Showing papers in "Journal of Experimental Psychology: Animal Behavior Processes in 1983"

A mode control model of counting and timing processes

Abstract: The similarity of animal counting and timing processes was demonstrated in four experiments that used a psychophysical choice procedure. In Experiment 1, rats initially learned a discrimination between a two-cycle auditory signal of 2-sec duration and an eight-cycle auditory signal of 8-sec duration. For the number discrimination test, the number of cycles was varied, and the signal duration was held constant at an intermediate value. For the duration discrimination test, the signal duration was varied, and the number of cycles was held constant at an intermediate value. Rats were equally sensitive to a 4:1 ratio of counts (with duration controlled) and a 4:1 ratio of times (with number controlled). The point of subjective equality for the psychophysical functions that related response classification to signal value was near the geometric mean of the extreme values for both number and duration discriminations. Experiment 2 demonstrated that 1.5 mg/kg of methamphetamine administered intraperitoneally shifted the psychophysical functions for both number and duration leftward by approximately 10%. Experiment 3 demonstrated that the magnitude of cross-modal transfer from auditory signals to cutaneous signals was similar for number and duration. In Experiment 4 the mapping of number onto duration demonstrated that a count was approximately equal to 200 msec. The psychophysical functions for number and duration were fit with a scalar expectancy model with the same parameter values for each attribute. The conclusion was that the same internal mechanism is used for counting and timing. This mechanism can be used in several modes: the "event" mode for counting or the "run" and the "stop" modes for timing.

Contextual control of the extinction of conditioned fear: tests for the associative value of the context.

Abstract: Four conditioned suppression experiments examined the influence of contextual stimuli on the rat's fear of an extinguished conditioned stimulus (CS). When rats received pairings of a CS with shock in one context and then extinction of the CS in another context, fear of the CS was renewed when the CS was returned to and tested in the original context (Experiments 1 and 3). No such renewal was obtained when the CS was tested in a second context after extinction had occurred in the conditioning context (Experiment 4). In Experiment 2, shocks presented following extinction reinstated fear of the CS, but only if they were presented in the context in which the CS was tested. In each experiment, the associative properties of the contexts were independently assessed. Contextual excitation was assessed primarily with context-preference tests in which the rats chose to sit in either the target context or an adjoining side compartment. Contextual inhibition was assessed with summation tests. Although reinstatement was correlated with demonstrable contextual excitation present during testing, the renewal effect was not. Moreover, there was no evidence that contextual inhibition developed during extinction. The results suggest that fear of an extinguished CS can be affected by the excitatory strength of the context but that independently demonstrable contextual excitation or inhibition is not necessary for contexts to control that fear.

Selective adjustment of the speed of internal clock and memory processes.

Abstract: Four experiments studied the scaling of time by rats. The purpose was to determine if internal clock and memory processes could be selectively adjusted by pharmacological manipulations. All of the experiments used a temporal discrimination procedure in which one response ("short") was reinforced following a 2-sec noise signal and a different response ("long") was reinforced following an 8-sec noise signal; unreinforced signals of intermediate duration were also presented. The proportion of "long" responses increased as a function of signal duration. All drugs were administered intraperitoneally (ip) and their effect on clock or memory processes was inferred from the observed pattern of change in the point of subjective equality of the psychophysical functions under training and testing conditions. Experiment 1 demonstrated that methamphetamine (1.5 mg/kg) can selectively increase clock speed and that haloperidol (.12 mg/kg) can selectively decrease clock speed. Experiment 2 demonstrated that footshock stress (.2 mA) can selectively increase clock speed during continuous administration but leads to a decrease in clock speed below control values when the footshock is abruptly terminated. Experiment 3 demonstrated that vasopressin (.07 pressor units/kg) and oxytocin (.02 pressor units/kg) can selectively decrease the remembered durations of reinforced times, which suggests that memory storage speed increased. Experiment 4 demonstrated that physostigmine (.01 mg/kg) can selectively decrease the remembered durations of reinforced times and that atropine (.05 mg/kg) can selectively increase these remembered durations, which suggests that memory storage speed was differentially affected. The conclusion is that internal clock and memory processes can be dissociated by selectively adjusting their speed of operation and that these changes can be quantitatively modeled by a scalar timing theory.

Facilitation of instrumental behavior by a Pavlovian appetitive conditioned stimulus.

Abstract: Three experiments examined appetitive Pavlovian-instrumental interactions by presenting separately trained conditioned stimuli (CSs) during reinforced instrumental responding in rabbits. Intra-oral reinforcement was used to minimize interference from peripheral responses such as magazine approach. In experiment 1, the rabbits were first trained to perform an instrumental head-raising response for sucrose reward. A conditioned jaw movement response was then established to a 2-sec CS by pairing it with sucrose; a control stimulus was unpaired with sucrose. Instrumental responding maintained by a variable-interval 40-sec schedule was enhanced during 10-sec presentations of the paired, but not the unpaired, CS. Responding on a variable-ratio 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 Experiment 2, a CS that had been conditioned at a 10-sec duration produced the same pattern of effects as in the first study, indicating that facilitation resulted from CS presentation rather than from the frustrative effects of non-reinforcement of the CS. In Experiment 3 an inhibitory CS blocked facilitation by the excitatory CS but did not itself affect instrumental responding. These results support the view that Pavlovian processes play a positive role in instrumental performance and suggest that previous findings of suppression by a short-duration CS reflect peripheral interference. The dependence of facilitation on the baseline level of responding is discussed in terms of associative and motivational theories of Pavlovian mediation.

Visual search and selection of natural stimuli in the pigeon: the attention threshold hypothesis.

Abstract: During visual search for samples of varying proportions of familiar, natural food grains displayed against a complex gravel background, pigeons exhibited "matching selection," a tendency to overselect the more common grain. The matching-selection effect was decreased at low levels of stimulus/background contrast and reversed when the grains were highly conspicuous. The results were consistent with the hypothesis that stimulus detectability should be enhanced by recent experience with a particular grain type, but they showed no convincing indications of a corresponding effect on the response criterion. An explanatory model, termed the attention threshold hypothesis, argues that the mean latency of discovery can be minimized by selectively attending to one stimulus type at a time and switching to a more generally receptive state when the rate of discovery falls below a threshold value. The model appears to account for the fact that the response rate was highest toward samples containing a single grain type and decreased as the relative proportions approached equality. Additional consequences of the adoption of this theoretical perspective were explored in some detail. Among other results, the evidence suggests that the switching threshold might be chosen so as to optimize the rate of food discovery.

Effect of signaling intertrial unconditioned stimuli in autoshaping.

Abstract: Context-unconditioned-stimulus (US) associations have been suggested as the mediator of the response decrement that occurs when extra USs are added to the intertrial intervals (ITIs) of an otherwise standard Pavlovian conditioning situation. The present autoshaping experiments were concerned with the effect of signaling those extra USs, since such signaling might be expected to lessen their ability to condition the context. Experiments 1 and 2 showed that signaling the ITI USs did reduce their detrimental effects on responding to the conditioned stimulus (CS). To determine whether that reduction was due to an impact of signaling on the target-CS-US association or on performance to the target-CS, Experiment 3 examined responding to differentially trained CSs in a common context, as well as responding to identically trained CSs in differentially trained contexts. Whether the CS was tested in a context of relatively high or low associative strength, more responding occurred to the CS trained with signaled, as compared with unsignaled, ITI USs; further, there was more responding to that CS in the more highly valued context. The pattern of results suggests that contextual value does interact with CS-US learning and may also affect performance to the CS.

The opioid/nonopioid nature of stress-induced analgesia and learned helplessness.

Abstract: Exposure to a variety of stressors produces a subsequent analgesic reaction. This stress-induced analgesia (SIA) is sometimes opioid in nature (reversed by opiate antagonists and cross-tolerant with morphine) and sometimes nonopioid. Both 30 min of intermittent footshock and 60-80 five-sec tailshocks have been shown to produce opioid SIA, whereas 3 min of continuous footshock and 5-40 tailshocks produce nonopioid SIA. We report that both of the opioid SIA procedures produce a learned helplessness effect as assessed by shuttlebox escape acquisition and an analgesia that is reinstatable 24 hr. later. The nonopioid procedures produce neither a learned helplessness effect nor a reinstatable analgesia. It is argued that these data implicate the learning of uncontrollability in the activation of opioid systems.

Bisection of temporal intervals by pigeons.

Abstract: Two experiments investigated temporal bisection in pigeons using a procedure similar to that of Stubbs (1976). This procedure measures the point in time at which the bird switches from the shorter to the longer valued of two fixed-interval reinforcement schedules with a common starting point. The first experiment substantiated previous findings of switching at the geometric mean of the two interval values and strengthened identification of this switching with bisection by eliminating the possibility that the birds simply switched to the longer interval when the shorter one was perceived to have expired. The experiment also extended the range of values for which temporal intervals have been found to be bisected at their geometric mean. A second experiment demonstrated that the usefulness of the present procedure for determining temporal bisection points is limited to cases in which the longer interval is no more than four times the duration of the shorter interval. Greater separation of the two interval durations produced a period of nonresponding during which the location of the switching or bisection point was totally ambiguous.

Sequential effects in pigeon delayed matching-to-sample performance.

Abstract: Pigeons were tested in a three-alternative delayed matching-to-sample task in which second-choices were permitted following first-choice errors. Sequences of responses both within and between trials were examined in three experiments. The first experiment demonstrates that the sample information contained in first-choice errors is not sufficient to account for the observed pattern of second choices. This result implies that second-choices following first-choice errors are based on a second examination of the contents of working memory. Proactive interference was found in the second experiment in the form of a dependency, beyond that expected on the basis of trial independent response bias, of first-choices from one trial on the first-choice emitted on the previous trial. Samples from the previous trial were not found to exert a significant influence on later trials. The magnitude of the intertrial association (Experiment 3) did not depend on the duration of the intertrial interval. In contrast, longer intertrial intervals and longer sample durations did facilitate choice accuracy, by strengthening the association between current samples and choices. These results are incompatible with a trace-decay and competition model; they suggest strongly that multiple influences act simultaneously and independently to control delayed matching-to-sample responding. These multiple influences include memory for the choice occurring on the previous trial, memory for the sample, and general effects of trial spacing.

Characteristics of spatial memory in pigeons.

Abstract: Pigeons learned a delayed-alteration (DA) task in a T-maze. Very few trials were needed prior to accurate performance. Similarly, after little training the birds performed accurately with delays of 8-16 min. End-of-delay cues, possibly provided by the experimenter, response-based cues, and intramaze cues were all experimentally examined and rejected as bases for the birds' performances; pigeons appear to rely on spatial (extramaze) cues. Long-delay performances were undisturbed by changes in delay-interval stimuli (illumination shifts and transportation around the laboratory). Finally, birds were shown to acquire DA so quickly because of a potent tendency to avoid recently visited locations (i.e., a preexisting "win-shift" tendency). Characteristics of pigeon spatial memory thus include temporal persistence, resistance to retroactive interference, and a win-shift bias. In these respects spatial memory of pigeons parallels spatial memory of rats.

Signaled tailshock is perceived as similar to a stronger unsignaled tailshock: implications for a functional analysis of classical conditioning.

Abstract: Water-deprived rats given fixed-electrode, variable-intensity tailshock at random times rated each trial by pressing either a "high-aversiveness" or "low-aversiveness" lever in order to obtain water. Trials on which a warning signal preceded tailshock resulted in more "high-aversiveness" leverpressing than did otherwise equivalent unsignaled trials. The magnitude of this effect increased and decreased as a function of several parameters including signal-shock interval, signal duration, and range and absolute value of shock intensities but was never reversed despite efforts to achieve such a reversal. Variation in the size of the effect as a function of signal parameters as well as lick suppression scores indicated that the signal had acquired aversive characteristics, which suggests that the effect of the signal on lever choice was due largely to the aversiveness of the signal summating with the aversiveness of the tailshock. Several hypotheses concerning factors that might have either masked or prevented classically conditioned preparatory responses elicited by the signal from reducing tailshock aversiveness were tested and rejected. Despite the greater aversiveness of the signaled condition, when given the choice of receiving or not receiving the signal, the animals displayed a preference for signaled tailshock. Implications for the role of preparatory responding both in the preference-for-signaled-shock phenomenon and in classical conditioning are discussed.

Relationships between the determinants of performance in serial feature-positive discriminations

Abstract: Three experiments using an appetitive behavioral observation procedure with rats investigated the effects of various pre- and postdiscrimination treatments on learning and performance in serial feature-positive discriminations. Previous work suggests that performance in this discrimination is based on feature-unconditioned stimulus (US) associations, feature-common element associations, and a conditional occasion-setting relation. Experiment 1 examined the effects of prediscrimination reinforcement of the various components of the discrimination. Experiments 2 and 3 investigated the effects of various postdiscrimination nonreinforcement and reinforcement procedures, respectively, on performance of previously established discriminative responding. The results of the present studies and those of previous work are interpreted to show that the conditional occasion-setting relation may be independent of feature-US associations and may not be dependent on feature-common element associations. The implications of assumming that rats used conditional information independently of simple associations are discussed.

A test of the Pfanzagl bisection model in rats.

Abstract: The bisection method of animal psychophysical scaling was examined as a measurement procedure. The critical assumptions of bisection scaling, as described by Pfanzagl (1968), were tested to determine if a valid equal-interval scale could be derived. A valid scale was derived in which subjective time for the rat was a power function of real time. Bisection points were found to be context dependent, because the spacing of stimuli significantly affected the bisection points. Such context effects were directly related to the size of the interval bisected, whereas measurement errors in estimates of the exponent of the power function were an inverse function of interval size.

The role of marking when reward is delayed.

Abstract: Two-choice spatial discrimination by rats is enhanced if a salient stimulus marker occurs immediately after every choice response and again after a delay interval (Lieberman, McIntosh & Thomas, 1979). Three experiments further explore this effect. Experiment 1 found that the second marker is unnecessary. Experiment 2 found that a marker presented before a response is as effective as one presented after. Both effects could be explained in terms of markers focusing attention on subsequent cues. Experiment 3, however, found that markers after choice enhance learning even when no discriminative cues are present following the marker. Markers thus appear to initiate both a backward search through memory and attention to subsequent events; both processes help to identify events that might be related to the unexpected marking stimulus.

CS-US contiguity and CS intensity in conditioning of the rabbit's nictitating membrane response to serial compound stimuli.

Abstract: The present experiments examined acquisition of the rabbit's nictitating membrane response to serial compound stimuli. Each compound consisted of two distinctive conditioned stimuli (CSA and CSB) that were followed by a shock unconditioned stimulus (US). In Experiment 1, CSA was a highly salient 93-dB tone, and CSB was a moderately salient flashing light. The CSA-US interval was 800 msec, and the CSB-US interval was varied across 400, 600, and 800 msec. In Experiment 2, the flashing light served as CSA, and CSB was either a 73-, a 85-, or a 93-dB tone. The CSA-US interval remained 800 msec, and the CSB-US interval was fixed at 400 msec. The experiments revealed that the CSB-US interval and CSB intensity determined the rate of conditioned response (CR) acquisition to the compound. Yet, CR acquisition to CSB as measured on test trials showed impairments relative to the level of responding in single CS-control conditions. However, the impairment in CR acquisition to CSB was attenuated by increasing CSB-US contiguity, that is, by decreasing the CSB-US interval (Experiment 1) or by increasing CSB intensity (Experiment 2). In Experiment 1, the impairment in acquisition to the light CSB appeared to be primarily a consequence of the tone CSA's greater salience. However, in Experiment 2, impairments in CR acquisition to CSB appeared even when CSB had the combined advantages of CS-US contiguity and great salience relative to CSA. Thus, the results indicated a role for CSA's temporal primacy in determining CR acquisition to the components of a serial compound. The results are discussed in terms of selective-attention, generalization-decrement, and information hypotheses.

Exposure to the unconditioned stimulus alone: effects on retention and acquisition of conditioned suppression.

Abstract: Three experiments demonstrated that repeated exposure to an electric-shock unconditioned stimulus (US) resulted in a decrement in retention of conditioned suppression evoked by a previously established excitatory conditioned stimulus (CS) and retarded subsequent acquisition of conditioned suppression to a novel CS paired with shock Experiment 1 showed that 10 sessions of exposure to shock alone were required to produce a decrement in retention of conditioned suppression, whereas retardation in the acquisition of conditioned suppression was obtained following either 5 or 10 sessions of exposure to shock alone Experiment 2 demonstrated that the magnitude of both the decrement in retention of conditioned suppression and the retardation in the acquisition of conditioned suppression produced by exposure to shock alone was directly related to the intensity of those shocks Experiment 3 demonstrated that the decrement in retention of conditioned suppression produced by 10 sessions of exposure to shock alone was inversely related to the interval between the last exposure to shock and the test of the target CS These findings are discussed in terms of associative and nonassociative accounts of the effects of US-alone procedures