Mark A. Krause

Learning with arbitrary versus ecological conditioned stimuli: Evidence from sexual conditioning

Laboratory investigations of Pavlovian conditioning typically involve the association of an arbitrary conditioned stimulus (CS) with an unconditioned stimulus (US) that has no inherent relation to the CS. However, arbitrary CSs are unlikely to become conditioned outside the laboratory, because they do not occur often enough with the US to result in an association. Learning under natural circumstances is likely only if the CS has a preexisting relation to the US. Recent studies of sexual conditioning have shown that in contrast to an arbitrary CS, an ecologically relevant CS is resistant to blocking, extinction, and increases in the CS-US interval and results in sensitized responding and stronger secondorder conditioning. Although the mechanisms of these effects are not fully understood, these findings have shown that signature learning phenomena are significantly altered when the kinds of stimuli that are likely to become conditioned under natural circumstances are used. The implications of these findings for an ecological approach to the study of learning are discussed. An earlier version of this article was presented by M. Domjan as an invited address at the 2001 meetings of the Pavlovian Society of North America in New Brunswick, NJ. The preparation of the manuscript and the original research by the authors were supported by Grant MH 39940 from the National Institutes of Health.

Body size plasticity and local variation of relative head and body size sexual dimorphism in garter snakes ( Thamnophis sirtalis )

For snakes, prey size and sex are two possible determinants of head and body size. In garter snakes Thamnophis sirtalis , females are generally longer and have greater body weights than males, and also have larger relative head sizes, which may facilitate foraging success. The selective pressures that account for sexual size dimorphism in garter snakes have not been unequivocally demonstrated. In this study, the body (length and mass) and head (head length, head width, jaw length, inter-ocular distance) sizes of garter snakes inhabiting two nearby but ecologically dissimilar sites with different types of available prey were compared. Overall, the adult female snakes were larger and had greater relative head sizes than males. Males from the two sites did not differ significantly in body or head sizes. However, the mean body length and mass of females from a site where vertebrates are included in the diet were greater than that of females feeding almost exclusively on earthworms. There were also significant site differences in all four head measurements in females, although the direction of the difference varied by site. Diet-induced morphological plasticity is well documented and was evident in this study, although the relative roles of genotype, ontogeny, and competing selective forces in the expression of such plasticity can only be ascertained through future experimental studies.

NEONATAL PLASTICITY AND ADULT FORAGING BEHAVIOR IN GARTER SNAKES (THAMNOPHIS SIRTALIS) FROM TWO NEARBY, BUT ECOLOGICALLY DISSIMILAR, HABITATS

The widely distributed Common Gartersnake (Thamnophis sirtalis) thrives in a va- riety of environments and preys upon a diversity of species. Phenotypic plasticity (including learn- ing), as well as genetic diversity, may underlie the success of this species. We examined how different types of feeding experience influence the ontogeny of foraging behavior in garter snakes from two populations with different adult diets (earthworm or amphibian/worm/mammal diets) living on Bea- ver Island in Lake Michigan. Times to approach, capture, handle, and swallow prey were recorded in controlled laboratory settings. In Experiment I, neonatal snakes reared on fish, earthworms, or a mixed diet were tested for feeding skills at their first feeding, and at 5 subsequent intervals after feeding experience and diet-switching over a period of nearly 8 months. Snakes in all three groups decreased their latencies to consume prey after feeding experience and there were some litter, but no site or sex, differences. Snakes fed initially on worms were slow at consuming fish upon diet switching, whereas snakes that initially fed on fish rapidly consumed worms upon their first feeding. Feeding skills for initial prey were retained following the diet-switching phase. Experiment II de- termined the effects of long-term feeding experience on the abilities of field-caught adult snakes to detect, capture, and consume frogs, fish, and worms. Most foraging measures differed for all three prey, but there were few site differences and no sex differences. The effects of prior feeding ex- perience appear to be less evident for adults than for neonates, which may be due to the effects of changing predator-prey body size relationships, changes in prey availability, or to constraints of the captive testing environment. Although populations on the island eat different prey, there is little evidence for genetic differentiation in foraging behavior during the several thousand years that the island has existed.

Extinction of Conditioned Sexual Responses in Male Japanese Quail (Coturnix japonica): Role of Species-Typical Cues

The authors examined how a conditioned stimulus (CS) that included species-typical cues affected the acquisition and extinction of conditioned sexual responses in male quail (Coturnix japonica). Some subjects were conditioned with a CS that supported sexual responses and included a taxidermic head of a female quail. Others were conditioned with a similar CS that lacked species-typical cues. Pairing the CSs with access to live females increased CS-directed behavior, with the head CS eliciting significantly more responding than the no-head CS. Responding to the head CS persisted during the 42-day, 126-trial extinction phase; responses to the no-head CS extinguished. Responding declined when the cues were removed or the subjects were sexually satiated. Possible functions and mechanisms of these effects are discussed.

Cognitive and locomotor/exploratory behavior after chronic exercise in the olfactory bulbectomy animal model of depression

Despite the evidence that exercise improves cognitive behavior in animal models, little is known about these beneficial effects in animal models of pathology. We examined the effects of activity wheel (AW) running on contextual fear conditioning (CFC) and locomotor/exploratory behavior in the olfactory bulbectomy (OBX) model of depression, which is characterized by hyperactivity and changes in cognitive function. Twenty-four hours after the conditioning session of the CFC protocol, the animals were tested for the conditioned response in a conditioned and a novel context to test for the effects of both AW and OBX on CFC, but also the context specificity of the effect. OBX reduced overall AW running behavior throughout the experiment, but increased locomotor/exploratory behavior during CFC, thus demonstrating a context-dependent effect. OBX animals, however, displayed normal CFC behavior that was context-specific, indicating that aversively conditioned memory is preserved in this model. AW running increased freezing behavior during the testing session of the CFC protocol in the control animals but only in the conditioned context, supporting the hypothesis that AW running improves cognitive function in a context-specific manner that does not generalize to an animal model of pathology. Blood corticosterone levels were increased in all animals at the conclusion of the testing sessions, but levels were higher in AW compared to sedentary groups indicating an effect of exercise on neuroendocrine function. Given the differential results of AW running on behavior and neuroendocrine function after OBX, further exploration of the beneficial effects of exercise in animal models of neuropathology is warranted.

Research productivity in animal learning from 1953 to 2000

Searches conducted with Medline and PsycInfo showed that the number of publications dealing with learning in animals increased between 1975 and 2000 and that the increase was substantially greater in Medline than in PsycInfo. An examination of major journals dealing with behavioral studies of conditioning and learning for the years 1953, 1963, 1973, 1983, 1993, and 2000 revealed a different pattern of results. The number of papers published in these journals increased from 1953 to 1973 but has been declining steadily since then. However, this decline was partially offset by an increase in the number of experiments published in each paper. Substantially more experiments were published in 2000 than in 1963 or 1953. The number of core authors in the field also peaked in 1973 and has been declining since. However, there were only seven fewer core authors in 2000 than in 1983, and 1983 had as many core authors as 1963. These data suggest that pessimism about the status of behavioral studies of learning is not warranted if research activity is considered over a 40-year period. Furthermore, increased interest in the neural and biological mechanisms of learning should bode well for the status of behavioral research, because one cannot examine the physiological mechanisms of a behavioral process without first clearly understanding the phenomenon at the behavioral level.

Animal pointing: Changing trends and findings from 30 years of research.

The past 30 years have witnessed a continued and growing interest in the production and comprehension of manual pointing gestures in nonhuman animals. Captive primates with diverse rearing histories have shown evidence of both pointing production and comprehension, though there certainly are individual and species differences, as well as substantive critiques of how to interpret pointing or “pointing-like” gestures in animals. Early literature primarily addressed basic questions about whether captive apes point, understand pointing, and use the gesture in a way that communicates intent (declarative) rather than motivational states (imperative). Interest in these questions continues, but more recently there has been a dramatic increase in the number of articles examining pointing in a diverse array of species, with an especially large literature on canids. This proliferation of research on pointing and the diversification of species studied has brought new and exciting questions about the evolution of social cognition, and the effects of rearing history and domestication on pointing production and, more prolifically, comprehension. A review of this work is in order. In this article, we examine trends in the literature on pointing in nonhumans. Specifically, we examine publication frequencies of different study species from 1987 to 2016. We also review data on the form and function of pointing, and evidence either supporting or refuting the conclusion that various nonhuman species comprehend the meaning of pointing gestures.

Generality of the Laws of Learning: From Biological Constraints to Ecological Perspectives

Investigators of conditioning phenomena at the behavioral level have always sought to identify general principles or processes. That effort has been challenged by instances of learning that are specific to the responses, stimuli, and reinforcers involved in a particular instrumental or Pavlovian conditioning situation. This chapter reviews the theoretical and empirical efforts that have been pursued to integrate specialized conditioning effects into a general theory, and then illustrates how evidence from naturalistic learning paradigms offers a more ecologically and evolutionarily relevant basis for identifying adaptive specializations of learning and the developing general theories of learning.

There is more to biological behavior than causation and control

Biorobots may model the causation of relatively simple behaviors, but many animal behaviorists are concerned with complex cognitive traits and their evolution. Biorobotics seems limited in its ability to model cognition and to provide evolutionary explanations. Also, if robots could model complex traits, such as theory of mind, underdetermination could be problematic. Underdetermination is also a challenge for comparative psychologists.