No description available.

Issued also as thesis - Univ. of Chicago. / Also available on the Internet.

No description available.

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No description available.

Five experiments with rats were conducted to determine the extent to which associative processes could be used to explain how rats seem able to learn complex CS-US contingencies during Pavlovian conditioning. Rats were exposed to positive, zero and negative CS-US contingencies and conditioned behaviour was compared with predictions derived from both associative models of conditioning and nonassociative normative theories of causal reasoning. A common measure of contingency, Deltap, when used to analyze Pavlovian conditioning requires defining the likelihood of the US in the presence and absence of the CS. Experiments 1 and 2 involved a novel preparation in which, in addition to standard CS presence trials, the absence of the CS was signalled by a second CS, called the trial marker (a lever). Rats were trained to learn relationships in which the CS was either a positive predictor of the US or in which it was unrelated to the US. More conditioned tray entries were observed when the CS signalled an increased likelihood of the US (positive contingency). Consistent with the associative explanations, the trial marker elicited conditioned lever pressing when the CS signalled no change in the likelihood of the US (zero contingency). Experiments 3, 4 and 5 extended the analysis with multiple CSs. These experiments examined whether learning about one CS was determined by its contingency relative to the contingency of other concurrently trained CSs. In experiments 3 and 4 conditioned responding to a moderately predictive CS was determined by its contingency relative to a perfectly predictive CS. Experiment 5 extended this effect to a case in which conditioning was influenced by the presence of a perfect predictor of the absence of the US. Together these results support the hypothesis that relative contingencies determine the strength of conditioned responding. The results are discussed from the perspective of both associative and nonassociative theory.

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The mamalian visual system contains a limited number of receptors, which project to a limited number of cells in the visual cortex. This projection provides a point-to-point representation of the retinal stimulation onto the visual cortex. Data reported by Marshall and Talbot (1942) suggest that contours in the environment are represented on the visual cortex by a process involving the summation of neural activity around the area receiving the retinal projection. Such anatomical and physiological evidence suggests a simple mechanism by which forms are perceived; the perception of form should correspond to retinal stimulation by form. [...]

The role of sex in the organization of movement is not commonly addressed in the literature. The objective of this thesis was to determine whether differences exist between males and females in the way they organize their movements during dodging to protect a food item. Detailed kinematic analysis of these movements in adult rats shows that females move their snout through a greater spatial curvature, relative to the pelvis, than males. The sex of the robbing animal did not alter the sex-typical movement paterns exhibited. Manipulation of neonatal androgens altered the sex-typical dodge patterns of both males and females. Removal of androgens at weaning however, did not affect the male-typical pattern. The existence of sex differences in the organization of movement provides a new level of analysis for the study of sexual dimorphism in behavior. / x, 228 leaves : ill. ; 28 cm.

Playing with Play: Movement and experience in the development of play fighting in rats. Juvenile rats are more gentle in the way they play fight than are adult rats. I used Laban Movement Analysis (LMA), a form of movement notation used in the theatre arts, to identify and characterize the movements that underlie this age-related difference in 'roughness'. To standardize the behavioural context for comparison, the rats were compared when in the 'pinning' configuration. During a 'pin', the attacker stands over the supine defender. In the first experiment, male and female rats, from the juvenile phase to early adulthood were videotaped and analyzed using LMA. The results show that with age, rats become more 'forceful' in the way they move. In part, this change in 'forcefulness' seems to be related to the degree of control an individual exercises, over its own body, and that of its partner. I have identified a reliable and objective behavioural makre for such 'control'. This marker, which I call anchoring, can be scored without prior knowledge of LMA. When anchored, the attacker stand with its hind feet on the ground and its fore feet on the supine defender, whereas when unanchored, the attacker stands on the defender with all four feet. With increasing age, the proportion of occasions with the attacker being anchored increases. One possibility is that younger rats are motorically less competent to gain and maintain an anchored posture. Therefore, in a second experiment, playful pins were anlayzed from around the time of weaning, when play fighting first begins, and onwards. The infant rats were just as able to anchor during pins as were postpubertal rats, and so motoric immaturity cannot account for the reduced levels of anchoring in juveniles. Additional experiments were conducted in an attempt understand what modulates this development modulation in anchoring. Thus, in the third main experiment of this study, rats were reared in isoloation from weaning and tested socially once at 30, 60 and 90 days. The results show that the age-related changes in anchoring is not dependent on social experience. Finally, in the fourth experiment, the cortex was removed in neonatal rats, and their play was examined from the juvenile period onwards. Anchoring in decorticates does not show the developmental modulation present in intact rats, rather, anchoring remains at the juvenile typical level at all ages. These data include that the developmental changes in anchoring are regulated by cortical mechanisms. The findings from this thesis suggest that juveniles have an age-modulated change in how strongly the rats control their own movements and those of their partners during play fighting. That is, juveniles exhibit reduced control just when they are the most playful. This reduced control may increase the range and variability of experiences gained during play fighting, and so may have evolved to maximize the benefits to be gained by engaging in play at the juvenile phase of the life cycle. / xiii, 130 leaves ; 28 cm.