Relationship between response rate and reinforcement frequency in variable-interval schedules: the effect of the concentration of sucrose reinforcement.

The team used variable-interval (VI) schedules with lab rats. They kept the timing of sugar the same but changed how sweet it was.

Low, medium, and high sucrose doses were tested while the computer counted every lever press.

Sweeter water made the rats press faster. The curve followed Herrnstein’s hyperbola: quick rise, then a ceiling.

Weak sugar lowered the ceiling and slid the whole curve to the right, meaning more sugar was needed for the same speed.

Wilkie et al. (1981) swapped volume for concentration and saw the same right-shift, a clean conceptual replication.

Rose et al. (2000) later proved the ceiling itself moves with reinforcer size, updating the 1978 view that only sideways shift occurs.

Dougherty et al. (1994) extended the idea into the matching law, showing the boost happens only when reinforcement is scarce.

For BCBAs running VI schedules, reinforcer size is a dial, not an on-off switch. If client responding is sluggish, first check the potency of your edible or token before you tighten the schedule. Document the magnitude you use so future staff can keep the curve in the same place.