title: Signalled and unsignalled free-operant avoidance in the pigeon.
abstract: Pigeons were trained to depress a lever to avoid electric shock under free-operant avoidance schedules without a warning signal, or with a warning signal that could be terminated only by a response. Most birds in the signalled avoidance procedure terminated more than 50% of the warning signals before shock. In the unsignalled avoidance procedure, several birds formed a temporal discrimination and received relatively few shocks; other birds responded only in post-shock bursts, and received many more shocks.
authors.forename: D D
authors.initials: DD
authors.lastname: Foree
authors.forename: V M
authors.initials: VM
authors.lastname: Lolordo