Choice, contingency discrimination, and foraging theory

Four pigeons were trained on eight or nine pairs of independent concurrent variable-interval schedules. The range of reinforcement ratios included extreme ratios (up to 532 to 1). Large samples of stable performance were gathered. Contrary to the findings of Davison and Jones (1995), the generalized matching law described choice more accurately than a contingency-discriminability model. Taking small samples (5 to 10 sessions) and applying a more liberal stability criterion used by Davison and Jones only increased the unsystematic variance in the data and in estimates of generalized-matching-law sensitivity. Because changing to dependent scheduling and inserting a changeover delay had no systematic effect, the deviations from generalized matching reported by Davison and Jones probably arose from imperfectly discriminated stimuli. Analysis of visits revealed that visits to the nonpreferred alternative were brief and approximately constant. When choice between the preferred (rich) and nonpreferred (lean) alternatives, regardless of position, was analyzed according to the generalized matching law, sensitivities approximated 1.0, with bias in favor of the lean alternative. This bias, which arose from an excessive frequency of visits to the lean alternative, explains undermatching as the result of fitting one line to a choice relation that consists of two displaced lines, both with a slope of 1.0. The pattern of deviation from the generalized matching line confirmed this account. The findings suggest an alternative analysis of choice that focuses on probability of visiting the lean alternative as the dependent variable. This probability was directly proportional to ratio of reinforcement. Matching, undermatching, and overmatching may all be explained by a view of concurrent performance based on foraging theory, in which responding occurs primarily at the rich alternative and is occasionally interrupted by brief visits to the lean alternative.     

How pigeons discriminate the relative frequency of events.

This study examined how pigeons discriminate the relative frequencies of events when the events occur serially. In a discrete-trials procedure, 6 pigeons were shown one light nf times and then another nl times. Next, they received food for choosing the light that had occurred the least number of times during the sample. At issue were (a) how the discrimination was related to two variables, the difference between the frequencies of the two lights, D = nf - nl, and the total number of lights in the sample, T = nf + nl; and (b) whether a simple mathematical model of the discrimination process could account for the data. In contrast with models that assume that pigeons count the stimulus lights, engage in mental arithmetic on numerons, or remember the number of stimuli, the present model assumed only that the influence of a sample stimulus on choice increases linearly when the stimulus is presented, but decays exponentially when the stimulus is absent. The results showed that, overall, the pigeons discriminated the relative frequencies well. Their accuracy always increased with the absolute value of the difference D and, for D > 0, it decreased with T. Performance also showed clear recency, primacy, and contextual effects. The model accounted well for the major trends in the data.     

Quantifiers and Congruence Closure

We prove some results about the limitations of the expressive power of quantifiers on finite structures. We define the concept of a bounded quantifier and prove that every relativizing quantifier which is bounded is already first-order definable (Theorem 3.8). We weaken the concept of congruence closed (see [6]) to weakly congruence closed by restricting to congruence relations where all classes have the same size. Adapting the concept of a thin quantifier (Caicedo [1]) to the framework of finite structures, we define the concept of a meager quantifier. We show that no proper extension of first-order logic by means of meager quantifiers is weakly congruence closed (Theorem 4.9). We prove the failure of the full congruence closure property for logics which extend first-order logic by means of meager quantifiers, arbitrary monadic quantifiers, and the Härtig quantifier (Theorem 6.1).     

Personality Profiles and Political Parties

This paper explores relationships between basic personality profiles of voters and their political party preferences. The Italian political system has moved recently from previously extreme, ideologically distinctive parties to form complex coalitions varying around more centrist orientations. Significant evidence was found for the utility of the Five-Factor Model of Personality in distinguishing between voters' expressed preferences, even given this greater subtlety in proposed values and agendas. More than 2,000 Italian voters who self-identified as having voted for new center-left or center-right political coalitions differed systematically in predicted directions on several personality dimensions measured by the Big Five Questionnaire. In the context of the model, center-right voters displayed more Energy and slightly more Conscientiousness than center-left voters, whose dominant personality characteristics were Agreeableness (Friendliness) and Openness; Emotional Stability was unrelated to either group. This relationship between individual differences in personality and political preferences was not influenced by the demographic variables of voters' gender, age, or education. Thus, personality dimensions proved to be stronger predictors of political preference than any of these standard predictor variables. Implications are discussed regarding links among personality, persuasion, power, and politics.     

Anxiety and counter-conditioning: the role of the behavioral inhibition system in the ability to associate aversive stimuli with future rewards

A total of 130 female undergraduates performed a counter-conditioning choice-task. This task presented two response alternatives and subjects were instructed to earn the maximum number of points. Responses to button 1 were normally followed by an immediate reward (an average gain of 7.5 points). Responses to button 2 were always followed by a punishment (an average loss of 20 points), but caused the next-but-one press on button 1 to give an average gain of 115 points. Thus, subjects were required to learn and maintain this counter-conditioning association. Four groups of subjects were formed according to the scores on the Sensitivity to Punishment and Sensitivity to Reward scales (which are measures of individual differences of Gray's anxiety and impulsivity personality dimensions, respectively). A 69.2% of subjects learned and maintained the counter-conditioning association. As predicted, personality results confirmed that subjects with lower scores on the Sensitivity to Punishment scale learned the counter-conditioning association better and faster when compared with high scorers. Results are consistent with Gray's Behavioral Inhibition System (BIS) model of anxiety which holds that individual differences in anxiety may relate to the ability to associate aversive stimuli with a future reward. Assuming that anxiety depends on BIS functioning, our results show that high trait anxious subjects, if compared with low anxious ones, would have a lower ability for associating an aversive event with a later appetitive one. This learning process would serve non-anxious subjects to reduce the aversiveness of cues of punishment and to cope better with stressful situations.     

Why Don't Continents Move? Why Don't People Change?

People don't change because they can't, don't want to, don't know how, or don't know what to change. The transtheoretical model provides an integ-rative model for understanding reasons for not changing, as well as readiness to change. Stages and levels of change guide therapists in their work in helping clients change. Clients in the precontemplative stage typically cannot change without special help. Those in the contemplation stage are not sure they want to change. Those in the preparation stage are afraid they do not know how to successfully change. The levels of change help guide therapists and clients on what to change.     

Discovery algorithms for hierarchical relations

Two algorithms based on a latent class model are presented for discovering hierarchical relations that exist among a set ofK dichotomous items. The two algorithms, stepwise forward selection and backward elimination, incorporate statistical criteria for selecting (or deleting) 0–1 response pattern vectors to form the subset of the total possible 2 ^k vectors that uniquely describe the hierarchy. The performances of the algorithms are compared, using computer-constructed data, with those of three competing deterministic approaches based on ordering theory and the calculation of Phi/Phi-max coefficients. The discovery algorithms are also demonstrated on real data sets investigated in the literature.     

Values education in a democratic society

A democratic society requires a degree of consensus on values. But it is argued that the model of values education as the transmission of certain predetermined values is inadequate in a democracy, since for several reasons the transmission of predetermined values can itself be undemocratic. Education for individual autonomy in matters of values is also, by itself, inadequate. Each generation needs the resources by which it can work out its own interpretation of democratic values. What is also needed, then, is an education in a common language of discourse — which can be drawn primarily from philosophy — which will facilitate public debate.     

Partially Interpreted Relations and Partially Interpreted Quantifiers

Logics in which a relation R is semantically incomplete in a particular universe E, i.e. the union of the extension of R with its anti-extension does not exhaust the whole universe E, have been studied quite extensively in the last years. (Cf. van Benthem (1985), Blamey (1986), and Langholm (1988), for partial predicate logic; Muskens (1996), for the applications of partial predicates to formal semantics, and Doherty (1996) for applications to modal logic.) This is not so with semantically incomplete generalized quantifiers which constitute the subject of the present paper. The only systematic study of these quantifiers from a purely logical point of view, is, to the best of my knowledge, that by van Eijck (1995). We shall take here a different approach than that of van Eijck and mention some of the abstract properties of the resulting logic. Finally we shall prove that the two approaches are interdefinable.     

Matching under nonindependent variable-ratio schedules of drug reinforcement.

Response-contingent deliveries of oral pentobarbital maintained responding of 3 rhesus monkeys during daily 3-hr sessions. Deliveries of pentobarbital were arranged under nonindependent concurrent variable-ratio variable-ratio schedules. Responses to either schedule counted toward completion of both variable-ratio schedule requirements. This schedule is similar in some respects to conventional concurrent variable-interval variable-interval schedules, in which passage of time counts toward completion of the interval value on both schedules. Restricted nonindependent concurrent variable-ratio variable-ratio schedules were also studied. On that schedule, when a drug delivery was assigned to one spout, it had to be collected before responses on the opposite spout again counted toward completion of the schedule requirements. Relative reinforcer magnitude was varied by changing the drug concentration on one schedule while keeping the drug concentration constant on the other variable-ratio schedule. Under both types of concurrent variable-ratio schedules, the relative rate of responding corresponded to the relative drug intake. Unlike earlier studies of concurrent variable-interval variable-interval intravenous cocaine reinforcement, preference was proportionate to concentration, and exclusive preferences did not develop. The relationship between relative rate of responding and relative drug intake was well described by the generalized matching law.