Signaled avoidance in the eye withdrawal reflex of the green crab.
A single clear warning lets even a crab learn to dodge fast and keep dodging, showing the power of signaled avoidance.
01Research in Context
What this study did
Scientists worked with green crabs on a beach-inspired task. A brief vibration warned that a puff of air would hit the eye soon.
The crab could dodge the puff by pulling its eye stalk into its shell. Each dodge counted as a successful avoidance response.
What they found
Most crabs learned the trick in about thirty trials. They dodged on three out of every four warning signals.
When the warnings kept coming but the air puff stopped, the crabs still dodged for many more trials. Extinction took a long time.
How this fits with other research
Attwood et al. (1988) taught rats to jump up to avoid shock. Both studies show a quick take-off for signaled avoidance, even with very different bodies.
Schroeder et al. (1969) used eye movements in people under reward schedules. Together the papers prove eye-type responses can be shaped by both reward and avoidance.
Catania et al. (1966) ran free-operant avoidance with no signal. Their rats needed longer intervals to cut shocks, while the crabs mastered a clear warning fast. The difference highlights how a discrete signal speeds learning.
Why it matters
You now have proof that a simple warning stimulus can lock in an avoidance response after only a few pairings. When you teach safety skills, give one clear cue for each danger and allow the learner to escape early. Keep the cue short and the escape action simple, just like the crabs’ quick eye tuck.
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02At a glance
03Original abstract
Learning in a signaled avoidance procedure was studied in the eye withdrawal reflex of the green crab, Carcinus maenas. A puff of air to the eye, which causes eye retraction, was used as the unconditioned stimulus (US). A mild vibration on the carapace, which has no effect on untrained animals, was used as a warning (conditioned) stimulus (CS). Eye withdrawal during the CS led to the omission of the otherwise scheduled US. Acquisition was rapid, reaching about 75% avoidance after 30 trials. Extinction occurred slowly over the course of 40 CS-only trials. Yoked controls did not perform as well. The behavior of experimental animals in the avoidance procedure was found to be essentially identical to the performance of animals subjected to a classical conditioning paradigm in which CS responses had no effect on US presentation. Additional groups of animals were subjected to experiments in which (a) avoidance conditioning (60 trials) was followed by classical conditioning (40 trials) or (b) classical conditioning was followed by avoidance. The behavior of these groups was, again, essentially identical. The results suggest that there may be an underlying Pavlovian mechanism for the learned response, although the contribution of an operant process is not excluded. The results expand the range of invertebrate animals in which fundamental conditioning phenomena can be demonstrated, and may provide a neuronal model for learning in a signaled avoidance procedure.
Journal of the experimental analysis of behavior, 1988 · doi:10.1901/jeab.1988.50-483