Terminal Link Research Articles

Resurgence of response duration in human participants

Previously reinforced responses can reappear when reinforcement is withdrawn from current responding. This is known as resurgence. Although resurgence of response topography, spacing, and patterns over time has been demonstrated, there is no evidence of resurgence of response duration. This experiment explored resurgence of response duration in humans. In Phase 1 a multiple schedule of reinforcement with two components was used. In each component a chained variable-interval 30s, variable-ratio 3 schedule was implemented. In the terminal link of the chained schedule, response durations between 0.1 and 0.5s were reinforced during one component, and between 2 and 8s in the other component. In Phase 2, response requirement during the terminal link of the chained schedule was inverted between components relative to Phase 1. In Phase 3 the chained schedule was changed to a variable-interval 30-s, extinction 30s. Resurgence of the durations trained during Phase 1 was observed. It was concluded that duration is a response dimension that reappears during extinction.

Impulsivity in spontaneously hypertensive rats: Within-subjects comparison of sensitivity to delay and to amount of reinforcement

Previous research has shown that spontaneously hypertensive rats (SHR) display higher levels of impulsive choice behavior, which is accompanied by a higher sensitivity to the delay of reinforcement, and by a normal sensitivity to the amount of reinforcement. Because those results were based on three different samples of subjects, in the present report we evaluated these three processes in the same individuals. SHR and WIS rats were exposed to concurrent-chains schedules in which the terminal links were manipulated to assess impulsivity, sensitivity to delay, and sensitivity to amount. For exploring impulsivity, a terminal link was associated with a small reinforcer (1 pellet) delivered after a short delay (2s) while the other terminal link was associated with a larger reinforcer (4 pellets) delivered after a longer delay (28s). For assessing sensitivity to delay, both alternatives delivered the same amount of reinforcement (1 pellet) and the only difference between them was in the delay before reinforcement delivery (2s vs 28s). For assessing sensitivity to amount, both alternatives were associated with the same delay (15s), but the alternatives differed in the amount of reinforcement (1 vs 4 pellets). In addition to replicating previously observed effects within-subjects, we were interested in analyzing different aspects of the regularity of rats’ actions in the choice task. The results confirmed that previous findings were not a consequence of between-group differences: SHR were more impulsive and more sensitive to delay, while their sensitivity to amount was normal. Analyses of response regularity indicated that SHR subjects were more periodic in their responses to levers and in their feeder entries, had a higher number of short-duration bouts of responding, and made a substantially higher number of switches between the alternatives. We discuss the potential implications of these findings for the possible behavioral mechanisms driving the increased sensitivity to delay in SHR.

Short-frame Prior Scheduling with WRR Transmission Strategy in AFDX Terminal System

A new scheduling strategy of terminal system virtual link (VL) is put forward, which is based on the short-frame prior scheduling and integrated with weighted round robin (WRR).The new approach, ensured the priority of the important short-frame and balanced the delay upper bound of other different priority signals. Based on the theory of network calculus, the paper derived the delay upper bound of different virtual links through the new combinatorial scheduling strategy and researched the relation among the maximum delay upper bound, weight ratio and frame length. The AFDX network model based on OPNET is established, the terminal system data transmission delay under the three scheduling strategy is simulated and compared. The results show that, the new scheduling strategy can reduce the maximum delay time of short-frame virtual link, and improve the processing bandwidth of relatively important task in long-frame data transmission. Above all, it is feasible and applicable to airborne network with more short-frame and different priority data flows.

Semi-lazy probabilistic roadmap: a parameter-tuned, resilient and robust path planning method for manipulator robots

An indispensable feature of a modern intelligent robot is its capability to plan short and safe motions in the presence of obstacles in its workspace, which is highly important for industrial manipulators in charge of automatic picking and placing, welding, painting, etc. On the other hand, collision-free motion planning of serial manipulators becomes exponentially hard with the increase of number of joints, and so efficient methods like sampling-based ones are vastly used for most real-world problems. In this paper, we propose a new variation of sampling-based methods called semi-lazy probabilistic roadmap (SLPRM) for motion planning of industrial manipulators, which benefits from the advantages of the basic probabilistic roadmap (PRM) and lazy-PRM (LPRM) methods. Unlike the exhaustive and zero collision-checking policies implemented respectively in PRM and LPRM, the SLPRM collision-checks random configurations for only m terminal links (i.e., from end-effector backwards) of the manipulator in the roadmap construction phase. As a result, on one hand, the roadmap construction time reduces compared with PRM due to less collision checks, and on the other hand, query times decrease compared with LPRM due to a better quality of the initial roadmap. A central decision in SLPRM is to properly determine the value of m, which has a direct effect on its speed. For this purpose, a new parameter tuning approach based on a combination of Shannon’s Entropy and VIKOR methods is implemented to determine the best values for m and all other parameters of the algorithm. The proposed method has been tested and implemented in simulated and real workspace scenarios for an RV-E3J Mitsubishi industrial manipulator robot, and the results showed that the mean planning time of the SLPRM was shorter compared with that of the PRM and LPRM. To make the algorithm resilient and robust to internal faults and environmental variations such as positional errors, joint failures, and obstacle displacements, we have also proposed the resilient and robust SLPRM, which through concentrated sampling and roadmap-amending procedures, can handle unexpected failures and changes.

Suboptimal Choice in Pigeons: Stimulus Value Predicts Choice over Frequencies.

Pigeons have shown suboptimal gambling-like behavior when preferring a stimulus that infrequently signals reliable reinforcement over alternatives that provide greater reinforcement overall. As a mechanism for this behavior, recent research proposed that the stimulus value of alternatives with more reliable signals for reinforcement will be preferred relatively independently of their frequencies. The present study tested this hypothesis using a simplified design of a Discriminative alternative that, 50% of the time, led to either a signal for 100% reinforcement or a blackout period indicative of 0% reinforcement against a Nondiscriminative alternative that always led to a signal that predicted 50% reinforcement. Pigeons showed a strong preference for the Discriminative alternative that remained despite reducing the frequency of the signal for reinforcement in subsequent phases to 25% and then 12.5%. In Experiment 2, using the original design of Experiment 1, the stimulus following choice of the Nondiscriminative alternative was increased to 75% and then to 100%. Results showed that preference for the Discriminative alternative decreased only when the signals for reinforcement for the two alternatives predicted the same probability of reinforcement. The ability of several models to predict this behavior are discussed, but the terminal link stimulus value offers the most parsimonious account of this suboptimal behavior.

A cumulative decision model for three-alternative choice in concurrent chains.

Traditional models for choice in the concurrent-chains procedure have assumed that terminal-link stimuli acquire value as conditioned reinforcers, and that 2-alternative choice provides a measure of relative value according to the matching law. By contrast, the cumulative decision model (CDM; Christensen & Grace, 2010) explains choice as the aggregate effect of comparing delays to a criterion on initial-link responding, not conditioned reinforcement. Here we test whether the CDM can account for choice in 3-alternative concurrent-chains (3ACC) and compare it with the hyperbolic value-added model (HVA; Mazur, 2001), which assumes that choice depends on the increase in conditioned reinforcement value signaled by terminal-link stimuli and has been successful in previous 3ACC research (Mazur, 2000). In Experiment 1, 4 pigeons responded in 3ACC in which the terminal links were fixed-interval schedules, and parameter estimates from fits of CDM and HVA were used to calculate predictions for conditions with variable-interval terminal links. The predictions of CDM were more accurate than those of HVA. In Experiment 2, 7 pigeons responded in 3ACC in which the terminal links were fixed-interval schedules. Although both models described the data well, residuals from HVA fits showed a systematic pattern predicted by CDM, characterized by a third-order polynomial with a negative cubic coefficient. Finally, we conducted a residual meta-analysis (Sutton, Grace, McLean, & Baum, 2008) of data from prior 3ACC studies. HVA residuals showed the same negative cubic pattern as in Experiment 2, whereas no systematic pattern was found in the CDM residuals. Overall, results support the CDM and suggest that the same principles which describe binary choice in concurrent chains generalize without modification to 3-alternative choice. (PsycINFO Database Record

Environmental dynamics modulate covariation of choice and timing

Response allocation between delayed reinforcers is presumably a function of the discrimination of those delays. In the present experiment, we analyzed the functional relation between response allocation and temporal discrimination across different environmental dynamics. Three pigeons pecked for food in a concurrent-chain schedule. Concurrent variable-interval initial links produced fixed-interval (FI) terminal links. Start and stop times, single-trial measures of temporal discrimination, were obtained from occasional ‘no-food’ terminal links. In dynamic, rapid-acquisition conditions, terminal links were FI 10s and 20s and the location of the initial link leading to the shorter terminal link varied unpredictably across sessions. In the static conditions, both terminal links were either “uniform” FI 15-s schedules or one terminal link was “fixed” at FI 10s and the other at 20s. Response allocation and start and stop times adjusted within sessions in dynamic conditions and across sessions of static conditions. Residuals from regressions of expected on programmed immediacy ratios were positively correlated to a greater magnitude in dynamic than static conditions. This change in residual covariation demonstrated that environmental dynamics modulated the relation between choice and timing.

Human choice under schedules of negative reinforcement

The generalized matching equation provides a good description of response allocation in concurrent schedules of positive reinforcement in nonhumans as well as in humans. The present experiment was conducted to further investigate the allocation of responding under concurrent schedules of negative reinforcement (i.e., timeouts from pressing a force cell) in humans. Each of three participants was exposed to different reinforcement ratios (9:1, 1:1 and 1:9) in the terminal links of a concurrent-chains schedule of negative reinforcement. The allocation of responding under this schedule was well described by the generalized matching equation, for each participant. These results replicate previous findings obtained with nonhumans and humans under concurrent schedules of positive reinforcement. In addition, they extend the results reported by Alessandri and Rivière (2013) showing that human behavior maintained by timeouts from an effortful response is sensitive to changes in relative reinforcement ratios as well as relative delays of reinforcement.

Evidence for a magnitude effect in probability discounting with pigeons.

A magnitude effect in probability discounting is well established with humans, in which the value of a larger reward decreases more with uncertainty than the value of a smaller reward. We report 2 experiments that show that an analogous result is obtained with pigeons choosing between probabilistic food rewards in a 2-component concurrent-chains procedure. In Experiment 1, the terminal links delivered large (4-s access to food) and small (2-s access to food) rewards with either 100% or 50% probability across components. Preference for the larger reward was greater in the 100% component. In Experiment 2, the terminal links delivered reinforcement on 100% or 50% of terminal links and the rewards were large (4-s access to food) or small (2-s access to food) across components. Preference for the 100% alternative was greater when rewards were large. In both experiments, results indicate that the value of the larger reward decreased more when its probability was 50% than the value of the smaller reward, confirming the magnitude effect, and were similar regardless of whether the food and no-food outcomes for the 50% terminal links were differentially signaled. Results were predicted by an extension of the cumulative decision model (Christensen & Grace, 2010; Grace & McLean, 2006), which accounts for the effects of magnitude and probability on choice and can also explain the apparently contradictory results of prior research on the magnitude effect in delay discounting with pigeons. The model shows that a single process can account for delay and probability discounting in nonhumans, including the opposite effects of reward magnitude.

Impulsivity and sensitivity to amount and delay of reinforcement in an animal model of ADHD

Previous research has been inconclusive about the degree of impulsivity displayed by spontaneously hypertensive rats (SHR), an animal model of Attention Deficit Hyperactivity Disorder (ADHD). In the present set of experiments, concurrent-chains schedules were employed in order to explore SHR's impulsivity, sensitivity to delay, and sensitivity to amount of reinforcement; Wistar rats (WIS) were used as comparison group. In the three experiments – performed with different subjects – non-independent variable interval 30s schedules were presented in the initial links; the difference between experiments was in the terminal links. For exploring impulsivity, one of the terminal links (SS) was associated to a short delay (2s) and a small reinforcer (1 pellet), whereas the other terminal link (LL) was associated to a longer delay (28s) and a larger reinforcer (4 pellets). The results indicated a remarkably higher impulsivity in SHR. Because this impulsivity may have as potential mechanisms an increased sensitivity to delay and/or a decreased sensitivity to the amount of reinforcement, in experiments 2 and 3 these possibilities were examined. For assessing sensitivity to delay, the following pairs of fixed interval (FI) schedules were used in the terminal links in five conditions: 2–28, 6–24, 15–15, 24–6, 28–2s; the magnitude of reinforcement was 1 pellet in all conditions for both alternatives. For assessing sensitivity to amount, in five conditions the alternatives were associated with different magnitudes of reinforcement: 1–5 pellets, 2–4, 3–3, 4–2 and 5–1 in left–right alternatives, respectively; the delay to reinforcement was controlled by a FI 15s in all conditions and for both alternatives. The sensitivity to delay and the sensitivity to amount were calculated according to the Generalized Matching Law. The results indicated a higher sensitivity to delay in SHR, and the same sensitivity to amount in SHR and WIS rats. These results suggest that the increased sensitivity to delay influences the high level of impulsivity observed in SHR.

Regularities in responding during performance of a complex choice task

Systematic variations in the rate and temporal patterns of responding under a multiple concurrent-chains schedule were quantified using recurrence metrics and self-organizing maps to assess whether individual rats showed consistent or idiosyncratic patterns. The results indicated that (1) the temporal regularity of response patterns varied as a function of number of training sessions, time on task, magnitude of reinforcement, and reinforcement contingencies; (2) individuals showed heterogeneous, stereotyped patterns of responding, despite similarities in matching behavior; (3) the specific trajectories of behavioral variation shown by individuals were less evident in group-level analyses; and (4) reinforcement contingencies within terminal links strongly modulated response patterns within initial links. Temporal regularity in responding was most evident for responses that led to minimally delayed reinforcers of larger magnitude. Models of response production and selection that take into account the time between individual responses, probabilities of transitions between response options, periodicity within response sequences, and individual differences in response dynamics can clarify the mechanisms that drive behavioral adjustments during operant conditioning.

Effects of the relative values of alternatives on preference for free-choice in humans.

Organisms often prefer conditions that allow selection among alternatives (free-choice) to conditions that do not (forced-choice), particularly when response alternatives in free-choice produce equal or greater reinforcer magnitudes than those available under forced-choice. We present data on free-choice preference for human participants who gained or lost points by selecting images of cards on a computer screen under a concurrent-chains schedule. Responding during the initial link gained access to a terminal link offering a single-card set (forced-choice) or a three-card set (free-choice). The alternatives in free-choice produced reinforcer magnitudes (points) that were: (a) equal to forced-choice; (b) equal to and greater than forced-choice; and (c) equal to and less than forced-choice. Participants showed reliable preference for free-choice under some conditions; however, preference decreased as reinforcer magnitude for some alternatives in free-choice was reduced. This occurred even though it was possible to obtain the same number of points across free- and forced-choice. Although preference for free-choice was clearly demonstrated, the effect of points available in the terminal link suggests that this phenomenon is subject to modulation by other processes, such as reinforcement or punishment by obtained outcomes in the terminal link. Context (reinforcer-gain or -loss) was not a reliable predictor of preference.

Modeling and Simulating a Narrow Tilting Car Using Robotics Formalism

Modeling and simulation are fundamental tools to develop new urban vehicles. The aim of this work is to model and simulate a narrow urban tilting car, which should significantly decrease traffic congestion, pollution, and parking problems. The structure of the vehicle contains closed kinematic chains. The modeling approach is based on the modified Denavit and Hartenberg description, which is commonly used in robotics, by considering the vehicle as a mobile robot composed of a multibody poly-articulated system in which the terminal links are the wheels. This description allows automatic calculating of the symbolic expressions of the geometric, kinematic, and dynamic models. A simulator is developed with MATLAB/Simulink, and the simulation of different scenarios is performed and analyzed.

Quantifying transitions in response allocation with change point analysis in concurrent chains

Research based on the matching law has demonstrated empirically that the physical and temporal properties of the events, the context in which they occur and the signals that mark them in space and time all contribute to response allocation. When the physical or temporal properties of different outcomes change in ways that affect their relative value, the ratio of responses to each outcome adjusts with time and exposure to the new contingency. Five pigeons pecked in concurrent-chain schedules with fixed-interval terminal links. Terminal-link schedules were changed each session. In most sessions, response allocation was initially indifferent to terminal-link schedules but shifted to favor the initial link associated with the shorter terminal link. As a first step to disambiguating response allocation in transition from stable response allocation, transition durations were interpolated from change points in cumulative response plots. The relation between transition duration and absolute log immediacy ratio was negative: the number of initial links until the shift occurred was longer when terminal-link schedules were relatively similar than when they were relatively different.

IMPULSIVE CHOICE IN LEWIS AND FISCHER 344 RATS: EFFECTS OF EXTENDED TRAINING

Delay discounting in Lewis and Fischer 344 was compared using a novel concurrent-chains procedure. In the initial-link, two levers were available and a random-interval schedule was in effect. One terminal link provided a smaller reinforcer (1 pellet) and the other terminal provided a larger reinforcer (4 pellets). Terminal-link entry was scheduled randomly, with the constraint that entries to each occurred equally often. The terminal link associated with the smaller reinforcer was always a fixed-interval (FI) 5-s (i.e., the delay to the smaller reinforce was always 5 s). Delay discount functions were obtained by varying the terminal-link FI associated with the larger reinforcer across blocks of cycles within each session. The order of the delays (5, 10, 20, 40, and 80 s) within each session was randomly determined to minimize carryover effects. Graded delay-discount functions were obtained which were well described by a hyperbolic-delay equation. Initially, the Lewis rats were more sensitive to the effects of delay to larger reinforcer than the Fischer 344 rats. With extended training, however, the Fischer 344 rats showed a greater change in sensitivity to the delayed larger reinforcer, achieving levels of impulsivity comparable to those reached by the Lewis rats. These data suggest that a) the concurrent-chains procedure arranged here provides an efficient method for producing within-sessions graded discount functions in individual subjects, and b) differences in delay discounting between Lewis and Fischer rats often reported (and attributed to neurobiological differences) are not apparent after extended training.

Modeling Method for Mechanism Configuration of the Articulated Industrial Robot

Modeling method for mechanism configuration of the articulated industrial robot is proposed. Each link of mechanism configuration is modeled by a type of variable coordinate system based on UG system. The variable coordinate system is changed with a type of variable kinematical parameter of the links. Thus the position and direction vector of terminal link by reference to frame at any time can be obtained by using inquiry command in UG system. The typical modeling example of the FANUC articulated industrial robot which possesses 6 rotation freedoms in space is as shown in figure. It is appearance that the Modeling method by this way is simple and the modeling result of the articulated industrial robot is visual, believable and reliable.

Sensitivity to delay is affected by magnitude of reinforcement in rats

Previous research has provided discrepant results about how reinforcement delay and magnitude are combined to determine the value of the alternatives in concurrent-chains schedules. In the present experiment, we analyzed a possible interaction between these characteristics of reinforcement, employing a two component concurrent-chains schedule, with rats as experimental subjects. Non-independent VI schedules were presented in the initial links of each component. In the terminal links, the following pairs of delays to reinforcement were presented in 4 conditions: 2-28, 6-24, 24-6, 28-2s (fixed time schedules for a group, fixed interval schedules for the other). Magnitude of reinforcement was maintained constant within components: one pellet for one component, and four pellets for the other. The results indicated that in both groups, the sensitivity to delay – calculated according to the generalized matching law – was higher in the component with the larger reinforcer. This result is in contrast with those reported in the literature of temporal discounting with human participants.

PREFERENCE REVERSAL BETWEEN IMPULSIVE AND SELF‐CONTROL CHOICE

In a concurrent-chains procedure, pigeons chose between reinforcers varying in delay and amount. Reinforcer amount was determined by duration of access to grain, and delay was determined by fixed-interval schedules in the terminal links. Preference was measured by the ratio of responses in initial links. Dependent scheduling of variable-interval schedules in initial links ensured that delay and amount were not confounded with frequency of outcomes, which remained equal for the two choices. In Experiment 1, in components signaled by red keys in the initial links, small and large reinforcers were delivered after delays of 1 s and 10 s respectively. In components signaled by green, additional time was added to both delays. Smaller-sooner reinforcers were preferred in red components. In green components, smaller-sooner reinforcers were preferred at short delays, and choices for the larger-later reinforcer generally increased with increasing duration of the added delay. At longer delays, up to 15 s, the larger-later reinforcer was preferred. That is, the pigeons showed within-session preference reversal, with impulsive choice at short delays in red components and self-control choice at long delays in green components. In Experiment 2, added delay to both reinforcement and reinforcer amount were varied. Sensitivity of initial-link response ratios to ratios of amount increased with increasing duration of the added delay. This interaction between delay and amount was predicted if the temporal discounting functions assumed the magnitude effect in which discounting rate was inversely proportional to amount. It was also predicted by the contextual choice model of performance in concurrent-chains procedures.

CONDITIONED REINFORCEMENT IN CHAIN SCHEDULES WHEN TIME TO REINFORCEMENT IS HELD CONSTANT

Two alternative approaches describe determinants of responding to a stimulus temporally distant from primary reinforcement. One emphasizes the temporal relation of each stimulus to the primary reinforcer, with relative proximity of the stimulus determining response rate. A contrasting view emphasizes immediate consequences of responding to the stimulus, the key factor being the conditioned reinforcement value of those immediate consequences. To contrast these approaches, 4 pigeons were exposed to a two-component multiple schedule with three-link chain schedules in each component. Only middle-link stimuli differed between chains. Baseline reinforcement probabilities were 0.50 for both chains; during discrimination phases it was 1.0 for one chain and 0.0 for the other. During discrimination phases pigeons responded more to the reinforcement-correlated middle link than to the extinction-correlated middle link, demonstrating that responding was affected by the probability change. Terminal link responding was also higher in the reinforced chain, even though the terminal link stimulus was identical in both chains. Of greatest interest is initial link responding, which was temporally most distant from reinforcement. Initial link responding, necessarily equal in the two chains, was significantly higher during the 1.0/0.0 discrimination phases, even though overall reinforcement probability remained constant. For 3 of 4 birds, in fact, initial-link response rates were higher than terminal-link response rates, an outcome that can be ascribed only to the potent conditioned reinforcement properties of the middle-link stimulus during the discrimination phases. Results are incompatible with any account of chain behavior based solely on relative time to reinforcement.

Excavation Dynamics and Control of Shallow Lunar Soil Sampling Manipulator

The lunar soil excavation dynamics and control are complicated because of the high coupling among manipulator, backhoe device and lunar soil with uncertain parameters. To solve this problem, a multi-body dynamic model, regard the lunar soil backhoe device as the terminal link of the manipulator is developed using supposed link method, and then the excavation dynamics is modeling on the combination of the multi-body dynamic and Balovnev soil-tool interaction formula. Based on this model, an excavation trajectory tracking controller is realized via fuzzy-computed torque method. To reduce the affection of the excavation resistance to control precision, online lunar soil parameters estimation is held in the early stage of the excavation process, and the excavation resistance compensation, determined by those estimation results, is added to the tracking controller using feed-forward form. Simulation results indicate that the controller effective, which has the characteristics of fast tracking and high control precision.