By comparing himself with others a member finds out that his position is uncomfortably discrepant, e.g., he is overly cautious or overly risky. Knowledge of this discrepancy presumably is necessary and sufficient to induce him to change his initial choice. Another class of theories holds that merely knowing one is different from others is unimportant. Shifts in choice occur because during discussion a member is exposed to persuasive arguments which prior to discussion were not available to him. Two experiments were conducted, the results of which give considerable support to persuasive-argument theories and none to those based on interpersonal comparison: When a member did not know whether others were arguing for their own position or were forced to support a position contrary to the one they had originally chosen, and the former in fact was the case, typical shifts in choice were obtained. However, if a member had to argue for a position contrary to the one he had initially chosen (and thus he would not be able to muster highly persuasive arguments) typical shifts did not occur, even though another's initial choice could be accurately inferred.     

The effect of meaning on the allocation of visually induced movement

The directional characteristics of a meaningful target were found to affect its apparent motion when it was displaced relative to a neutral object. The effect was destroyed, however, when the target was surrounded by a frame. This was because the frame imparted a meaning which tended to override that conveyed by the target.     

The effect of adults' eating on young children's acceptance of unfamiliar foods

Adults presented unfamiliar foods to 14- to 20- and 42- to 48-month-old children individually in their homes. More children put the food in their mouths when the adults also were eating than when the adults simply were offering the food. More children put food in their mouths when their mothers were the source than when the source was a friendly adult “visitor”. However, even when alone with a child, the visitor's eating elicited reliably more tasting. Analysis of requesting behavior indicated that the adults' eating aroused a desire to eat in the children. There were no consistent sex differences or interactions between sex of visitor and sex of child in children's food acceptance. There was a suggestion that younger children were more affected by repeated offerings than were older children. It is concluded that a relatively “low level” form of observational learning—“social facilitation”—can account for the data.     

The effect of food and water deprivation and satiation on recognition

Food and water deprived and satiated subjects, as well as control subjects, were shown words presented tachistoscopically for .01 sec until word recognition. Five food-relevant, five water-relevant, and five neutral (animal) words of high string frequency were matched for letter confusability and letter predictability. Analyses of the data, in terms of number of presentations until recognition as well as number of words recognized at selected presentations, revealed that the amount but not the type of deprivation significantly altered word recognition. Moreover, the effect of motivation was significant already on the first slide presentation, while the effects of word characteristics (word category and generated value) occurred only after a number of presentations.