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PubMed2002

Learning to vary and varying to learn.

We compared two sources of behavior variability: decreased levels of reinforcement and reinforcement contingent on variability itself. In Experiment 1, four groups of rats were reinforced for different levels of response-sequence variability: one group was reinforced for low variability, two groups were reinforced for intermediate levels, and one group was reinforced for very high variability. All of the groups experienced three different reinforcement frequencies for meeting their respective variability contingencies. Results showed that reinforcement contingencies controlled response variability more than did reinforcement frequencies. Experiment 2 showed that only those animals concurrently reinforced for high variability acquired a difficult-to-learn sequence; animals reinforced for low variability learned little or not at all. Variability was therefore controlled mainly by reinforcement contingencies, and learning increased as a function of levels of baseline variability. Knowledge of these relationships may be helpful to those who attempt to condition operant responses.

Animals↗
PubMed2005

Implicit operant learning of pain sensitization.

Operant conditioning mechanisms have been demonstrated to be important in the development of chronic pain behavior, but it is not clear whether and how this extends to pain perception itself. The fear-avoidance theory suggests that hypersensitivity may be induced by anticipatory pain avoidance learned through negative reinforcement by acute reductions of pain and fear. But the precise mechanism of the assumed 'sensory decalibration' has not been specified. The present study with healthy subjects investigated whether operant learning of enhanced short-term sensitization may provide the 'proximal' mechanism and whether gradual learning of hypersensitivity can take place without subjects' awareness. We used an experimental model of implicit learning based on a behavioral adjustment method of sensitization measurement developed and validated previously, combining it with standard methods of operant response shaping of increased sensitization or habituation. Results indicated that operant discrimination training with reinforcement of short-term sensitization in the seconds range can produce gross up or down changes in sensitivity within an hour without subjects' awareness of reinforcement contingencies. Consequently, implicit learning of enhanced pain sensitization may be a suitable model to investigate operant plasticity of pain perception in addition to basic sensory and neuronal mechanisms and to link these with the clinical construct of pain-fear avoidance.

Adaptation, Physiological↗
PubMed1994

Social learning in animals: categories and mechanisms.

There has been relatively little research on the psychological mechanisms of social learning. This may be due, in part, to the practice of distinguishing categories of social learning in relation to ill-defined mechanisms (Davis, 1973; Galef, 1988). This practice both makes it difficult to identify empirically examples of different types of social learning, and gives the false impression that the mechanisms responsible for social learning are clearly understood. It has been proposed that social learning phenomena be subsumed within the categorization scheme currently used by investigators of asocial learning. This scheme distinguishes categories of learning according to observable conditions, namely, the type of experience that gives rise to a change in an animal (single stimulus vs. stimulus-stimulus relationship vs. response-reinforcer relationship), and the type of behaviour in which this change is detected (response evocation vs. learnability) (Rescorla, 1988). Specifically, three alignments have been proposed: (i) stimulus enhancement with single stimulus learning, (ii) observational conditioning with stimulus-stimulus learning, or Pavlovian conditioning, and (iii) observational learning with response-reinforcer learning, or instrumental conditioning. If, as the proposed alignments suggest, the conditions of social and asocial learning are the same, there is some reason to believe that the mechanisms underlying the two sets of phenomena are also the same. This is so if one makes the relatively uncontroversial assumption that phenomena which occur under similar conditions tend to be controlled by similar mechanisms. However, the proposed alignments are intended to be a set of hypotheses, rather than conclusions, about the mechanisms of social learning; as a basis for further research in which animal learning theory is applied to social learning. A concerted attempt to apply animal learning theory to social learning, to find out whether the same mechanisms are responsible for social and asocial learning, could lead both to refinements of the general theory, and to a better understanding of the mechanisms of social learning. There are precedents for these positive developments in research applying animal learning theory to food aversion learning (e.g. Domjan, 1983; Rozin & Schull, 1988) and imprinting (e.g. Bolhuis, de Vox & Kruit, 1990; Hollis, ten Cate & Bateson, 1991). Like social learning, these phenomena almost certainly play distinctive roles in the antogeny of adaptive behaviour, and they are customarily regarded as 'special kinds' of learning (Shettleworth, 1993).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Drinking saccharin increases food intake and preference--III. Sensory and associative factors.

Rats that drink saccharin solution increase their short-term food intake and develop a preference for flavored food eaten when saccharin is ingested. Here we describe experiments that examined whether these changes in feeding behavior were due to learning and/or the reinforcing sensory properties of saccharin solution. It was found that learning was unnecessary for the feeding response, as rats that drank saccharin increased food intake whether or not their food contained saccharin-contingent flavor cues. However, learning helped support and maintain the response, as rats repeatedly given flavored food together with saccharin to drink later increased intake when given the flavored food without saccharin (i.e. in extinction). The rewarding or hedonic effects of the immediate orosensory properties of saccharin were not responsible for its effects on feeding, as drinking saccharin before but not after eating flavored food increased food intake and food preference. Furthermore, hungry rats developed an aversion to flavored food paired with saccharin ingestion when the quantity of food was limited. This implies that the flavored food preference produced by drinking saccharin involves an association between sensory aspects of the food and the metabolic consequences of food ingestion, which interact with a postingestive action of drinking saccharin that is related to the rat's metabolic state.

Animals↗
PubMed1982

The relative importance of reinforced versus nonreinforced stimuli in visual discrimination learning by redwinged blackbirds (Agelaius phoeniceus).

Redwinged blackbirds were trained to locate and peck apple slices in two discrimination problems with four times more training on one problem than on the other. The birds were then given transfer tests with the stimuli re-paired. Nonreinforced (S-) stimuli exerted greater control over behavior than did reinforced (S+) stimuli. We inferred that the blackbirds learned more about what to avoid than what to approach when searching for food in the two-choice situation. That inference is contrary to the notion that, by being alert to the visual cues which signal foods (i.e., S+ stimuli), birds can more successfully cope with irrelevant visual information encountered during foraging. Rather, being alert to cues which signal the absence of food (i.e., S- stimuli) may be relatively more important.

Animals↗
PubMed2004

Acquisition and performance of delayed-response tasks: a neural network model.

We study the time evolution of a neural network model as it learns the three stages of a visual delayed-matching-to-sample (DMS) task: identification of the sample, retention during delay, and matching of sample and target, ignoring distractors. We introduce a neurobiologically plausible, uncommitted architecture, comprising an "executive" subnetwork gating connections to and from a "working" layer. The network learns DMS by reinforcement: reward-dependent synaptic plasticity generates task-dependent behaviour. During learning, working layer cells exhibit stimulus specialization and increased tuning of their firing. The emergence of top-down activity is observed, reproducing aspects of prefrontal cortex control on activity in the visual areas of inferior temporal cortex. We observe a lability of neural systems during learning, with a tendency to encode spurious associations. Executive areas are instrumental during learning to prevent such associations; they are also fundamental for the "mature" network to keep passing DMS. In the mature model, the working layer functions as a short-term memory. The mature system is remarkably robust against cell damage and its performance degrades gracefully as damage increases. The model underlines that executive systems, which regulate the flow of information between working memory and sensory areas, are required for passing tests such as DMS. At the behavioural level, the model makes testable predictions about the errors expected from subjects learning the DMS.

Animals↗