Contrast and undermatching as a function of reinforcer duration and quality during multiple schedules.

Researchers worked with pigeons in a lab.

They used two-part schedules. In one part, the birds got short or weak grain. In the other part, they got longer or better grain.

The team watched how the birds’ peck rates shifted when the grain changed.

When the grain in one part got shorter or worse, pecking in the other part rose. This is positive contrast.

When the grain in one part got longer or better, pecking in the other part dropped. This is negative contrast.

The birds also undermatched. Their peck ratios did not keep up with the grain-value ratios.

REYNOLDS et al. (1961) and Bloomfield (1967) saw the same up-and-down peck shifts years earlier. They used extinction instead of grain changes. The new study shows grain length and quality work the same way.

Pilgrim et al. (2000) and Nasr et al. (2000) later asked if steady grain times feel safer. They found birds like fixed durations more. Epstein et al. (1981) adds that even small duration or quality gaps still twist response rates.

Parsons et al. (1981), printed the same year, warns that sloppy set-ups can hide contrast. Their tidy method agrees with the clear effects seen here.

Your client’s world is a string of schedule parts: work time, break time, home time. If one part delivers richer or longer reinforcers, behavior in the other parts can dip or surge without warning. Keep reinforcer size, quality, and timing steady across settings to avoid surprise contrast. When you must change reinforcers, do it across the board or alert the client so the shift does not punish the wrong response.