Preference for a Forced-Choice Fixed-Ratio Schedule over an Equivalent Free-Choice Response Chain in the Pigeon

Abstract

Three pigeons were trained on a concurrent fixed-ratio chain schedule. During the first 10 trials of each session, the birds had to satisfy a fixed-ratio x schedule. During Trials 11 to 20 each bird had to satisfy a chain schedule consisting of x links. During the last 10 trials the birds could choose to satisfy the fixed-ratio x or the chain schedule. That is, the birds could peck one key x times, or x keys once each. A different lighted key served as each link of the chain schedule. A response to any of the keys darkened that key. When all keys were darkened, a reinforcer was delivered. The fixed-ratio schedule was always satisfied on one key that never served as part of the chain. Over sessions the number of chain keys was increased to nine, i.e., a concurrent fixed-ratio 9 chain schedule, with a nine-key response chain. Each bird preferred the fixed-ratio option to the chain until the fixed-ratio value was three to five times greater than the number of required chain responses. The number of chain link keys appeared to be more influential than either overall response requirements or the time required to complete each option. Response stereotypy emerged during the chain trials.