Mixed Schedule Research Articles

Averaging of temporal memories by rats.

Rats were trained on a mixed fixed-interval schedule in which stimulus A (tone or light) indicated food availability after 10 s and stimulus B (the other stimulus) indicated food availability after 20 s. Testing consisted of nonreinforced probe trials in which the stimulus was A, B, or the compound AB. On single-stimulus trials, rats responded with a peak of activity around the programmed reinforced time. On compound-stimulus trials, rats showed a single scalar peak of responding at a time midway between those for stimulus A and B. These results suggest that when provided with discrepant information regarding the temporal predictability of reinforcement, rats compute an average of the scheduled reinforcement times for the A and B stimuli and use this average to generate an expectation of reward for the compound stimuli.

Auditory Model

An experiment was conducted to determine the impact of an auditory model on blocked, random, and mixed practice schedules of three five-segment timing sequences (relative time constant). We were interested in whether or not the auditory model differentially affected the learning of relative and absolute timing under blocked and random practice. Participants (N = 80) were randomly assigned to one of eight practice conditions, which differed in practice schedule (blocked-blocked, blocked-random, random-blocked, random-random) and auditory model (no model, model). The results indicated that the auditory model enhanced relative timing performance on the delayed retention test regardless of the practice schedule, but it did not influence the learning of absolute timing. Blocked-blocked and blocked-random practice conditions resulted in enhanced relative timing retention performance relative to random-blocked and random-random practice schedules. Random-random and blocked-random practice schedules resulted in better absolute timing than blocked-blocked or random-blocked practice, regardless of the presence or absence of an auditory model during acquisition. Thus, considering both relative and absolute timing, the blocked-random practice condition resulted in overall learning superior to the other practice schedules. The results also suggest that an auditory model produces an added effect on learning relative timing regardless of the practice schedule, but it does not influence the learning of absolute timing.

Effect of mixed protein schedules combined with choline and betaine on the growth performance of Nile tilapia (Oreochromis niloticus)

Reducing feed cost has been a major issue in fish nutrition. Mixed protein schedules have been proposed as one of the methods successfully tested in many fish species to reduce feed cost. Meanwhile, the effect of dietary choline and betaine supplementation on fish performance was assessed. The aim of the present study was to investigate the effect of mixed protein schedules, combined with choline and betaine, on Nile tilapia performance. This experiment was conducted in a (4 × 3) factorial arrangement of treatments. Four mixed protein schedules were examined, in the presence of choline 0.3% and/or betaine 0.5%. The four mixed protein schedules were achieved by alternating diet (A; 31%CP) and diet (B; 24%CP) as follows: (6 days-A), (5 days-A/1 day-B), (4 days-A/2 days-B) and (3 days-A/3 days-B). The results indicated that in the presence of betaine 0.5% and choline 0.3%, the optimal mixed protein schedule for tilapia was (3A/3B). Fish fed on the 4A/2B or 3A/3B schedules utilized protein more efficiently than fish fed on the (6A) schedule. Fish fed diets supplemented with betaine (b) only showed the highest energy retention. The lowest feed cost was recorded for fish fed on (3A/3B) in the presence of betaine 0.5% and choline 0.3% in fish diet.

Schedule discrimination in a mixed schedule: Implications for models of the variable-ratio, variable-interval rate difference

In Experiment 1, each of three humans knowledgeable about operant schedules used mouse clicks to respond to a "work key" presented on a monitor. On a random half of the presentations, work-key responses that completed a variable ratio (VR) 12 produced a tone. After five tones, the work key was replaced by two report keys. Pressing the right or left report key, respectively, added or subtracted yen50 from a counter and produced the work key. On the other half of the presentations, a variable interval (VI) associated with the work key was defined so its interreinforcer intervals approximated the time it took to complete the variable ratio. After five tone-producing completions of this schedule, the report keys were presented. Left or right report-key presses, respectively, added or subtracted yen50 from the counter. Subjects achieved high yen totals. In Experiment 2, the procedure was changed by requiring an interresponse time after completion of the variable interval that approximated the duration of the reinforced interresponse time on the variable ratio. Prior to beginning, subjects were shown how a sequence of response bouts and pauses could be used to predict schedule type. Subjects again achieved high levels of accuracy. These results show humans can discriminate ratio from interval schedules even when those schedules provide the same rate of reinforcement and reinforced interresponse times.

Metronomic irinotecan and standard FOLFIRI regimen as first-line chemotherapy in metastatic colorectal cancer (MCRC). Final results of phase II study

14520 Background: Angiogenesis is necessary to sustain the growth of both the primary tumour and the development of metastases in colorectal cancer. Before the clinical use of bevacizumab, metronomic chemotherapy was the only mean to block the growth of tumor microvessel. CPT-11 showed, in preclinical model, to have antiangiogenetic properties using low doses and weekly administration. We carried out this study in order to evaluate the activity and toxicity of mixed metronomic and standard FOLFIRI regimen in MCRC. Methods: From 10/03 to 9/05 we treated 46 pts (24M 22F), median age 66 years (range 41–79), ECOG PS 0–2 with this schedule: CPT- 11 10 mg/mq days 1, 7, 10 and CPT-11 150 mg/mq day 2, l-Folinic Acid 100 mg/mq days 2 and 3, 5-FU 400 mg/mq bolus days 2 and 3 and 5- FU 600 mg/mq 44 hours c.i. days 2 and 3 every two weeks for a maximum of 12 cycles. Results: All pts have been evaluable activity and toxicity. We obtained 9 CR (20%), 12 PR (26%) with an ORR of 46% (CI 95%: ±13%) and 17 SD. After a median follow-up of 24 months we registered a median TTP of 10 months and a median OS of 22 months. As regard toxicity, the chemotherapy has been well tolerated; no toxic deaths occurred and no therapy ended for toxicity. 6 pts had 25% dose reduction (standard schedule) for diarrhea G4 after the first cycle. The main toxicities recorded on a total of 440 cycles (cy) delivered were: diarrhea G4 1.7% and G3 2.3% of the cy. Neutropenia G3 5.8% and vomiting G3 0.5% of the cy. Anemia G2 was recorded in 14 pts. All pts suffered from partial alopecia and half of the pts from mild oral mucositis. Conclusions: This mixed schedule seems to be active and well tolerated, ORR, TTP and OS are similar to Hurwitz results (NEJM 2004; 350: 2335–42) but with less adverse events. The combination of this schedule with bevacizumab deserves further studies. No significant financial relationships to disclose.

Manual and Ocular Observing Behavior in Human Subjects

The present experiment analyzed manual and ocular observing behavior during a Wyckoff observing-response procedure. Following visual discrimination training with a multiple variable-interval extinction schedule, four human subjects pressed a key to earn points under the corresponding mixed schedule. Subjects could emit a manual response, touching a spot on a computer touchscreen, that produced S+ and S- stimuli correlated with the variable-interval and extinction components, respectively, thus converting the mixed schedule into a multiple schedule. Eye-tracking apparatus measured ocular observing behavior in both multiple and mixed schedules. Under the multiple schedule, subjects tended to look at S+ for longer durations than S-. Under the mixed schedule, in contrast, most subjects manually produced S- for longer durations than S+. Comparisons of the ocular and manual observing responses indicate that direct measurements of eye movements reveal characteristics of observing behavior that do not derive from manual observing responses alone.

EFFECT OF MIXED PROTEIN SCHEDULES ON NILE TILAPIA {ORE0CHROMIS NILOTICUS) PERFORMANCE IN COMBINATION WITH SOME FEED ADDITIVES I-MIXED PROTEIN SCHEDULES AND SODIUM CHLORIDE

The experiment was designed in a (4x3) factorial arrangement of treatments to investigate the effect of four different mixed protein schedules and three dietary Na/K ratios on Nile tilapia performance. The four protein schedules were achieved by alternating the diet (A ; 31%CP)and diet (B;24°/oCP)as follows (6-days~AX(5days~A/lday-B), (4days-A /2days-B) and (3days-A /3days-B).Meanwhile, sodium chloride was added to study the effect of Na/K ratio of 0.5 ,1.5 and 2 on utilization of dietary protein, amylase and lipase activity and serum thyroid hormone level. Moreover, the interaction between mixed protein schedules and Na/K ratio has been investigated. The results are summarized as follows: - The optimal protein schedule for tilapia performance was either

Complexity of shop-scheduling problems with fixed number of jobs: a survey

The paper surveys the complexity results for job shop, flow shop, open shop and mixed shop scheduling problems when the number n of jobs is fixed while the number r of operations per job is not restricted. In such cases, the asymptotical complexity of scheduling algorithms depends on the number m of machines for a flow shop and an open shop problem, and on the numbers m and r for a job shop problem. It is shown that almost all shop-scheduling problems with two jobs can be solved in polynomial time for any regular criterion, while those with three jobs are NP-hard. The only exceptions are the two-job, m-machine mixed shop problem without operation preemptions (which is NP-hard for any non-trivial regular criterion) and the n-job, m-machine open shop problem with allowed operation preemptions (which is polynomially solvable for minimizing makespan).

THE EFFECTIVENESS OF AND PRESCHOOLERS' PREFERENCES FOR VARIATIONS OF MULTIPLE‐SCHEDULE ARRANGEMENTS

Multiple schedules of reinforcement have been used to teach children to recruit attention only when it is available, thereby minimizing disruptive requesting during instructional activities. This procedure involves alternating periods of continuous reinforcement (CRF) with periods of extinction and correlating each period with a distinct and continuous discriminative stimulus. The present study evaluated the effectiveness of and children's preferences for multiple schedules in which (a) two different stimuli, one correlated with reinforcement (S+) and another correlated with extinction (S-), were presented; (b) only an S+ was presented (i.e., no stimulus was correlated with extinction), and (c) neither an S+ nor an S- was presented (i.e., a mixed schedule). S+/S- and S+ arrangements were similarly effective for 7 children, but 3 preferred the S+/S- condition and 4 preferred the S+ condition. Correlational analyses suggested that children who responded more effectively given the S- (discrimination indexes were relatively high) preferred the S+/S- condition, whereas children who responded less effectively given the S- preferred the S+ condition. The implications of these findings for arranging multiple schedules for social responses are discussed.

Effects of mixed feeding schedules on growth performance, body composition, and nitrogen- and phosphorus balance in rainbow trout, Oncorhynchus mykiss

Background. Reducing feed cost and the pollution originating from feed have been principal matters in fish nutrition. Mixed feeding schedules have been proposed as one of the methods to reduce both of them and successfully tested in many fish species. The aim of the present study was to determine the mixed feeding schedules′ suitability for culture of rainbow trout. Materials and methods. Five different feeding schedules were tried by alternating the presentation of a low-protein (28.1%) diet (A) and a high-protein (49.9%) diet (B). The feeding schedules employed were 1A/1B, 1A/2B, 1A/3B, 2A/2B, and 2A/3B where the numerical values refer to the number of days each diet (A and B) was offered continuously. Fish given diets A and B continuously served as controls. Totally, seven dietary treatments were tested in triplicate for 10 weeks. Results. The fish maintained on the different mixed feeding schedules exhibited lower weight gain than those fed continuously on the high-protein diet (P < 0.05). The fish reared on schedule 1A/3B (1 day diet A alternated with 3 days diet B) had similar specific growth rate (SGR), feed conversation ratio (FCR), and protein efficiency ratio (PER) to those fed diet B continuously and was best among all mixed feeding schedules. However, the most cost-effective treatment was 2A/2B. In addition, this group compared to B resulted in significant increase and reduction of phosphorus retention and discharge, respectively (P < 0.05). The treatments significantly effected body moisture, fat- and ash levels (P < 0.05), but not protein. Conclusion. The study shows that mixed feeding schedules are promising for use in rainbow trout culture as they result in feed cost saving and reduced phosphorus discharge in the effluents.

MATCHING AND CONDITIONED REINFORCEMENT RATE

Attempts to examine the effects of variations in relative conditioned reinforcement rate on choice have been confounded by changes in rates of primary reinforcement or changes in the value of the conditioned reinforcer. To avoid these problems, this experiment used concurrent observing responses to examine sensitivity of choice to relative conditioned reinforcement rate. In the absence of observing responses, unsignaled periods of food delivery on a variable-interval 90-s schedule alternated with extinction on a center key (i.e., a mixed schedule was in effect). Two concurrently available observing responses produced 15-s access to a stimulus differentially associated with the schedule of food delivery (S+). The relative rate of S+ deliveries arranged by independent variable-interval schedules for the two observing responses varied across conditions. The relation between the ratio of observing responses and the ratio of S+ deliveries was well described by the generalized matching law, despite the absence of changes in the rate of food delivery. In addition, the value of the S+ deliveries likely remained constant across conditions because the ratio of S+ to mixed schedule food deliveries remained constant. Assuming that S+ deliveries serve as conditioned reinforcers, these findings are consistent with the functional similarity between primary and conditioned reinforcers suggested by general choice theories based on the concatenated matching law (e.g., contextual choice and hyperbolic value-added models). These findings are inconsistent with delay reduction theory, which has no terms for the effects of rate of conditioned reinforcement in the absence of changes in rate of primary reinforcement.

Diurnal Urinary 6‐Sulfatoxymelatonin Levels among Healthy Danish Nurses during Work and Leisure Time

The present study aims to examine the influence of evening and night shift work, compared to day shift work, on melatonin secretion in nurses in a field setting. Effects were examined during a workday and during a day off. Both fixed schedules and mixed or rotating schedules were studied. In total, 170 nurses were studied: 89 nurses worked fixed schedules, 27 nurses worked the day shift, 12 nurses worked the evening shift, 50 nurses worked the night shift, and 82 nurses worked mixed schedules, with data collected during a day (n=17), evening (n=14), or night shift (n=50). All spot urine samples were collected during 24 h from the participants on a work day and on a day off and were analyzed for 6‐sulphatoxymelatonin. On the day of urine sampling, participants filled in the Karolinska Sleep Diary. Additional information was collected through a telephone interview. Data were analyzed using a mixed procedure with autoregressive covariance structure. The present study showed that shift work affected the concentrations of 6‐sulphatoxymelatonin in the short term by lower excretion in urine from nurses working the night compared to day shift on a workday and on a day off as well. No significant differences were observed between a workday and a day off when doing day and evening shifts, irrespective of mixed and fixed schedules. Sleep length was reduced workdays (from 6.1–6.8 h) among all nurses, compared to days off (from 7.8–8.7 h).

AN EXAMPLE OF DISCOVERY RESEARCH INVOLVING THE TRANSFER OF STIMULUS CONTROL

The initial purpose of the present study was to replicate procedures for teaching preschool children to recruit attention at appropriate times by having an experimenter signal the availability and unavailability of attention (i.e., arrange a multiple schedule involving reinforcement and extinction; Tiger & Hanley, 2004). Following the development of discriminated social responding, the schedule-correlated stimuli were removed (i.e., a mixed schedule of reinforcement was arranged). However, discriminated responding continued during these conditions. Further evaluation suggested that stimulus control over children's social responding had transferred from the schedule-correlated stimuli to the delivery of reinforcement. The effect of a history of reinforcement under multiple-schedule conditions on performance under mixed schedules was then replicated with 2 participants in a reversal design. These findings suggest that following experience with schedule-correlated stimuli, these stimuli may be removed with only modest disruption to discriminated responding.

Metro-FOLFIRI as first line chemotherapy in metastatic colorectal cancer (MCRC). Preliminary report of a phase II trial

3722 Background: FOLFIRI regimen is standard therapy in MCRC. Angiogenesis is a critical step in the metastatic process of colorectal cancer. New agents with antiangiogenic effect showed to be active in MCRC. In preclinical studies irinotecan demonstrated to have at metronomic dose (1/6 standard dose) antiangiogenic activity. For these reasons we carried out this pilot study in order to evaluate the safety and the activity of metronomic FOLFIRI regimen as first line chemotherapy in inoperable MCRC. Methods: From 10/03 to 10/04 we treated 26 pts (14M 12F), median age 66 years (range 41–77) with this mixed FOLFIRI schedule: CPT-11 10 mg/mq days 1, 7, 10 and CPT-11 150 mg/mq day 2, Folinic Acid 100 mg/mq days 2 and 3, 5-FU 400 mg/mq bolus days 2 and 3 and 5-FU 600 mg/mq 44 hours c.i. days 2 and 3 every two weeks for a maximum of 12 cycles. Results: All pts are evaluable for toxicity and 22 for activity. The chemotherapy was well tolerated; no toxic deaths occurred, no therapy ended for toxicity. 3 pts had 25% reduction dose for diarrhea G4 after the first cycle. The main toxicities recorded on a total of 173 cycles (cy) delivered were: diarrhea G4 1.7% and G3 2.3% of the cy. Neutropenia G3 5.8% and vomiting G3 0.5% of the cy. Anemia G2 was recorded in 7 pts. All pts suffered from partial alopecia and half of the pts from mild oral mucositis. As regard activity we registered 3 CR (13.6%), 9 PR (40.9%), 7 SD (31.8%) and 3 PD (13.6%). Before start therapy and after 4th, 8th and 12th cycle we collected blood samples of the pts in order to evaluate sVEGF modifications in relation to objective response. These data will be presented. Conclusions: Metro-FOLFIRI regimen appears to be safe and active in MCRC. No significant financial relationships to disclose.

Effect of mixed feeding schedules with varying dietary protein levels on the growth of sutchi catfish, Pangasius hypophthalmus (Sauvage) with silver carp, Hypophthalmichthys molitrix (Valenciennes) in ponds

A 6-month feeding trial was conducted in field condition using 10 farm ponds (400–600 m2) to investigate the effect of mixed feeding schedules on the growth of sutchi catfish, Pangasius hypophthalmus with silver carp, Hypophthalmichthys molitrix. Fish were stocked at a ratio of 80:20 (sutchi catfish, 4.9±0.5 g: silver carp, 12.0±0.8 g) at the total rate of 25 000 ha−1. Two diets of high protein (30%, HP) and low protein (16%, LP) were prepared using locally available feed ingredients. Five different feeding schedules of high-protein diet continuously (HP), low-protein diet continuously (LP), 1-day low–protein/1-day high-protein diet (1LP/1HP), 7 days low–protein/7 days high-protein diet (7LP/7HP) and 14 days low–protein/14 days high-protein diet (14LP/14HP) were tested. The fish were fed twice daily at the rate of 15%, 10%, 8% and 5% of their body weight for first, second, third month and rest of experimental period respectively. Feeding rate was calculated only on the basis of sutchi catfish weight only and was adjusted every 2 weeks according to weight gain. Fish fed LP and HP on alternate day (1LP/1HP) resulted in significantly (P 0.05) between the growth rates and production of fish fed HP regularly and fish fed 7 days LP followed by 7 days HP (7LP/7HP). Fish maintained on LP grew the least. The feed conversion ratio (FCR) values for sutchi catfish ranged between 2.04 and 2.79 with feeding schedule 1LP/1HP showing the best FCR. The total production of fish (including silver carp) ranged between 8310 and 12 422 kg ha−1 6 months−1 with 1LP/1HP feeding schedule resulting in the highest production and net profit. The study demonstrated that feeding fish continuously with HP is less economical. Thus, for profitable sutchi catfish culture with silver carp, farmers can use the mixed feeding schedule of alternate day feeding of LP and HP as a means of reducing feed costs.

A fast tabu search algorithm for the group shop scheduling problem

Three types of shop scheduling problems, the flow shop, the job shop and the open shop scheduling problems, have been widely studied in the literature. However, very few articles address the group shop scheduling problem introduced in 1997, which is a general formulation that covers the three above mentioned shop scheduling problems and the mixed shop scheduling problem. In this paper, we apply tabu search to the group shop scheduling problem and evaluate the performance of the algorithm on a set of benchmark problems. The computational results show that our tabu search algorithm is typically more efficient and faster than the other methods proposed in the literature. Furthermore, the proposed tabu search method has found some new best solutions of the benchmark instances.

Construção de intervalos variáveis de reforçamentoemplanilha eletrônica de cálculo

A elaboração de seqüências de intervalos variáveis (VI) em esquemas de reforçamento obedece a alguns parâmetros importantes. Este artigo procura indicar quais são esses parâmetros e qual sua origem na análise do comportamento. Outro objetivo deste artigo é a elaboração de passos simples para a produção de seqüências de intervalos variáveis em uma planilha eletrônica de cálculo de forma a fornecer modelo para pesquisadores que necessitam construir seqüências de intervalos de reforçamento. O método apresentado serve, também para a elaboração de componentes de duração variável em esquemas compostos por dois ou mais esquemas simples (por exemplo, esquemas múltiplos ou esquemas mistos).

EFFECTS OF ANORECTIC DRUGS ON FOOD INTAKE UNDER PROGRESSIVE‐RATIO AND FREE‐ACCESS CONDITIONS IN RATS

The effects of two anorectic drugs, dexfenfluramine and phentermine, on food intake under different food-access conditions were examined. Experiment 1 compared the effects of these drugs on food intake under a progressive-ratio (PR) schedule and free-access conditions. Dexfenfluramine decreased food intake under both conditions, but the doses required to decrease intake under free-access conditions were higher than those required to reduce intake under the PR condition. Intermediate doses of phentermine sometimes increased breaking points, and higher doses decreased them. Phentermine decreased food intake at the same doses under both access conditions. Thus the potency of dexfenfluramine, but not phentermine, to decrease food-maintained behavior depended upon the food-access condition. Experiment 2 used a novel mixed progressive-ratio schedule of food delivery to study the duration of drug effects. Sessions consisted of five components separated by 3-hr timeouts. The ratio requirement reset at the beginning of each component and a new breaking point was obtained. Both dexfenfluramine and phentermine dose-dependently decreased breaking points early in the session. In some rats, compensatory increases in breaking point were observed. That is, breaking points later in the session increased over control levels, resulting in no change in the total number of food pellets earned for the session compared to control. The present findings suggest that the effects of some anorectic drugs depend upon the access conditions for food; increasing the effort to obtain food may enhance their ability to decrease food-maintained behavior.

Visual afferent information dominates other sources of afferent information during mixed practice of a video-aiming task

The goal of the present study was to determine whether learning of a manual video-aiming task that would have to be performed in a target-only condition (transfer test) would be improved, unaffected or hindered by alternating practice between a normal vision and a target-only condition. The results of the present study indicate that a mixed schedule of practice hindered learning of the task. Specifically, participants who practiced the task in the mixed schedule showed larger direction constant error in transfer than participants who practiced only in the target-only condition. The results suggest that participants in the mixed condition continued to rely on the rapidly decaying information that was extracted in the normal vision condition to plan and control their movement in the target-only condition, which ultimately led to biased movement endpoints.

Acquisition of discriminated operant responding: The effects of brief reinforcement delays

In a first series of experiments, 9 groups of rats were exposed to 30 20-minute sessions of successive visual discrimination training (“go/no-go,” or mult FR-1 ext), where components (SD and SA) were equal (1 min) in length. Responses during SD were reinforced with a nonresetting delay (Experiment 1a) or a resetting delay (DRO, Experiment 1b) of 1 s, 2 s, 3 s, or 5 s (a “no delay” control group was also run). The terminal level and rate at which stimulus control developed was inversely related to the obtained delay, irrespective of cumulative reinforcers or reinforcement rate. A second series of experiments explored the role of reinforcer delivery as a discriminative stimulus, and the temporal regularity of the component changes. In Experiment 2a, 4 groups of rats were exposed to a mixed schedule where a delay factor (no delay and 5 s) was crossed with component type factor (fixed and variable lengths), yielding a 2 × 2 design. A 5th group was exposed to a 2-s delay with fixed components in Experiment 2b. Discriminative responding was not observed for any of the delay groups, and only a small effect of reinforcers was seen in the no-delay groups; no effect of component type was found. The results from these experiments demonstrate that delays to reinforcement retard the acquisition of a visual discrimination and may decrease the degree of stimulus control independent of the effects of delays on rate of responding, rate of reinforcement, and reinforcer delivery, per se. In addition, functions relating rate of responding in SD to rate of reinforcement were differentiated on the basis of the type of delay contingency (nonresetting vs. resetting) in contrast to an apparently undifferentiated function relating rate of responding to obtained delay.