Variability of response location on fixed-ratio and fixed-interval schedules of reinforcement.

Hamm et al. (1978) watched pigeons peck on two kinds of schedules.

One schedule paid every 20 pecks (fixed-ratio). The other paid the first peck after 60 seconds (fixed-interval).

They tracked where on the key each peck landed to see if the schedule changed the birds’ aim.

Fixed-ratio birds hit the same tiny spot again and again—stereotypy.

Fixed-interval birds spread pecks across the whole key—variability.

The pattern showed up even when both schedules gave food equally often.

Sachs et al. (1969) saw the same swing earlier: steady pay tightens topography, intermittent pay loosens it.

Clarke et al. (1998) later moved the idea into a classroom: teens with severe ID did fewer stereotypic hand-moves when staff used fixed-ratio token boards instead of variable-interval ones.

Morris (1987) added a twist: if you want variability on purpose, add a brief timeout after each response; free-operant methods accidentally lock in repetition.

When you pick a schedule you are also picking a variability setting. Use fixed-ratio to lock in one clean response form—great for fluency drills. Use fixed-interval or add brief pauses when you need flexible, creative responding. Match the schedule to the topography goal, not just to the rate you want.