Early pavlovian studies on the effects of starvation

This communication is based on the pioneering studies performed by I. P. Pavlov’s associates, Yu. P. Frolov (in 1918) and I. S. Rozental’ (in 1918/1919) at the Institute of Experimental Medicine, in Petrograd. The changes in the “independent variable”—the dogs’ diet—were not planned but were the consequences of severe shortages of food for man and beast. The principal generalization concerns the order in which different forms of “complex nervous activity” were impaired: the order is opposite to the order in which they emerge in the process of ontogenesis. First to suffer was “internal inhibition,” as documented by the failure of stimulus differentiation. This was followed by the decrease in the magnitude of well-established conditional responses (CRs). As a result of a more severe impairment of the excitatory processes, it became difficult or impossible to establish new CRs. In time, previously established CRs to artificial stimuli, visual and acoustic, disappeared totally. The CRs to natural conditional stimuli (CSs) were maintained fairly well but, eventually, they too decreased markedly. In the terminal phase of starvation, the unconditional salivary reflexes continued to function, although their magnitude was depressed.     

The effects of escape conditioning and shock intensity on responding during inescapable shock

Eight albino rats, conditioned to press a lever to escape shock, continued to lever press during short inescapable shocks presented subsequently. The rate of this behavior was found to be higher for higher shock intensities regardless of the order in which shock values were presented. Relative to the immediately preceding escape rate, responding during inescapable shock was higher following conditioning at higher fixed-ratio escape requirements. Four subjects not conditioned to escape shock pressed the lever very infrequently during inescapable shock and showed little change with changes in shock intensity. The escape conditioning effects suggest that responding during inescapable shock is superstitious escape behavior. The effects of shock intensity on this behavior appear to be similar to reported effects of shock intensity on escape behavior.     

The effects of active choice,shock duration,shock experience,and probability on the choice between immediate and delayed shock

The choice between immediate and delayed shock was investigated in three experiments with college students. Some Ss were required to choose between a longer-duration shock immediately and a shorter-duration shock later. Immediate, as opposed to delayed, choices were more frequent when: (a) Ss were required to choose the immediate or the delayed shock in contrast to other procedures in which Ss were required to choose immediate shock or passively wait for automatic shock to occur, (b) the duration of the immediate shock was reduced, (c) the S was given prior experience with shock, and (d) the probability of the immediate shock was reduced. Under some circumstances, shock delay and anxiety increased the frequency of immediate choices.     

Punishment: the interactive effects of delay and intensity of shock

A discrete-trial punishment procedure, with rats, was used to examine how delay-of-shock intervals of 0 to 28 sec and shock intensity interact to decrease the frequency and increase the latency of a positively reinforced response. For delay-of-shock intervals of 0, 7, 14, and 28 sec, there was a range of shock intensities, for some subjects, over which the punishing effect of shock was an increasing, monotonic function of shock intensity. For other subjects this transition was abrupt. Functions relating response frequency and latency measures to shock intensity were displaced toward higher values on the shock intensity axis with an increase in delay-of-shock interval. The effects of “gradual” and “abrupt” introduction to “severe” shock, as well as re-exposure to previously used shock intensities, were examined under both the immediate and delay-of-shock conditions. With delay-of-shock intervals of 7, 14, or 28 sec, shock intensities of approximately 0.50 milliamperes or greater were necessary to decrease substantially the number and increase the latency of the lever-pressing response. For the immediate punishment group this intensity was approximately 0.20 ma. These facts were related to Annau and Kamin's (1961) conditioned emotional response experiment in which a shock intensity of 0.49 ma or greater was required to suppress the rate of a positively reinforced response.     

The effects of electroconvulsive shock on the action of a reinforcing stimulus

Three experiments sought to evaluate the effect of electroconvulsive shock on the action of a reinforcing stimulus. In all experiments behavior was maintained on a 2 min variable interval schedule for food reinforcement. Foot shock at the termination of a buzzer stimulus served as the reinforcing stimulus for conditioned suppression during the ensuing buzzer interval. Omission of foot shock at the termination of the buzzer stimulus was followed by normal responding (no conditioned suppression) during the next buzzer interval. In Exp I electroconvulsive shock followed foot shock at varying time intervals. In the first subsidiary experiment electroconvulsive shock followed an unreinforced buzzer stimulus at varying time intervals. In the second subsidiary experiment electroconvulsive shock followed foot shock at varying time intervals and an additional buzzer stimulus was sounded between the termination of foot shock and the onset of electroconvulsive shock. These three experiments demonstrated that electroconvulsive shock invariably abolished the effects of the reinforcing stimulus if it followed conditioning by no more than 10.0 sec and never had an effect if it followed conditioning by 12.5 sec or more; electroconvulsive shock was not acting as a reinforcing stimulus in this situation.     

Stimulus aspects of aversive controls: the effects of response contingent shock

A tone ending with electrical shock was periodically presented to pigeons while they pecked a key for food. Pairs of birds were run simultaneously under a yoked program which insured that both birds received the same number and temporal distribution of shocks. For one of the birds, shock was always initiated by a peck; for the other, shock was unavoidable. Both procedures led to reduced rates of pecking in the presence of the tone, and gradients of stimulus generalization were obtained. But the effects of response contingent shock extinguished more rapidly than the effects of unavoidable shock. In general, birds exposed to unavoidable shock tended to respond at intermediate rates throughout tone, whereas those exposed to response contingent shock ceased to peck for part or all of the tone period.     

Some effects of punishment shock intensity upon discriminative responding

Three pigeons received visual discrimination training under both multiple variable-ratio extinction and variable-interval extinction schedules. All birds developed nearly perfect discrimination. When punishment for every tenth response during food reinforcement was presented, responding decreased as shock intensity increased. At the same time, responding during extinction, which was not punished, increased at intermediate punishment intensities, but returned to low levels under severe punishment. A second procedure, in which punishment and no-punishment sessions alternated unsystematically, was employed with two of the birds. The results under this procedure essentially replicated the data obtained as punishment shock intensity increased gradually.     

Some effects of correlation between response-contingent shock and reinforcement

Rats responded on a two-component chain schedule in which a response-contingent electric shock at the end of the first component was either positively correlated, negatively correlated, or uncorrelated with reinforcement availability in the second component. With 0.4-ma shocks, rate in the first component depended on the shock-reinforcement correlation: when shock and reinforcement availability were positively correlated, after extended exposure to the contingencies, rates exceeded those in the absence of shock; when shock and reinforcement availability were negatively correlated, responding was generally suppressed throughout. The discriminative control of shock over responding in the second component, in which reinforcement was available 50% of the time, also depended somewhat on correlation. However, rate change in the first component was not specifically related to discrimination in the second component. With 0.8-ma shocks, responding was substantially suppressed in the first component at all three values of shock-reinforcement correlations.