Warmup in avoidance as a function of time since prior training

On avoidance procedures, rats and pigeons typically show warmup effects, characterized by improving performance within sessions and loss of the improvement (“warmup decrement”) between sessions. Between-session losses were examined by varying the time between periods of avoidance training. In one experiment, rats lived fulltime in conditioning chambers while intermission intervals were varied. In a second experiment, the animals lived in home cages between sessions; timeout intervals were introduced at midession, producing recurrence of warmup in the second half-session. In both experiments, the warmup decrements increased substantially as the timeout or intersession intervals were increased from zero to 30 minutes. With intervals of 60 or 120 minutes, the decrements approached or exceeded those obtained with intervals of a day or more. When avoidance was interposed between appetitive sessions, the appetitive responding was disrupted, but this seemed unrelated to the warmup or to the proficiency of avoidance. The warmup in avoidance shares characteristics with transient punishment effects, with the Kamin effect, and with habituation phenomena, but it is premature to assume that they reflect common processes.     

Concurrent avoidance of shocks by pigeons pecking a key

Three pigeons were studied on concurrent, unsignaled, avoidance schedules in a two-key procedure. Shock-shock intervals were two seconds in both schedules. The response-shock interval on one key was always 22 seconds, while the response-shock interval associated with the other key was varied from 7 to 52 seconds in different experimental conditions. Response rates on the key associated with the varied schedule tended to decrease when the response-shock interval length was increased. Responding on the key associated with the constant schedule was not systematically affected.     

Timing the second response in two-response avoidance.

Rats were trained on a free-operant avoidance task requiring two lever presses within R seconds, with the opportunity for each response distinguished by differing stimuli. Response latencies at a variety of response-shock intervals were found to be proportional to the time available for the response. These results are shown to be consonant with a scalar expectancy model of timing behavior.     

Duration-reduction of avoidance sessions as negative reinforcement

Five rats were exposed to a shock-postponement procedure in which responses on each of two levers initially had equivalent effects. After an initial training sequence that ensured at least some responding on each lever, an additional consequence was made conjointly operative on the previously less-preferred lever for each animal. Each response on this lever continued to postpone shock, but also reduced the session duration by one minute. The conjoint contingencies were operative until, through session-shortening responses and the passage of time, the session was scheduled to end in two minutes; during the final two minutes the session-shortening contingency was disabled while the shock-postponement contingency continued to be operative on both levers. When responding shifted to a predominance on the session-shortening lever, the conjoint contingency was shifted to the other lever; for four of the five rats this reversal was followed by two additional reversals. Two of the rats' responding showed clear, strong, and unambiguous sensitivity to the session-shortening contingency. The responding of two others was also systematically controlled by that contingency, but the effects were less clearcut. The fifth animal showed an initial shift when session-shortening was introduced, but its subsequent behavior proved insensitive to reversals of procedure. The results clearly indicate a sensitivity of behavior to events on a time scale quite distinct from that of immediate consequences. They also support an interpretation of avoidance sessions, considered in their entirety, as events whose contingent relationship to behavior can affect that behavior—even in the absence of stimuli that delineate those relationships. Finally, these results support an interpretation of aversively based conditioning within a broader context, analogous to the “open versus closed economy” interpretation of appetitively controlled behavior.     

Performance of humans in concurrent avoidance/positive-reinforcement schedules

Performance maintained under concurrent schedules consisting of a variable-interval avoidance component and a variable-interval positive-reinforcement component was studied in three human subjects using points exchangeable for money as the reinforcer. The rate of responding in the avoidance component increased, and the rate of responding in the positive-reinforcement component declined, as a function of the frequency of point-losses avoided in the avoidance component. The performance of all three subjects conformed to equations proposed by Herrnstein to describe behavior in concurrent schedules. The logarithms of the ratios of the response rates in the two components, and the logarithms of the ratios of the times spent in the two components, were linearly related to the logarithms of the ratios of the frequency of loss avoidance in the avoidance component to the frequency of reinforcement in the positive-reinforcement component. When a changeover delay of 5.0 sec was imposed, the slopes of the linear functions were close to 1.0 in the case of two subjects, whereas the third subject exhibited significant undermatching. For two subjects the changeover delay was then reduced to 2.0 sec; in both cases the slopes of the linear functions were lower than under the 5.0-sec condition. One subject participated in a third phase, in which no changeover delay was imposed; there was a further reduction in the slopes of the linear functions.     

Signalled free-operant avoidance of shock by pigeons pecking a key

Two pigeons were trained to peck a key under a free-operant avoidance schedule. Then, changes in key color signalled the beginning (safe period) and the end (warning period) of the response-shock interval, with a response required to change the key color. Finally, a change in key color signalled the warning period and either a response or a shock reinstated the safe stimulus. During signalled avoidance, response rate was higher during the warning stimulus than during the safe stimulus. More responding tended to occur in the warning stimulus when it was terminated by either a response or a shock than by only a response. In either procedure, response latency during the warning stimulus was a function of the duration of the warning stimulus. In general, response and shock rate were higher during unsignalled than during signalled avoidance. When the warning stimulus was brief, the results were similar to those of unsignalled avoidance. These results confirm previous findings with pigeons, are in general agreement with data provided by other species in studies of signalled avoidance, and thereby indicate the transituationality of the key-pecking operant.     

Clock control of human performance on avoidance and fixed-interval schedules

The avoidance and fixed-interval performances of human subjects were studied in two experiments. Addition of time-correlated stimuli (added clock) improved behavioral efficiency, since response rates decreased without decreases in reinforcement rates. Response-dependent display of the clock maintained a second, observing response and reductions in clock duration weakened such observing behavior. Generally, the reinforcing properties of the clock were more apparent with the avoidance than with the fixed-interval schedule, a finding attributed to temporal cues already provided by delivery of the fixed-interval reinforcers. Reduced rates of the main response when the clock was dependent on an observing response were more than offset by rates of the observing response in the majority of subjects. Thus, the results do not support an interpretation of the reinforcing properties of added clocks simply in terms of work reduction.     

The effects of exposure to political and domestic violence on preschool children and their mothers

The purpose of this study was to examine the effects of exposure to political violence on preschool children and their mothers. We explored whether these dyads are different from dyads with no known history of exposure to violence and from mother–child dyads with known exposure to domestic violence. Specifically, we explored differences in mothers' psychological status (depression and anxiety), dyadic emotional availability (EA), children's social information processing, and children's social behaviour, in a sample of 216 dyads divided into three groups (exposure to political violence, no exposure to violence, and exposure to domestic violence). We found evidence to support our hypotheses that children exposed to domestic violence exhibit the highest levels of social maladjustment with smaller but still significant differences between children exposed to political violence and children in the comparison group. As expected, the lowest EA scores were found in the exposure to domestic violence group, followed by dyads in the exposure to political violence group. Dyads belonging to the comparison group (no exposure) exhibited the highest levels of EA. These findings contribute to our understanding of the meaning of exposure to political violence, as well as sharpen the difference between exposure to political and domestic violence.     

Human social defeat and approach–avoidance: Escalating social-evaluative threat and threat of aggression increases social avoidance

Basic research on avoidance by Murray Sidman laid the foundation for advances in the classification, conceptualization and treatment of avoidance in psychological disorders. Contemporary avoidance research is explicitly translational and increasingly focused on how competing appetitive and aversive contingencies influence avoidance. In this laboratory investigation, we examined the effects of escalating social-evaluative threat and threat of social aggression on avoidance of social interactions. During social-defeat learning, 38 adults learned to associate 9 virtual peers with an increasing probability of receiving negative evaluations. Additionally, 1 virtual peer was associated with positive evaluations. Next, in an approach–avoidance task with social-evaluative threat, 1 peer associated with negative evaluations was presented alongside the peer associated with positive evaluations. Approaching peers produced a positive or a probabilistic negative evaluation, while avoiding peers prevented a negative evaluation (and forfeited a positive evaluation). In an approach–avoidance task with social aggression, virtual peers gave and took money away from participants. Escalating social-evaluative threat and aggression increased avoidance, ratings of feeling threatened and threat expectancy and decreased ratings of peer favorableness. These findings underscore the potential of coupling social defeat and approach–avoidance paradigms for translational research on the neurobehavioral mechanisms of social approach–avoidance decision-making and anxiety.