The fixed-interval scallop in human affairs.

Pisacreta (1982) looked at everyday patterns people call 'fixed-interval scallops.' These are the pause-then-burst work rhythms you see when a deadline looms.

The paper is a narrative review. It lists eleven other things that can shape the same curve.

The author says the scallop is rarely just a simple FI effect. Motivation, instructions, feedback, and eight more variables twist the curve.

Calling a client's last-minute rush a 'fixed-interval scallop' hides all that extra control.

Critchfield et al. (2003) seems to disagree. They show 52 years of Congressional bill data that line up almost perfectly with lab FI curves. The difference is scope: Congress works under strict calendar reinforcement, while the 1982 review mixes in messy human settings like homework or sales reports.

Nakamura et al. (1986) fit the same FI data into the matching law. They accept FI control but add 'under-matching' tweaks, showing both papers want richer variables, not just 'it's an FI.'

Baum (2021) sides with Pisacreta (1982). He says stop counting single responses and look at long, continuous streams. Both push BCBAs to zoom out from tiny moment-to-moment units.

Before you label a client's procrastination 'FI scalloping,' check the extra cues: clear deadlines, peer competition, staff prompts, or token delivery. Add those variables to your graph or treatment plan. You might find the pause-and-burst pattern is driven by instructions or social praise, not time alone, so your intervention can target those real controls instead of trying to change a schedule that isn't there.

On a fixed-interval schedule, reinforcement is available only after a set amount of time passes. Responding drops right after reinforcement and then accelerates as the interval ends, producing a curved, scallop-shaped cumulative record.

The scallop is a signature of fixed-interval responding in the lab. It reflects a post-reinforcement pause followed by rising response rates as the moment of reinforcement approaches.

This paper cautions that textbooks stretch the term to describe everyday human patterns, such as cramming before a deadline. That framing implies the schedule alone accounts for the behavior.

The author reviews eleven other variables that better explain such complex human patterns and reviews the evidence on each. The lesson is to avoid attributing real-world scalloping to a fixed-interval schedule without checking for those additional controlling variables.