Fixed-interval responding under second-order schedules of food presentation or cocaine injection.

Squirrel monkeys operated a key under second-order schedules in which every tenth completion of a 5-minute fixed interval resulted in either presentation of food or intravenous injection of cocaine. When a 2-second light was presented at the completion of the component fixed-interval schedules, positively accelerated responding developed and was maintained in each component. Over a tenfold range of doses of cocaine(30 to 300 microgram/kg/injection) and amounts of food (0.75 to 7.5 g/presentation); the second-order schedule of cocaine injection maintained higher average rates of responding than the second-order schedule of food presentation. Substituting saline for cocaine or eliminating food presentation decreased average rates of responding. When no stimulus change occurred at the completion of the first nine component fixed-interval schedules, but the 2-second light and food presentation or cocaine injection still occurred after the tenth component, only low and relatively constant rates of responding were maintained in each component. Patterns of responding characteristic of 5-minute fixed-interval schedules were maintained by the 2-second light paired with either cocaine injection or food presentation, though the maximum frequency of cocaine injection or food presentation was less than once per 50 minutes.     

Fixed-interval schedules of electric shock presentation: extinction and recovery of performance under different shock intensities and fixed-interval durations

In squirrel monkeys responding under a schedule in which responding postponed the delivery of electric shock, the presentation of response-dependent shock under a fixed-interval (FI) schedule increased the rate of responding. When the schedule of shock-postponement was eliminated, so that the only shocks delivered were those produced by responses under the FI schedule, a pattern of positively accelerated responding developed and was maintained over an extended period. When responses did not produce shocks (extinction), responding decreased. When shocks were again presented under the FI schedule, the previous pattern of responding quickly redeveloped. In general, response rates were directly related to the intensity of the shock presented, and inversely related to the duration of the fixed-interval. These results raise fundamental questions about the traditional classification of stimuli as reinforcers or punishers. The basic similarities among FI schedules of food presentation, shock termination, and shock presentation strengthen the conclusion that the schedule under which an event is presented and the characteristics of the behavior at the time the event is presented, are of overriding importance in determining the effect of that event on behavior.     

Behaviour of rats in multiple schedules of response-contingent and response-independent food presentation

During Phase I, three rats were exposed to two-component multiple schedules of response-independent food presentation. Low rates of lever-pressing were observed, and response rates in one component did not increase when food presentation was withheld in the other component. During Phase II, the same rats were exposed to two-component multiple schedules of response-contingent reinforcement. Much higher rates of lever-pressing were observed. Moreover, when reinforcement was withheld in one component, response rates in the other component increased (positive contrast), and when reinforcement was reinstated in the changed component, response rates in the other component declined (negative contrast). During Phase III, when food was again delivered independently of responding, the response rates declined again to low levels. These results indicate that the occurrence of non-instrumental lever-pressing is not a prerequisite for the occurrence of behavioural contrast in the rat, and thus cast doubt on the general applicability of the autoshaping theory of behavioural contrast     

Fixed-interval schedule of cocaine reinforcement: effect of dose and infusion duration

Rhesus monkeys were trained on a fixed-interval 9-min limited-hold 3-min schedule of intravenous cocaine reinforcement. A 15-min timeout followed each reinforcement or limited-hold expiration. An identical schedule of food reinforcement was interspersed in the session to assess rate-modifying effects of the drug infusions not specific to drug reinforcement. In one experiment, response rate for cocaine reinforcement was shown to be a positive function of reinforcement magnitude for a dose range from 0 to 800 ug/kg/inj. At these doses, there was little effect on food reinforced responding except at the highest dose, where responding decreased. Results of the second experiment indicated that increasing the duration of the cocaine infusion produced a change in response rate similar to decreasing unit dose. The response rate change for a given increase in infustion duration was less at a unit dose of 400 ug/kg than at 200 ug/kg.     

A comparison of responding maintained under second-order schedules of intramuscular cocaine injection or food presentation in squirrel monkeys.

Key pressing by squirrel monkeys was maintained under second-order schedules of either intramuscular cocaine injection or food presentation. Under one schedule, each completion of a 10-response fixed-ratio unit produced a brief visual stimulus; the first fixed-ratio unit completed after 30 minutes elapsed produced the stimulus paired with either cocaine injection or food presentation. Generally, short pauses followed by high rates of responding were maintained within the fixed-ratio units, and responding was positively accelerated over the 30-minute interval. Under another schedule, each completion of a 3-minute fixed-interval unit produced the brief stimulus; completion of the 10th fixed-interval unit produced the stimulus paired with either cocaine injection or food presentation. Generally, short pauses followed by high rates of responding were maintained within the fixed-ratio units, and responding was positively accelerated over the 30-minute interval. Under another schedule, each completion of a 3-minute fixed-interval unit produced the brief stimulus; completion of the 10th fixed-interval unit produced the stimulus paired with either cocaine injection or food presentation. Rates of responding increased within the fixed-interval units, and to a greater extent over the entire 10 fixed-interval units. Patterns of responding depended more on the schedule of reinforcement than on whether cocaine or food maintained responding. Omitting the brief stimuli following all but the last fixed-ratio or fixed-interval units decreased average rates and altered the patterns of responding. Substituting a visual stimulus that was never paired with cocaine or food following all but the last fixed-ratio or fixed-interval units decreased response rates to a lesser extent and did not substantially alter patterns of responding. When the duration of the paired stimulus was varied from .3 to 30.0 seconds, the highest response rates occurred at intermediate durations (1.0 to 10.0 seconds). The manner in which the stimulus changes affected performances depended more on the schedule of reinforcement than on whether cocaine injection or food presentation maintained responding.     

Response-dependent shock in second-order fixed-ratio schedules of food presentation

Three pigeons key pecked under second-order schedules in which the completion of two successive fixed-ratio 50 components constituted a reinforcement cycle. Tandem, chained, and brief-stimulus second-order schedules were studied when completion of the initial fixed-ratio 50 component delivered brief intense electric shock in every nth reinforcement cycle and n assumed values between one and nine. During sessions without shock, the brief-stimulus (unpaired with food) schedule generated higher rates of responding in the initial component than did the tandem schedule. Electric shock engendered increased time to the fifth response and a repeated pause-run pattern of not responding and responding, particuuarly in the initial component, even with shock scheduled in every ninth reinforcement cycle. The results were consistent with those reported for shock of a shorter duration scheduled in every reinforcement cycle. The overall rate of responding decreased as a function of increasing shock density and was lower in brief-stimulus than in tandem schedules.     

Signal recognition as influenced by presentation schedules

Performance in a recognition task involving two amplitudes of the same tone was investigaled over a wide range of presentation schedules. The task was arranged so that there was no trial-to-trial feedback or other information regarding the relative frequencies of the two tones. The hit and false alarm rates (the proportion of “loud” responses to loud and soft stimuli, respectively) on any given trial were strongly influenced by the stimulus and response on the preceding trial. In general, Ss tended to repeat the last response and were more accurate after a stimulus alternation than after a stimulus repetition. In addition, hit and false alarm rates were inversely related to the presentation probability of the loud tone, in contrast to the direct relation typically found in signal detection experiments and in recognition experiments with trial-to-trial feedback. A mathematical model incorporating three processes (memory, comparison, and decision) was shown to give a good account of these data.     

Response timing and development: Fixed-interval performance in precociously weaned rats

Young rats weaned at 16 days were taught to press a lever by shaping at 18 days and trained for 11 days (from 20 to 30 days of age) on a fixed-interval 60-sec schedule, at a rate of 5 half-hour sessions per day. Comparison with rats weaned at 16 or 20 days, trained at 21 days, and subjected for 8 days (from 23 to 30 days of age) to the same procedure showed that the temporal regulation of behaviour, as evaluated by the Curvature Index, was mostly training-dependent. Post-reinforcement pause durations depended upon the mixed influence of age and training. The evolution of running rates mostly depended upon training, whereas trends in overall rates seemed to depend essentially upon the age of the subjects. Precocious weaning per se or raising conditions prior to weaning did not significantly influence the temporal regulation of behaviour under FI. The results support previous ideas that overall response rate and response timing were dissociated and indicate high sensitivity to periodic stimuli in weanling rats. Finally, they show that, within an information processing model of timing, FI data of weanling rats might be compatible with their having an “internal clock” that runs at a higher rate than in older subjects.     

Responding under sequence schedules of electric shock presentation

Lever pressing by squirrel monkeys was examined under second-order schedules of electric shock presentation in which different discriminative stimuli were associated with consecutive components (sequence schedules). Components were always two-minute fixed-interval schedules, and three different overall schedules were studied. Under an overall eight-minute fixed-interval schedule, the first component completion after at least eight minutes had elapsed produced electric shock. The number of components actually completed ranged from one to four; thus, different discriminative stimuli were occasionally associated with electric shock presentation. Under an overall “yoked” variable-ratio schedule, electric shock was presented after completion of a variable number of components; the required number and the distribution of components were matched to those obtained under the overall eight-minute fixed-interval schedule. Under an overall fixed-ratio schedule, electric shock was presented after completion of four components (chained schedule). Under all three sequence schedules, responding in early components was characterized by a pause followed by a single response after the end of the two-minute interval; responding in later components was characterized by a shorter pause followed by positively accelerated responding. Manipulation of overall schedules of shock presentation in these complex behavioral situations produced changes in responding comparable to those ordinarily obtained after similar manipulation of dependencies under both single and second-order schedules of food presentation. These experiments extend the range of conditions and levels of complexity under which responding can be maintained by presentation of electric shock.     

Matching under concurrent fixed-ratio variable-interval schedules of food presentation

Four pigeons were exposed to concurrent fixed-ratio, variable-interval schedules of food presentation. The fixed-ratio requirement was either 25, 50, 75, or 100 responses, with the variable-interval schedule parameter held constant at 4 minutes. A delay time was imposed between a changeover from one schedule to the other and subsequent food availability. The delay time was varied at each ratio requirement over four values; no delay, 0-second delay, 1.5-second delay, and 5.0-second delay. As the fixed-ratio requirement or the delay time increased, a greater proportion of the total responses and time spent responding occurred under the variable-interval schedule relative to the proportion of food deliveries under that schedule. Neither relative overall response rate nor relative time spent responding equalled the relative frequency of food presentation, as would be predicted by a linear “matching” model. Rather, these data were described by power functions with slopes of approximately 1.0 and intercepts greater than 1.0. In the terms of Baum's (1974) analysis, these deviations from linear matching represent bias in favor of responding under the interval schedule. Bias, as reflected in the intercept of the power function, was greater for the ratio of time than the ratio of responses.     

Schedule-induced biting under fixed-interval schedules of food or electric-shock presentation

Squirrel monkeys pressed a lever under fixed-interval schedules of food or of electric-shock presentation. Both schedules induced repeated biting on a latex hose. Whether lever pressing was controlled by food or by electric shock, a pattern of decreasing hose biting and increasing lever pressing occurred within fixed-interval cycles. As the fixed-interval duration was increased from 6 to 600 sec, average rates of lever pressing decreased under both schedules. Average rates of hose biting first increased with increasing parameter value, reaching a maximum at values that varied from 60 to 337 sec in different monkeys, and then declined at higher values. d-Amphetamine at appropriate doses increased overall rates of lever pressing maintained by food or by shock, but either did not affect or decreased overall rates of hose biting. When no timeout period occurred between fixed-interval cycles, the monkeys bit most frequently immediately after food or electric shock was presented. When there was a timeout period, hose biting began shortly after the start of the fixed-interval cycles, with little or no hose biting immediately after food or electric shock was presented. Most hose biting appeared to be schedule-induced rather than food- or shock-induced.     

Induced attack during fixed-ratio and matched-time schedules of food presentation

Adjunctive or induced behavior is generated during a variety of schedules of reinforcement. Several theoretical conceptualizations suggest that rate of reinforcement is the primary variable controlling the strength or levels of induced behavior. The operant response requirement within the schedule context has not been extensively studied as a determinant of induced responding. In the present study, levels of induced attack by food-deprived pigeons against restrained conspecifics were compared during response-dependent and response-independent schedules of food presentation equated or yoked interval-by-interval for reinforcement frequency. Experiment 1 compared levels of attack induced by fixed-ratio schedules of key pecking and yoked "matched-time" schedules. Experiment 2 similarly compared chained fixed-ratio 1 fixed-ratio 74 and yoked chained matched-time matched-time schedules. In both experiments, the response-dependent schedules generated greater levels (amount and probability) of induced attack than the response-independent time-based schedules. Thus, the ratio response requirement may be an important determinant of levels of induced responding, and the lower levels of attack observed during the response-independent condition may not be due to the absence of stimuli predicting food presentations. It is concluded that rate of reinforcement is not the sole variable determining levels of induced responding and that response-based and time-based schedules differ in their generation of induced responding.     

Fixed-interval punishment of running in hamsters

Four hamsters received brief electric shocks contingent upon running in a wheel. The fixed interval between shocks was varied systematically from 0 to 60 sec. Time spent running was directly related to the length of the fixed interval, while running speed remained roughly constant. Running depended on the fixed interval between shocks in the same way as bar-pressing maintained by food reinforcement, despite the fact that running was not established with nor maintained by explicit reinforcement.     

Concurrent responses during multiple schedules in rats

Abstract.— Rats' lever pressing was reinforced with a sucrose solution. In the presence of a tone pressing one lever was reinforced on a FR 40 schedule, in the absence of the tone pressing another lever was reinforced on a FR 20 schedule. The components alternated every fourth minute. In both components, the duration of pauses in lever pressing after reinforcement was positively correlated with the duration of licking the empty sucrose-delivery mechanism. In the FR 40 component, the duration of pauses was also positively correlated with the number of presses on the non-reforced lever. Licking and non-reinforced lever pressing were decreased when the rate of reinforced lever pressing was high. The response interactions were similar to those described for concurrent reinforcement schedules.     

Fixed-interval work habits of Congress

The rate at which Congress passes bills during its legislative session exhibits a fixed-interval pattern: the rate of passage is extremely low three to four months after commencement followed by a positively accelerated growth rate that continues until the time of adjournment. This scalloped configuration appears uniformly in each of the eight Congresses sampled, from 1947 to 1968, and in both sessions of each Congress.     

Effects of chlordiazepoxide and cocaine on concurrent food and avoidance-of-timeout schedules.

Five rats were trained on a concurrent schedule in which responses on one lever produced a food pellet on a random-interval 30-s schedule during 10 s of food availability associated with distinctive exteroceptive stimuli. Responses on another lever postponed for 20 s the presentation of a 50-s timeout, during which all stimuli were extinguished and the schedule contingencies on the food lever were suspended. The response rates maintained by the random-interval schedule exceeded those maintained by the avoidance contingency, but both provided a stable baseline to assess the behavioral effects of different drugs. Low doses of cocaine hydrochloride (1 and 3 mg/kg) did not affect food-reinforced responding or avoidance response rates. Intermediate doses (5.6, 10, and 13 mg/kg) produced a dose-dependent decrease in food-maintained and avoidance response rates, and both types of responding were virtually eliminated after administration of the highest doses (17 and 30 mg/kg) of cocaine. Low doses of chlordiazepoxide (1 and 3 mg/kg) increased food-maintained and avoidance response rates, and both rates decreased systematically after 10 and 30 mg/kg of this drug. The effects of cocaine and chlordiazepoxide on response rates maintained by avoidance of timeout from food presentation were unlike those reported when subjects responded to avoid shock presentation. The results of this experiment thus provide evidence to suggest that the effects of drug administration on avoidance behavior may be a function of the nature of the consequent event to be avoided.     

Fixed versus variable sequences of food and stimulus presentation in second-order schedules

Three pigeons were exposed to a second-order schedule in which the behavior specified by a fixed-interval component schedule was reinforced according to a ratio overall schedule. The completion of components not followed by food was signalled by a brief stimulus never paired with food. Food and the stimulus occurred in a random sequence or in fixed alternation, but the overall schedules (variable ratio 2 or fixed ratio 2) ensured that an equal number of food and brief-stimulus presentations occurred in each session. The control exerted by the food and by the brief stimulus was measured by overall response rates, mean pauses, frequency distributions of pauses, and response patterning across components. In general, the stimulus controlled patterns of behavior more similar to those controlled by food when food and the stimulus occurred in a random sequence than when they occurred in fixed alternation.     

Maintenance and suppression of responding under schedules of electric shock presentation

In squirrel monkeys previously trained under a continuous avoidance schedule, characteristic patterns of responding were maintained under a 3-min variable-interval schedule of shock presentation (response-produced shock). Responding in the presence of a periodically presented stimulus, the termination of which coincided with the delivery of a response-independent electric shock (Estes-Skinner procedure), was not reliably affected. When shocks followed every response during certain signalled portions of the session, and were presented under the variable-interval schedule during the rest of the session (multiple 1-response fixed-ratio, 3-min variable-interval schedule of shock presentation), responding was suppressed during the fixed-ratio component and maintained during the variable-interval component. Environmental consequences do not have immutable properties, and may either support or suppress behavior, depending on the schedule of presentation.     

Responding maintained under fixed-interval and fixed-time schedules of electric shock presentation

Following initial histories under a schedule of electric shock postponement, lever pressing in squirrel monkeys was maintained under fixed-interval and fixed-time schedules of electric shock presentation. No difference in either rate or pattern of responding was obtained when these schedules were presented as components of a multiple schedule. When they were presented singly for long periods of time, the fixed-interval schedule consistently maintained a higher response rate than the fixed-time schedule. The pattern of responding under both schedules was similar, typically consisting of a pause at the beginning of each interval followed by either a steady or a positively accelerating rate of responding. The results suggest that the response-shock dependency is of critical importance in the maintenance of high rates of responding under schedules of electric shock presentation, and support the general view that such responding may be conceptualized as operant behavior under control of many of the same variables that control responding under comparable schedules of food or water reinforcement.