Parametric manipulation of interresponse-time contingency independent of reinforcement rate.

The pecking of 4 White Carneaux pigeons was reinforced under a modified interval-percentile procedure that allowed independent manipulation of overall reinforcement (RFM) rate and the degree to which RFM depended on interresponse-time (IRT) duration. Results show that increasing the contingency, as measured by the phi coefficient, between RFM and long IRTs while controlling the overall rate of RFM systematically increased the frequency of those IRTs and decreased response rate under both of the RFM rates studied. Increasing RFM rate also generally increased response rate, particularly under weaker IRT contingencies. Random-interval schedules with comparable RFM rates generated response rates and IRT distributions similar to those obtained with moderate-to-high IRT RFM contingencies. It is suggested that IRT RFM contingencies inherent in random-interval and constant-probability VI schedules exercise substantial control over responding independent of overall RFM rate effects. The IRT RFM contingencies inherent in these schedules may actually mask the effects of overall RFM rate; thus differences in response rate as a function of RFM rate when IRT RFM is eliminated may be underestimated. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An investigation of responding on schedules of electrical brain-stimulation reinforcement.

In Exp I, the leverpressing responses of rats (8 male hooded Long-Evans) were maintained by reinforcement consisting of single trains of electrical stimulation of the brain (ESB) presented on random-interval (RI) schedules ranging in value from RI 3-min to RI 10-min. Both the cumulative response patterns and the relationship of response rates to reinforcement density were similar to those observed for Ss reinforced conventionally. In Exp II with 19 male hooded Long-Evans rats, leverpressing was reinforced with single trains of signalled ESB, unsignalled response-contiguous ESB, or sweetened condensed milk presented on random-ratio schedules. Most of the ESB-reinforced Ss and half of the milk-reinforced Ss stopped responding at ratio values exceeding 50:1, while the remaining Ss responded at higher ratios. Response rates were higher at lower ratio values for the ESB groups than for the milk group, but as ratio values increased, all groups showed similar decreases in rate. All Ss were observed to initiate responding faster than inexperienced controls, and priming was not required. (French summary) (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Response rate and sensitivity to the molar feedback function relating response and reinforcement rate on VI+ schedules of reinforcement.

In 5 experiments, the author examined rats' sensitivity to the molar feedback function relating response rate to reinforcement rate on schedules of reinforcement. These studies demonstrated that, at lower rates of responding, rats' performance on variable ratio (VR), variable interval (VI), and variable interval with linear feedback loop (VI+) schedules was determined largely by reinforcement of interresponse times; response rates were faster on VR than on both VI and VI+ schedules. In contrast, when procedures were adopted to maintain high rates of response, rats showed sensitivity to the molar characteristics of the schedules; they responded as fast on a VI+ schedule as on a VR schedule and faster on both of these schedules than on a yoked VI schedule. When the variance of response rate was manipulated, this factor was noted as an important element in determining sensitivity to the molar characteristics of the schedule. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Schedules of reinforcement as determinants of human causality judgments and response rates.

Experiments examined the effect of relationships between a response and an outcome on human judgments of causal effectiveness. In Experiment 1, the time between outcomes obtained on a variable ratio (VR) schedule became the intervals for a yoked variable interval (VI) schedule. Response rates were higher on the VR than on the VI schedule. In Experiment 2, the number of responses required per outcome on a VR schedule were matched to that on a master VI 20-s schedule. Both ratings of causal effectiveness and response rates were higher in the VR schedule. In Experiment 3, tandem VI fixed-ratio (FR) schedules produced higher rates and judgments than equivalent conjunctive VI FR schedule. In Experiment 4, a VI schedule with a reinforcement requirement for a short interresponse time (IRT) produced higher rates and judgments than a simple VI schedule. These results corroborate the view that schedules are a determinant of both response rates and causal judgments. Few current theories of causal judgment predict this pattern of results. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus–response overshadowing: Effects of signaled reward on instrumental responding as measured by response rate and resistance to change.

If every food reinforcer delivered on a VI schedule is preceded by a brief flash of light, rats leverpress for food more slowly than if light flashes are given independent of the food and their responding. This retardation in rate has been attributed to the overshadowing of the response–food association by the light–food association. Such an explanation assumes that response rate is positively correlated to the response association strength. Exps I and II investigated this account by using prefeeding and extinction procedures to test the strength of responding in 44 Long-Evans rats that had received food-correlated or random-light signals. Acquisition response rate was lower in the signaled condition (consistent with previous studies), but responding was more resistant to both extinction and satiation, regardless of whether the light cues were presented during the extinction/prefeeding phase. Exp III, with 27 Ss, revealed no difference between the signaled and random conditions either in terms of acquisition response rates or resistance to satiation when a VR schedule of reinforcement was used. Results are inconsistent with an overshadowing account of the acquisition rate difference. Instead, the signal seems to enhance the rat's sensitivity to the contingencies present on VI schedules. (44 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The delay-reduction hypothesis: Extension to three-alternative choice.

Choice was assessed for 2 and 3 VI schedules arranged in the terminal links of concurrent-chains schedules (Exps I–IV) and simple concurrent schedules (Exp IV). Ss were 14 male White King pigeons. When the 3rd VI schedule provided a relatively high rate of reinforcement, its addition resulted in a divergence of the distribution of responses between the 2 other schedules (Exps I and II). When the 3rd VI schedule provided a sufficiently low rate of reinforcement, its addition resulted in a convergence of the distribution of responses between the other schedules. Both sets of results are consistent with the delay-reduction hypothesis but not the constant-ratio rule. In Exp IV, the 3rd VI schedule was selected so that the delay-reduction hypothesis required no change in the distribution of responses between the other 2 schedules. This experiment also assessed the effects of adding a 3rd VI schedule in a simple concurrent schedule. In both cases the distribution of responses between the other 2 schedules was not affected systematically. Results support an extension of the delay-reduction hypothesis to 3-alternative choice. (35 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Some aspects of preference between immediate and delayed periods of reinforcement.

Two studies, with 6 homing pigeons, investigated an analog of the usual self-control paradigm by investigating choice between differently delayed reinforcer rates. Ss were trained on a concurrent-chain schedule in which the initial links (ILs) were equal VI schedules. The immediate terminal link (TL) consisted of an immediate 30-sec access to a VI schedule of food reinforcers, followed by a 30-sec blackout. The delayed TL consisted of an immediate 30-sec blackout followed by a 30-sec access to a VI food reinforcer schedule. Exp I comprised 3 parts, in each of which the TL VI schedules were varied. In Exp Ia, the IL responses that produced entries into both TLs were additionally reinforced with food; in Exp Ib, only the IL responses that produced entries into the delayed TL were additionally reinforced with food; and in Exp Ic, none of the IL responses that produced TL entries were additionally reinforced. When no TL entry responses were reinforced, IL response allocation was highly sensitive to variations in the TL schedules. Reinforcing entries into the delayed TLs (Exp Ib) decreased this sensitivity, and reinforcing entries into both TLs (Exp Ia) completely eliminated differential control by the TL reinforcer rates. Exp II varied the frequency of reinforcers for entries into the delayed TL and showed that even infrequent reinforcers strongly affected IL behavior allocation. Results are consistent with theories in which reinforcer value is a function of the summation of individual delays to reinforcing events. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hypothalamic self-stimulation in rats following immunosympathectomy or central nerve growth factor antiserum injection.

In Exp I 5 immunosympathectomized rats self-stimulated at a much lower rate on high variable ratio schedules of reinforcement than 7 injected controls. No differences were found for responding on continuous reinforcement or low variable-ratio reinforcement schedules. In Exp II, using 2 groups of 9 naive Sprague-Dawley rats, a similar reduction in variable-ratio response rate was found for Ss centrally injected with nerve growth factor antiserum relative to controls. Results suggest a reduction in central catecholamine levels as a result of antiserum treatment. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of interresponse time reinforcement on signalled-reward effect.

Examined the conditions under which presenting a signal for reinforcement decreases or increases the rate of leverpressing in rats. Response rate on a variable-interval (VI) schedule of reinforcement was decreased by a brief signal for reinforcement. In Experiment 1, requiring 1 short IRT to occur on completion of the VI requirement attenuated this response decrement. Requiring three responses to be emitted within a minimum amount of time at the end of the VI resulted in the reinforcement signal's enhancement of response rates. Experiment 2 replicated this increase in responding and showed that the reinforcement signal attenuated response rates on a simple VI schedule that yielded the same overall rate of reinforcement. In Experiment 3, the reinforcement signal enhanced response rates when 3 responses were required at the end of a VI schedule, but the signal attenuated response rates when the 3 responses could occur at any time in relation to the VI. These results suggest that the pattern of responding emitted immediately prior to reinforcement is a critical factor in determining the effect of reinforcement signal on response rate. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interresponse-time reinforcement and behavior under aperiodic reinforcement schedules: A case study using computer modeling.

Computer modeling was used to investigate the extent to which response rates under variable-interval and variable-ratio schedules are compatible with a simple process of interresponse time (IRT) reinforcement, as argued by Peele, Casey, and Silberberg (1984). Their computer model was duplicated, as well as its principal result of a large response rate difference between the interval and ratio schedules. After their model was run under a variety of interval and ratio schedules, it was found that the response rates produced did not exhibit patterns of sensitivity to schedule parameter variation found experimentally. Furthermore, the model predicted a large response rate difference between a variable-ratio and a "linear feedback" variable-interval schedule, contrary to the results of McDowell and Wixted (1986). We concluded that simple IRT reinforcement was probably not adequate as an explanation of schedule effects under aperiodic interval and ratio schedules, although a modification of the Peele et al. model incorporating behaviors that were not measured operants could exhibit schedule sensitivity. This suggested that realistic molecular models of schedule phenomena must involve more than simple IRT reinforcement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Free-operant performance on variable interval schedules with a linear feedback loop: No evidence for molar sensitivities in rats.

Four experiments examined rats' sensitivity to molar and molecular factors on instrumental schedules of reinforcement. rats were exposed to a variable interval schedule with a positive feedback loop (VI+), such that faster responding led to a shorter interreinforcement interval. In Experiments 1 and 2, rats responded faster on a variable response (VR) schedule than on either a VI schedule matched for reinforcement rate or a VI + schedule matched for the feedback function. In Experiment 3, rats responded no differently on a VI schedule than they did on a VI+ schedule with equated rates of reinforcement. In Experiment 4, rats responded faster on a VI+ schedule with an interresponse time requirement yoked to that experienced on a VR schedule, than on a VI+ schedule with the same feedback function as the VR schedule. Taken together these results suggest that rats are more sensitive to the molecular than the molar properties of the schedules. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Long-term retention of a complex operant in pigeons.

Examined the effects of a 60-day retention interval on sequence performance when White Carneaux pigeons were required to peck each of 2 keys 4 times in any order for reinforcement. In Exp I, with 20 Ss, it was shown that if the retention interval contained no interpolated experimental experience, it had no effect on sequence performance. If Ss pecked a key for food on a VI schedule during the retention interval, sequence disruption occurred. In Exp II, with 10 Ss, it was found that variations in the location and color of a key pecked during VI had no effect on disruption. In Exp III, with 20 Ss, it was found that disruption did not occur when Ss were simply placed in the experimental chamber during the retention interval, or given response-independent food, or given VI reinforcement for hopping on a foot treadle. In Exp IV, with 15 Ss, disruption was found even when interpolated keypeck training demanded a temporal pattern different from what had occurred on the sequence task. In Exp V, with 5 Ss, it was demonstrated that disruption could be prevented if Ss were exposed to an alternation of the sequence and VI procedures during initial acquisition. (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Paleostriatal lesions in the pigeon (Columba livia) potentiate classical conditioning: Evidence from fixed-interval responding, free operant go–no-go discrimination, and alternation.

Explored the existence of behavioral deficits in the paleostriatum augmentatum in 4 experiments in which pigeons were given bilateral electrolytic lesions. Exp I, conducted with 16 Ss, investigated the effects of lesions on keypecking for reinforcement on a 1-min FI schedule. The lesions increased total response rates, but response timing was not disrupted in paleostriatal Ss. In Exp II, 17 naive Ss were given VI baseline training and, in contrast to the results of Exp I, paleostriatal lesions did not increase responding. Go–no-go discrimination, which followed baseline training, revealed enhanced positive behavioral contrast in paleostriatal Ss, which was explained in terms of additivity theory. The results of Exps I and II suggest that potentiated classical conditioning occurred in paleostriatal Ss. In Exp III, 16 naive Ss were given spatial alternation training, and performance was temporarily impaired following paleostriatal lesions. The same paleostriatal Ss showed superior differentiation performance in Exp IV with a classical go–no-go alternation procedure (which also suggested potentiated classical conditioning). It is argued that disruption of (irrelevant) response-produced information may account for paleostriatal superiority. (55 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An experimental analysis of steady-state response rate components on variable ratio and variable interval schedules of reinforcement.

Three experiments explored a novel approach to analyzing the different components of response rate that are produced by exposure to free-operant schedules of reinforcement. It has been suggested that overall response rate comprises a tendency to initiate responding, and to continue to respond once the bout is initiated. Previous post hoc analyses of interresponse times (IRT) data have suggested several features of these different aspects of responding that the current experimental procedure broadly confirmed. Increasing the size of a variable interval (VI) schedule decreases the number of “burst-initiation” responses, but has less effect on responding once the burst has been initiated (Experiment 1); that the major difference between a variable ratio (VR) schedule and a VI schedule, is not in the number of “burst-initiation” responses, but in the number of “within-burst” responses, with shorter interresponse times that are emitted, with greater numbers of such “within-burst” responses being emitted on a VR schedule (Experiments 2 and 3). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Variability is an operant.

In 6 experiments, a total of 7 pigeons were rewarded if their pattern of 8 pecks to left and right response keys during the current trial differed from the patterns in each of the last n trials. In Exps I and II, B. Schwartz's (1980, 1982a) negative findings (variability was not controlled by reinforcement) were compared with the present positive results. In Exp III, n was manipulated, and it was found that Ss generated highly variable patterns even when the current response sequence had to differ from each of the last 50 sequences. In Exp IV, the number of responses per trial was manipulated; variability increased with increasing responses per trial, indicating that the Ss were acting as quasi-random generators. In Exp V, it was shown that for high levels of variability to be engendered, reinforcement had to be contingent on response variability. In a yoked condition, where variability was permitted but not required, little response variability was observed. In Exp VI, stimulus control was demonstrated: Under red lights the Ss generated variable patterns, and under blue lights they repeated a particular fixed pattern. It is concluded that behavioral variability is an operant dimension of behavior controlled by contingent reinforcement. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Facilitation of instrumental behavior by a Pavlovian appetitive conditioned stimulus.

In Exp I, 16 New Zealand white rabbits were trained to perform an instrumental head-raising response for sucrose reward. A jaw-movement CR was established to a 2-sec CS by pairing it with sucrose; a control stimulus was unpaired with sucrose. Instrumental responding maintained by a VI 40-sec schedule was enhanced during 10-sec presentations of the paired, but not the unpaired, CS. Responding on a VR 15 schedule was unaffected except on trials on which the pre-CS baseline response rate was low; in such cases the paired CS caused a long-lasting acceleration of responding. Noncontingent presentation of the sucrose reinforcer itself briefly suppressed responding but had no long-term effect. In Exp II (6 Ss), a CS that had been conditioned at a 10-sec duration produced the same pattern of effects as in Exp I, indicating that facilitation resulted from CS presentation rather than from the frustrative effects of nonreinforcement of the CS. In Exp III (16 Ss), an inhibitory CS blocked facilitation by the excitatory CS but did not itself affect instrumental responding. (53 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Verbal operant conditioning of hospitalized psychiatric patients.

In Exp. I, 81 male psychiatric patients were divided into 9 subgroups according to age and length of hospitalization. Plural nouns were reinforced by positive verbal feedback. Results were: (1) least chronic Ss increased their operant rates; (2) most chronic Ss did not; and (3) there was significant interaction with respect to age and chronicity. In Exp. II, 60 schizophrenics were divided into 6 subgroups with respect to length of hospitalization and mode of reinforcement, i.e., verbal, primary, or combination. Acute-type schizophrenics responded positively to all types of reinforcement. Chronics responded only to primary reinforcement and to the combination procedure. Mode of reinforcement was a significant variable affecting operant rate. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of changes in response requirement and deprivation on the parameters of the matching law equation: New data and review.

The relation between response rate and reinforcement rate is described by the matching law equation. For an experiment in which there is just 1 explicit source of reinforcement, the equation has 2 parameters. The magnitude of 1 is equal to the response rate asymptote; the magnitude of the other is equal to the rate of reinforcement that maintains a one-half asymptotic response rate. This report describes experimental manipulations that affect these 2 parameters. Rats were trained on a series of variable-interval reinforcement schedules that provided reinforcement rates ranging from about 20 to 700 reinforcements per hour. The response was a lever press, and the reinforcer was water. In Exp I, the duration of the deprivation period was varied. Response rates maintained by the lower reinforcement rates showed the largest changes, and the parameter that is equal to the reinforcement rate for a one-half asymptotic response rate changed. In Exp II, the weight of the lever was varied. Response rates changed independently of reinforcement rate, and the parameter that is equal to the asymptotic response rate changed. In Exp III, manipulations from Exps I and II were combined. Results replicated those of Exps I and II. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Operant responding and stimulus control in tawny owls (Strix aluco).

Trained 2 tawny owls to make a bar-pecking response, reinforced by the presentation of small cubes of ox heart. Ss readily acquired the response, and their pattern of responding under fixed-ratio, variable-ratio, and VI schedules of reinforcement were similar to the typical response patterns of other species. Stimulus control was demonstrated in 3 Ss by training them to simultaneously discriminate between horizontally and vertically striped patterns. A high degree of control was obtained in all Ss. However, a small increase in the spatial separation of stimulus and response resulted in a considerable loss of stimulus control, suggesting that it would be difficult to employ the tracking method of threshold determination with this species. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Response–reinforcer associations after caudate-putamen lesions in the rat: Spatial discrimination and overshadowing–potentiation effects in instrumental learning.

Exp I, with 12 male hooded rats, demonstrated that Ss with caudate-putamen lesions exhibited an impairment in the acquisition and reversal of a spatial maze task when compared with unoperated control Ss. Exp II, with 24 Ss, investigated leverpress responding supported by a VI schedule in 3 groups of Ss: a group with caudate-putamen lesions, a group with lesions of the posterior cortex, and an unoperated control group. The presentation of a 0.5-sec, response-contingent light correlated with reinforcement generated an elevated response rate in the 2 operated groups but tended to suppress responding in the control group, perhaps by overshadowing the response–reinforcer relation. Only the group with cortical lesions maintained the elevated rate when the light was uncorrelated with food delivery. Exp III confirmed for these same Ss that caudate-putamen lesions produced a spatial learning deficit. No deficit was observed in the posterior cortex group. It is suggested that caudate-putamen lesions disrupt the mechanism underlying the response–reinforcer association on which spatial maze learning and free operant responding in part depend. (48 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)