Key-peck probability and topography in a concurrent variable-interval variable-interval schedule with food and water reinforcers.
Response form changes more slowly than response rate when contingencies switch—shape may lag behind probability.
01Research in Context
What this study did
O and colleagues set up two keys for hungry pigeons. One key gave food. The other gave water. Both keys paid off on variable-interval schedules.
The team filmed every peck. They scored how wide each bird opened its beak. Then they swapped the payoffs and watched what happened next.
What they found
Food-key pecks stayed bigger and happened more often. Water-key pecks stayed smaller and rarer.
After the swap, response probability flipped fast. Beak-gape size took longer to follow. Form lagged behind frequency.
How this fits with other research
Duncan et al. (1972) first showed that negative contingencies make short pecks while positive ones make long pecks. O’s team extends that idea: even when the schedule stays positive, reinforcer type can still sculpt the same peck into two shapes.
Smith (1974) warned that short IRTs can be bill-bounce artifacts. O’s high-speed films now prove that real gape changes—not just mechanical bounce—drive the topography differences.
Davidson et al. (1992) ran concurrent VI-VI with signaled delays and saw rate shifts. O kept the VI-VI shell but swapped delays for reinforcer type and added shape data. Together they show concurrent schedules can pull apart rate, probability, and form.
Why it matters
When you switch reinforcers, watch the body, not just the counter. A child’s mand may sound correct today, but lip or tongue placement could still be old shaped. Give the new topography extra time to catch up before you declare mastery.
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02At a glance
03Original abstract
The relation between variables that modulate the probability and the topography of key pecks was examined using a concurrent variable-interval variable-interval schedule with food and water reinforcers. Measures of response probability (response rates, time allocation) and topography (peck duration, gape amplitude) were obtained in 5 water- and food-deprived pigeons. Key color signaled reinforcer type. During baseline, response rates and time allocations were greater to the food key than to the water key, and food-key pecks had larger gapes and shorter durations. Relative probability measures (for the food key) were increased by prewatering and decreased by prefeeding. Deprivation effects upon topography measures were apparent only when food- and water-key pecks were analyzed separately. Food-key gape amplitudes increased with prewatering and decreased with prefeeding. The clearest effect occurred with prewatering. There were no consistent effects upon water-key gapes. The key color-reinforcer relation was reversed for 3 pigeons to determine how response topography was modulated during the transition from food- to water-key pecks. Reacquisition was faster for the probability than for the topography measures. Analysis of gape-amplitude distributions during reversal indicated that response-form modulation proceeded through the generation of intermediate gape sizes.
Journal of the experimental analysis of behavior, 1997 · doi:10.1901/jeab.1997.67-109