Signal-controlled responding

Pigeons' key pecks were reinforced with grain, then extinguished. An 8-second tone preceded the availability of peck-dependent grain 1 second after tone offset. When a tone signalled grain and an 8-second clicking sound did not, three pigeons pecked during a high percentage of tone periods, but they pecked during a low percentage of click periods. When the roles of the tone and clicking sound were reversed, performance reversed. For other birds, when a key peck during the tone cancelled the availability of grain (omission procedure), the tendency to key peck during the tone decreased some, but still remained high. A third group of pigeons received the omission procedure with the addition that the tone could not end unless 2 seconds had elapsed without a key peck. The pigeons continued to respond in a high percentage of tone periods. The experiments favor an explanation based on the pairing of the tone with a reinforced response, such as Pavlovian conditioning.     

The effect of contingency upon the appetitive conditioning of free-operant behavior

The problem of maintaining independence between response rates and reinforcement probabilities when determining the effect of varying the response-reinforcement contingency upon free-operant behavior was solved by programming local reinforcement probabilities for response and no response on a second-by-second basis. Fifty-seven rats were trained to lever-press on schedules of water reinforcement involving different values of contingency. All rats were first trained on a high positive contingency and then shifted to less positive, zero, or negative contingencies. Under these conditions, rate of lever-pressing declined appropriately when the contingency between response and reinforcement decreased or was made negative. The decline in rate produced by a zero contingency cannot be attributed to extinction, since the probability of reinforcement given the occurrence of a response was the same as for the positive contingency from which the shift to zero was made. That is, there was no change in the opportunity for response-reinforcement contiguity. It was concluded that the technique of programming local reinforcement probabilities offers promise for more critical examinations of the effects of contingency upon free-operant behavior.     

Second-order autoshaped key pecking based on an auditory stimulus.

In Experiment 1, pigeons were exposed either to paired or to unpaired presentations of a tone and grain, and then to paired presentations of a keylight with the tone. Substantial second-order conditioned pecking to the keylight was produced in the birds that had received paired presentations of tone and grain. In Experiment 2, second-order pecking to the keylight increased in probability across four groups that had received, respectively, 20, 80, 140, or 200 paired presentations of tone and grain. In Experiment 3, the amount of pecking directed towards a keylight which predicted the first-order, tone CS was as substantial in birds without a prior history of key pecking as in birds with such a history. A further experiment failed to discover any significant differences in the levels of second-order pecking to a keylight paired with a first-order tone CS or with a first-order keylight CS. Thus, an auditory signal that does not itself support pecking may enable a localized visual stimulus to evoke key pecking.     

Post-training amphetamine administration enhances memory consolidation in appetitive Pavlovian conditioning: Implications for drug addiction

It has been suggested that some of the addictive potential of psychostimulant drugs of abuse such as amphetamine may result from their ability to enhance memory for drug-related experiences through actions on memory consolidation. This experiment examined whether amphetamine can specifically enhance consolidation of memory for a Pavlovian association between a neutral conditioned stimulus (CS-a light) and a rewarding unconditioned stimulus (US-food), as Pavlovian conditioning of this sort plays a major role in drug addiction. Male Long-Evans rats were given six training sessions consisting of 8 CS presentations followed by delivery of the food into a recessed food cup. After the 1st, 3rd, and 5th session, rats received subcutaneous injections of amphetamine (1.0 or 2.0 mg/kg) or saline vehicle immediately following training. Conditioned responding was assessed using the percentage of time rats spent in the food cup during the CS relative to a pre-CS baseline period. Both amphetamine-treated groups showed significantly more selective conditioned responding than saline controls. In a control experiment, there were no differences among groups given saline, 1.0 or 2.0 mg/kg amphetamine 2 h post-training, suggesting that immediate post-training amphetamine enhanced performance specifically through actions on memory consolidation rather than through non-mnemonic processes. This procedure modeled Pavlovian learning involved in drug addiction, in which the emotional valence of a drug reward is transferred to neutral drug-predictive stimuli such as drug paraphernalia. These data suggest that amphetamine may contribute to its addictive potential through actions specifically on memory consolidation.     

Cuttlefish (Sepia officinalis: Cephalopoda) hunting behavior and associative learning

Because most learning studies in cephalopods have been performed on octopods, it remains unclear whether such abilities are specific to octopus, or whether they correlate with having a larger and more centrally organized brain. To investigate associative learning in a different cephalopod, six sexually mature cuttlefish (Sepia officinalis) participated in a counterbalanced, within-subjects, appetitive, classical conditioning procedure. Two plastic spheres (conditioned stimuli, CSs), differing in brightness, were presented sequentially. Presentation of the CS+ was followed 5 s later by a live feeder fish (unconditioned stimulus, US). Cuttlefish began to attack the CS+ with the same type of food-acquisition seizures used to capture the feeder fish. After seven blocks of training (42 presentations of each CS) the difference in seizure probability between CS+ and CS– trials more than doubled; and was found to be significantly higher in late versus early blocks. These results indicate that cuttlefish exhibit autoshaping under some conditions. The possible ecological significance of this type of learning is briefly discussed.Electronic Supplementary Material Supplementary material is available for this article at     

Cerebral asymmetry in autonomic conditioning to facial expressions: Sex differences

In the present experiment, sex differences in hemispheric asymmetry during classical conditioning to emotional stimuli are reported. 125 subjects (62 females and 63 males) were shown a slide of a happy face in the right (or left) visual half field (VHF), and simultaneously a slide of an angry face in the left (or right) VHF. Eight groups were formed by the combination of male and female subjects; left and right VHF positions of the angry/happy faces; and the administration/omission of the shock unconditioned stimulus (UCS). Dependent measures were skin conductance responses recorded from both hands. The results during extinction showed a significant larger SCR magnitude to the shock compared to the no-shock groups only for the female subjects. CS position during conditioning was also important in revealing differential responding to either the happy or angry faces. A right hemisphere effect was found for the angry face CS for both the male and female subjects, however with a greater difference for the females.     

Conditioned nausea after cancer chemotherapy and autonomic nervous system conditionability

There are marked individual differences in conditioned nausea after cancer chemotherapy. To examine if part of this variation is associated with individual differences in autonomic nervous system conditionability, the present study addressed whether patients with conditioned nausea acquired conditioned heart rate and electrodermal responses at a different rate than patients without conditioned nausea. Of 28 relapse-free patients who had completed cisplatinum treatment for testicular cancer between 1981 and 1986, 10 reported persistent conditioned nausea, 8 extinguished conditioned nausea and 10 no conditioned nausea. These three groups were subjected to a differential conditioning paradigm with 8 sec pictorial stimuli (circles and triangles) serving as conditioned stimuli for an unconditioned electric shock while heart rate and electrodermal activity was monitored. There were 4 habituation, 8 acquisition and 8 extinction trials with each of the two cues. Analyses of variance using nausea status as the independent variable and physiological responses as the dependent lended some support to the notion that conditioned heart rate deceleration developed in response to the reinforced compared to the nonreinforced cue during acquisition in the two groups with persistent or extinguished conditioned nausea but not in the group with no conditioned nausea. In addition, patients that displayed good, as compared to poor heart rate conditionability during acquisition, were more likely to have persistent conditioned nausea, whereas those who showed poor heart rate conditioning mostly were those without conditioned nausea. Electrodermal variables revealed no systematic differences between groups. This tentatively supports that individual differences in parasympathetic but not sympathetic nervous system conditionability may be associated with individual differences in conditioned nausea resulting from cancer chemotherapy.     

A comparison of classical eyelid conditioning in adults and infants

In a classical conditioning procedure an eyeblink-eliciting tap to the glabella (the flat region of skin between the eyebrows) was presented 500 ms after the onset of a mild l-kHz tone. As tone-tap presentations proceeded, the probability of an eyeblink during the latter part of the tone increased in both infants (median age 8 months) and adults, but the infants were slower to condition than the adults and were more variable. Overall, the latency of the conditioned response to tone was significantly longer for infants than for adults, but the latency of the unconditioned response to tap was significantly shorter for infants than for adults.     

Post-extinction conditional stimulus valence predicts reinstatement fear: Relevance for long-term outcomes of exposure therapy

Exposure therapy for anxiety disorders is translated from fear conditioning and extinction. While exposure therapy is effective in treating anxiety, fear sometimes returns after exposure. One pathway for return of fear is reinstatement: unsignaled unconditional stimuli following completion of extinction. The present study investigated the extent to which valence of the conditional stimulus (CS+) after extinction predicts return of CS+ fear after reinstatement. Participants (N = 84) engaged in a differential fear conditioning paradigm and were randomised to reinstatement or non-reinstatement. We hypothesised that more negative post-extinction CS+ valence would predict higher CS+ fear after reinstatement relative to non-reinstatement and relative to extinction retest. Results supported the hypotheses and suggest that strategies designed to decrease negative valence of the CS+ may reduce the return of fear via reinstatement following exposure therapy.     

Unique characteristics of neonatal classical conditioning: The role of the amygdala and locus coeruleus

The central nervous system of altricial infants is specialized for optimizing attachments to their caregiver. During the first postnatal days, infant rats show a sensitive period for learning and particularly susceptible to learning an attraction to their mother’s odor. Classical conditioning appears to underlie this learning that is expressed behaviorally as anincreased ability to acquire odor preferences and a decreased ability to acquire odor aversions. Specifically, in neonatal rats, pairing an odor with moderately painful shock (0.5mA) or milk produces a subsequent relativepreference for that odor. The neural circuitry supporting theincreased ability to acquire odor preferences appears to be the heightened functioning of the noradrenergic pontine nucleus locus coeruleus. Indeed, norepinephrine from the locus coeruleus appears to be both necessary and sufficient for learning during the sensitive period. On the other hand, thedecreased ability to acquire odor aversions seems to be due to the lack of participation of the amygdala in at least some aversive learning situations. The site of plasticity in the pup’s brain appears to be limited to the olfactory bulb. This neonatal sensitive period for learning ends around postnatal day 9–10, at which time pups make the transition from crawling to walking and classical conditioning becomes “adultlike”. The neonatal behavioral and neural induced changes are retained into adulthood where it modifies sexual behavior.