If you were rewarded for following a particular pattern of behavior, wouldn't you keep doing it?
The answer turns out to be more nuanced than you might think.
In a new study, University of Iowa researchers report that pigeons rewarded with food after pecking five buttons in any order did, indeed, decrease the variety of their sequences. However, the birds kept their options open, never gravitating toward a single sequence and consistently electing to try different sequences.
Ed Wasserman, professor in the Department of Psychological and Brain Sciences, calls the pigeons' pattern of behavior "responding at the edge of chaos."
"What we learned is there's something that keeps the birds from becoming fully machinelike in their responses," says Wasserman, the study's corresponding author. "Maybe it's in their best interest to keep some variability in their behavior. You don't want to be too locked in, because things happen, and the world could change."
The study also extends the notion of the edge of chaos beyond evolutionary biology, where flexibility to a changing environment can be beneficial to a species' survival.
"Might other, more intricate and innovative behaviors like playing an instrument, composing music, and creating visual art involve similarly adaptive variation?" says Odysseus Orr, study co-author and third-year graduate student in the Department of Psychological and Brain Sciences who earned his undergraduate degree from Iowa in 2023. "Only time will tell, but the pigeons provide a convenient gateway for answering those questions under highly controlled circumstances."
Wasserman, Orr, and study co-author Sophia Li devised an experiment to test the Law of Effect. This law posits that animals, including humans, will repeat a response — and winnow other options — when it produces a rewarding outcome. The researchers enlisted six pigeons to peck five buttons in any order they chose, yielding a set of 120 possible sequences. The birds were given no instructions; in fact, any of the 120 total possible five-button sequences generated a treat.
"Under these cushy conditions, how would the birds behave?" Wasserman asks.
To find out, the pigeons were placed into separate chambers, where five buttons were lit on a computerized touch screen. Each button had a unique, colored geometric pattern that disappeared when the pigeon pecked it. After the bird pecked all five buttons, in any order, it received food.
The researchers found that each of the pigeons performed all 120 sequences. The birds also increasingly performed some sequences at the expense of others, consistent with the century-old Law of Effect.
But the researchers were surprised to discover that the pigeons never fully committed to any of their most-favored sequences. More surprising, the pigeons' most preferred five-button sequences rose and fell throughout the eight months and 30,000 times they performed the task.
"Such dramatic behavioral instability is most definitely not consistent with the Law of Effect," says Wasserman, who has studied pigeon cognition and behavior for more than five decades. "The pigeons maintain this exploratory tendency and keep trying multiple sequences. They do not abide by the familiar maxim: 'If it ain't broke, don't fix it.'"
The results generally followed earlier behavioral-reward studies with other animals — including mice, rats, cats, and guinea pigs — that found they reduced their range of options when finding one that consistently produced a reward, the authors write. But while the variability in the pigeons' response sequences decreased, the Iowa team's study showed clearly that the pigeons also repeatedly switched among their favorite sequences and never ceased considering even seemingly less preferred sequences.
The study, "Variability, Stability, and the Law of Effect," was published online on April 6 in the Journal of Experimental Psychology: Animal Learning and Cognition.
Wasserman's Comparative Cognition Laboratory funded the research.
