Effects of initial-link duration on preference and resistance to change in concurrent-chains schedules

Previous studies with concurrent-chains procedures have shown that preference for a terminal-link signaling a higher reinforcement rate decreases as initial-link durations increase. Using a concurrent-chains procedure, the present experiment examined the effects of manipulating initial-link duration on preference and resistance to disruption with rats nose poking for different rates of food reinforcement in the terminal links. Consistent with previous findings, preference for a terminal link with a higher reinforcement rate decreased with longer initial links. Conversely, relative resistance to disruption in the terminal link with a higher reinforcement rate increased with longer initial links. These findings are counter to the prediction of behavioral momentum theory that preference and resistance to change should be positively related.     

Varying initial-link and terminal-link durations in concurrent-chains schedules: a comparison of three models

In Experiment 1, pigeons responded on concurrent-chains schedules with equal variable-interval schedules as initial links and fixed delays to food as terminal links. One terminal-link delay was always three times as long as the other. As terminal-link delays increased, response percentages on the key with the shorter terminal link increased according to a curvilinear function. This result supported the predictions of the hyperbolic value-added model and the contextual-choice theory but not delay-reduction theory. In Experiment 2, the terminal links were always delays of 2s and 12s, followed by food, and the durations of the initial links varied across conditions. As initial-link durations increased, pigeons' response percentages on the key with the shorter terminal link decreased, but toward an asymptote greater than 50%, indicating a continued preference for the shorter terminal link with very long initial links. This result was more consistent with the predictions of the hyperbolic-value added model than with those of the contextual-choice model or of delay-reduction theory.     

Effects of reinforcer quality and step size on rats' performance under progressive ratio schedules

The Mathematical Principles of Reinforcement (MPR) model accurately predicts performance in fixed ratio (FR) schedules of reinforcement. The aim of the present study was to assess the generality of MPR with rats responding under progressive ratio (PR) schedules of different step sizes (PR1 or PR3) that provided either food or saccharin pellets. The results showed that the rats responding for saccharin pellets produced higher breakpoints (i.e., completed higher ratios) than those responding for food pellets. In terms of theoretical parameters, one finding unanticipated on the basis of MPR was that the a parameter (specific activation) was higher for the PR3 schedules. This finding suggests that specific activation may be affected indirectly by motor parameters of the task.     

Effects of industrialization on working schedules.

Recent increase in industrialization has resulted in attention being drawn to diversity of working schedules and their interrelation with content of work. The results of joint research revealed that adaptation to industrial jobs is made difficult because of urban conditions and modern work-control systems, such as workers in flexible-working-time systems who apparently favored regular daily working cycles. Long overtime work in smaller undertakings and the spread of shift systems are two important features of industrial work schedules, each being dominant among skilled and non-skilled jobs. Another important facet is the problem of intra-shift work-rest schedules significant for machine operations and vigilance tasks. It is suggested that phases of work that become intolerable are correlated with unnatural work rhythms. More emphasis should thus be laid on both phase-shifted work and non-self-governing work, the key factor being the relevance of attained data to real work in the whole course of schedules of work and rest.     

Optimizing construction schedules and material deliveries in city logistics: a case study from the building industry

We consider the problem of designing a logistics system to assure efficient urban construction processes for an innovative urban building area in the city of Vienna. We address the challenges of coordinating workers and the timely delivery and storage of material with the objective of optimizing resource-efficiency as well as reducing traffic related to construction tasks. The problem is formulated as a hierarchical optimization problem, incorporating tactical construction logistics planning as well as operational construction logistics planning. On the tactical level a time schedule of tasks for different construction phases and the corresponding material transports and storage decisions are optimized on a weekly basis, while on the operational level the daily optimization of material transports, modeled as an inventory routing problem, is addressed. A mixed-integer programming formulation of the problem on each planning level is provided and solved using CPLEX. The suggested approach is tested on realistic data from the city of Vienna. The results associated with different scenarios are analyzed to illustrate the value of the proposed approach for the design of construction logistics processes.

     

Effects of melatonin administration on embryo implantation and offspring growth in mice under different schedules of photoperiodic exposure

Background

Embryo implantation is crucial for animal reproduction. Unsuccessful embryo implantation leads to pregnancy failure, especially in human-assisted conception. Environmental factors have a profound impact on embryo implantation. Because people are being exposed to more light at night, the influence of long-term light exposure on embryo implantation should be explored.

Methods

The effects of long photoperiodic exposure and melatonin on embryo implantation and offspring growth were examined. Long photoperiodic exposure (18:6 h light:dark) was selected to resemble light pollution. Melatonin (10^?2, 10^?3, 10^?4, 10^?5 M) was added to the drinking water of mice starting at Day 1 (vaginal plugs) until delivery.

Results

Melatonin treatment (10^?4,10^?5 M) significantly increased litter sizes compared to untreated controls (12.9 ± 0.40 and 12.2 ± 1.01 vs. 11.5 ± 0.43; P < 0.05). The most effective concentration of melatonin (10^?4 M) was selected for further investigation. No remarkable differences were found between melatonin-treated mice and controls in terms of the pups’ birth weights, weaning survival rates, and weaning weights. Long photoperiodic exposure significantly reduced the number of implantation sites in treated mice compared to controls (light/dark, 12/12 h), and melatonin rescued this negative effect. Mechanistic studies revealed that melatonin enhanced the serum 17β-estradiol (E₂) levels in the pregnant mice and upregulated the expression of the receptors MT1 and MT2 and p53 in uterine tissue. All of these factors may contribute to the beneficial effects of melatonin on embryo implantation in mice.

Conclusion

Melatonin treatment was associated with beneficial effects in pregnant mice, especially those subjected to long photoperiodic exposure. This was achieved by enhanced embryo implantation. At the molecular level, melatonin administration probably increases the E₂ level during pregnancy and upregulates p53 expression by activating MT1/2 in the uterus. All of the changes may improve the microenvironment of the uterus and, thus, the outcomes of pregnancy.

     

Contingency discriminability and the generalized matching law describe choice on concurrent ratio schedules of wheel-running reinforcement

Belke (2010) showed that on concurrent ratio schedules, the difference in ratio requirements required to produce near exclusive preference for the lower ratio alternative was substantively greater when the reinforcer was wheel running than when it was sucrose. The current study replicated this finding and showed that this choice behavior can be described by the matching law and the contingency discriminability model. Eight female Long Evans rats were exposed to concurrent VR schedules of wheel-running reinforcement (30s) and the schedule value of the initially preferred alternative was systematically increased. Two rats rapidly developed exclusive preference for the lower ratio alternative, but the majority did not - even when ratios differed by 20:1. Analysis showed that estimates of slopes from the matching law and the proportion of reinforcers misattributed from the contingency discriminability model were related to the ratios at which near exclusive preference developed. The fit of these models would be consistent with misattribution of reinforcers or poor discrimination between alternatives due to the long duration of wheel running.     

Superstitious responding and reinforcement rate under concurrent variable-interval extinction schedules

To examine superstitious responding, four pigeons key pecked under multiple concurrent variable-interval 45 s variable-interval 90 s concurrent variable-interval 90 s variable-interval 180 s schedules in the absence of a changeover delay. The two variable-interval 90 s schedules then were replaced by extinction, and key-peck responding during extinction was examined as a function of the prevailing reinforcement rate. During the first several sessions, extinction-key responding was maintained closer to baseline levels in the presence of the higher reinforcement rate, and this effect dissipated or even reversed with continued exposure to extinction. Although extinction-key responding generally decreased to near-zero levels after several sessions, in a few instances, it continued for 30 and 45 sessions. These results demonstrate how concurrent variable-interval extinction schedules can be used to investigate what often has been labeled superstitious responding.     

Variability of force and interresponse time under random interval reinforcement schedules

Response variability was examined under five random interval schedules with minimum mean interreinforcement intervals of 15, 30, 60, 120, and 240 sec. Distributions of response force-time integrals showed no systematic variability changes with increases in reinforcement intermittency. Corresponding distributions of interresponse times revealed increases in variability accompanying increases in reinforcement intermittency. The relationship of variability to these two measures, and the potential effect of behavior outside the experimentally measured response class, on recorded variability within the class, are considered.     

Effects of unsignaled delays of reinforcement on fixed-interval schedule performance

Key pecking of pigeons was maintained by a fixed-interval (FI) 61-s schedule. The effects of resetting and nonresetting unsignaled delays of reinforcement then were examined. The resetting delay was programmed as a differential-reinforcement-of-other-behavior schedule, and the nonresetting delay as a fixed-time schedule. Three delay durations (0.5, 1 and 10 s) were examined. Overall response rates were decreased by one and 10-s delays and increased by 0.5-s delays. Response patterns changed from positively accelerated to more linear when resetting or nonresetting 10-s delays were imposed, but remained predominantly positively accelerated when resetting and nonresetting 0.5- and 1-s delays were in effect. In general, temporal control, as measured by quarter-life values, changed less than overall response rates when delays of reinforcement were in effect. The response patterns controlled by FI schedules are more resilient to the nominally disruptive effects of delays of reinforcement than are corresponding overall response rates.     

Effects of three feeding schedules on tumor and host of Lewis lung carcinoma-bearing mice

The effect of three feeding schedules on tumor and host were examined in Lewis Lung bearing (TB) and nontumor bearing (NTB) C57/B1 mice. Both NTB and TB animals were divided into three groups: the control groups which were fed ad libitum; the intermittent fed (IMF) groups were fed for 32 hr and fasted for 16 hr in each 48-hr cycle, and the alternate day fed (ADF) groups were fed for a 24-hr interval in each 48-hr cycle. The animals were killed at the end of the fifteenth day, following a fed day for all groups. In the NTB groups, only the ADF group showed decreased food intake and lower body weight gain as compared to their control group. In the TB mice, as compared to their control group, the IMF group showed a significant reduction in the mean tumor weight with no change in the mean host weight, even though the daily food intakes of these two groups were the same over the experimental interval. In contrast, the ADF group showed reductions in both host and tumor weights as compared to their control group. The tumor to host weight ratios were significantly reduced for both the IMF and ADF groups as compared to the ratios found for the control groups, which suggests a differential effect on the tumor and on the host due to the feeding schedule. As assessed by the protein, RNA, and DNA concentrations, no compositional differences were noted for the tumors obtained from the animals that were maintained on each of the three different feeding schedules. In the NTB mice, no differences in tissue leucine (Leu) oxidation occurred between the groups for liver and skeletal muscle, whereas in the TB animals in vitro Leu oxidation capability by skeletal muscle specimens was markedly enhanced in the ADF group, but no difference was noted for the IMF group of the TB mice when compared to the control group. Taken together, these results suggest that the 32-hr fed:16-hr fast schedule (IMF) was beneficial and the 24-hr fed:24-hr fast schedule was detrimental compared to the ad libitum feeding schedule with respect to tumor and host relationships.     

Effects of concurrent random-time schedules on the spatial distribution of behavior in rats

We evaluated the effects of concurrent random temporal contingencies of water delivery on the location of rats' behavior. In this experiment, two concurrent random-time schedules delivered water in two dispensers that were located at opposite ends of the chamber, and provided complementary frequencies of water deliveries while the overall number of deliveries stayed constant. Time allocation in the areas adjacent to each water dispenser covaried with water deliveries, although no proportional relation was found. Rats showed a preference for the area where water was initially presented. The results point to the importance of examining spatial properties and patterning of behavior.     

Effects of reflex delays on postural control during unstable seated balance

Patients with low-back pain (LBP) exhibit longer trunk muscle reflex latencies and poorer postural control than healthy individuals. We hypothesized that balance during a simulated postural control task would become impaired when the delays exhibited by LBP patients were incorporated into neuromuscular control. The task chosen for this investigation was seated balancing, which emphasizes trunk muscles’ contribution in postural control. This task was modeled in Simulink? as a fourth order linearized dynamic system with feedback delays. Optimization (minimizing error between experimental and model data) of state variables was used to determine neuromuscular control parameters. Experimental data were obtained from 7 subjects during 5 perturbation trials while balancing on the seat with eyes closed. Model accuracy, reflecting the ability of the model to capture the dynamics of seated balance, was correlated with seated balance performance (r=0.91, p<0.001). To minimize the risk of erroneous findings from inaccurate modeling, only the best five balancers’ data were used for hypothesis testing. In these five subjects, feedback delays in modeled neuromuscular control were increased to determine their effect on task stability, trunk displacement and trunk moment. Simulations showed that longer delays found in LBP, in general, did not produce unstable balancing, but did result in increased trunk displacement (p<0.001) and trunk moment (p=0.001). This impairment in neuromuscular control in chronic LBP patients could possibly exacerbate their condition by increasing tissue strain (more spinal displacement) and stress (more spinal loading).