Effects of spatial rearrangement of object components on picture recognition in pigeons.

Five pigeons were first trained to discriminate among line drawings of four objects: a watering can, an iron, a desk lamp, and a sailboat. The birds were then tested with eight versions of each object, in which the object's components were vertically and horizontally rearranged. The pigeons displayed different degrees of generalization decrement to the different scrambled versions of the objects. Two analyses helped to clarify the nature of the varied accuracy scores. First, cluster analyses disclosed subsets of components that were related to test performance. Second, although the clusters varied somewhat across birds for a given object, there was reliable concordance among the subjects in their rankings of the individual scramblings, suggesting that the pigeons may have attended to common aspects of the drawings.     

Discrimination of contour-deleted images by pigeons.

Three experiments attempted to determine which properties of pictorial representations of objects control their discrimination by pigeons. A particular focus was whether the representation mediating such discriminations could be described by the simple viewpoint-invariant primitive volumes of Biederman's (1987) recognition-by-components theory of object recognition or by Cerella's (1990) particulate features. In all 3 experiments, pigeons were first trained to discriminate drawings of 4 stimulus objects with half of the contour deleted but with the component geons postulated by Biederman's theory recoverable. Discrimination accuracy was then compared for test items containing the original particulate features, affording the retrieval of the original component geons, or having neither of these properties of the training stimuli. Although response accuracy was significantly greater when the component geons of the original objects were retrievable, measurable control over recognition by the particulate features of the objects and by their specific locations was also found. The results are consistent with the idea of component geon recognition as one of the important factors in object discrimination.     

Contributions of specific cell information to judgments of interevent contingency

College students considered the possible effect of an experimental drug on a skin rash. The information came from a 2 x 2 contingency table involving receipt or nonreceipt of the drug and improvement or nonimprovement of the rash: Cell A = receipt-improvement; Cell B = receipt-nonimprovement; Cell C = nonreceipt-improvement; Cell D = nonreceipt-nonimprovement. Without numerical information. Ss judged cells to be ordered A greater than B greater than C greater than D. The same order held when the contribution of each cell was derived from the contingency judgments of other subjects given numerical information. No such consistency was seen when one group of Ss made both judgments: whether individual Ss equally or unequally assessed the importance of the four cells, their contingency estimates showed cell use to be ordered A greater than B greater than C greater than D. These findings may result from strong biases that Ss harbor in processing contingency information.     

Secondary generalization and categorization in pigeons

In Experiment 1, one group of pigeons learned to classify a set of stimuli into the human language classes cat, flower, car, and chair (categorization); another group learned to classify the same set into arbitrary classes (pseudocategorization). Then, both groups were trained on a new categorization task and their performance compared to that of a control group that had no initial classification training. Hull's (1943) notion of secondary generalization (generalization that is not based on physical similarity but on mediating associations) predicts that categorization experience will facilitate the learning of a new categorization task, whereas pseudocategorization experience will impair it. However, in Experiment 1, performance on the new categorization task was not differently affected by prior experience. In Experiment 2, pigeons initially trained to classify a set of 48 stimuli (original training) were later trained to classify a subset of four of these stimuli using new responses (reassignment training). Then, they were tested on the 44 remaining stimuli. Performance better accorded with original than with reassignment training, indicating that categorization training did not lead to the formation of equivalence classes of stimuli, in which the equivalence relationship is mediated by secondary generalization. The lack of evidence of secondary generalization implies that our pigeons failed to meet Lea's (1984) criterion for conceptual behavior.     

Statistical analysis of binary relational data: Parameter estimation

Binary interaction data, measuring the presence or absence of a relation between pairs of actors in a “dyadic interaction situation,” are commonly gathered to study the social structure of the group of actors. Recent developments have made the statistical analysis of such data statistically easier and more substantively sophisticated. These developments allow researchers to simultaneously study several sociometric structural properties, such as reciprocity, differential popularity, and equivalence of actors. Building on this research, we review the stochastic models responsible for this breakthrough, and discuss methods for estimating expected values and model parameters. Throughout, we also highlight recent advances designed to incorporate nodal or actor attribute data into the relational data analysis. We conclude with an example illustrating these ideas based on conversational activities among actors in a group of eight people.     

Infant sex differences: Ecological effects

Mothers and their firstborn. year-old infants (30 girls, 30 boys) were observed during two counterbalanced situations. In the nonavailability situation, mothers were not to initiate interaction; during free play, mothers were free to interact. As in previous studies, sex differences in infant touching and proximity seeking appeared, dependent here upon the level of interaction, with girls higher on both measures. Boys and girls did not differ during free play. Sex differences in maternal behavior were rare in either situation. Moreover, the pattern of associations between maternal and infant behavior changed as the level of interaction changed. Maternal availability, manipulated by experimental instructions, should be considered as a factor in interpreting investigations of early sex differences.     

Same-different categorization in rats

Same-different categorization is a fundamental feat of human cognition. Although birds and nonhuman primates readily learn same-different discriminations and successfully transfer them to novel stimuli, no such demonstration exists for rats. Using a spatial discrimination learning task, we show that rats can both learn to discriminate arrays of visual stimuli containing all same from all different items and transfer this discrimination to arrays composed of novel visual items. These results are consistent with rats' engaging in same-different categorization. As such, they pave the way for investigations into the perceptual, cognitive, and neurobiological substrates of abstract categorization behavior.     

Visual object categorization in birds and primates: Integrating behavioral,neurobiological, and computational evidence within a “general process” framework

Previous comparative work has suggested that the mechanisms of object categorization differ importantly for birds and primates. However, behavioral and neurobiological differences do not preclude the possibility that at least some of those mechanisms are shared across these evolutionarily distant groups. The present study integrates behavioral, neurobiological, and computational evidence concerning the “general processes” that are involved in object recognition in vertebrates. We start by reviewing work implicating error-driven learning in object categorization by birds and primates, and also consider neurobiological evidence suggesting that the basal ganglia might implement this process. We then turn to work with a computational model showing that principles of visual processing discovered in the primate brain can account for key behavioral findings in object recognition by pigeons, including cases in which pigeons’ behavior differs from that of people. These results provide a proof of concept that the basic principles of visual shape processing are similar across distantly related vertebrate species, thereby offering important insights into the evolution of visual cognition.     

Later language development in narratives in children with perinatal stroke

Studies of young children with unilateral perinatal stroke (PS) have confirmed the plasticity of the developing brain for acquiring language. While recent studies of typically developing children have demonstrated the significant development of language well into adolescence, we know little regarding the course of language development in the PS group as they mature. Will children with PS continue to show the same remarkable plasticity that they exhibited at younger ages? In the present paper we investigate later language and discourse in children with perinatal stroke (ages 7–16) using spoken personal narrative as the discourse context. In contrast to the findings of the discourse studies of younger children with PS, children with left hemisphere lesions made more morphological errors, used less complex syntax and fewer syntactic types than controls; they also produced more impoverished story settings. In contrast, those with right hemisphere lesions performed comparably to controls, except in their impoverished use of complex syntax. The findings provide insight into the nature of later spoken language development in these children, revealing both the nature and extent of neuroplasticity for language as well as potential regional biases.