Burying by rats in response to aversive and nonaversive stimuli

Previous investigations have shown that rats bury a variety of conditioned and unconditioned aversive stimuli. Such burying has been considered as a species-typical defensive reaction. In the present studies, rats buried spouts filled with Tabasco sauce, or condensed milk to which a taste aversion was conditioned, but did not bury water-filled spouts or spouts filled with a palatable novel food (apple juice) to which a taste aversion was not conditioned. However, in other experiments rats consistently and repeatedly buried Purina Rat Chow, Purina Rat Chow coated with quinine, and glass marbles. This indicates that a variety of stimuli, not all aversive or novel, evoke burying by rats. Whereas the behavior may reasonably be considered as a species-typical defensive behavior in some situations, the wide range of conditions that occasion burying suggests that the behavior has no single biological function.     

Trace autoshaping: Acquisition, maintenance, and path dependence at long trace intervals

The pigeon's tendency to acquire and maintain signal-directed key pecking under a trace conditioning procedure was parametrically examined. In Experiment 1, the percentage of CS trials with a key peck response was a decreasing function of the trace interval for separate groups of pigeons. The majority of subjects acquired signal-directed key pecking with trace intervals as long as 36 sec. In Experiment 2, differential maintenance of key pecking occurred across trace intervals in a within-subject procedure. Maintenance of key pecking at 36- and 60-sec trace intervals was path dependent in that responding depended on the subject's performance under the preceding trace interval.     

Early behaviour and its relation to behaviour at 3 years

In 34 healthy 1-month-old infants sleep, waking, crying and conditioning were analysed in detail. Intellectual functioning and coping with an unfamiliar situation were assessed at the age of 3 years. Likewise, the social environment including mother-infant interaction was considered. The majority of sleep and waking parameters assessed during the first month did not correlate with outcome data at 3 years. Rather, it was those concerning conditioning at 1 month that significantly correlated with coping in an unfamiliar situation at 3 years, a finding in accordance with neurophysiological concepts concerning stimulus sensitivity. More sensitive infants at 1 month had problems in coping with an unfamiliar situation at 3 years. In the light of these results we suggest that factors related to central nervous system processes play a role in coping with unfamiliar situations.     

Bilaterally recorded multiple-unit activity of the cingulate cortex during head turning conditioning with unilateral medial forebrain bundle stimulation

Cats were conditioned to turn their heads using a tone conditioned stimulus (CS) and medial forebrain bundle stimulation (MFB) unconditioned stimulus (US). The CS+ was delivered to one ear at a time, in random order, followed by the US. A tone of a different frequency was used as a CS-. The cats learned to respond differentially to the CSs showing head movements of greater acceleration to the CS+ than CS- over sessions. Bilateral recordings of cingulate cortex multiple-unit activity showed increased response amplitudes over sessions and larger responses in the hemisphere ipsilateral to the US. Since ipsilateral multiple-unit responses did not differ for the CSs, the asymmetry was probably due to the sensitizing effect of the unilateral US. Although increases in cingulate cortex neural activity coincided with increases in conditioned head movements, larger activation of the cingulate cortex ipsilateral to the US suggests that the neural changes were independent of these movements.     

The nature of sexual reinforcement.

Sexual reinforcers are not part of a regulatory system involved in the maintenance of critical metabolic processes, they differ for males and females, they differ as a function of species and mating system, and they show ontogenetic and seasonal changes related to endocrine conditions. Exposure to a member of the opposite sex without copulation can be sufficient for sexual reinforcement. However, copulatory access is a stronger reinforcer, and copulatory opportunity can serve to enhance the reinforcing efficacy of stimulus features of a sexual partner. Conversely, under certain conditions, noncopulatory exposure serves to decrease reinforcer efficacy. Many common learning phenomena such as acquisition, extinction, discrimination learning, second-order conditioning, and latent inhibition have been demonstrated in sexual conditioning. These observations extend the generality of findings obtained with more conventional reinforcers, but the mechanisms of these effects and their gender and species specificity remain to be explored.     

Reversibility of single-incentive selective associations.

Rats were trained to press a lever in the presence of a tone-light compound stimulus and not to press in its absence. In each of two experiments, schedules were designed to make the compound a conditioned punisher for one group and a conditioned reinforcer for the other. In Experiment 1, one group's responding produced food in the presence of the compound but not in its absence. The other group's responding terminated the compound stimulus, and food was presented only in its absence. When tone and light were later presented separately, light controlled more responding than did tone in the former group, but tone gained substantial control in the latter. The same effects were also observed within subjects when the training schedules were switched over groups. In Experiment 2, two groups avoided shock in the presence of the compound stimulus. In the absence of the compound, one group was not shocked, and the other received both response-independent and response-produced shock. When tone and light were presented separately, the former group's responding was mainly controlled by tone, but the latter group's responding was almost exclusively controlled by light. These effects were also observed within subjects when the training schedules were switched over groups. Thus, these single-incentive selective association effects (appetitive in Experiment 1 and aversive in Experiment 2) were completely reversible. The schedules in which the compound should have been a conditioned reinforcer consistently produced visual control, and auditory control increased when the compound should have become a conditioned punisher. Currently accepted accounts of selective associations based on affinities between shock and auditory stimuli and between food and visual stimuli (i.e., stimulus-reinforcer interactions) do not adequately address these results. The contingencies of reinforcement most recently associated with the compound and with its absence, rather than the nature of the reinforcer, determined whether auditory or visual stimulus control developed.     

Attenuation of latent inhibition after compound conditioning

Using a conditioned suppression procedure with rats, three experiments examined the effects of compound conditioning on the degree of latent inhibition. Experiment 1 suggested that latent inhibition of the preexposed target was not enhanced but rather attenuated when a second stimulus was presented in compound conditioning. Experiment 2 showed that a similar result was obtained when, in subjects given only compound conditioning, the salience of the target was reduced to the level where it was overshadowed by the second stimulus. Experiment 3 proved that addition of the second stimulus only during preexposure, or during both preexposure and conditioning, did not attenuate the latent inhibition to the target. These results are difficult to explain by any model of Pavlovian conditioning which assumes that both latent inhibition and overshadowing effects are a consequence of acquisition deà cit; other possible accounts are discussed.     

The S-R issue: its status in behavior analysis and in Donahoe and Palmer''s learning and complex behavior.

The central focus of this essay is whether the effect of reinforcement is best viewed as the strengthenng of responding or the strengthening of the environmental control of responding. We make the argument that adherence to Skinner's goal of achieving a moment-to-moment analysis of behavior compels acceptance of the latter view. Moreover, a thoroughgoing commitment to a moment-to-moment analysis undermines the fundamental distinction between the conditioning process instantiated by operant and respondent contingencies while buttressing the crucially important differences in their cumulative outcomes. Computer simulations informed by experimental analyses of behavior and neuroscience are used to illustrate these points.     

I. V. Zavadskii and the beginnings of behavioral pharmacology: an historical note and translation.

I. V. Zavadskii, who worked in Pavlov's laboratory between 1907 and 1909, performed a study that has many of the characteristics of modern behavioral pharmacology. He studied the effects of alcohol, morphine, cocaine and caffeine on the conditioned salivary reflex. A translation of his paper and some brief comments on his life are presented.     

Time-dependent changes in conditioned suppression

Time-dependent changes in a response following aversive conditioning were investigated using a conditioned suppression procedure in a within-subjects design. Four groups of pigeons received Pavlovian conditioning “off the baseline”, immediately followed by an operant task. During the Pavlovian phase, two groups received a forward pairing of a tone with shock, one group received a backward pairing, and one group received a truly random pairing. One of the forward pairing groups also received a delay between the Pavlovian and operant phases. For all groups, key pecking was reinforced on a variable-interval schedule during the operant phase. Testing sessions were identical to training sessions, except that the tone used during Pavlovian conditioning was presented either 0, 15, 30, 45, of 60 minutes after the operant phase began. Testing sessions in which the Pavlovian phase was omitted were also included. The results showed suppression to change as a function of the retention interval, with maximum suppression occurring at intermediate intervals. This U-shaped function was obtained for 11 of the 12 pigeons in the forward-pairing groups and for three of the five in the truly random group. Pigeons in the background pairing group did not show changes in suppression as a function of the retention interval.