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)     

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)     

Simultaneous conditioning in honeybees (Apis mellifera).

Honeybees were classically conditioned with odor as conditioned stimulus/stimuli (CS), sucrose as unconditioned stimulus/stimuli (UCS), and proboscis extension as response. The purpose of Exp 1 (Ns?=?26 and 27) was to look for facilitation of forward conditioning by CS–UCS overlap, but rapid conditioning without overlap left little room for improvement. In 2 further experiments, CS and UCS were simultaneous, and response to odor alone was measured in subsequent tests. In Exp 2, a simultaneous group (N?=?25) responded more to the training odor than did an unpaired control group (N?=?25). In Exp 3, a differentially conditioned simultaneous group (N?=?29) responded more to an odor paired with sucrose in training (S+) than to an odor presented alone (S–). The implications of the results for the problem of the role of amount of reward in honeybee learning are considered. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differences in strains of rats during extinction of shuttle box avoidance responding.

In 2 experiments differences between strains of rats in the extinction of shuttle box avoidance responding were examined as a function of the classical conditioned stimulus-unconditioned stimulus (CS-UCS) and instrumental CS termination contingencies. Ss were a total of 68 female albino Fischer, Lewis, and Long-Evans rats. When classical CS-UCS pairings were given on all trials, responding declined somewhat. When this contingency was altered by omitting shock entirely or preventing the pairing of CS and shock, behavior weakened even further. Whereas responding was indistinguishable under both prompt and delayed CS termination during the paired-shock procedure, it was generally higher under prompt CS termination during the no-shock and unpaired-shock procedures. However, the strains differed widely during extinction, with Fischer rats responding more often during the paired and unpaired procedures and Long-Evans rats more often in the no-shock procedure. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquisition of conditioned associations in Hermissenda: Additive effects of contiguity and the forward interstimulus interval.

Examined conditioned suppression of photokinesis (CSPK) by the marine mollusc in 3 experiments. In each experiment, groups of Ss received light (conditioned stimulus, CS) paired with high-speed orbital rotation (unconditioned stimulus, UCS), light and rotation explicitly unpaired, or no exposure to these stimuli. 24 hrs after training, all Ss were tested for CSPK in the presence of the light. 50 CS–UCS pairings resulted in a marginal CSPK, whereas 100 and 150 pairings produced strong CSPK. In Exp 2, delay between CS onset and UCS onset was varied between 1 and 10 s. The 10-s interstimulus interval (ISI) did not support conditioning, whereas 1-s and 2-s ISIs were effective. In Exp 3, CS–UCS pairings in which the CS preceded the onset of the UCS and ended with the offset of the UCS evoked stronger CSPK than either a CS that preceded the UCS and ended with its onset or a CS that was paired in simultaneous compound with the UCS. CS–UCS contiguity and the forward ISI act additively to establish the CS–UCS association. No differences were observed between groups that were untreated and that received the CS and UCS unpaired. Similarities are noted in the temporal characteristics of associative learning in these Ss and vertebrate species. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquired appetitive responding to intravenous nicotine reflects a Pavlovian conditioned association.

Recent research examining Pavlovian appetitive conditioning has extended the associative properties of nicotine from the unconditioned stimulus or reward to include the role of a conditional stimulus (CS), capable of acquiring the ability to evoke a conditioned response. To date, published research has used presession extravascular injections to examine nicotine as a contextual CS in that appetitive Pavlovian drug discrimination task. Two studies in the current research examined whether a nicotine CS can function discretely, multiple times within a session using passive iv infusions. In Experiment 1, rats readily acquired a discrimination in conditioned responding between nicotine and saline infusions when nicotine was selectively paired with sucrose presentations. In Experiment 2, rats were either trained with nicotine paired with sucrose or explicitly unpaired with sucrose. The results showed that rats trained with explicitly unpaired nicotine and sucrose did not increase dipper entries after the infusions. Nicotine was required to be reliably paired with sucrose for control of conditioned responding to develop. Implications of these findings are discussed in relation to tobacco addiction, learning theory, and pharmacology. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Strain differences in avoidance conditioning as a function of the classical CS-US contingency.

Examined rates of shuttle box avoidance responding in 3 strains of rats as a function of classical and instrumental contingencies in 2 experiments. Ss were a total of 126 female albino Fischer, Lewis, and Long-Evans rats. In Exp I, during classical conditioned-stimulus-unconditioned-stimulus (CS-UCS) pairings in the absence of an avoidance contingency, there were large differences between the 3 strains in rates of anticipatory responding to the CS. The same pattern of differences was observed in Exp II when the avoidance contingency was added. None of the instrumental contingencies of CS termination, UCS termination, or the avoidance contingency differentially affected the strains. Classically elicited anticipatory responses and their compatibility with the required avoidance response were viewed as central factors in both the acquisition and maintenance of skeletal avoidance responses. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pavlovian second-order conditioned analgesia.

Three experiments, with 118 Sprague-Dawley rats, assessed conditioned analgesia in a Pavlovian 2nd-order conditioning procedure by using inhibition of responding to thermal stimulation as an index of pain sensitivity. In Exp I, Ss receiving 2nd-order conditioning showed longer response latencies during a test of pain sensitivity in the presence of the 2nd-order conditioned stimulus (CS) than Ss receiving appropriate control procedures. Exp II found that extinction of the 1st-order CS had no effect on established 2nd-order conditioned analgesia. Exp III evaluated the effects of post 2nd-order conditioning pairings of subcutaneous morphine sulfate (10–20 mg/kg) and the shock unconditioned stimulus/stimuli (UCS). Ss receiving paired morphine–shock presentations showed significantly shorter response latencies during a hot-plate test of pain sensitivity in the presence of the 2nd-order CS than did Ss receiving various control procedures; 2nd-order analgesia was attenuated. Data extend the associative account of conditioned analgesia to 2nd-order conditioning situations and are discussed in terms of the mediation of both 1st- and 2nd-order analgesia by an association between the CS and a representation or expectancy of the UCS, which may directly activate endogenous pain inhibition systems. (52 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hippocampus and trace conditioning of the rabbit's classically conditioned nictitating membrane response.

In 2 experiments, 36 New Zealand albino rabbits received classical conditioning of the nictitating membrane response in a trace conditioning paradigm. In this paradigm, a 250-msec tone conditioned stimulus (CS) occurred, after which there was a 500-msec period of time in which no stimuli occurred (the trace interval), followed by a 100-msec air-puff unconditioned stimulus (UCS). In Exp I, lesions of the hippocampus or cingulate/retrosplenial cortex (CRC) disrupted acquisition of the long-latency or adaptive conditioned response (CR) relative to unoperated controls and Ss that received neocortical lesions that spared the CRC. When Ss with hippocampal or CRC lesions were switched to a standard delay paradigm in which the CS and UCS were contiguous in time, they acquired in about the same number of trials as naive Ss. In Exp II, multiple-unit activity in area CA1 of the hippocampus was examined during acquisition of the trace CR. Ss had a 500-msec trace interval (Group T-500), received explicitly unpaired presentations of the CS and UCS, or underwent conditioning with a 2-sec trace interval. Group T-500 acquired the CR in about 500 trials. Early in training, there was a substantial increase in neuronal activity in the hippocampus that began during the CS and persisted through the trace interval. Later in conditioning as CRs emerged, the activity shifted to later in the trace interval and formed a model of the amplitude–time course of the behavioral CR. (65 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned-reflex facilitation in young and older adults

Young (18-30 years) and elderly (63-88 years) human subjects received 70 trials of single-cue classical eyeblink conditioning (paired group), or 70 explicitly unpaired presentations of the tone conditioned stimulus (CS) and airpuff unconditioned stimulus (unpaired group). Before and after conditioning, reflex-eliciting white noise and corneal airpuff stimuli were presented alone or paired with the CS to investigate the effects of conditioning on eyeblink reflex amplitude. The results showed increased conditioned responses in the paired group compared to the unpaired group for the young but not the elderly subjects. There was, however, evidence of conditioned facilitation of noise-elicited reflexes in both young and elderly subjects. These data indicate that conditioned facilitation of the startle reflex may be a sensitive indicator of classical conditioning processes in human subjects.     

Paradoxical enhancement of learned fear.

Conducted 2 experiments to demonstrate that presentation of the CS alone, after conditioning, can enhance learned fear. In Exp. I, groups of 12 Holtzman albino rats received 0-, 1/2-, 5-, 15-, or 50-min postconditioning exposure to the apparatus (the CS) in which they had previously been shocked. Results suggest that the 5-min exposure group was more fearful than the nonexposed controls. In Exp. II, 32 male Holtzman albino weanling rats were conditioned to fear 1 compartment in a shuttle box, followed 2 wk. later by interpolated exposures to the fear cues alone for 0, 30, 60, or 300 sec. 30- and 60-sec exposures produced significantly more spatial avoidance than 0- and 300-sec exposures. (34 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of signaling intertrial unconditioned stimuli in autoshaping.

Context–UCS associations have been suggested as the mediator of the response decrement that occurs when extra UCSs are added to the intertrial intervals (ITIs) of a standard Pavlovian conditioning situation. The present autoshaping experiments were concerned with the effect of signaling those extra UCSs, since such signaling might be expected to lessen their ability to condition the context. In Exp I, 16 female Carneaux pigeons were trained in Skinner boxes before receiving pretraining with the CS to be used as the signal of the ITI UCSs. During the main training, Ss were given autoshaping with a keylight CS. Exp II used a tone CS with 31 Ss. Results show that signaling the ITI UCSs did reduce their detrimental effects in responding to the CS. To determine whether that reduction was due to an impact of signaling on the target-CS/UCS association or on performance to the target-CS, Exp III examined responding to differentially trained CSs in a common context, as well as responding to identically trained CSs in differentially trained contexts with 32 Ss. More responding occurred to the CS trained with signaled, as compared with unsignaled, ITI UCSs; further, there was more responding to that CS in the more highly valued context. Results suggest that contextual value does interact with CS–UCS learning and may also affect performance to the CS. (42 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)     

Extinction and retention of a classically conditioned flexor nerve response in acute spinal cat.

Conditioned adult male and female cats by pairing a mild electrical stimulus to the superficial peroneal sensory nerve (CS) with a stronger electrical stimulus to the ankle skin (UCS) of the same leg. Subsequent extinction was produced by presenting CS-alone trials. In Exp I (42 Ss), Ss given massed extinction trials showed response decrements to base levels, but Ss that received distributed extinction trials showed no decrements. In Exp II, .5-, 1-, 2-, 3-, or 4-hr intervals between acquisition and extinction produced no significant differences in the extinction data. In Exp III (20 Ss), Ss received extinction trials immediately or 30 min after acquisition trials, followed by 20 additional extinction trials 30 min later. Data indicated significant acquisition and extinction in the 10- and 20-acquisition trial groups. As in Exp II (35 Ss), varying the interval between acquisition and extinction did not produce any group differences in the extinction data. These results demonstrate that response increases produced by paired trials in the spinal preparation do not decay spontaneously over time and are not caused by sensitization effects. (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Excitatory conditioning of individual Drosophila melanogaster..

Demonstrated, in 5 studies, conditioning of the proboscis extension reflex in D. melanogaster. The presentation of paired (conditioning) stimuli produced (a) an increase in the average number of conditioned responses (CRs) over trials, (b) measured differences in performance levels among individual Ss, and (c) greater conditioning among males than females. The presentation of unpaired (control) stimuli produced significantly lower average levels of acquisition responding and a change in the distribution of individual response patterns. Neither central excitatory state nor sensitization induced by the conditioned stimulus/stimuli (CS) or the unconditioned stimulus/stimuli (UCS) directly affected the CR, whereas UCS preexposure adversely affected performance levels. Presenting the unpaired (extinction) stimuli after conditioning produced less of a decline in responding than did an extinction procedure with removal of the UCS. With the ability to identify individual differences in acquisition and extinction patterns, and given the relatively large samples that can be tested simultaneously on the automated stimulation apparatus, it is suggested that it is now possible to make precise behavioral measurements for the behavior-genetic analysis of D. melanogaster with conditioning as the phenotype. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Habituation of the shortening reflex in the medicinal leech.

Conducted 3 experiments in which the shortening reflex was elicited in 46 food-sated leeches (Hirudo medicinalis) by light flashes delivered at 20-sec intervals over a 40-trial session. In Exp I, the reflex was enhanced if Ss were stored at 5-7° C rather than 20° C. Short-term (within sessions) habituation was readily observed. In Exp II, dishabituation could be produced by a single electric shock at Trial 30. However, in Exp III, the shock also enhanced responding when delivered before Trial 1 (sensitization). No long-term (between-sessions) habituation occurred over 6 consecutive days of testing in Exp I; on the contrary, responding gradually increased. It is suggested that the simplicity of these short-term processes in leeches makes them particularly suitable for electrophysiological investigations into the neural basis of habituation and sensitization. (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential control by context in the inflation and reinstatement paradigms.

Examined, in 5 conditioned suppression experiments, the influence of summation between fear of the CS and the context in experimental paradigms in which the rat is exposed to UCSs following conditioning or extinction. Context-preference tests assessed contextual fear. In Exps I–III with 88 female Wistar rats, the inflation paradigm, in which fear of a CS paired with a weak UCS is enhanced by exposure to intense UCS alone, was investigated. Results show that the contextual fear that was present when the target CS was tested was reduced by presenting the intense UCSs in a different context, by exposing Ss to the context following their presentation, and by signaling the intense UCSs with a 2nd CS. In Exp IV with 32 female Wistar rats, UCS exposures following conditioning or extinction both produced contextual fear, but only fear of the extinguished CS was reinstated by that fear. In Exp V with 32 female Wistar rats, identical amounts of contextual fear reinstated fear of an extinguished CS, but not a nonextinguished CS, when the 2 types of CSs were arranged to evoke comparable amounts of fear prior to testing. It is suggested that contextual fear plays a role in the reinstatement paradigm but not in the inflation paradigm. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Periodic behavior in a random environment.

Studied the tendency of animals to search periodically in temporally random environments by presenting 10 male rats with random-interval (RI) 60- and 120-sec schedules. Power spectra revealed a periodicity of responding of 20–50 sec for all Ss regardless of condition. A 2nd periodicity of 5–20 sec was strongest under the RI 60-sec schedule. Optimality theory suggested that periodic responding is better than random responding in obtaining food sooner on average, but the theory did not account for multiple periodicities. These multiple periodicities also could not be explained by a single-oscillator, information-processing version of the scalar expectancy theory proposed by J. Gibbon and R. M. Church (see record 1992-41865-001) or by the behavioral theory of timing proposed by P. R. Killeen and J. G. Fetterman (see record 1988-28629-001). The periodicities were consistent with a connectionist version of scalar expectancy theory that has nonscalar emergent properties. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intact text-specific reading skill in amnesia.

Amnesic patients were studied to determine whether the acquisition and retention of item-specific skills can be supported by nondeclarative (implicit) memory. In Exp 1, Ss read 2 different passages 3 times in succession. Reading speed improved at a similar rate in both amnesic patients and normal Ss and was specific to the text that was read. In Exp 2, amnesic patients and normal Ss read a passage 3 successive times and then reread the same passage after a 0-sec, 10-min, 2-hr, or 1-day delay. In both groups, facilitation persisted for at least 10 min and disappeared within 2 hrs. It is suggested that facilitated reading speed depends importantly on both semantic and perceptual information and that such information can be supported by nondeclarative memory. (PsycINFO Database Record (c) 2011 APA, all rights reserved)