The microanalysis of fixed-interval responding.
Fixed-interval scallops are built from three sharp behavioral states, not smooth speed-up.
01Research in Context
What this study did
The team watched pigeons peck a key during fixed-interval 5-min schedules. They timed every peck to the millisecond and looked for patterns inside each interval.
Instead of drawing a smooth curve, they split the data into three chunks: pause, interim, and terminal. They asked which chunk predicts the next peck time.
What they found
The birds did not speed up smoothly. They sat still, then pecked a little, then burst at the end. Each chunk had its own rhythm and the switch points were sharp, not gradual.
Long pauses early in the interval made the next pause even longer. Late pauses shortened. These local rules, not a single clock, built the classic scallop.
How this fits with other research
Dews (1966) saw the same scallop even when most of the interval was filled with an extinction stimulus. Both studies show the pattern survives disruption, so the brain does not need hidden mediating behaviors.
McKearney (1970) got the scallop when the consequence was electric shock instead of food. The three-state model holds even when the reinforcer hurts, proving schedule control is robust.
Leigland (2000) treated concurrent intervals as stay/switch pairs. Pierce et al. (1983) treat fixed intervals as pause/interim/terminal pairs. Both break big schedules into smaller, countable units.
Why it matters
If you run fixed-interval or variable-interval programs, stop expecting smooth acceleration. Watch for three clear states: silence, slow, and sprint. Teach staff to mark when the learner shifts from one state to the next; those shift points are your data. Shaping can target the terminal burst earlier, and you can reinforce the switch into it rather than waiting for the whole interval to pass.
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02At a glance
03Original abstract
The fixed-interval schedule of reinforcement is one of the more widely studied schedules in the experimental analysis of behavior and is also a common baseline for behavior pharmacology. Despite many intensive studies, the controlling variables and the pattern of behavior engendered are not well understood. The present study examined the microstructure and superstructure of the behavior engendered by a fixed-interval 5- and a fixed-interval 15-minute schedule of food reinforcement in the pigeon. Analysis of performance typical of fixed-interval responding indicated that the scalloped pattern does not result from smooth acceleration in responding, but, rather, from renewed pausing early in the interval. Individual interresponse-time (IRT) analyses provided no evidence of acceleration. There was a strong indication of alternation in shorter-longer IRTs, but these shorter-longer IRTs did not occur at random, reflecting instead a sequential dependency in successive IRTs. Furthermore, early in the interval there was a high relative frequency of short IRTs. Such a pattern of early pauses and short IRTs does not suggest behavior typical of reinforced responding as exemplified by the pattern found near the end of the interval. Thus, behavior from clearly scalloped performance can be classified into three states: postreinforcement pause, interim behavior, and terminal behavior.
Journal of the experimental analysis of behavior, 1983 · doi:10.1901/jeab.1983.39-327