Key-peck durations under behavioral contrast and differential reinforcement.

Three pigeons pecked a key under two schedules. In one schedule every peck paid off. In the other schedule only short pecks (under 0.14 s) or long pecks (over 0.28 s) paid off.

The birds switched between these schedules many times each session. Researchers watched whether contrast changed peck length and whether the duration rule really mattered.

When the payoff rule stayed the same, peck length hardly moved. Contrast did not shorten or lengthen the birds’ key contacts.

When short pecks were required, two birds quickly trimmed their time. When long pecks were required, the same two birds stretched their contacts. One bird never changed length, but the rule still worked for most.

Ginsburg et al. (1971) showed that longer extinction before reinforcement makes contrast bigger. R et al. add the new detail: contrast may boost rate, yet it leaves response shape alone.

Grant (1989) later found contrast in visual-search reaction times. Together the three studies show the effect jumps across tasks, but duration itself stays plastic under direct differential reinforcement.

Schmidt et al. (1969) used grain length as a cue and got sharper discrimination. R et al. flip that idea: instead of using duration as a signal, they used it as the response to be shaped.

If you want to refine topography—like soft touches on an iPad or quick releases on a leash—use clear duration rules. Contrast from other schedules won’t erase your shaping work, so you can run mixed programs without fear of slop.