The distribution of response bout lengths and its sensitivity to differential reinforcement.
Boosting the share of larger ratio trials reliably lengthens each burst of responses.
01Research in Context
What this study did
Lemons et al. (2015) asked pigeons to peck under two tandem schedules. One schedule mixed easy FR1 with harder FR5. The other schedule used only FR1.
The team slowly changed how often each ratio appeared. They then counted how long each burst of pecking lasted.
What they found
When FR5 trials showed up more often, the birds produced longer bursts of rapid pecking. The easy FR1-only schedule kept bursts short.
In plain words, more work per reward stretches the pecking run.
How this fits with other research
Gildea et al. (2025) later saw the same stretch in rats pressing a lever. Their study adds space to the story: bout length grows even when the animal must walk back to the lever each time.
Crossman et al. (1985) once reported the opposite trend in tiny FR1-FR7 schedules: pauses shrank as the ratio grew. The clash disappears when you notice they looked only at very small ratios and measured pause, not burst length.
Older work by Abrahamsen et al. (1990) and Crossman et al. (1973) already showed that mixing ratio sizes changes overall response rate. J et al. zoom in to show the change lives inside the length of each burst.
Why it matters
For BCBAs, the lesson is simple: if you want longer fluent runs of a skill, slip in occasional bigger ratio requirements. A child tracing letters might breeze through FR1 trials, but adding some FR3 or FR5 stretches each fluent bout. Start small, watch the burst grow, and keep reinforcement coming.
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02At a glance
03Original abstract
Response bouts are clusters of responses that occur in rapid succession and are punctuated by pauses during which the response does not occur. Under variable interval schedules of reinforcement, the number of responses in each bout (the bout length) varies among bouts. This experiment was aimed at determining whether the relative rate of reinforcement influenced the relative frequency of bouts of different lengths. Lever pressing in rats was reinforced under a tandem variable time (VT) 150-s fixed ratio (FR) X, where X could be 1 or 5 and varied randomly after each reinforcer. Two conditions were included: majority FR1 (mFR1) and majority FR5 (mFR5). In mFR1, 75% of reinforcers had a tandem FR requirement of 1 and 25% had a tandem FR requirement of 5; this distribution was reversed in mFR5. The dynamic bi-exponential refractory model of response bouts was fitted to the interresponse times (IRTs) in each condition. Model parameter estimates and IRTs were then used to simulate probable distributions of bout lengths. These distributions comprised a mixture of short geometrically-distributed bout lengths and long negative-binomially-distributed bout lengths. Long bouts were significantly longer in the mFR5 condition than in the mFR1 condition. In conjunction with previous data, the present study suggests that the prevalence of long bouts increases with the proportion of reinforcers with FR5 requirement. These results suggest that bouts of different lengths are sensitive to the rate at which they are reinforced.
Journal of the experimental analysis of behavior, 2015 · doi:10.1002/jeab.168