Economic and biological influences on key pecking and treadle pressing in pigeons.
Free reinforcement feeds innate moves but leaves novel moves unchanged unless the learner must act to get it.
01Research in Context
What this study did
Leonard and team worked with pigeons in a lab chamber.
Birds could earn grain two ways: peck a lit key or press a small treadle with a foot.
The twist was extra grain. Sometimes it just dropped, no response needed. Sometimes the bird had to peck or press to get it.
The researchers watched which response grew stronger under each rule.
What they found
Key pecking rose whenever extra grain appeared, even if the bird did nothing.
Treadle pressing only rose when the extra grain required a press.
When the session used short 30-second parts, the pattern flipped faster than during long 5-minute parts.
In plain words: built-in behavior (pecking) is easier to nudge with free food than brand-new behavior (treadle pressing).
How this fits with other research
Green et al. (1975) saw the same key-peck boost from free grain 28 years earlier, but they never tested a second response. Leonard adds the treadle and shows the boost is selective.
Kendall (1974) also found brief stimuli before free food can spike key pecks. Leonard widens the lens: the spike only hits biologically ready responses.
Fujita (1983) proved treadle pressing can show contrast effects, so the foot-press is not a dead response. Leonard’s null effect with free food is therefore not about the treadle being useless; it is about contingency.
Together the four papers draw a clean line: built-in responses obey one law, arbitrary responses obey another.
Why it matters
When you shape a new skill, watch what the client already does.
Built-in actions like looking, reaching, or vocalizing will soak up free reinforcement that drifts into the room.
Arbitrary actions like touching a card or pressing a switch need clear, response-linked payoff.
Design your teaching so the new skill, not the old one, earns the bonus.
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02At a glance
03Original abstract
Pigeons were studied on a two-component multiple schedule in which the required operant was, in different conditions, biologically relevant (i.e., key pecking) or nonbiologically relevant (i.e., treadle pressing). Responding was reinforced on a variable-interval (VI) 2-min schedule in both components. In separate phases, additional food was delivered on a variable-time (VT) 15-s schedule (response independent) or a VI 15-s schedule (response dependent) in one of the components. The addition of response-independent food had different effects on responding depending on the operant response and on the frequency with which the components alternated. When components alternated frequently (every 10 s), all pigeons keypecked at a much higher rate during the component with the additional food deliveries, whether response dependent or independent. In comparison, treadle pressing was elevated only when the additional food was response dependent; rate of treadling was lower when the additional food was response independent. When components alternated infrequently (every 20 min), pigeons key pecked at high rates at points of transition into the component with the additional food deliveries. Rate of key pecking decreased with time spent in the 20-min component when the additional food was response independent, whereas rate of pecking remained elevated in that component when the additional food was response dependent. Under otherwise identical test conditions, rate of treadle pressing varied only as a function of its relative rate of response-dependent reinforcement. Delivery of response-independent food thus had different, but predictable, effects on responding depending on which operant was being studied, suggesting that animal-learning procedures can be integrated with biological considerations without the need to propose constraints that limit general laws of learning.
Journal of the experimental analysis of behavior, 2003 · doi:10.1901/jeab.2003.80-43