Free-operant performance on variable interval schedules with a linear feedback loop: No evidence for molar sensitivities in rats.

Four experiments examined rats' sensitivity to molar and molecular factors on instrumental schedules of reinforcement. rats were exposed to a variable interval schedule with a positive feedback loop (VI+), such that faster responding led to a shorter interreinforcement interval. In Experiments 1 and 2, rats responded faster on a variable response (VR) schedule than on either a VI schedule matched for reinforcement rate or a VI + schedule matched for the feedback function. In Experiment 3, rats responded no differently on a VI schedule than they did on a VI+ schedule with equated rates of reinforcement. In Experiment 4, rats responded faster on a VI+ schedule with an interresponse time requirement yoked to that experienced on a VR schedule, than on a VI+ schedule with the same feedback function as the VR schedule. Taken together these results suggest that rats are more sensitive to the molecular than the molar properties of the schedules. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Response rate and sensitivity to the molar feedback function relating response and reinforcement rate on VI+ schedules of reinforcement.

In 5 experiments, the author examined rats' sensitivity to the molar feedback function relating response rate to reinforcement rate on schedules of reinforcement. These studies demonstrated that, at lower rates of responding, rats' performance on variable ratio (VR), variable interval (VI), and variable interval with linear feedback loop (VI+) schedules was determined largely by reinforcement of interresponse times; response rates were faster on VR than on both VI and VI+ schedules. In contrast, when procedures were adopted to maintain high rates of response, rats showed sensitivity to the molar characteristics of the schedules; they responded as fast on a VI+ schedule as on a VR schedule and faster on both of these schedules than on a yoked VI schedule. When the variance of response rate was manipulated, this factor was noted as an important element in determining sensitivity to the molar characteristics of the schedule. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The kinetics of choice: An operant systems analysis.

The behaving organism and its environment constitute interacting elements of a feedback system. Starting with a kinetic model of the effects of reinforcement on preference and incorporating feedback functions describing the effects of responding on reinforcement rate, a systems analysis of concurrent reinforcement schedule situations was developed. Correct predictions were generated of both the form of the acquisition of preference and of asymptotic preference levels for choice between probabilistic reinforcement schedules (i.e., VI and VR). A kinetic model was then formulated at the level of switching behavior. All predictions at the molar (preference) level followed also from this molecular analysis. In addition, the switching model correctly predicted a constant sum of transition probabilities (local switching rates) and a decrease in overall switching rate as both preference strength and the difference between reinforcement rates increased. The present systems analysis is seen as being unique among recent theoretical efforts concerned with schedules of reinforcement in its ability to describe molecular as well as molar properties of both transition-state and steady-state behavior. (41 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

System-specific differences in behavior regulation: Overrunning and underdrinking in molar nondepriving schedules.

In two experiments we tested the molar regulation prediction that animals adjust schedule performance to reduce deviations from baseline response totals. Both experiments constrained the baseline drink-burst length under molar nondepriving schedules but allowed rats to continue running without drinking. In Experiment 1, rats were required to run in order to drink. In Experiment 2, water was delivered independently of running by fixed-time (FT) schedules. Under the run-to-drink contingency, rats exceeded their baseline amounts of running (overrunning) but failed to maintain their baseline water intake (underdrinking). The total amount of running that did not lead to drinking approximated a baseline running. Under the FT schedules, rats again underdrank, but total running approximated baseline. These results do not support previous studies that have shown molar equlibrium effects under nondepriving reciprocal schedules. We conclude that (a) contingent running may not substitute for independent running; (b) intermittent access to water reduces the total instigation for drinking; (c) molar regulation differs under reciprocal and nonreciprocal schedules; and (d) more dynamic, system-specific regulatory models need to be developed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Primacy of interresponse-time reinforcement in accounting for rate differences under variable-ratio and variable-interval schedules.

Pigeons' keypeck rates under VR schedules are typically higher than under VI schedules when between-schedule reinforcement rates are equated. Exp I, with 4 male White Carneaux pigeons, reproduced this between-schedule rate difference in a multiple VR-VI schedule. However, when the short interresponse times (IRTs) typically reinforced under VRs were required for VI reinforcement, between-component rate differences diminished. Exp II (4 Ss) replicated Exp I except that long IRTs reinforced under VI schedules were required for VR reinforcement. This manipulation eliminated between-schedule rate differences. In Exp III (4 Ss), VR/VI and VI/VR tandems had the same correlation between response and reinforcement rates. In a simulation, C. P. Shimp's (1969) IRT response rule was used as an algorithm to mimic between-schedule rate difference. Findings show that IRT reinforcement (a molecular factor), rather than the feedback function between response rate and reinforcement rate (a molar factor), accounts for the higher response rates under VR schedules. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interresponse-time reinforcement and behavior under aperiodic reinforcement schedules: A case study using computer modeling.

Computer modeling was used to investigate the extent to which response rates under variable-interval and variable-ratio schedules are compatible with a simple process of interresponse time (IRT) reinforcement, as argued by Peele, Casey, and Silberberg (1984). Their computer model was duplicated, as well as its principal result of a large response rate difference between the interval and ratio schedules. After their model was run under a variety of interval and ratio schedules, it was found that the response rates produced did not exhibit patterns of sensitivity to schedule parameter variation found experimentally. Furthermore, the model predicted a large response rate difference between a variable-ratio and a "linear feedback" variable-interval schedule, contrary to the results of McDowell and Wixted (1986). We concluded that simple IRT reinforcement was probably not adequate as an explanation of schedule effects under aperiodic interval and ratio schedules, although a modification of the Peele et al. model incorporating behaviors that were not measured operants could exhibit schedule sensitivity. This suggested that realistic molecular models of schedule phenomena must involve more than simple IRT reinforcement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Some tests of molar models of instrumental performance.

In Experiment 1 a reciprocal equilibrium schedule suppressed the running, drinking, and switching of 3 rats whose baselines were recovered. In Experiment 2 the 2 rats whose baselines were recovered deviated from their baseline distributions of responding on four equilibrium schedules that permitted unscheduled responding. In Experiment 3 four rats that had to lever press on four variable-requirement schedules to gain unconstrained access to water performed more lever pressing in some conditions than calculations of the maximum amount they could have drunk per bout suggested was necessary. In Experiment 4 the responding of 3 rats was found to decrease systematically on a schedule with a fixed running to drinking ratio, as the size of the terms was increased. These findings challenge two assumptions of many molar models of instrumental performance: that the paired baseline distribution of responding is a behavioral ideal that subjects attempt to approach when performing on schedules and that performance on a schedule depends on the ratio of instrumental to contingent responding that it requires, and not on the way that ratio is made up. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Structure and process in semantic memory: Evidence from event-related brain potentials and reaction times.

Through scalp measurements of the electrical activity of the brain (ERPs) recorded while Ss verified the truth of sentences relating exemplars and categories (e.g., all dogs are animals), inferences were made about aspects of semantic processing that were not directly reflected by overt responses. In particular, it is suggested that a negative ERP component that peaks about 400 msec after the onset of the sentence predicate (i.e., N400) is sensitive to structural aspects of semantic memory. The amplitude of this component was modulated by the relatedness of the subject and predicate terms, as well as the hierarchical level of both these terms, but was not sensitive to the truth value of a sentence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of chronic estradiol treatment on delayed spatial alternation and differential reinforcement of low rates of responding.

Estrogens have been shown to both enhance and impair cognitive function depending on several factors, including regimen of hormone treatment, age of subject, and task attributes. In rodent models, estradiol tends to enhance spatial learning and impair response or cued learning, but effects on executive functions are less well-studied. In this experiment, spatial working memory and response inhibition were tested using delayed spatial alternation (DSA) and differential reinforcement of low rates of responding (DRL) tasks in ovariectomized rats that were given chronic estradiol via Silastic implants resulting in serum estradiol concentrations of 86.2 ± 8.2 (SEM) pg/ml. Rats were tested for 25 days DSA with variable delays of 0, 3, 6, 9, and 18 seconds between lever presentations, followed by 30 days on a DRL-15s operant schedule. Estradiol-replaced rats showed a significantly lower proportion of correct responses on the DSA task compared to vehicle-implanted ovariectomized animals. On DRL, estradiol-treated rats showed a lower ratio of reinforced to nonreinforced presses. These data suggest that chronic estrogen exposure may impair rats' abilities on measures of executive function including working memory and response inhibition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A model for the responses of low-frequency auditory-nerve fibers in cat

A computational model was developed for the responses of low-frequency auditory-nerve (AN) fibers in cat. The goal was to produce realistic temporal response properties and average discharge rates in response to simple and complex stimuli. Temporal and average-rate properties of AN responses change as a function of sound-pressure level due to nonlinearities in the auditory periphery. The input stage of the AN model is a narrow-band filter that simulates the mechanical tuning of the basilar membrane. The parameters of this filter vary continuously as a function of stimulus level via a feedback mechanism, simulating the compressive nonlinearity associated with the mechanics of the basilar membrane. A memoryless, saturating nonlinearity and two low-pass filters simulate transduction and membrane properties of the inner hair cell (IHC). A diffusion model for the IHC-AN synapse introduces adaptation. Finally, a nonhomogeneous Poisson process, modified by absolute and relative refractoriness, provides the output discharge times. Responses to several different stimuli are presented. These responses illustrate nonlinear temporal response properties that cannot be achieved with linear models for AN fibers.     

Integrating Efficient Resource Optimization and Linear Schedule Analysis with Singularity Functions

Resources perform or enable physical operations and thus are vital on construction projects, yet are subject to various constraints. Their use within a project schedule must therefore be carefully planned. A major objective is optimizing when they are active within the float of noncritical activities to avoid disruptive and costly fluctuations. This paper builds on analyzing criticality of linear schedules with the unique singularity functions. The new approach keeps resources intact and derives one flexible equation for the complete resource profile of a schedule, including any timing or resource rate changes. Another equation models its first moment of area to minimize the objective function toward a level profile. A genetic algorithm is suitable for an iterative optimization. The parameters of its chromosomes are recombined evolutionarily and can model any permutation. Analyzing a road project illustrates how singularity functions integrate resource optimization with its linear schedule and facilitate a subsequent optimization.     

Multiple peaks in high-performance liquid chromatography of proteins. beta-Lactoglobulins eluted in a hydrophobic interaction chromatography system

The hypothesis of Geisler (Brain Res. 212 (1981) 198-201), in which the different spontaneous-rate classes of primary auditory neurons were accounted for by the different sizes of uniquantal EPSPs relative to the gap between resting membrane and threshold potentials, was represented with an expanded model which included relative refractory effects. The spike rates generated by the expanded model, when plotted vs. estimated sound level, are qualitatively similar to those of experimentally obtained rate-level curves. The hypothesis is also consistent with recent ultrastructural data which suggest that average quantal-release rates for any particular primary auditory neuron are inversely related to its spontaneous rate. The model's recovery processes following spike generation (hazard functions) are also similar to those observed experimentally.     

Glucocorticoids and aging

In this review we analyze the morphologic changes, hypothalamic-pituitary-adrenal (HPA) axis functions, glucocorticoid (GC) receptors, and steroidogenic enzyme activities in both animals and humans during aging. In rodent studies, older animals tend to show: 1) hypertrophy of adrenal zona fasciculata (ZF) cells; 2) neuronal loss in the hypothalamic area; 3) loss of GC receptors in the hippocampus; 4) raised circulating adrenocorticotropic hormone (ACTH) and GC levels, and increased release of corticotropin-releasing hormone from the hypothalamus; 5) reduced suppression of endogenous GC secretion after administration of dexamethasone; 6) decreased attenuation of response to chronic stress; and 7) increased activity of P450scc and 21-hydroxylase. According to the GC cascade hypothesis, stress and GCs facilitate the aging process in rats. Stress induces downregulation of GC receptors in the hippocampus, then impairs GC feedback on stress-induced HPA axis activation. Finally, an increase in the basal level of corticosterone and extended GC secretion following stress occurs. Because activation of the hippocampus decreases HPA axis function, the unrestrained elevation of GC concentration and the reduction in the level of GC receptors in the hippocampus may gradually weaken the feedback mechanisms and halt the response to stress. In humans, there are conflicting reports of HPA axis function during aging, so it is difficult to make a final conclusion regarding the relationship between aging and HPA axis function.     

Interaction of the epiphysis and the immune system

First indications that the pineal gland may be involved in endocrine immunomodulation came from early reports on anti-tumor effects of pineal extracts in animals and humans. In the meantime, evidence has accumulated suggesting that melatonin, the major endocrine product of the pineal gland-as a well preserved molecule during evolution-is indeed involved in the feedback between neuroendocrine and immune functions. At present we are beginning to understand the mechanisms of action by which melatonin affects cellular functions, and from the variety of possible direct and indirect interactions it appears that melatonin may play a complex physiological role in neuroimmunomodulation. In this article we present a critical review of the numerous reports on the influence of melatonin on immune functions and discuss the possible underlying molecular pathways. In addition, a short comment is given on the current public discussion as to the clinical value of melatonin.     

Choice of optimality criteria for the design of crossbreeding experiments

Crossbreeding experiments carried out over several generations and analyzed using genetic models including additive, dominance, and epistatic effects deserve careful planning. Designs should be optimized with respect to the specific aim of the experiment. Using an experiment with guinea pigs as an example, designs were optimized for three different criteria: D-optimality, where the determinant of the variance-covariance matrix of all parameters in the genetic model is minimized, DS-optimality, where a specific subset of parameters is of special interest and the respective determinant is minimized, and DA-optimality, where a linear function or a set of linear functions of the parameters in the model is of interest. The linear function used in this particular case relates to the comparison of a composite line of two breeds and a rotational crossbreeding system at equilibrium. The designs produced by a sequential design algorithm depend very much on the optimality criterion. Designs that are optimal for the comparison of composites and rotations are very inefficient for the estimation of the whole set of parameters in the model or the specific subset of special interest in this case. Assuming that the underlying genetic model is correct, composites and rotations at equilibrium may be compared extremely efficiently using only crosses arising in the first three generations of crossbreeding.     

Animals foraging in the lab: Problems and promises.

Foraging has become a popular catchword in literature like that published in this Journal. Several different kinds of psychological research on foraging can be distinguished. These include tests of optimal foraging models using operant schedules and other simulations, analyses of the mechanisms assumed as constraints in optimality models, tests of the optimality of behavior on arbitrary schedules, and use of seminaturalistic laboratory situations. This kind of work is not without problems. One is that the gap between "real" and simulated foraging has been insufficiently explored. More important, accounts of behavior in terms of function (e.g., optimal foraging theory) are often confused with those in terms of mechanisms of learning, memory, and choice. The most productive research strategy in this area is to juxtapose predictions of functional and mechanistic models and attempt to understand any differences between them. Studies of foraging behavior can also reveal new or poorly studied phenomena. Because optimal foraging theory makes ideas about function explicit and precise, well-formulated investigations of foraging behavior can contribute substantially to understanding learning, memory, and decision processes as biological adaptations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Regulation during challenge: A general model of learned performance under schedule constraint.

Develops a general behavior-regulation model of learned performance related to the equilibrium approach of W. Timberlake (1980) and W. Timberlake and J. Allison (1974). The model is based on 4 assumptions: (1) Both the instrumental and contingent responses are regulated with respect to their own set points; (2) these set points can be measured in a free baseline when both responses are relatively unconstrained and simultaneously available; (3) a reinforcement schedule can be seen as a constraint function that cross–couples the environmental effects of regulatory systems underlying the instrumental and contingent responses, thereby challenging their set points; and (4) molar behavior change under a schedule represents a compromise between the deviations from set points forced by the constraint function. These assumptions are translated into a set of coupled differential equations describing 2 regulatory systems related by a schedule. After providing an exact solution for this model, 2 special cases are derived as current alternative models of learned performance, those of J. Allison (see record 1976-23479-001) and J. R. Staddon (see record 1980-27259-001). The model is consistent in form with data from a variety of simple schedules. (53 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of chronic morphine administration upon a modified Sidman avoidance schedule that utilizes response-independent shock

Six male squirrel monkeys were subjected to a Sidman nondiscriminated avoidance schedule (R-S, S-S-20 sec) that superimposed 3-min conditioned stimuli (CS) unavoidable shock pairings upon the ongoing avoidance behavior. Five of the 6 animals demonstrated facilitated avoidance response rates during the CS, while one animal demonstrated suppressed rates during the CS. Morphine sulfate (0.5, 1.0, 2.0, 3.0, 4.0 mg/kg) altered these patterns, causing the suppressor to facilitate, while the facilitators demonstrated reduced levels of response elevation during the aversive CS. Morphine also led to a reliable reduction in overall response rate and an increase in the number of shocks received. No consistent drug effects were noted with regard to general motor activity. These results were interpreted to suggest that a potent analgesic agent, such as morphine, was able to reduce the level of fear motivation normally generated by the aversive CS. Since changes in relative rate during the aversive CS were quite reliable both within and between animals, it was suggested that this behavioral schedule might prove useful in assaying the fear-reducing qualities of a variety of drugs. A cautionary note, however, indicated that other explanations, most notably, a rate dependent hypothesis, could account for the data without assuming the level of fear was altered.