Escape from serial stimuli leading to food.
In a stimulus chain, the nearer a cue is to food, the less animals work to escape it—so 'psychological distance' rules behavior.
01Research in Context
What this study did
Researchers worked with pigeons in a three-link chain. Each link ended with a different colored light. Food came only after the final light.
The birds could peck a key to turn off the current light early. The team counted pecks at each position to see if escaping the stimulus helped or hurt.
What they found
Pecking to escape the last light dropped sharply. Pecking to escape the first light went up.
The closer the stimulus was to food, the less the birds wanted to escape it. Time to reward, not just the light itself, controlled the behavior.
How this fits with other research
Cohen et al. (1990) later showed that simple stimulus-food links, without any escape option, still shaped a scalloped response pattern. Together the studies prove that contiguity to food drives performance, not the chance to flee.
Horner (1971) had already seen lowest response rates in early chain links and highest in the last. Neef et al. (1986) add the twist: escaping early links can rise because those stimuli are psychologically "far" from food.
Allen et al. (2008) flipped the setup and found that turning a light on could also reinforce early-chain pecks. Escape and onset both work, as long as the stimulus change shortens wait time to food.
Why it matters
When you build chained schedules for learners, remember that each stimulus gains or loses value by its distance to the reinforcer. If a client tries to skip or escape an early task, it may mean that task feels too far from the payoff. You can test this by moving the reinforcer closer, adding extra conditioned reinforcers mid-chain, or simplifying the sequence. Check response effort at each step; adjusting temporal proximity can do more than punishing escape.
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02At a glance
03Original abstract
If the functional relations governing the strength of a conditioned reinforcer correspond to those obtained with other Pavlovian procedures (e.g., Kaplan, 1984), the termination of stimuli appearing early in the interval between successive food deliveries should be reinforcing. During initial training we presented four key colors, followed by food, in a recurrent sequence to each of 6 pigeons. This established a baseline level of autoshaped pecking. In later sessions, we terminated each of these colors or only the first color for a brief period following each peck, replacing the original color with a standard substitute to avoid darkening the key. Pecking decreased in the presence of the last color in the sequence but increased in the presence of the first. In accord with contemporary models of Pavlovian conditioning, these and other data suggest that the behavioral effects of stimuli in a chain may be better understood in terms of what each stimulus predicts, as measured by relative time to the terminal reinforcer, than in the exclusively positive terms of the traditional formulation (Skinner, 1938). The same model may also account for the initial pause under fixed-interval and fixed-ratio schedules of reinforcement.
Journal of the experimental analysis of behavior, 1986 · doi:10.1901/jeab.1986.46-259