The following schedule of reinforcement as a fundamental determinant of steady state contrast in multiple schedules

Two experiments investigated whether steady-state interactions in multiple schedules depend exclusively on the following schedule of reinforcement. Experiment 1 used a four-component multiple schedule in which two components were associated with the same constant schedule of reinforcement, and where rate of reinforcement was varied in the component that followed one of these. Contrast effects were reliable only in the component that preceded the point of reinforcement variation, although some contrast did occur otherwise. In those instances where contrast other than the following-schedule effect did occur, it was accounted for by the effect of the preceding schedule, an effect for which there were consistent individual differences among subjects, and which varied with component duration. Experiment 2 used a three-component schedule, in which reinforcement rate was varied in the middle component. The results were consistent with Experiment 1, as the following-schedule effect was the only consistent effect that occurred, although an effect of the preceding schedule did occur for some subjects under some conditions, and was especially evident early in training. The conclusion from both experiments is that there is no general effect of relative rate of reinforcement apart from the sum of the effects of the preceding and following schedules, and that the following-schedule effect is the fundamental cause of steady-state interactions.     

Choice, changeover, and travel

Since foraging in nature can be viewed as instrumental behavior, choice between sources of food, known as “patches,” can be viewed as choice between instrumental response alternatives. Whereas the travel required to change alternatives deters changeover in nature, the changeover delay (COD) usually deters changeover in the laboratory. In this experiment, pigeons were exposed to laboratory choice situations, concurrent variable-interval schedules, that were standard except for the introduction of a travel requirement for changeover. As the travel requirement increased, rate of changeover decreased and preference for a favored alternative strengthened. When the travel requirement was small, the relations between choice and relative reinforcement revealed the usual tendencies toward matching and undermatching. When the travel requirement was large, strong overmatching occurred. These results, together with those from experiments in which changeover was deterred by punishment or a fixed-ratio requirement, deviate from the matching law, even when a correction is made for cost of changeover. If one accepted an argument that the COD is analogous to travel, the results suggest that the norm in choice relations would be overmatching. This overmatching, however, might only be the sign of an underlying strategy approximating optimization.     

The role of the response-reinforcer relation in delay-of-reinforcement effects

The role of the response-reinforcer relation in maintaining operant behavior under conditions of delayed reinforcement was investigated by using a two-operandum (i.e., two-key) procedure with pigeons. Responding on one key was reinforced under a tandem variable-interval differential-reinforcement-of-other-behavior (tandem VI DRO) schedule. The schedule defined a resetting unsignaled delay-of-reinforcement procedure in that a response was required when the interfood interval of the VI schedule lapsed, but further responding during the DRO component on either key reset the time interval. This ensured a fixed delay duration between any response and reinforcement. Responding on another key, physically identical to the first one except for spatial location, otherwise was without consequence. The location of the key correlated with the delay-of-reinforcement procedure varied between sessions according to a semirandom sequence. Differences in response rates between the two keys were greater, with proportionally higher rates on the key correlated with the delay-of-reinforcement procedure, the longer the delay-of-reinforcement procedure remained correlated with the same key. Differences in responding on the two keys also increased within individual sessions. These results suggest that the response-reinforcer relation is the primary determinant of responding when responding is acquired and maintained with delayed reinforcement.     

The Vatican and Europe: Political Theology and Ecclesiology in Papal Statements from Pius XII to Benedict XVI

The article examines the origins and evolution of the Vatican's political theology and ecclesiology for Europe from Pius XII (especially after the Second World War) and including the pontificates of John XXIII, Paul VI, John Paul II and Benedict XVI. It seeks to examine the continuities of the ‘Idea of Europe’ in papal thought against a background of changing political context – the end of the Second World War, the Cold War, the fall of the communist state system, the emergence of a united but diverse Europe after 1989. The political structures of the continent now include within its geographic sweep Western and Eastern Christian churches which, divided by tradition and modern history, find their relationship a key marker in the contemporary religious identity of Europe. This reality is a significant framework for Vatican thinking on Europe especially for John Paul II and Benedict XVI.     

Perspectives on the future of ecumenism: the 50th anniversary of Unitatis Redintegratio

Unitatis Redintegratio, the decree on the participation of the Catholic Church in the ecumenical movement, was promulgated by Pope Paul VI on Saturday 21 November 1964, now just over 50 years ago. This article reminds us of the events leading up to that day, which shaped the text and which must be understood, if we are to arrive at a proper evaluation of the decree and its consequences.     

A model for residence time in concurrent variable interval performance

A component-functions model of choice behavior is proposed for performance on interdependent concurrent variable-interval (VI) variable-interval schedules based on the product of two component functions, one that enhances behavior and one that reduces behavior. The model is the solution to the symmetrical pair of differential equations describing behavioral changes with respect to two categories of reinforcers: enhancing and reducing, or excitatory and inhibitory. The model describes residence time in interdependent concurrent VI VI schedules constructed from arithmetic and exponential distributions. The model describes the data reported by Alsop and Elliffe (1988) and Elliffe and Alsop (1996) with a variance accounted for of 87% compared to 64% accounted for by the Davison and Hunter (1976) model and 42% by Herrnstein's (1970) hyperbola. The model can explain matching, undermatching, and overmatching in the same subject under different procedures and has the potential to be extended to performance on concurrent schedules with more than two alternatives, multiple schedules, and single schedules. Thus, it can be considered as an alternative to Herrnstein's quantitative law of effect.     

Does school desegregation change occupational goals of Negro males?

Instruments, designed to assess values which affect the motivation to work and aspiration levels, were administered to over 600 Negro male seniors in Texas high schools. Results indicate that the degree and duration of school desegregation these students have experienced, ranging from less than 1 to more than 5 years, have had little effect on work values and occupational aspirations.     

Effects of adding a second reinforcement alternative: implications for Herrnstein's interpretation of r(e)

Herrnstein's hyperbola describes the relation between response rate and reinforcer rate on variable-interval (VI) schedules. According to Herrnstein's (1970) interpretation, the parameter r(e) represents the reinforcer rate extraneous to the alternative to which the equation is fitted (the target alternative). The hyperbola is based on an assumption that extraneous reinforcer rate remains constant with changes in reinforcer rate on the target alternative (the constant-r(e) assumption) and that matching with no bias and perfect sensitivity occurs between response and reinforcer ratios. In the present experiment, 12 rats pressed levers for food on a series of 10 VI schedules arranged on the target alternative. Across conditions, six VI values and extinction were arranged on a second alternative. Reinforcer rate on the second alternative, r2, negatively covaried with reinforcer rate on the target alternative for five of the six VI values on the second alternative, and significant degrees of bias and undermatching occurred in response ratios. Given covariation of reinforcer rate on the second and target alternatives, the constant-r(e) assumption can be maintained only by assuming that reinforcer rate from unmeasured background sources, rb, covaries with reinforcer rate on the second alternative such that their sum, r(e), remains constant. In a single-schedule arrangement, however, r(e) equals rb and thus rb is assumed to remain constant, forcing a conceptual inconsistency between single- and concurrent-schedule arrangements. Furthermore, although an alternative formulation of the hyperbola can account for variations in bias and sensitivity, the modified equation also is based on the constant-r(e) assumption and therefore suffers from the same logical problem as the hyperbola when reinforcer rate on the second alternative covaries with reinforcer rate on the target alternative.     

IS MATCHING COMPATIBLE WITH REINFORCEMENT MAXIMIZATION ON CONCURRENT VARIABLE INTERVAL,VARIABLE RATIO?1

Four pigeons on concurrent variable interval, variable ratio approximated the matching relationship with biases toward the variable interval when time spent responding was the measure of behavior and toward the variable ratio when frequency of pecking was the measure of behavior. The local rates of responding were consistently higher on the variable ratio, even when there was overall preference for the variable interval. Matching on concurrent variable interval, variable ratio was shown to be incompatible with maximization of total reinforcement, given the observed local rates of responding and rates of alternation between the schedules. Furthermore, it was shown that the subjects were losing reinforcements at a rate of about 60 per hour by matching rather than maximizing.     

Histological data: Hollard and Davison (1971)

As Mogenson and Cioé (1977) have assumed that our electrodes aimed at the ectostriatum (Hollard and Davison, 1971) were actually located there, we feel that a presentation of the histological data is necessary. Following termination of further experiments (Hollard, 1974) the pigeons, numbered 93, 95, and 119, were sacrificed and perfused with saline followed by 10% formalin. Sections, 50 microns thick, were cut on a freezing microtome. Prints were made by mounting each unstained section of a microscope slide and placing them in a standard photographic enlarger. The electrode tips of Pigeons 93 and 119 were located in the paleostriatal complex. The sections of Pigeon 95 were damaged and precise localization was not possible. Further work in this laboratory has also found that, using the same coordinates, electrode tips tend to fall in the paleostriatum, rather than in the more dorsal ectostriatum at which they are aimed. The paleostriatal placements tended to sustain self-stimulation, whereas others located in the ectostriatum sustained relatively low or unstable rates.