Partial avoidance contingencies.
Weakening avoidance rules splits learners into contingency-only detectors and shock-density trackers.
01Research in Context
What this study did
Weisman et al. (1975) weakened the avoidance rule for rats. If the rat pressed a lever, shock sometimes still came. The team watched who kept pressing and who quit.
Trials were discrete. Each press bought a chance, not a promise, of safety. The shock density also drifted across blocks.
What they found
Half the rats stopped pressing when the rule weakened. The other half kept going. These persistent rats still tracked how often shocks came, not just whether the rule held.
Two styles showed up: contingency-only detectors and density-plus-contingency trackers.
How this fits with other research
Mosk et al. (1984) later held the rule steady but turned the shock volume up and down. They found a floor: once shock passed a minimum level, louder zaps did not help and sometimes hurt. Together the papers show both rule clarity and shock level matter, but in different windows.
Sachs et al. (1969) had already shown that extra shocks after a response can suppress pressing. Their punishment setup seemed to clash with G et al.’s finding that some rats press more when shocks grow. The gap is procedure: A punished every press; G merely diluted the safety rule. The rat is not crazy; the contingency changed.
Dallemagne et al. (1970) let rats dial shock intensity down by pressing. That titration study mirrors the density-tracking seen here; both reveal rats monitor and adjust to shock load, not just response-shock pairings.
Why it matters
When you thin escape or avoidance schedules, watch for these two response styles. If the learner stops, the rule may have faded too fast. If they keep going but errors rise, they might still feel the aversive density. Probe with brief rule reversals or count the aversive events, not just the responses. Match the thinning step to the style you see.
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02At a glance
03Original abstract
Rats were trained in a discrete-trial paradigm with no intertrial interval. The first response changed an auditory stimulus for the remainder of the trial. Shocks were delivered only at the end of the trial cycle. Avoidance contingencies were defined by the conditional probability of shock, given no response (P(0)), and the conditional probability of shock given a response (P(1)). The maximal avoidance contingency was P(0)=1.0, P(1)=0, and noncontingent conditions were those for which P(0)=P(1). In Experiment I, after training on the maximal contingency, three groups of subjects experienced either P(0)=P(1)=0, P(0)=P(1)=0.5, or P(0)=P(1)=1.0. Eight of 10 subjects stopped responding under the noncontingent conditions. Experiment II studied partial contingencies by varying P(0) and P(1). For one group, P(0) was reduced holding P(1)=0. Responding decreased to zero as P(0) approached zero. A second group was studied under P(1)>0, holding P(0)=1.0. For three of the six rats in this group, responding decreased to zero with increasing P(1). The other three maintained responding as P(1) was increased up to the noncontingent, P(1)=P(0)=1.0 value. The P(0) group was also studied with P(0)=P(1)>0, and half of these subjects responded. The results demonstrated two modes of response to weakening or eliminating the avoidance contingency. Some subjects were sensitive to contingency only, and insensitive to changes in shock density. Approximately one half of the subjects were sensitive to both contingency and shock density. This shared control was observed only when P(1)> 0.
Journal of the experimental analysis of behavior, 1975 · doi:10.1901/jeab.1975.23-437