Reliability and sources of control of preference for signaled shock

Five experiments investigated the reliability of, and a possible explanation for, the preference for signaled shock (PSS) phenomenon, in which animals show a preference for signaled over unsignaled, unmodifiable shock. Experiment 1 demonstrated the generality of our previous PSS shuttlebox data. In an attempt to explain some of the studies in which a failure to obtain a PSS has been reported, Experiments 2 and 3 found that under certain conditions the PSS effect could be overridden by an innate preference for dark; however, the series of experiments in toto speaks clearly for the robustness of the phenomenon. Consistent with the recently proposed “crossover consequence hypothesis,” Experiments also revealed that shuttling behavior during manifestations of PSS is not randomly distributed in time. However, Experiments 4 and 5 found that PSS could not generally be attributed to an interaction between the acquired aversiveness of the signal and the spatially asymmetrical probability of shuttling being punished, as proposed by this hypothesis.     

Does shock modifiability contribute to preference for signaled shock?

The central question asked was whether differential shock modification occurs (posturally induced differences in shock contact time) under signaled and unsignaled conditions using scrambled shock. Shock modifiability was tested with two different shock sources, intensities, and scrambling units by measuring the duration of time subjects were in contact with shock. Subjects were then given a choice between the signaled and unsignaled conditions. Results showed that differential modification of shock contact time did not occur between signaled and unsignaled conditions with any shock source, intensity, or scrambler unit. In addition, subjects preferred the signaled condition. It was concluded that experiments using scrambled shock are not confounded by posturally induced differences in shock contact time.     

Preference for signaled shock: A test of two hypotheses

In a test of safety signal and preparatory response explanations of the preference for signaled vs. unsignaled shock, three groups of rats were exposed to a different light-tone-shock contingency on each of the two sides of a shuttlebox. One contingency (S/P) provided both a safety signal and a warning stimulus, another (NS/NP) provided neither, and a third (S/NP) provided a safety period but no warning stimulus. Rats preferred either the S/P or the S/NP side of the shuttlebox when the alternate side provided neither safety signal nor warning stimulus. When the safety signal was available on both sides, the side without the warning stimulus was preferred. Results are interpreted as supporting the safety signal hypothesis.     

External stimulus control of target-directed attack and biting elicited by tailshock

Two experiments evaluating the effects of external stimuli on attack and biting in rats elicited by electric tailshock are reported. In the first experiment, stimuli presented to four groups of test subjects consisted of a stimulus animal, a stimulus animal plus taped vocalizations of a rat experiencing shock, an inanimate object, and an inanimate object plus taped vocalizations. Subjects in a fifth (control) group were tested in the absence of these stimuli. The presence of another animal in the test situation significantly increased the amount of target-directed responding. A decrease in responding, rather than increase, was shown by the subjects tested under the stimulus-object plus taped-vocalization conditions. Experiment 2 investigated the salient features of the stimulus animal and found a combination of both olfactory and visual cues to be most effective in eliciting target-directed responding. These studies indicate that the amount of target-directed attack and biting shown in this situation may be related causally to the type of sensory input received by the test animal.     

Effects of duration of feedback on signaled avoidance

Two experiments were carried out to study vertical jumping avoidance learning in rats. In particular, we examined the effects of the duration of a feedback stimulus and of the interval between the end of the feedback stimulus and the start of the next trial on acquisition and extinction of avoidance. In Experiment 1, the duration of feedback was manipulated while intertriai interval (feedback plus no-feedback) was held constant. Animals with feedback lasting more than 1 sec needed fewer trials to reach the acquisition criteria than did animals with no feedback or with 1-sec feedback. No differences were observed in extinction. In Experiment 2, the durations of both feedback and no-feedback were manipulated. Animals without feedback needed more trials to reach the acquisition criterion than did animals with feedback, but the performance of the feedback animals did not differ as a function of feedback duration, no-feedback duration, or total intertrial interval. Again, no differences were observed in extinction. These results indicate that the presentation of feedback improves the acquisition of vertical jumping avoidance, but that this effect is independent of the temporal characteristics of feedback.     

Differential acquisition of discriminated autoshaping as a function of stimulus qualities and locations

In each of two experiments, different groups of pigeons were required to discriminate between one of two basic kinds of stimulus differences: stimulus quality or stimulus location. For stimulus-quality groups, a key was illuminated by one of two colors on trials ending with food delivery and by the other color on trials ending with no food. For stimulus-location groups, a key was illuminated at one of two locations on trials ending with food delivery and at the other location on trials ending with no food. The birds began to respond differentially to the stimuli (i.e., peck the keys on food trials and not peck the keys on no-food trials) earlier in acquisiton if the stimulus qualities served as the signals for trial outcomes than if the stimulus locations served as those signals. The results from both experiments are consistent with predictions from a hypothesis regarding interactions among the qualities and locations of stimuli and responses (the “quality-location hypothesis”). Furthermore, the present results support other recent demonstrations of the important role that spatial relations among stimuli can play in classical conditioning.     

A concurrent assessment of the positive and negative properties of a signaled shock schedule

A choice and a conditioned suppression procedure were used to assess concurrently the positive and negative properties of stimuli within a signaled shock schedule, Occasional shocks were presented to Ss responding on a variable-interval food schedule. Ss could choose whether shocks occurred alone or whether they were preceded by a 1-min signal. All Ss chose the signaled shock condition over the unsignaled one, even though food reinforced responding in the presence of the signal was suppressed. Rate of responding for food varied across stimulus conditions, with the lowest rate in the presence of the signal and the highest rate in its absence. An intermediate rate occurred under the unsignaled shock schedule. A safety analysis was applied to the data.     

The role of response-reinforcer correlation in signaled reinforcement effects

In three experiments, we examined the effects of signaling reinforcement during operant responding in order to illuminate the factors underlying instrumental overshadowing and potentiation effects. Specifically, we examined whether signaling reinforcement produces an enhancement and attentuation of responding when the response-reinforcer correlation is weak and strong, respectively. In Experiment 1, rats responded on variable-ratio (VR) or variable-interval (VI) schedules that were equated for the number of responses emitted per reinforcer. A signal correlated with reinforcement enhanced response rates on the VR schedule, but attenuated response rates were produced by the signal on the VI schedule. In Experiment 2, two groups of rats responded on a VI schedule while the two other groups received a conjoint VI, negative fixed-ratio schedule in which the subjects lost the availability of reinforcements if they emitted high response rates. A reinforcement signal attenuated responding for the simple VI groups but not for the animals given the negative fixed-ratio component, although the signal improved response efficiency in both groups. In Experiment 3, a poor correlation between responding and reinforcement was produced by a VI schedule onto which the delivery of response-independent food was superimposed. A signal for reinforcement initially elevated responding on this schedule, relative to an unsignaled condition; however, this pattern was reversed with further training. In sum, the present experiments provide little support for the view that signaling reinforcement enhances responding when the response-reinforcer correlation is weak and attenuates responding when this correlation is strong.     

Effects of signaled retention intervals on pigeon short-term memory

In three delayed matching-to-sample experiments, pigeons were given distinctive stimuli that were either correlated or uncorrelated with the scheduled retention intervals. Experiment 1 employed a single-key, go/no-go matching procedure with colors as the sample and test stimuli; lines of differing orientations signaled short or long delays for one group, whereas the lines and the delays were uncorrelated for the other group. The function relating discriminative test performance to delay length was steeper in the correlated group than in the uncorrelated group. In addition, the line orientation stimuli controlled differential rates of sample responding in the correlated group, but not in the uncorrelated group. In Experiment 2, subjects extensively trained with correlated line orientations were exposed to reversed cues on probe trials. Miscuing decreased discriminative test responding at the short delay, but enhanced it at the long delay. As in the correlated group of the first experiment, rates of sample keypecking were higher in the presence of the “short” time tag than in the presence of the ”long” time tag. Experiment 3 used a three-key choice-matching procedure and a within-subjects design, and equated reinforcement rate at the short and long delays. When auditory stimuli were correlated with delay length, the function relating choice accuracy to delay was steeper than when the stimuli and the delays were uncorrelated. The consistent effects of signaled retention intervals on memory performance may be understood in terms of differential attention to the sample stimuli.     

The role of signaled periods of nonreinforcement in responding on a random schedule in autoshaping

Little responding develops to a conditioned stimulus (CS) that is placed in a random relation to an unconditioned stimulus (US). However, if the USs not preceded by that CS are themselves signaled by another stimulus, then the CS does come to elicit responding. This result has been attributed (e.g., by Durlach, 1983) to the signal’s blocking of conditioning to background cues that otherwise would prevent conditioning of the CS. However, Goddard and Jenkins (1987) have suggested the alternative that signaling the USs promotes responding due to the adventitious creation of periods of signaled nonreinforcement. Two experiments were conducted to assess this alternative, involving an autoshaping preparation in pigeons. In Experiment 1, little responding to a keylight CS presented in a random relation to a food US occurred, despite the explicit presentation of a discrete noise signaling periods of no food in the intertrial interval (ITI). Experiment 2 was designed to replicate the procedure of Goddard and Jenkins, in which an auditory stimulus extended throughout the ITI of a random schedule, terminating only prior to extra USs and during the CS. Contrary to their findings, little responding developed to the target CS. However, responding did develop when the sound-free period occurred only prior to the extra USs. These results offer little support for the hypothesis that signaled periods of nonreinforcement promote responding on random schedules. However, they are consistent with the view that signaling of ITI USs acts by preventing conditioning of potentially competitive background cues.     

Changeover from unsignaled to signaled avoidance with and without a feedback stimulus in rats

Two experiments are reported in which, by pressing a lever, unsignaled avoidable shocks could be changed to signaled avoidable shocks for periods of 1 min, after which unsignaled avoidance was automatically reinstated. A correlated stimulus identified the signaled schedule. Under these conditions, Ss changed over at a rate sufficient to remain in the signaled schedule more than 90% of the time. Both experiments showed that changeover performance was under the control of the correlated stimulus. Presenting the signaled schedule without the correlated stimulus did not maintain changing over. The second experiment showed that a 1-sec presentation of the correlated stimulus was sufficient to maintain changeover performance. The results were attributed to the conditioned reinforcing properties of the correlated stimulus.     

A future of reversals: Dyslexic talents in a world of computer visualization

With the recent revival of visual approaches at the forefront of several scientific, mathematical, and technological developments, this paper proposes that visually oriented dyslexics may be in an increasingly favorable position in future years. The same set of traits which has caused them so much difficulty in traditional verbally-oriented educational systems, may confer special advantages in emerging new fields which rely heavily on visual methods of analysis—fields which employ powerful graphic workstations and supercomputers to visualize complex scientific data. Recent trends have also led some technical professionals to become aware that their own special talents seem to be closely associated with certain dyslexic traits. It is argued that similarly mixed talents have been major factors in the accomplishments of a number of important historical figures.     

The effects of signaled reward on sign tracking and response rate

If, while responding on a variable interval schedule, rats are given a brief cue prior to reward, their response rate is markedly lower than the rate for yoked partners who receive the cue randomly with respect to reward. This signaled-reward phenomenon has been explained in terms of sign tracking. Two experiments reported here replicated the phenomenon and examined sign tracking directly through visual inspection of the animals’ behavior. Although sign tracking did, indeed, occur more in the signaled reward condition, it did not fully account for the difference in response rates.     

Preference for signaled shock phenomenon: Direct and indirect evidence for modifiability factors in the shuttlebox

The experiments reported here investigated whether unauthorized shock modification is a factor which mediates the preference for signaled shock phenomenon (PSS) in the shuttlebox. This factor appearednot to have a critical role in PSS on the basis of earlier experiments which reported that PSS occurred in the shuttle-box even when shock was made unmodifiable by scrambling. However, the scrambling used in these experiments was not complete. In Experiments I and II reported here, no PSS occurred with completely scrambled grids; the phenomenon emerged only with unscrambled shock. Experiment III reports evidence indicating a connection between directly assessed modification and PSS with unscrambled shock, with PSS emerging only when modification had begun to occur. The pattern of results from these shuttlebox experiments parallels that found in an earlier study of PSS using a symmetrical-choice, barpress preparation.     

Consumer preference for flexible education

Sam Ayer and Catherine Smith of the School of Health at the University of Hull, England, present the findings of a market research project to identify consumer preferences for flexible education. The research con‐centrated on two major aspects of flexible education: access to learning and choices within courses. It explores what specific aspects of flexibility within education and training provision are most relevant to prospective students of flexible education and thus highlights potential market opportunities.     

强化辗转相除法原理的教学

本文讨论高等代数课程一元多项式部分辗转相除法内容的教学,给出了以辗转相除法原理为核心的教法.     

An analysis of “signaled double-alternation patterning” in the rat

Rats given training with double alternation of rewards and nonrewards in which the first reward or nonreward of each pair occurred in a black runway and the second in a white runway developed fast running on rewarded trials in both runways and slow running on nonrewarded trials in both runways—signaled double alternation patterning. A subsequent shift in the reinforcement schedule produced a period of reversed patterning—slow on rewarded trials and fast on nonrewarded trials. The results are consistent with a compound stimulus discrimination interpretation of signaled double-alternation patterning rather than with a selective memory-retrieval explanation.     

Stimulus preference and the transitivity of preference

Four pigeons were exposed to multiple schedules with concurrent variable interval (VI) components and then tested for preference transfer. Half of the pigeons were trained on a multiple concurrent VI 20-sec, VI 40-sec/cuncurrent VI 4G-sec5 VI 80-sec schedule. The remaining pigeons were trained on a multiple concurrent VI 80-sec, VI 40-sec/concurrent VI 40-sec, VI 20-sec schedule-After stability criteria for time and response proportions were simultaneously met, four preference transfer tests were conducted with the stimuli associated with the VI 40-sec schedules. During the transfer tests, each pigeon allocated a greater proportion of responses (M=0,79) and time (M=0.82) to the stimulus associated with the VI 40-sec schedule that was paired with the VI 80-sec schedule than lo the VI 40-sec schedule stimulus paired with the VI 20-sec schedule. Absolute reinforcement rates on the two VI 40 sec schedules were approximately equal and unlikely to account for the observed preference. Nor was the preference consistent with the differences in local reinforcement rates associated with the two stimuli. Instead, the results were interpreted in terms of the differential value that stimuli acquire as a function of previous pairings with alternative schedules of reinforcement.