Studies on responding under fixed-interval schedules of reinforcement: II. The scalloped pattern of the cumulative record.
Expect response speed to keep climbing inside an FI, unless the learner’s reinforcement history already taught a different tempo.
01Research in Context
What this study did
Two monkeys worked under a fixed-interval 1000-second schedule.
The researchers drew cumulative records to see if response speed rises steadily inside each interval.
What they found
The monkeys kept pressing faster as the interval moved toward food.
The curve looked like a scallop—slow start, steep climb—every time.
How this fits with other research
Wanchisen et al. (1989) later showed the scallop can vanish. Rats that first lived under a VR20 schedule later showed flat or two-level FI curves.
The two studies sit side-by-side: Dews (1978) shows the clean pattern; Wanchisen et al. (1989) shows it breaks when the learner brings ratio history.
Thomson (1974) had already seen the rise inside chained FIs, but used pigeons and added matching-law math. Dews (1978) keeps it simple—just monkeys and time.
Why it matters
When you run FI schedules in practice, expect the scallop. If you do not see it, ask what the client did before. A past ratio program can flatten the curve and hide the learning you want to track.
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Join Free →Graph each FI session in 10% time bins; if the line stays flat, probe for past ratio history before you change the interval.
02At a glance
03Original abstract
Responding under fixed-interval schedules usually generates either scalloped or break-and-run cumulative records. Earlier, it was generally accepted that the characteristic pattern was the scallop, but in recent years there has been an increasing emphasis on the break-and-run pattern. The break-and-run pattern has been shown quantitatively to provide a good fit of certain fixed-interval patterns. In the present work, responding during fixed-interval 1000-second components of a multiple fixed-interval 1000-second fixed-ratio 50 responses schedule was examined in two rhesus monkeys. Even after responding had started in an interval, there was a high tendency for responding to accelerate over subsequent 100-second segments of the interval. In segments with responding, the rate increased from one segment to the next in 303 of 389 segments in one monkey and in 310 of 419 segments in the other. The size of the increase was substantial, the rate in the fifth segment after responding started being an average of 4.5 times higher than the rate in the first segment after responding started. Hence, the usual pattern of responding in individual intervals was of sustained and substantial acceleration, vindicating numerically the conclusion derived from inspection of the scalloped patterns of the cumulative records.
Journal of the experimental analysis of behavior, 1978 · doi:10.1901/jeab.1978.29-67