Some effects of punishment shock intensity upon discriminative responding

Three pigeons received visual discrimination training under both multiple variable-ratio extinction and variable-interval extinction schedules. All birds developed nearly perfect discrimination. When punishment for every tenth response during food reinforcement was presented, responding decreased as shock intensity increased. At the same time, responding during extinction, which was not punished, increased at intermediate punishment intensities, but returned to low levels under severe punishment. A second procedure, in which punishment and no-punishment sessions alternated unsystematically, was employed with two of the birds. The results under this procedure essentially replicated the data obtained as punishment shock intensity increased gradually.     

The effect of shock intensity upon responding under a multiple-avoidance schedule

The effect of two shock intensities (1.00 and 2.00 mA) were studied in the acquisition, maintenance, and extinction of unsignalled avoidance by albino rats. Single and multiple avoidance schedules were employed, with shock intensity being the principal condition that differed between schedule components. The higher shock intensity was generally more effective in producing avoidance. Higher response rates and lower shock rates were observed under high-intensity shock when performance stabilized. When the multiple schedule was introduced, the six rats trained under a single shock intensity all showed poorer performance under the new shock intensity, whether it was higher or lower than the training intensity. Performance under the original shock intensity did not change substantially with the introduction of a different shock intensity in the other multiple schedule component. Performance under the new shock intensity showed gradual improvement with continued exposure to it. All of the rats showed persistent “warm-up”, receiving approximately 40% of the total session shocks in the first one-sixth of the session. The degree of warm-up was unrelated to avoidance shock intensity.     

The effect of reinforcement magnitude upon responding under fixed-ratio schedules

Responding under fixed-ratio schedules was studied as a function of two durations of food presentation. Latency of the first response after food presentation (post-reinforcement pause) was consistently shorter when food was presented for the longer duration. Only one of the four pigeons studied showed a consistently higher response rate, exclusive of post-reinforcement pause, as a function of the longer access to food. When ratio size was reduced, pause durations decreased, and the differences related to the two durations of food presentations became progressively smaller.     

The effect of shock intensity on concurrent and single-key responding in concurrent-chain schedules

Pigeons were trained to respond in a two-link, concurrent-chain schedule. Pecks on each key during the concurrent initial links occasionally produced a 5-min terminal link, during which only that key was operative. Food reinforcement and various intensities of shock were scheduled during the terminal links. When shock was contingent on response, the effect of shock was greater on terminal-link responding than on initial-link responding. When shock was independent of response, the effect was reversed, with larger changes in initial-link responding than terminal-link responding. In general, shock was found to affect behavior most drastically when behavior could, in turn, affect the rate of shock.     

The relative law of effect: effects of shock intensity on response strength in multiple schedules

Key pecking of four birds was reinforced with food according to a two-component multiple variable-interval 1-minute variable-interval 4-minute schedule. In addition, key pecking was punished by a brief shock according to a variable-interval 30-second schedule during both components of the multiple schedule. The intensity of the shock was varied. For all birds, punishment had a stronger suppressive effect on the responding maintained by the leaner food schedule, and the ratio of responding during the two components of the multiple schedule became closer to the ratio of reinforcement as shock intensity was increased, as the relative law of effect predicts. At the higher shock intensity, there was some evidence that the ratio of responses overmatched the ratio of reinforcements.     

Some effects of punishment upon unpunished responding

Animals permitted free access to a running wheel and drinking tube increased the amount of running when drinking was punished with electric shock. Additional experiments demonstrated that the simple presence or absence of a drinking tube (or running wheel) was a sufficient condition to observe a decrease or an increase in the alternative response. A quantitative analysis of these interactions observed between the incompatible running and drinking responses suggested that each response occupied a constant proportion of the time available for it. These results question an interpretation of the increase in unpunished alternative responding based upon its avoidance properties.     

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.     

Spaced responding in multiple DRL schedules

Rats were able to adjust to two different temporal requirements within several multiple DRL schedules of reinforcement, and a slight induction between pairs of components was found. Initial administration of dl-amphetamine differentially disrupted spaced responding in the components of a multiple DRL 36 DRL 18 schedule, but did not eliminate discrimination between the components. After maximum drug effects, the continued administration of dl-amphetamine was accompanied by a progressive recovery of the behavior towards the characteristics of saline control.     

Factors influencing responding under multiple schedules of conditioned and unconditioned reinforcement

Two experiments examined pigeons' responses under multiple schedules of conditioned and unconditioned reinforcement. In one component, responses produced food according to a fixed-interval schedule; in a second component, responses produced brief stimuli according to a fixed-ratio schedule. When brief-stimulus presentations were paired with food in the first component, rates in the second component were usually higher than 10 responses per minute. When pairing in the first component was eliminated, responding continued to be maintained in the second component. Elimination of food presentation from the first component substantially decreased responding in the second component, even though the brief stimulus had not been paired with food. Experiment II demonstrated that response rate was affected by the duration of both the second component and the brief stimulus. The results suggest that three conditions are important in maintaining responding with brief-stimulus presentations: (1) pairing the brief stimulus, at least initially, with food, (2) maintaining unconditioned reinforcement in one component, and (3) employing optimal brief-stimulus and component durations.     

Drugs and punished responding I: rate-dependent effects under multiple schedules

The effects of drugs were studied in pigeons whose responses were punished with electric shock during one component of a multiple fixed-interval 5-min fixed-interval 5-min schedule of food presentation. Most of the drugs analyzed for rate-dependent effects increased low rates of both punished and unpunished responding, while increasing higher rates less, or decreasing them; however, low rates of punished responding sometimes were increased more by pentobarbital, diazepam, and chlordiazepoxide than were matched rates of unpunished responding. In contrast, d-amphetamine and chlorpromazine usually increased low rates of unpunished responding more than matched rates of punished responding. These two drugs also decreased high rates of unpunished responding less than they decreased high rates of punished responding. Thus, the effects of drugs on punished responding depend on the control rate of punished responding; however, the rate-dependent effects of drugs on punished responding are not always the same as they are for unpunished responding.     

Reversal of preference under progressive-ratio schedules by punishment

A progressive-ratio reinforcement schedule, in which successive reinforcements required an additional 50 responses, was programmed on one key. A response on a second key reset the progressive-ratio schedule to the first step. Before punishment, all pigeons consistently reset the schedule after reinforcement on the first step, thereby minimizing the number of responses required for reinforcement. Punishment was a brief electric shock contingent upon each response on the reset key. The first effect of punishment was to change the frequency of extra responses on the reset key. Under higher intensities of punishment, the pigeons completed the advanced steps of the progressive-ratio schedule before resetting to the first step. Completions of advanced steps were accompanied by decreases in the overall rate of responding and the rate of reinforcement. When the punishment contingency was removed, the major features of pre-punishment performance were recovered.     

Punished and unpunished responding in multiple variable-interval schedules

The performance of rats trained on multiple variable-interval schedules was examined before, during, and after punishment. The same linear function related relative response rates to relative density of reinforcement both in the presence and absence of punishment. Equal relative suppression was seen in both the high and low reinforcement density components. The intercept value of the function was zero. Each component of the schedule was programmed on a separate lever: thus during any component, there was an opportunity for responses on the nonoperative lever (errors). The proportions of these errors declined to a near-zero value during punishment and did not regain their prepunishment values after punishment was removed, suggesting that some discrimination learning occurred during punishment. Recovery of response rate during punishment was seen only where a greater-than-zero probability of reinforcement was associated with the response.     

The effects of terminal-link fixed-interval and variable-interval schedules on responding under concurrent chained schedules

Previous work using variable-interval schedules in the terminal links of concurrent chained schedules suggested that relative choice proportion in the initial links equalled relative rate of reinforcement in the terminal links. With fixed-interval terminal-link schedules, however, matching was not obtained. The present study held pairs of fixed-interval terminal-link schedules in a constant ratio but varied absolute sizes. Relative choice for the smaller terminal-link fixed-interval schedule was a negatively accelerated, increasing function of absolute size of the fixed-interval pairs. Matching was found only with the fixed-interval pair of 5 and 10 sec. When pairs of variable-interval schedules were arranged so that the harmonic mean of the intervals equalled the fixed-interval parameter values, relative choice functions were like those for fixed-interval schedules.     

The effects of escape conditioning and shock intensity on responding during inescapable shock

Eight albino rats, conditioned to press a lever to escape shock, continued to lever press during short inescapable shocks presented subsequently. The rate of this behavior was found to be higher for higher shock intensities regardless of the order in which shock values were presented. Relative to the immediately preceding escape rate, responding during inescapable shock was higher following conditioning at higher fixed-ratio escape requirements. Four subjects not conditioned to escape shock pressed the lever very infrequently during inescapable shock and showed little change with changes in shock intensity. The escape conditioning effects suggest that responding during inescapable shock is superstitious escape behavior. The effects of shock intensity on this behavior appear to be similar to reported effects of shock intensity on escape behavior.     

Responding under fixed-ratio and multiple fixed-interval fixed-ratio schedules of electric shock presentation

Squirrel monkeys, initially trained under a schedule of electric shock postponement and then under fixed-interval schedules of electric shock presentation, were studied under multiple fixed-interval fixed-ratio and under fixed-ratio schedules of shock presentation. Under the fixed-interval (10-min) component of the multiple schedule, a pause was followed by a gradual increase in responding to a rate maintained until shock presentation; under the fixed-ratio (3-, 10-, or 30-response) component of the multiple schedule, a brief pause was typically followed by a relatively high and uniform rate of responding until shock was presented. When the 60-sec timeout periods, which usually followed shock presentation, were eliminated from the multiple schedule for one monkey, responding was only transiently affected. In the one monkey studied, responding was maintained under a fixed-ratio schedule alone (with timeout periods), but rates of responding were lower than under the fixed-ratio component of the multiple schedule. Characteristic patterns of responding, similar to those engendered under schedules of food presentation or shock termination, can be maintained under fixed-ratio schedules of shock presentation; further, patterns of responding can be controlled by discriminative stimuli in multiple schedules.     

Local patterns of responding maintained by concurrent and multiple schedules

Local patterns of responding were studied when pigeons pecked for food in concurrent variable-interval schedules (Experiment I) and in multiple variable-interval schedules (Experiment II). In Experiment I, similarities in the distribution of interresponse times on the two keys provided further evidence that responding on concurrent schedules is determined more by allocation of time than by changes in local pattern of responding. Relative responding in local intervals since a preceding reinforcement showed consistent deviations from matching between relative responding and relative reinforcement in various postreinforcement intervals. Response rates in local intervals since a preceding changeover showed that rate of responding is not the same on both keys in all postchangeover intervals. The relative amount of time consumed by interchangeover times of a given duration approximately matched relative frequency of reinforced interchangeover times of that duration. However, computer simulation showed that this matching was probably a necessary artifact of concurrent schedules. In Experiment II, when component durations were 180 sec, the relationship between distribution of interresponse times and rate of reinforcement in the component showed that responding was determined by local pattern of responding in the components. Since responding on concurrent schedules appears to be determined by time allocation, this result would establish a behavioral difference between multiple and concurrent schedules. However, when component durations were 5 sec, local pattern of responding in a component (defined by interresponse times) was less important in determining responding than was amount of time spent responding in a component (defined by latencies). In fact, with 5-sec component durations, the relative amount of time spent responding in a component approximately matched relative frequency of reinforcement in the component. Thus, as component durations in multiple schedules decrease, multiple schedules become more like concurrent schedules, in the sense that responding is affected by allocation of time rather than by local pattern of responding.     

A comparison of measures of responding under fixed-interval schedules

Average response rate, post-reinforcement pause, elapsed time to the fourth response, average quarter-life, and running rate were examined to see how they reflected changes in fixed-interval performance. Rats were exposed to a mixed schedule of water presentation comprising fixed-interval schedules of two durations. Changes in responding were produced by varying the duration of the shorter component. The five measures were derived only from the longer schedule component. Post-reinforcement pause, elapsed time to the fourth response in the interval, and quarter-life all showed high, positive inter-correlations (0.78<r<0.99). Running rate and post-reinforcement pause were not as highly correlated. Quarter-life reliably reflected changes in fixed-interval performance but changes in the quarter-life value did not necessarily result from similar changes in fixed-interval response pattern. The two measures that adequately described changes in response patterning were post-reinforcement pause and running rate. These two measures also had the advantage of being simple both computationally and in terms of the instrumentation involved in their recording.     

Selective punishment of interresponse times: The roles of shock intensity and scheduling

Two experiments investigated the roles of shock intensity and scheduling in selective punishment of interresponse times. In each experiment the punishment contingencies were imposed on a background of rats' responding maintained by a variable-interval schedule of food presentation. In Experiment 1 all interresponse times greater than 8 seconds produced shock. In Experiment 2 all interresponse times greater than 8 seconds but less than 12 seconds produced shock. In each experiment shock intensity was initially 0.3 milliamperes (mA) and then was varied through an ascending sequence ranging from 0.1 mA to 0.4 mA, in 0.1-mA increments. Experiment 1 produced response-rate increases at low intensities (0.1 and 0.2 mA) but eliminated responding at the remaining intensities. Experiment 2 produced response-rate increases only with 0.1-mA shock, although responding was maintained at all shock parameters investigated. Analysis of the interresponse times per opportunity showed differential suppression of the targeted responses in all cases except the high-intensity shock phases of Experiment 1. The current data support and extend previous studies of selective interresponse-time-dependent shock schedules but suggest that response-rate increases are not a necessary outcome of this type of procedure. The view that variable-interval schedules of shock presentation selectively target long interresponse times was also supported.     

An interresponse-time analysis of responding maintained by schedules of response-produced electric shock

The present study investigated ratio contingencies to evaluate factors that may determine the maintenance of responding when electric shock is the consequent event. Initially, squirrel monkeys (Saimiri sciureus) were exposed to a continuous-avoidance schedule to initiate bar pressing. Subsequently, a multiple random-interval variable-ratio yoked schedule of response-produced shock was used to maintain and to compare interval and ratio performance. A microcomputer recorded and stored the number of responses and interresponse times occurring between successive shock presentations during a given random-interval component, and these numbers determined the ratio requirements during the subsequent ratio component. Responding was maintained for more than 80 sessions in two of three monkeys under the multiple schedule with the ratio yoked to the interval component. Responding during the ratio component persisted in only one monkey, however, when the components were no longer yoked. An analysis of the interresponse times immediately preceding shock under the multiple yoked schedule revealed that the terminal interresponse times were longer under the interval schedule than under the ratio contingency. The interresponse-time analysis indicated that differential interresponse-time relationships may be major determinants of the maintenance of behavior controlled by schedules of electric-shock presentation.