Four groups of rats (n = 16) received 65 two-way avoidance learning trials. The groups differed with respect to the amount of exposure (0or 4 h] to the situational cues of the apparatus prior to avoidance learning and the intensity of shock (.3 or 1.6 mAl during learning. Superior avoidance performance with weak as compared to strong shock was obtained in the nonpreexposed groups. This inverse relationship between avoidance performance and shock intensity, typical of two-way avoidance learning, was eliminated in the preexposed groups. Presumably, a latent inhibition effect occurred in the strong-shock group, which resulted in a retardation of the conditioning of fear to the situational cues and a consequent improvement in performance. The results are consistent with the effective reinforcement theory, which emphasizes in aversive learning the detrimental effect of large amounts of fear remaining following a response.The use of strong shock as opposed to weak shock has consistently been found to degrade signaled two-way avoidance (e.g., McAllister, McAllister, & Dieter, 1976; McAllister, McAllister, & Douglass, 1971; Moyer & Korn, 1964). This finding poses a difficulty for all theories of avoidance learning including the traditional two-process theory. According to the latter theory (e.g., Mowrer, 1947), fear which is classically conditioned to the conditioned stimulus (CS) is assumed to serve as motivation and its reduction as reinforcement for the instrumental avoidance response. Because more fear is conditioned with strong than with weak shock, a direct relationship between shock intensity and avoidance performance would be predicted.Recently, however, an elaboration of two-process theory which emphasizes the role of fear conditioned to situational stimuli has been proposed to account for the inverse relationship (McAllister et al. , 1976; McAllister et al., 1971). According to this position, the amount of effective reinforcement for an avoidance response is directly related to the amount of fear reduction occurring with the termination of feararousing stimuli (CS and/or situational cues) and negatively related to the amount of fear elicited by the stimuli present after a response. That is, it is not simply the amount of fear reduction which determines the amount of reinforcement, but rather it is the amount of fear reduction relative to the amount of fear remaining after a response. In the two-way task, in which the subject moves back and forth between two identical compartments, fear is conditioned to the situational cues of both compartments. Therefore, an avoidance response does not remove the subject from fear-arousing situational cues. AIthough a greater amount of fear reduction occurs with CS termination when shock is strong than when it is weak, the theory assurnes that this increase in reinforcement is more than offset by the greater amount of situational-cues fear that remains after the response. Thus, two-way avoidance performance is degraded with strong, as compared to weak, shock. This position...

In Experiment I, four groups of subjects (n = 16 each) were exposed to the situational stimuli of a shuttlebox apparatus for 4 h. Subsequently, 200 two-way avoidance trials were administered (100/day) with either .3-or 1.6-mA shock and with either small or large reward (presence or absence of visual stimuli following the response). Avoidance performance was directly related to shock intensity on both days and to magnitude of reward on the 2nd day. In Experiment 2, four groups of subjects (n = 24 each) were given 4 h of exposure either to the situational stimuli of the shuttlebox or to a neutral box. Then, 10 two-way avoidance trials were given with 1.6-mA shock. Subsequently, subjects were allowed to escape from one of the shuttlebox compartments to an adjacent safe box. Following preexposure to situational stimuli, avoidance performance was superior whereas escape-from-fear performance was inferior. This latter finding demonstrated that less fear of situational cues was present during avoidance training in the preexposed condition. All of these results support the effective reinforcement theory, an extension of two-factor theory, which emphasizes the importance for avoidance learning of the amount of fear of situational cues present following a response. 165In a one-way task in which subjects can avoid shock by moving to an area distinctively different from the one where shock is administered, avoidance performance has been found to be directly related to shock intensity (Dieter, 1976;Moyer & Korn, 1966). However, when an avoidance response does not remove the subject from situational stimuli which have been paired with shock, as in signaled two-way or barpress avoidance tasks, performance has been found to be related inversely to shock intensity, at least within the range of intensities usually employed. This latter finding is, in fact, one of the most reliable in the avoidance learning literature (e. A theoretical position which seems to account for the above findings is the effective reinforcement theory proposed by McAllister et al. (1971McAllister et al. ( , 1976 as an extension of the two-factor theory of avoidance learning (Mowrer, 1947). According to this position, the effective reinforcement for an avoidance response is related (a) positively to the amount of fear reduction occurring with the response and (b) negatively to the amount of fear present following the response. In addition, as the total amount of fear increases, it is assumed that the amount of fear present following the response (b) becomes relatively more important than the amount of fear reduction (a) in determining effective reinforcement. In the signaled twoway avoidance task, fear becomes conditioned to both the discrete conditioned stimulus (CS) and to the situational cues of each shuttle compartment when shock occurs on escape trials, with more fear being conditioned to these stimuli the more intense the shock. Although the amount of fear reduction would be greater in a strong-than in a weak-shock group when the CS is terminated fo...

In Experiment I, eight groups of rats (n = 20) were given shuttlebox-avoidance training. Two levels of shock (.3 and 1.6 rnA) were combined factorially with two levels of reward (large and smail) under both continuous and discontinuous (.75 !:Iec on and 2.00 sec off) shock. Visual situational cues Wtlre absent after a shuttle response for the large-reward condition I:tnd present for the smail-reward condition. Superior performance was obtained with weak rather than strong shock under both reward conditions and with large rather thdll small reward only under the weak-shock cOlldition. Continuity of shock had no differential effect on performance. Experiment II allowed the conclusion that the reward effect was attributable to a reinforcement mechanism. The data were taken as support for the effective reinforcement theory, which emphasizes the importance in avoidance learning of fear conditioned to situational cues.In signaled avoidance learning, a discrete stimulus (CS) is presented at some interval of time prior to shock (UCS) onset. If the subject makes an mstrumental response (e.g., moves away from the ,hock area) during the CS-UCS interval, the CS is terminated and shock is avoided. A response occurring after the CS-UCS interval results in the termination of the CS and escape from the shock. Since escape responses predominate early in learning, the subject receives a number of shock presentations. It has consistently been found that the learning of a signaled shuttlebox-avoidance response is superior when weak rather than strong shock is used (e.g.,

Six groups of rats (n = 16) differed with respect to the continuity of shock (continuous or discontinuous) and the shock intensity (.3, .8, or 1.6 rnA) used during 65 one-way avoidance-conditioning trials. In general, a facilitative effect on one-way avoidance learning was obtained for continuous as opposed to discontinuous shock and for strong as opposed to weak shock. For both variables, the results are opposite to those obtained in discriminated shuttlebox-avoidance and barpress avoidance tasks. The data support an interpretation of the effect of continuity of shock which holds that discontinuous shock is, in effect, less intense than continuous shock. This interpretation allows the effects of the continuity-of-shock variable to be incorporated within the effective reinforcement theory of avoidance learning which has been proposed to account for shock-intensity effects in various avoidance tasks.Discontinuous shock has been found to facilitate discriminated avoidance learning relative to continuous shock in both barpress avoidance (e.g., 0 ' Amato & Fazzaro, 1966;Hurwitz, 1964) and shuttlebox-avoidance (Moyer & Chapman, 1966) tasks. Two interpretations of the continuity-of-shock effect have been offered, one based on stimulus generalization and the other on the punishment of freezing.The stimulus generalization interpretation (D' Amato & Fazzaro, 1966; D'Amato, Keller, & Biederman, 1965) holds that the stimuli present during the shock-off periods of discontinuous shock are highly similar to the stimuli present during the CS-US interval. As a result, escape responses which occur during shock-off periods should, through stimulus generalization, come to occur during the CS-US interval. Thus, avoidance responding should increase in frequency with discontinuous shock. With continuous shock, escape responses would not be expected to show such generalization because they would be made only during shock-on periods. This interpretation has been infirmed by data which indicate that the continuity-of-shock effect occurs even if the amount of generalization which should occur when shock is discontinuous is limited by presenting shock contiguous with escape responses