The effects of diazepam and triazolam on repeated acquisition and performance of response sequences with an observing response.

Drugs often disrupt the acquisition of new response sequences at doses that fail to disrupt the performance of a previously acquired response sequence. This selective drug effect may result from differences in the control exerted by the stimuli presented after each response in the acquisition and performance sequences. To examine the function of these stimuli, an observing procedure was incorporated into a multiple schedule of repeated acquisition and performance of response sequences, in which stimulus presentations were contingent upon an observing response. Three experiments were conducted with humans. Experiment 1 compared responding with and without the observing contingency. No difference was found in the overall percentage of errors across the two conditions. Within the observing condition, observing behaviour was maintained in the acquisition component as long as errors occurred, but was not maintained in the performance component. Experiment 2 examined whether a contingency that increased errors also would increase observing in both the acquisition and performance components. Specifically, reinforcer delivery in each component was contingent upon emitting 10 correct responses and one, two, or four errors. Observing responses increased in the acquisition component as the error requirement increased, whereas observing responses in the performance component increased only when the error requirement was four. Experiment 3 assessed the effects of diazepam (0, 7.5, 15, and 30 mg/70 kg, p.o.) and triazolam (0, 0.375, and 0.75 mg/70 kg, p.o.) on repeated acquisition and performance baselines with the observing contingency. Selective drug effects were obtained in this modified procedure; that is, the percentage of errors in the acquisition component increased at doses that failed to affect the percentage of errors in the performance components. Importantly, drug effects were selective, even though observing responses were not emitted in the performance component and, hence, the stimulus presentations did not occur in that component. These findings suggest that alternative explanations for these differential effects are needed; in that regard, a response-unit account of the selective drug effects is discussed.     

Development of complex, stereotyped behavior in pigeons

A pigeon's peck on one key moved a light down one position in a 5×5 matrix of lights, while a peck on another key moved the light across one position. Reinforcement depended upon the occurrence of four pecks on each key (moving the matrix light from the top left to the bottom right), and a fifth peck on either key ended a trial without food. Though there were 70 different sequences that led to reinforcement, each of 12 pigeons developed a particular, stereotyped sequence which dominated its behavior (Experiment 1). Extinction produced substantial increases in sequence variability (Experiment 2). Removal of the matrix cues disrupted performance, though it partially recovered with extended training (Experiment 3). The pigeons did not master a contingency which required a different sequence on the current trial than on the previous one (Experiment 4), though they were able to learn to emit sequences which began with either left-left or left-right response patterns (Experiment 5). The experiments suggest that contingencies of reinforcement may contribute to the creation of complex units of behavior, and that stereotypy may be a likely consequence of contingent reinforcement.     

Behavioral variability in SHR and WKY rats as a function of rearing environment and reinforcement contingency.

The spontaneously hypertensive rat (SHR) may model aspects of human attention deficit hyperactivity disorder (ADHD). For example, just as responses by children with ADHD tend to be variable, so too SHRs often respond more variably than do Wistar-Kyoto (WKY) control rats. The present study asked whether behavioral variability in the SHR strain is influenced by rearing environment, a question related to hypotheses concerning the etiology of human ADHD. Some rats from each strain were reared in an enriched environment (housed socially), and others were reared in an impoverished environment (housed in isolation). Four groups--enriched SHR, impoverished SHR, enriched WKY, and impoverished WKY--were studied under two reinforcement contingencies, one in which reinforcement was independent of response variability and the other in which reinforcement depended upon high variability. The main finding was that rearing environment did not influence response variability (enriched and impoverished subjects responded similarly throughout). However, rearing environment affected body weight (enriched subjects weighted more than impoverished subjects) and response rate (impoverished subjects generally responded faster than enriched subjects). In addition, SHRs tended to respond variably throughout the experiment, whereas WKYs were more sensitive to the variability contingencies. Thus, behavioral variability was affected by genetic strain and by reinforcement contingency but not by the environment in which the subjects were reared.     

Dynamic doxastic logic: why,how, and where to?

We investigate the research programme of dynamic doxastic logic (DDL) and analyze its underlying methodology. The Ramsey test for conditionals is used to characterize the logical and philosophical differences between two paradigmatic systems, AGM and KGM, which we develop and compare axiomatically and semantically. The importance of Gärdenfors’s impossibility result on the Ramsey test is highlighted by a comparison with Arrow’s impossibility result on social choice. We end with an outlook on the prospects and the future of DDL.     

Beliefs in conditionals vs. conditional beliefs

On the basis of impossibility results on probability, belief revision, and conditionals, it is argued that conditional beliefs differ from beliefs in conditionals qua mental states. Once this is established, it will be pointed out in what sense conditional beliefs are still conditional, even though they may lack conditional contents, and why it is permissible to still regard them as beliefs, although they are not beliefs in conditionals. Along the way, the main logical, dispositional, representational, and normative properties of conditional beliefs are studied, and it is explained how the failure of not distinguishing conditional beliefs from beliefs in conditionals can lead philosophical and empirical theories astray.

Jump Liars and Jourdain’s Card via the Relativized T-scheme

A relativized version of Tarski’s T-scheme is introduced as a new principle of the truth predicate. Under the relativized T-scheme, the paradoxical objects, such as the Liar sentence and Jourdain’s card sequence, are found to have certain relative contradictoriness. That is, they are contradictory only in some frames in the sense that any valuation admissible for them in these frames will lead to a contradiction. It is proved that for any positive integer n, the n-jump liar sentence is contradictory in and only in those frames containing at least an n-jump odd cycle. In particular, the Liar sentence is contradictory in and only in those frames containing at least an odd cycle. The Liar sentence is also proved to be less contradictory than Jourdain’s card sequence: the latter must be contradictory in those frames where the former is so, but not vice versa. Generally, the relative contradictoriness is the common characteristic of the paradoxical objects, but different paradoxical objects may have different relative contradictoriness. Presented by Heinrich Wansing     

Preferential theory revision

Employing a logic program approach, this paper focuses on applying preferential reasoning to theory revision, both by means of preferences among existing theory rules, and by means of preferences on the possible abductive extensions to the theory. And, in particular, how to prefer among plausible abductive explanations justifying observations.     

Eligible Contraction

When a belief set is contracted only some beliefs are eligible for removal. By introducing eligibility for removal as a new semantic primitive for contraction and combining it with epistemic entrenchment we get a contraction operator with a number of interesting properties. By placing some minimal constraint upon eligibility we get an explicit contraction recipe that exactly characterises the so called interpolation thesis, a thesis that states upper and lower bounds for the amount of information to be given up in contraction. As a result we drop the controversial property of recovery. By placing additional constraints on eligibility we get representation theorems for a number of contraction operators of varying strength. In addition it is shown that recovery contraction is a special case that we get if eligibility is explicitly constructed in terms of logical relevance. This revised version was published online in August 2006 with corrections to the Cover Date.     

Basic Entrenchment

In contrast to other prominent models of belief change, models based on epistemic entrenchment have up to now been applicable only in the context of very strong packages of requirements for belief revision. This paper decomposes the axiomatization of entrenchment into independent modules. Among other things it is shown how belief revision satisfying only the ‘basic’ postulates of Alchourrón, Gärdenfors and Makinson can be represented in terms of entrenchment.