Fixed-time Schedule Research Articles

INSTRUCTIONAL VERSUS SCHEDULE CONTROL OF HUMANS' CHOICES IN SITUATIONS OF DIMINISHING RETURNS

Four adult humans chose repeatedly between a fixed-time schedule (of points later exchangeable for money) and a progressive-time schedule that began at 0 s and increased by a fixed number of seconds with each point delivered by that schedule. Each point delivered by the fixed-time schedule reset the requirements of the progressive-time schedule to its minimum value. Subjects were provided with instructions that specified a particular sequence of choices. Under the initial conditions, the instructions accurately specified the optimal choice sequence. Thus, control by instructions and optimal control by the programmed contingencies both supported the same performance. To distinguish the effects of instructions from schedule sensitivity, the correspondence between the instructed and optimal choice patterns was gradually altered across conditions by varying the step size of the progressive-time schedule while maintaining the same instructions. Step size was manipulated, typically in 1-s units, first in an ascending and then in a descending sequence of conditions. Instructions quickly established control in all 4 subjects but, by narrowing the range of choice patterns, they reduced subsequent sensitivity to schedule changes. Instructional control was maintained across the ascending sequence of progressive-time values for each subject, but eventually diminished, giving way to more schedule-appropriate patterns. The transition from instruction-appropriate to schedule-appropriate behavior was characterized by an increase in the variability of choice patterns and local increases in point density. On the descending sequence of progressive-time values, behavior appeared to be schedule sensitive, sometimes even optimally sensitive, but it did not always change systematically with the contingencies, suggesting the involvement of other factors.

Schedule-induced timeout: Effects of timeout-contingent delayed reinforcement

Rats' lever pressing turned off stimuli associated with various response-independent fixed-time schedules of food delivery and produced a timeout period during which food delivery could not occur. A lever press during timeout turned on the schedule-associated stimuli and reinstated the fixed-time schedule. Every response that produced timeout ended the timing of fixed time intervals; timeout terminating responses started the timing of fixed-time schedules over again. The percentage of session time spent in timeout periods generally increased as the rate of food delivery decreased. When food delivery could not occur, about half of the session time was spent in the stimulus condition formerly associated with timeout. The majority of timeout periods were initiated after 15 seconds or more had lapsed since the last food delivery. When timeout periods could not be produced, lever pressing rates either decreased or were not affected. The rate of food delivery appeared to be a primary determinant of time spent in timeout periods. The results may be inconsistent with interpretations emphasizing escape from aversive aspects of schedules of positive reinforcement.

A QUANTITATIVE ANALYSIS OF SENSITIVITY TO THE CONDITIONED REINFORCING VALUE OF TERMINAL‐LINK STIMULI IN A CONCURRENT‐CHAINS SCHEDULE

Pigeons were exposed to a concurrent-chains schedule in which a single variable-interval 30-s schedule was used in the initial links and fixed-time schedules were used in the terminal links. Three types of keylight conditions were used in the terminal links. In the first condition, different delays were associated with different keylight stimuli (cued condition). In the second condition, different delays were associated with the same stimulus, either a blackout (uncued blackout condition) or a white key (uncued white condition). Paired values of terminal-link fixed-time schedules differed by a constant ratio of 3:1, while the absolute value of delays was varied from 3 s to 54 s. The results showed that choice proportions for the shorter of two delays increased when the absolute size of the delays was increased for all keylight conditions. Further, the choice proportions for the shorter delay increased from the uncued blackout condition, to the uncued white condition, to the cued condition. A modified version of Fantino's (1969) delay-reduction model (expressed as a function relating the response ratio to the delay-reduction ratio) can be applied to these data by showing that sensitivity to delay reduction increased from the uncued blackout condition, to the uncued white condition, to the cued condition. Thus, the present study demonstrated that a modified version of the delay-reduction model can be used to assess quantitative differences in the terminal-link keylight condition in terms of sensitivity to delay reduction (i.e., the conditioned reinforcing value of the terminal-link keylight stimuli).

HUMANS' CHOICES IN SITUATIONS OF TIME‐BASED DIMINISHING RETURNS

Three experiments examined adult humans' choices in situations with contrasting short-term and long-term consequences. Subjects were given repeated choices between two time-based schedules of points exchangeable for money: a fixed schedule and a progressive schedule that began at 0 s and increased by 5 s with each point delivered by that schedule. Under "reset" conditions, choosing the fixed schedule not only produced a point but it also reset the requirements of the progressive schedule to 0 s. In the first two experiments, reset conditions alternated with "no-reset" conditions, in which progressive-schedule requirements were independent of fixed-schedule choices. Experiment 1 entailed choices between a progressive-interval schedule and a fixed-interval schedule, the duration of which varied across conditions. Switching from the progressive- to the fixed-interval schedule was systematically related to fixed-interval size in 4 of 8 subjects, and in all subjects occurred consistently sooner in the progressive-schedule sequence under reset than under no-reset procedures. The latter result was replicated in a second experiment, in which choices between progressive- and fixed-interval schedules were compared with choices between progressive- and fixed-time schedules. In Experiment 3, switching patterns under reset conditions were unrelated to variations in intertrial interval. In none of the experiments did orderly choice patterns depend on verbal descriptions of the contingencies or on schedule-controlled response patterns in the presence of the chosen schedules. The overall pattern of results indicates control of choices by temporarily remote consequences, and is consistent with versions of optimality theory that address performance in situations of diminishing returns.

PIGEONS' WAIT‐TIME RESPONSES TO TRANSITIONS IN INTERFOOD‐INTERVAL DURATION: ANOTHER LOOK AT CYCLIC SCHEDULE PERFORMANCE

Recent developments reveal that animals can rapidly learn about intervals of time. We studied the nature of this fast-acting process in two experiments. In Experiment 1 pigeons were exposed to a modified fixed-time schedule, in which the time between food rewards (interfood interval) changed at an unpredictable point in each session, either decreasing from 15 to 5 s (step-down) or increasing from 15 to 45 s (step-up). The birds were able to track under both conditions by producing postreinforcement wait times proportional to the preceding interfood-interval duration. However, the time course of responding differed: Tracking was apparently more gradual in the step-up condition. Experiment 2 studied the effect of having both kinds of transitions within the same session by exposing pigeons to a repeating (cyclic) sequence of the interfood-interval values used in Experiment 1. Pigeons detected changes in the input sequence of interfood intervals, but only for a few sessions-discrimination worsened with further training. The dynamic effects we observed do not support a linear waiting process of time discrimination, but instead point to a timing mechanism based on the frequency and recency of prior interfood intervals and not the preceding interfood interval alone.

The role of attention in the treatment of attention-maintained self-injurious behavior: noncontingent reinforcement and differential reinforcement of other behavior.

Because there are potentially serious limitations to differential reinforcement of other behavior (DRO) (which is probably the most widely used treatment procedure for behavior problems), we examined an alternative procedure--noncontingent reinforcement (NCR). Three females with developmental disabilities, all of whom engaged in severe self-injurious behavior, participated. During a pretreatment functional analysis, each subject's self-injury was shown to be differentially sensitive to social attention as a maintaining consequence. Next, each subject was exposed to a DRO treatment and an NCR treatment. During DRO, attention was delivered contingent on the absence of self-injury for prespecified intervals. During NCR, attention was delivered on a fixed-time schedule that was not influenced by the subject's behavior. Results showed that both procedures were highly effective in reducing self-injury, probably because the functional reinforcer for self-injury was used during treatment. Furthermore, there was evidence that NCR attenuated several of the limitations of DRO. These results are particularly interesting in light of the long experimental history of NCR as a control rather than as a therapeutic procedure.

Further characterization of adjunctive behavior generated by schedules of cocaine self-administration.

Rhesus monkeys (n = 5), surgically implanted with double-lumen catheters, were allowed to self-administer cocaine (0.1 or 0.3mg/kg/injection, i.v.) on one lever (COC lever) under several fixed-interval schedules of reinforcement. Responding on a second lever (SAL lever) delivered saline (i.v.) under a fixed-ratio 1 schedule. Responding on both levers was a bitonic function of interval value and cocaine dose. A variety of experimental conditions were examined to determine whether SAL lever responding could be considered to be adjunctive in nature. SAL lever responding did not change when saline injections were discontinued, suggesting that SAL lever responding was not maintained by interoceptive stimuli associated with the injection. Discontinuation of various exteroceptive stimulus changes that had occurred as a consequence of SAL lever responding also did not affect the frequency of SAL lever responding. However, when there was no stimulus change following a SAL response, response rates on that lever decreased by approximately 40-60% indicating that stimulus change played some role in the maintenance of the behavior. The introduction of change-over-delays (2-16 s) between responding on the SAL and COC levers had little or no effect on responding on the SAL lever, suggesting that SAL lever responding was not maintained by adventitious reinforcement by cocaine injections. SAL lever responding also occurred in these same monkeys when cocaine was available under fixed-time or variable-interval schedules of reinforcement. These results confirm that presentation of cocaine under interval schedules of reinforcement can generate substantial amounts of behavior (pressing the SAL lever) that is not necessary for obtaining the drug. Further, the results strongly suggest that the behavior can be classified as an adjunctive behavior that is similar to adjunctive behaviors generated by the intermittent presentation of other positive reinforcers.

Adjunctive behavior in multiple schedules of reinforcement

A recent theory of timing (Killeen & Fetterman, 1988) suggests that adjunctive behaviors may act as discriminative cues for the passage of time and that the rate of transition between those behaviors is affected by the rate of reinforcement within the experimental context. Is the rate of transition between behaviors correlated with the rate of reinforcement? What is the context in which rate of reinforcement is calibrated? If rate of transition is correlated with reinforcement frequency, does this correlation change with extended training? Four pigeons were trained on multiple fixed-time schedules of reinforcement, with one component always FT 15 sec, the other either FT 15 sec, FT 45 sec, or FT 5 sec. Behavior was coded into one of 12 categories. Response distributions in the constant component shifted when rate of reinforcement was varied in the other component and eventually shifted back toward their original location.

Time Course of Wound Healing

Wound healing is a special kind of inflammation. Undisturbed wound healing is subject to a fixed time schedule of biochemical and cellular events. It is virtually impossible to deal with the time course of wound healing without describing the cellular and non-cellular events involved. The activity and mode of cell action after injury are coordinated by spatial and chronological factors, as well as by different mediators and cell-cell interacting signals. During wound healing the sequence of different signals and message substances, such as mediators of inflammation, fulfill a key function in wound repair. The report describes the time course of healing and the control of cellular events by different mediators and cell interactions. Emphasis is placed on temporal aspects, including the various signals leading to typical cellular events in wound healing.

Another look at “superstitions” in pigeons

Pigeons were exposed to fixed-time schedules of food delivery. The “ superstitious” behaviors observed were stable within subjects but differed markedly across subjects. These results are consistent with Skinner’s (1948) study but not with the data reported by Staddon and Simmelhag (1971) or Timberlake and Lucas (1985). However, our study was not an adequate test of Skinner’s hypothesis concerning the development of the various behaviors observed. Tests of his view are proposed.

SUBOPTIMAL CHOICE IN A PERCENTAGE‐REINFORCEMENT PROCEDURE: EFFECTS OF SIGNAL CONDITION AND TERMINAL‐LINK LENGTH

Pigeons' choice between reliable (100%) and unreliable (50%) reinforcement was studied using a concurrent-chains procedure. Initial links were fixed-ratio 1 schedules, and terminal links were equal fixed-time schedules. The duration of the terminal links was varied across conditions. The terminal link on the reliable side always ended in food; the terminal link on the unreliable side ended with food 50% of the time and otherwise with blackout. Different stimuli present during the 50% terminal links signaled food or blackout outcomes under signaled conditions but were uncorrelated with outcomes under unsignaled conditions. In signaled conditions, most pigeons displayed a nearly exclusive preference for the 100% alternative when terminal links were short (5 or 10 s), but with terminal links of 30 s or longer, preference for the 100% alternative was sharply reduced (often to below .5). In unsignaled conditions, most pigeons showed extreme preference for the 100% alternative with either short (5 s) or longer (30 s) terminal links. Thus, pigeons' choice between reliable and unreliable reinforcement is influenced by both the signal conditions on the unreliable alternative and the duration of the terminal-link delay. With a long delay and signaled outcomes, many pigeons display a suboptimal tendency to choose the unreliable side.

Schedule-induced kinesic and taxic behavioral stereotypy in the pigeon.

Two experiments explored the functional character of 2 schedule-induced interim behaviors (pacing and retreat) and 1 terminal behavior (keypecking) that developed on fixed-time (FT) schedules of food delivery with a keylight that increased in brightness throughout the interstimulus interval. In Experiment 1, this ramp procedure was compared with a less discriminable ramp, and FT and Random Time (RT) procedures without a signal. Decreased discriminability expanded keypecking in the trial. The FT schedule eliminated only keypecking and the RT procedure eliminated keypecking and retreat while pacing remained. In Experiment 2, predictive and unpredictive ramps were added to the RT procedure. The data suggest that schedule-induced stereotypy can be divided into kinesic stereotypy (pacing), which arises from repeated reinforcer presentations, and taxic stereotypy, which is tied to an increase (keypecking) or decrease (retreat) in the momentary probability of reinforcement.

Comparative effects of food and water deprivation on movement patterns in the pigeon (Columba Livia)

Groups of naive pigeons were either food or water deprived and exposed to response-independent fixed time schedules of reinforcement. Reinforcers were always appropriate to the deprivation state. After 15 Phase One sessions under the original deprivation state, an additional 15 Phase Two sessions were run under the alternate deprivation regimen. The Phase One results indicated that the frequency of movement over time, as measured by floorboard panels, had a characteristic distribution depending on deprivation state. After state-switch in Phase Two, both groups exhibited changes in frequency distribution over time, but the new distributions were different from those produced in subjects without any deprivation history. There appeared to be sustained effects on movement patterns due to prior exposure to alternate deprivation and periodic feeding regiments, results which confirm earlier experimental work. The findings are discussed in light of research on the effect of prior response-independent schedule training, the matching law, and the effects of contextual conditioning.

Performance of Decorticated Rats on Fixed Interval and Fixed Time Schedules.

Rats with neocortex totally removed (decorticates), rats with hippocampal lesions (hippocampals), and their surgical controls, were trained on a fixed interval (FI) 40 s schedule, where the first bar-press response made more than 40 s after a previous reinforcement was rewarded. The decorticates and hippocampals adopted similar patterns of behaviour to the control groups through there were between-group differences in the details of performance. Compared to controls the hippocampals showed shorter post-reinforcement pauses and faster overall rates of responding, whilst the reverse was true of the decorticates. Some of this performance difference in the decorticates was attributed to difficulty in retrieving and consuming solid food reinforcement. The performance of the decorticates and hippocampals, as reflected by the post-reinforcement pause, response distribution and running rate as a function of post-reinforcement pause duration, suggests that timing remains operational in both groups. The differences in response profiles between the two experimental groups, however, indicate that hippocampus and neocortex probably make independent contributions to performance in this situation. The decorticates and their control group were later transferred from the FI to a response-independent fixed time (FT) 40 s schedule. Both groups then returned to the former FI 40 s schedule. The decorticates adjusted their behaviour to the different schedules in the same way as the control animals. The results overall are consistent with previous findings that decortication does not abolish normal patterns of operant learning and extends them to include temporal schedules.

Dynamic attending and responses to time.

A temporally based theory of attending is proposed that assumes that the structure of world events affords different attending modes. Future-oriented attending supports anticipatory behaviors and occurs with highly coherent temporal events. Time judgments, given this attending mode, axe influenced by the way an event's ending confirms or violates temporal expectancies. Analytic attending supports other activities (e.g., grouping, counting), and if it occurs with events of low temporal coherence, then time judgments depend on the attending levels involved. A weighted contrast model describes over- and underestimations of event durations. The model applies to comparative duration judgments of equal and unequal time intervals; its rationale extends to temporal productions/extrapolations. Two experiments compare predictions of the contrast model with those derived from other traditional approaches. One characteristic of modern society is a preoccupation with fixed time schedules and standardized timekeepers. We maintain appointments at hourly intervals, rush to meet the 5:00 p.m. bus, and dine at predetermined hours. Yet our natural ability to judge time remains poorly understood. How often do we estimate the time elapsed since last glancing at a clock and discover with surprise that we were fairly accurate? Surprise is understandable because at least as often we lose track of time and err. The validity of these impressions is confirmed by laboratory research showing that duration judgments depend not only on actual physical duration but also on a variety of non

The Control of Schedule-Induced Polydipsia by Meal Size: Interaction with Prior Within-Session Eating and Drinking

An experiment was conducted that varied, within sessions, the number of pellets presented at each food delivery by two response-independent fixed-time (FT) schedules of reinforcement. Water intake was measured throughout. A reinforcer magnitude of either one or five pellets was delivered for each half of a session. The larger meal size generally produced more drinking, but only when this meal size was in effect for the first half of the session. Results are compared with equivocal findings of previous polydipsia studies that varied reinforcer magnitude. Results indicate that meal size is an important variable controlling polydipsia, but that its influence is mediated by other variables including prior within-session eating and drinking.

Fixed-Time Schedule-Induced Drinking in Rats During 24-Hour Sessions

Polydipsie drinking was induced by each of three fixed-time (FT 30 sec, FT 60 sec, and FT 432 sec) food schedules in food-deprived rats during 24-hour sessions. The FT 432-sec condition presented food without significant daily interruption. The stereotypical polydipsic drinking pattern emerged, confirming that previous open economy findings generalize to rats living in a closed economy where no supplemental feedings occur outside the experimental chamber. Furthermore, the present study showed that a response requirement is not a prerequisite for the development of schedule-induced polydipsia in the 24-hour session. Drinking occurred consistently following most food presentations during all conditions. These findings illustrate that when the opportunities for alternative activities are limited in a continuous experiment, polydipsia more closely resembles reflexive behavior than adaptive drinking occurring in the context of normal foraging.

PSYCHOLOGICAL DISTANCE TO REWARD: A HUMAN REPLICATION

Choice behavior in college students was examined in two experiments using the concurrent-chains procedure. In both experiments, the concurrent chains were presented on a microcomputer in the form of an air-defense game in which subjects used two radar systems to detect and subsequently destroy enemy aircraft. Access to one of two radar systems was controlled by a pair of independent concurrent variable-interval 60-s schedules with a 4-s changeover delay always in effect. In the terminal link, the appearance of an enemy aircraft was determined by a pair of differentially segmented fixed-time schedules (Experiment 1) or fixed-interval schedules (Experiment 2) of equal overall duration. In Experiment 1, the terminal-link duration was either 20 s or 40 s, and subjects preferred the unsegmented to the segmented intervals. In Experiment 2, the duration was either 10 s or 60 s, and the reinforcement contingencies required responding during the terminal link. Prior to the reinstatement of the initial link, subjects estimated the duration of the terminal-link schedule. Segmentation affected choice in the 60-s conditions but not in the 10-s ones. Preference for the unsegmented schedule was correlated with an overestimation of the durations for the segmented schedules. These results replicated those found in animal experiments and support the notion of increasing the psychological distance to reward by segmenting a time-based schedule of reinforcement.

Real-time data acquisition system for laser and radio frequency spectroscopy

A low-cost real-time data acquisition system utilising a master (PC-XT) and a slave (Z80) computer for high-resolution atomic spectroscopy is described. The master and the slave computer are linked by a high-speed parallel FIFO buffer permitting data acquisition on a fixed time schedule with 4 mu s time resolution. A modular interface box allows the system to control complex spectroscopic experiments. The use of commercial software packages allows fast and efficient data reduction and analysis on the same computer system. The performance of the system has been demonstrated in polarisation spectroscopy experiment on zirconium.

Anticipatory drinking in rats: Compensatory adjustments in the local rate of intake

The current experiment examined whether dehydrated rats could learn to anticipate disruption of access to water. Previous research showed that rats running in a wheel in order to drink compensated for local disruptions on intake by increasing their rate of intake after, but not prior to the initial disruption. The present experiment exposed rats to either a fixed-ratio (FR) schedule that required rats to run in order to drink or a matched, fixed-time (FT) schedule that allowed the animals intermittent access to water without running. Access to water was disrupted by restricting the quantity of water available per drink bout. Rats increased their local rate of water intake prior to the disruption under the FT schedule but not under the FR schedule. The results suggest that rats can learn to increase their local rate of intake in anticipation of local restrictions on water under response-independent (FT) schedules. It was hypothesized that these anticipatory increases in the local rate of intake resulted from a priming effect due to the motivating effects of stimuli associated with water and/or frustration resulting from attempts to drink prior to water availability.