Behavioral contrast in rats with different reinforcers and different response topographies

Experiment I demonstrated positive behavioral contrast in rats when one of two qualitatively different reinforcers (milk and pellets) was removed from a component of a multiple schedule. The contrast effect was larger and more enduring when milk was removed. Experiment II showed that the rats spent more time on the side of a shuttle-box on which milk was freely available than on the side on which pellets were freely available. Experiment III, a partial replication of Experiment I, failed to demonstrate the contrast effect of Experiment I. Experiment IV demonstrated contrast when two topographically distinct responses, nose-key poking and lever pressing, were required in different components of a multiple schedule. These results extend the conditions that generate behavioral contrast in rats.     

Effects of quantitative shifts in a visual reinforcer on the instrumental response of infants.

Two studies examined the effects of quantitative (“complexity”) differences in a visual reinforcer and subsequent reward shifts, on operant response rates. Footkicks and visual attention of 3-month-old infants were measured across daily sessions with conjugate reinforcement provided by an overhead mobile containing either two, six or ten identical components. In Experiment 1, initial rates to the three mobiles differed. The relation between components and kicking was not linear, but was an inverted U-shaped function of component numerosity. The infant responses as a function of numerosity from Experiment 1 were used to define “complexity” in Experiment 2, and all subjects were switched to an intermediate complexity level (two components) after achieving a criterion of stable responding. Although the number of mobile components did not differentially affect acquisition rates, infants who received a shift from six to two components exhibited a reliable and immediate response increase whereas those experiencing a ten- to two-component shift exhibited negative behaviors. These results imply that infants respond relationally, actively manipulating their visual environments as a function of their previous contextual experiences.     

Within-session changes in responding during concurrent schedules with different reinforcers in the components.

Rats and pigeons responded on several concurrent schedules that provided different reinforcers in the two components (food and water for rats, Experiment 1; wheat and mixed grain for pigeons, Experiment 2). The rate of responding and the time spent responding on each component usually changed within the session. The within-session changes in response rates and time spent responding usually followed different patterns for the two components of a concurrent schedule. For most subjects, the bias and sensitivity to reinforcement parameters of the generalized matching law, as well as the percentage of the variance accounted for, decreased within the session. Negative sensitivity parameters were sometimes found late in the session for the concurrent food-water schedules. These results imply that within-session changes in responding could cause problems for assessing the validity of quantitative theories of concurrent-schedule responding when the components provide different reinforcers. They question changes in a general motivational state, such as arousal, as a complete explanation for within-session changes in responding. The results are compatible with satiation for, or sensitization-habituation to, the reinforcers as explanations.     

Eliminating the cost of task set reconfiguration

With insufficient time to fully prepare for a switch in task, a deterioration in performance on the first trial of a new task would be expected. The interest of researchers has been captured by the residual switch costs that, surprisingly, remain despite sufficient time to prepare. We used avery simple task to investigate the costs to reaction time and accuracy associated with changing between two different instructional sets every eight trials. Subjects responded to left and right visual targets by making either spatially compatible or incompatible eye movements (Experiment 1) or buttonpress responses (Experiment 2). The subjects were cued as to whether to make the compatible or the incompatible response by the color of a border appearing on the perimeter of the display. In cases in which the subject alternated between making pro- and antisaccades, the large costs to reaction time and accuracy at the short cue-target stimulus onset asynchrony were completely eliminated when sufficient time was provided to prepare for the switch. This complete elimination of residual switch costs was not obtained when the same alternation was applied to manual responses. This pattern of results links residual costs to response selection processes and suggests that they are not a necessary component of the switch process. We propose that the elimination of "stubborn" residual switch costs is rooted in our use of a hypercompatible task (making saccades toward targets) that places minimal demands on response selection.     

The role of potential loss in the influence of affect on risk-taking behavior

In three experiments the influence of positive affect on risk-taking behavior was examined. In Experiment 1 subjects who received a free gift of candy, compared to those in a control group, were willing to pay increasingly more for lottery tickets as the prize rose from $10 to $90 and as the probability of winning rose from .10 to .90. In Experiment 2 subjects who received a free gift of candy, compared to those in a control group, were willing to pay more to buy insurance against loss, and were particularly more likely to do so when the potential loss was large. A third study, which found that subjects who received a free gift of candy were not willing to pay more for an item than were control subjects, led us to conclude that the results of the first two experiments are not best interpreted as merely due to a general increase in the willingness to spend as a consequence of having received a gift. Instead it was concluded that positive feelings can foster both risk-prone behavior (Experiment 1) and risk-averse behavior (Experiment 2). When a positive-affect subject faces a risk situation in which the potential loss is emphasized, the subject demonstrates risk aversion; when the potential loss is minimized, then risk proneness is observed.     

Unsignaled delay of reinforcement, relative time, and resistance to change

Two experiments with pigeons examined the effects of unsignaled, nonresetting delays of reinforcement on responding maintained by different reinforcement rates. In Experiment 1, 3-s unsignaled delays were introduced into each component of a multiple variable-interval (VI) 15-s VI 90-s VI 540-s schedule. When considered as a proportion of the preceding immediate reinforcement baseline, responding was decreased similarly for the three multiple-schedule components in both the first six and last six sessions of exposure to the delay. In addition, the relation between response rates and reinforcement rates was altered such that both parameters of the single-response version of the matching law (i.e., k and Re) were decreased. Experiment 2 examined the effects of unsignaled delays ranging from 0.5 s to 8.0 s on responding maintained by a multiple VI 20-s VI 120-s schedule of reinforcement. Response rates in both components increased with brief unsignaled delays and decreased with longer delays. As in Experiment 1, response rates as a proportion of baseline were affected similarly for the two components in both the first six and last six sessions of exposure to the delay. Unlike delays imposed between two stimulus events, the effects of delays between responses and reinforcers do not appear to be attenuated when the average time between reinforcers is longer. In addition, the disruptions produced by unsignaled delays appear to be inconsistent with the general finding that responding maintained by higher rates of reinforcement is less resistant to change.     

Instrumental performance on negative schedules

Three experiments examined the performance of rats pressing a lever for food reinforcement on a schedule in which high rates of response resulted in lowered rates of reinforcement (i.e. a schedule with a negative component). In Experiment 1, rats responded on a variable interval (VI) schedule with a conjoint component such that every 30 responses a reinforcement programmed by the VI schedule was cancelled. These subjects generally emitted a lower response rate than rats responding on a VI schedule yoked to the former subjects with respect to the delivery of reinforcement, although response rate differences were sometimes not large. Similar response-rate effects were obtained in Experiment 2 using a within-subject yoking procedure. In Experiment 3, reinforced interresponse times were matched on negative and VI schedules yoked in terms of reinforcement rate, and the response rate emitted in these conditions were similar. These results give support to theories of instrumental conditioning that stress the strengthening and shaping properties of reinforcement.     

Age Influences on Multi-Dimensional Set Switching

Using a task switching paradigm, we investigated age effects on switch costs as a function of the number of sets to be switched. In Experiment 1, younger and older subjects determined a color or shape of an object presented on the computer screen, responding either by moving the joystick or by pressing a button on the joystick. The switch costs were assessed with differences between switch trials (task-set switch, response-set switch, and double switch) and non-switch trials. Contrary to the prediction that age would negatively influence performance on the double switch trials, age effects on switch costs were observed only for the single switch trials (i.e., response-set switch condition). Additionally, both younger and older adults were capable of preparing for task and response-set switches in parallel. In Experiment 2, we manipulated the time available to prepare for a task and response-set switch. Both younger and older adults were able to utilize extra time to reduce switch costs. Furthermore, the age deficit found in Experiment 1 for response-set switching was eliminated in the second experiment in which preparation for task and response-set switching was temporally decoupled. The data are discussed in terms of task component coordination across the adult lifespan.     

Coding responses and the generalization of matching to sample in children.

Two experiments studied the conditions of stimulus control necessary for the generalization of relational matching to sample. Matching required the selection of comparison shapes rotated 90 degrees clockwise from the orientation of the corresponding sample. In Experiment 1, five children were taught to: (a) code the orientations of samples, (b) transform sample codings to account for the 90 degree rotation, and (c) repeat the transformed sample coding response to a comparison. High levels of generalization occurred with a set of novel stimuli for which stable sample-coding responses were initially available. In another novel set, where stable sample-coding responses were not initially available, low levels of generalized matching were recorded. Matching performance improved after stable coding responses were trained. In Experiment 2, two children and three adults were trained in a form of the matching task that produced poor generalization despite the presence of stable sample-coding responses. Retraining to modify the stimulus control exerted by these coding responses produced an immediate improvement in generalized matching to sample. Results suggest that the generalization of matching is dependent on structure of stimulus control that the component responses exert on each other.     

Marble burying and spontaneous motor activity in mice: interactions over days and the effect of diazepam

Spontaneous motor activity of mice was studied in the presence or absence of 24 coloured glass marbles with and without treatment with different doses of the anxiolytic compound, diazepam. The three parameters of motor activity, locomotion, rearing and total activity, were measured in automated test cages. All the groups exposed to the marbles exhibited considerable and comparable marble burying, but there was an important interaction between marble burying and locomotor activity over test days. The "marbles" group performed fewer locomotion counts than the "no marbles" group on Day 1 but more counts on Day 3. The "marbles" group performed more rearing and less total activity than the "no marbles" group generally and this relationship was not altered over test days. Diazepam caused a dose-dependent decrease of both marble burying and the three parameters of motor activity but did not cause further increases in motor activity in the groups exposed to the marbles. These results are discussed with regard to the effects of "coping" behaviours on measures of motor activity. In conclusion, the present motor activity-marble burying test appears to be a suitable animal model for testing potential anxiolytic compounds.     

Second-order schedules: discrimination of components

Pigeons were exposed to a series of second-order schedules in which the completion of a fixed number of fixed-interval components produced food. In Experiment 1, brief (2 sec) stimulus presentations occurred as each fixed-interval component was completed. During the brief-stimulus presentation terminating the last fixed-interval component, a response was required on a second key, the brief-stimulus key, to produce food. Responses on the brief-stimulus key before the last brief-stimulus presentation had no scheduled consequences, but served as a measure of the extent to which the final component was discriminated from preceding components. Whether there were one, two, four, or eight fixed-interval components, responses on the brief-stimulus key occurred during virtually every brief-stimulus presentation. In Experiment 2, an attempt was made to punish unnecessary responses on the brief-stimulus key, i.e., responses on the brief-stimulus key that occurred before the last component. None of the pigeons learned to withhold these responses, even though they produced a 15-sec timeout and loss of primary reinforcement. In Experiment 3, different key colors were associated with each component of a second-order schedule (a chain schedule). In contrast to Experiment 1, brief-stimulus key responses were confined to the last component. It was concluded that pigeons do not discriminate well between components of second-order schedules unless a unique exteroceptive cue is provided for each component. The relative discriminability of the components may account for the observed differences in initial-component response rates between comparable brief-stimulus, tandem, and chain schedules.     

Stimulus-response compatibility with wheel-rotation responses: Will an incompatible response coding be used when a compatible coding is possible?

Three experiments were conducted in which subjects responded to left-right tones with clockwise-counterclockwise rotations of a steering wheel using one of two stimulus-response assignments. When the hands were at the bottom of the wheel, where hand movement is opposite to wheel movement, subjects coded responses according to the frame that yielded a compatible mapping when the instructions did not emphasize either hand or wheel movements (Experiment 1). When instructions emphasized hand movements, responses were coded relative to the hand-referenced frame (Experiment 2), and when the wheel controlled a visual cursor, responses were coded relative to a cursor-referenced frame (Experiment 3). Coding with respect to these frames occurred even when the resulting mapping was incompatible.     

Cardiac activity and information processing: the effects of stimulus significance, and detection and response requirements.

In two experiments, measures of heart rate and electromyographic activity were obtained from 40 male undergraduates while they performed two series of trials involving a sequential information processing task. Each trial consisted of a warning light, three successive tones, and a responded light, separated by 6-sec intervals. In Experiment 1, subjects responded only if the three tones were of different frequencies. Acclerative heart-rate responses to the last tone increased as a function of the significance of that tone. Subsequent cardiac decelerations were only observed if the subject was preparing to make a response. These results were replicated in Experiment 2, in which subjects responded only if two of the preceding tones were of the same frequency. Electromyographic activity was not significantly affected by stimulus significance or response anticipation. The data indicate that cardiac acceleration and deceleration reflect two independent psychological processes, associated with information-processing and decision-making activity on the one hand, and preparatory activity on the other.     

Running-wheel avoidance learning in rats (Rattus norvegicus): effects of contingencies and comparisons of different strains

In Experiment 1, we showed that active- and passive-avoidance responding in a running wheel was learned because of the avoidance contingency. In Experiment 2, strain differences among four commercially bred rats were assessed in an active-avoidance paradigm. Wistar, Donryu, and Fischer rats learned faster than Sprague-Dawleys. In Experiment 3, learning in a multiple active/passive avoidance schedule was examined, and both components of this task were learned. This multiple schedule was used to investigate strain differences in selectively bred rats in Experiments 4 and 5. Tsukuba low-emotional (TLE) rats responded more than Tsukuba high-emotional (THE) rats in both components. However, discrimination of passive components was better in THE than in TLE rats. Syracuse high-avoidance rats were superior in the active component, whereas Syracuse low-avoidance rats showed superior performance in the passive component.     

Guilty or Not Guilty? A Look at the “Simulated” Jury Paradigm1

Three experiments examined the effects of real versus hypothetical consequences on juridic decision-making. Real consequences subjects believed their judgments would actually determine what happened to the defendant, while hypothetical consequences subjects believed the study simply dealt with jury decision-making. In Experiment I, the defendant's character attractiveness had no influence on guilt judgments made by real consequences subjects but did so for hypothetical consequences subjects. In addition, character attractiveness affected recommendations of punishment for both real and hypothetical consequences subjects. In Experiment II, the defendant's physical attractiveness influenced neither real nor hypothetical consequences subjects on either the guilt or punishment measures. Experiment III showed that real consequences subjects recalled more situational evidence of the case than did hypothetical consequences subjects. In all three studies, more guilty verdicts occurred in the real consequences condition than in the hypothetical consequences condition. It was concluded that much current research on hypothetical juries may be misleading and that more attention should be given in the future to the variable of real versus hypothetical consequences. Possible mediating factors leading to real and hypothetical consequences differences were explored.     

Competitive fixed-interval performance in humans

Two persons responded in the same session in separate cubicles, but under a single schedule of reinforcement. Each time reinforcement was programmed, only the first response to occur, that is, the response of only one of the subjects, was reinforced. “Competitive” behavior that developed under these conditions was examined in three experiments. In Experiment 1 subjects responded under fixed-interval (FI) 30-s, 60-s, and 90-s schedules of reinforcement. Under the competition condition, relative to baseline conditions, the response rates were higher and the pattern was “break-and-run.” In Experiment 2, subjects were exposed first to a conventional FI schedule and then to an FI competition schedule. Next, they were trained to respond under either a differential-reinforcement-of-low-rate (DRL) or fixed-ratio (FR) schedule, and finally, the initial FI competition condition was reinstated. In this second exposure to the FI competition procedure, DRL subjects responded at lower rates than were emitted during the initial exposure to that condition and FR subjects responded at higher rates. For all subjects, however, responding gradually returned to the break-and-run pattern that had occurred during the first FI competition condition. Experiment 3 assessed potential variables contributing to the effects of the competitive FI contingencies during Experiments 1 and 2. Subjects were exposed to FI schedules where (a) probability of reinforcement at completion of each fixed interval was varied, or (b) a limited hold was in effect for reinforcement. Only under the limited hold was responding similar to that observed in previous experiments.     

Extinction of a heterogeneous chain after several reinforcement schedules

Rats were conditioned to emit the following two-member chain of responses on two different operanda always available: responses on a vertical bar produced a discriminative stimulus for food-reinforced responding on a horizontal bar. Responses on the vertical bar produced a discriminative stimulus on a variable-interval 1-min schedule, and the horizontal bar produced food on a variable ratio of 10 responses. Control conditions were included in which vertical bar responses were also food-reinforced simultaneous with the onset of the discriminative stimulus for the horizontal bar response and a tandem schedule which had the same response requirements but without different exteroceptive stimuli associated with the separate components of the response chain. The latter condition greatly retarded acquisition of the response chain compared to the other schedules studied here and compared to reports in the literature on homogeneous (single operandum) response chains. Intermittent reinforcement of the chain led to greater resistance to extinction of both members and the chain remained intact longer in the sense that stimulus control was maintained.     

Drugs and punished responding II: d-amphetamine-induced increases in punished responding

The effects of d-amphetamine on punished responding were studied in two experiments. In Experiment I, pigeons responded under a multiple fixed-ratio 30 response fixed-interval 5-min schedule of food presentation with 60-sec limited holds in both components. Each response was punished with electric shock, the intensity of which was varied systematically. In Experiment II, another group of pigeons responded under a multiple fixed-interval 5-min fixed-interval 5-min schedule of food presentation with 40-sec limited holds. Each response was punished with shock during one component, and every thirtieth response was punished in the other component. d-Amphetamine increased overall rates of punished responding only rarely under any of the punishment conditions; however, response rates within the fixed-interval when rates were low were increased by d-amphetamine when the shock intensity was low (Experiment I), or when responses produced shock intermittently (Experiment II). The data suggest that the effects of d-amphetamine on punished responding depend on the control rate of responding, the punishment intensity, the punishment frequency, and the schedule of food presentation.     

Contrast and autoshaping in multiple schedules varying reinforcer rate and duration

Thirteen master pigeons were exposed to multiple schedules in which reinforcement frequency (Experiment I) or duration (Experiment II) was varied. In Phases 1 and 3 of Experiment I, the values of the first and second components' random-interval schedules were 33 and 99 seconds, respectively. In Phase 2, these values were 99 seconds for both components. In Experiment II, a random-interval 33-second schedule was associated with each component. During Phases 1 and 3, the first and second components had hopper durations of 7.5 and 2.5 seconds respectively. During Phase 2, both components' hopper durations were 2.5 seconds. In each experiment, positive contrast obtained for about half the master subjects. The rest showed a rate increase in both components (positive induction). Each master subject's key colors and reinforcers were synchronously presented on a response-independent basis to a yoked control. Richer component key-pecking occurred during each experiment's Phases 1 and 3 among half these subjects. However, none responded during the contrast condition (unchanged component of each experiment's Phase 2). From this it is inferred that autoshaping did not contribute to the contrast and induction findings among master birds. Little evidence of local contrast (highest rate at beginning of richer component) was found in any subject. These data show that (a) contrast can occur independently from autoshaping, (b) contrast assays during equal-valued components may produce induction, (c) local contrast in multiple schedules often does not occur, and (d) differential hopper durations can produce autoshaping and contrast.     

The effects of delayed reinforcement on variability and repetition of response sequences

Four experiments examined the effects of delays to reinforcement on key peck sequences of pigeons maintained under multiple schedules of contingencies that produced variable or repetitive behavior. In Experiments 1, 2, and 4, in the repeat component only the sequence right-right-left-left earned food, and in the vary component four-response sequences different from the previous 10 earned food. Experiments 1 and 2 examined the effects of nonresetting and resetting delays to reinforcement, respectively. In Experiment 3, in the repeat component sequences had to be the same as one of the previous three, whereas in the vary component sequences had to be different from each of the previous three for food. Experiment 4 compared postreinforcer delays to prereinforcement delays. With immediate reinforcement sequences occurred at a similar rate in the two components, but were less variable in the repeat component. Delays to reinforcement decreased the rate of sequences similarly in both components, but affected variability differently. Variability increased in the repeat component, but was unaffected in the vary component. These effects occurred regardless of the manner in which the delay to reinforcement was programmed or the contingency used to generate repetitive behavior. Furthermore, the effects were unique to prereinforcement delays.