Pigeons' discrimination of Michotte's launching effect

We trained four pigeons to discriminate a Michotte launching animation from three other animations using a go/no-go task. The pigeons received food for pecking at one of the animations, but not for pecking at the others. The four animations featured two types of interactions among objects: causal (direct launching) and noncausal (delayed, distal, and distal & delayed). Two pigeons were reinforced for pecking at the causal interaction, but not at the noncausal interactions; two other pigeons were reinforced for pecking at the distal & delayed interaction, but not at the other interactions. Both discriminations proved difficult for the pigeons to master; later tests suggested that the pigeons often learned the discriminations by attending to subtle stimulus properties other than the intended ones.     

The pigeon's discrimination of visual entropy: a logarithmic function

We taught 8 pigeons to discriminate 16-icon arrays that differed in their visual variability or "entropy" to see whether the relationship between entropy and discriminative behavior is linear (in which equivalent differences in entropy should produce equivalent changes in behavior) or logarithmic (in which higher entropy values should be less discriminable from one another than lower entropy values). Pigeons received a go/no-go task in which the lower entropy arrays were reinforced for one group and the higher entropy arrays were reinforced for a second group. The superior discrimination of the second group was predicted by a theoretical analysis in which excitatory and inhibitory stimulus generalization gradients fall along a logarithmic, but not a linear scale. Reanalysis of previously published data also yielded results consistent with a logarithmic relationship between entropy and discriminative behavior.     

Stimulus control by same-versus-different relations among multiple visual stimuli

The authors devised a go/no-go discrimination learning task that allowed but did not require pigeons to report (a) from which of 2 different sets a collection of visual items was drawn and (b) the relations between or among the items as being the same as or different from one another. The results of 2 experiments using this task disclosed stimulus control by the particular items in the arrays and by the same-different relations exemplified by those items. Relational and item control depended on how many items were in the arrays. Same-different discrimination was evident with 2-item displays, but it was much stronger with 6 or more items. These findings help to define the substrates of advanced conceptual behavior.     

Applying bubbles to localize features that control pigeons' visual discrimination behavior

The authors trained pigeons to discriminate images of human faces that displayed: (a) a happy or a neutral expression or (b) a man or a woman. After training the pigeons, the authors used a new procedure called Bubbles to pinpoint the features of the faces that were used to make these discriminations. Bubbles revealed that the features used to discriminate happy from neutral faces were different from those used to discriminate male from female faces. Furthermore, the features that pigeons used to make each of these discriminations overlapped those used by human observers in a companion study (F. Gosselin & P.G. Schyns, 2001). These results show that the Bubbles technique can be effectively applied to nonhuman animals to isolate the functional features of complex visual stimuli.     

Superordinate categorization via learned stimulus equivalence: quantity of reinforcement, hedonic value, and the nature of the mediator

Three experiments examined superordinate categorization via stimulus equivalence training in pigeons. Experiment 1 established superordinate categories by association with a common number of food pellet reinforcers, plus it established generalization to novel photographic stimuli. Experiment 2 documented generalization of choice responding from stimuli signaling different numbers of food pellets to stimuli signaling different delays to food reinforcement. Experiment 3 indicated that different numbers of food pellets did not substitute as discriminative stimuli for the photographic stimuli with which the food pellets had been paired. The collective results suggest that the effective mediator of superordinate categories that are established via learned stimulus equivalence is not likely to be an accurate representation of the reinforcer, neither is it likely to be a distinctive response that is made to the discriminative stimulus. Motivational or emotional mediation is a more likely account.     

Entropy and variability discrimination

Two experiments examined college students' discrimination of complex visual displays that involved different degrees of variability or "entropy." Displays depicted 16 black and white line drawings of various types (e.g., a brain, a clock, a hand); the participants were required to classify a display in terms of its variability (e.g., a low-variability display contains many identical items, whereas a high-variability display contains few identical items). The participants' accuracy and reaction time scores on a 2-alternative forced-choice discrimination disclosed that people can and do use entropy to classify different levels of visual display variability. Individuals differed in their use of absolute rather than relative entropy.     

Pigeons learn stimulus identity and stimulus relations when both serve as redundant,relevant cues during same-different discrimination training

The authors taught pigeons to discriminate displays of 16 identical items from displays of 16 nonidentical items. Unlike most same-different discrimination studies--where only stimulus relations could serve a discriminative function--both the identity of the items and the relations among the items were discriminative features of the displays. The pigeons learned about both stimulus identity and stimulus relations when these 2 sources of information served as redundant, relevant cues. In tests of associative competition, identity cues exerted greater stimulus control than relational cues. These results suggest that the pigeon can respond to both specific stimuli and general relations in the environment.     

Body image and dieting failure in college men and women: Examining links between depression and eating problems

The noted co-occurrence between depression and eating problems in women may be due to their common association with negative body image. Specifically, the western cultural ideal that equates feminine beauty with thinness leads a large number of women to be dissatisfied with their bodies. A recent model [M. McCarthy (1990) The Thin Ideal, Depression, and Eating Disorders in Women, Behavioral Research and Therapy, Vol. 28, pp. 205–215] suggests that this dissatisfaction, coupled with high importance placed on appearance, leads most women to engage in dieting to obtain this level of thinness. As dieting is typically unsuccessful as a means of long-term weight control, depression will result from the sense of failure and helplessness associated with dieting failure. This depression then leads to increasingly maladaptive eating behaviors that serve to assuage negative affect and regain control over body appearance. In a sample of 234 male and female, predominantly white, 17–22-year-old college students, we examined several components of this model, including the specificity of these relations for women. In accordance with the model, depressive symptoms and eating problems were predicted to be an interactive function of body image and body image importance, with negative body image/high importance subjects showing the greatest disturbance. In addition, we examined several components of the model to determine (a) the relation between failed dieting and depression, and (b) the extent to which depression could account for eating problems. Regardless of gender, eating problems were indeed highest among those with both negative body image and high body image importance. Depression, however, was higher in subjects with negative body image, regardless of body image importance. For both men and women, failed dieting was significantly related to depression, but only for women did depression account for significant variability in eating problems. Validity of the model is considered. Gender differences in the nature of these relations, and the need to consider possible alternative effects of the cultural standard for masculine attractiveness, are discussed.This research is based in part on an undergraduate honor's thesis submitted by the second author to the Emory University Department of Psychology under the direction of the first author. Funding was provided by a grant from Emory University to the first author. The authors would like to thank Robyn Fivush, Steven Nowicki, Irwin Waldman, Carol Worthman, and two anonymous reviewers for helpful comments on earlier drafts.