Negative behavioral contrast on multiple treadle-press schedules.
Negative contrast can pop up across two VI schedules, so enriching one skill area may quietly drain another unless you balance the rates or add clear setting cues.
01Research in Context
What this study did
Innis (1978) worked with pigeons on two VI treadle-press schedules. One schedule kept the same reinforcer rate while the other schedule changed.
The birds could press either treadle at any time. The team watched what happened to pressing when the richer side got even richer.
What they found
When the changing side paid off more often, birds pressed it more. Pressing on the steady side dropped. This drop is negative behavioral contrast.
Positive contrast did not show up. Making one side poorer did not boost pressing on the steady side.
How this fits with other research
Bloomfield (1967) saw positive contrast with FR schedules eleven years earlier. The two studies seem to clash, but the key is schedule type. FR makes birds work fast; VI lets them pace themselves. Fast FR work exaggerates contrast, steady VI tones it down.
Whalen et al. (1979) wrote the next year that we must compare equal baseline rates before calling any change "contrast." The 1978 data fit their new rule: the steady VI rate truly fell relative to its own baseline.
Pickering et al. (1985) later ran the same setup around the clock. Their birds pushed the rich side even harder than the payoff ratio predicted—an overmatch. Short lab sessions in Innis (1978) only caught the drop on the lean side; full-day access revealed the extra surge on the rich side.
Why it matters
When you run two reinforcement schedules for one client—say, DTT at the table and free play on the floor—watch for negative contrast. Boosting rewards in play could cut work at the table even if table rewards stay the same. To keep both sides strong, raise rewards together or add stimuli that signal which side is "rich" today.
Want CEUs on This Topic?
The ABA Clubhouse has 60+ free CEUs — live every Wednesday. Ethics, supervision & clinical topics.
Join Free →Count responses on both sides of your current mixed schedule for one day; if one side drops when the other gets richer, equalize reinforcer rate or add a distinct SD for each side.
02At a glance
03Original abstract
Eight pigeons pressed treadles for food reinforcers delivered by several multiple variable-interval schedules. The rate of reinforcement for responding during one component schedule was held constant at 30 reinforcers per hour. The rate of reinforcement for responding during the other component varied from 0 to 120 or 240 reinforcers per hour. The schedules were presented in different orders for different subjects. The rate of responding emitted during the variable component schedule varied directly with the rate of reinforcement it provided. The rate of responding during the constant component did not increase consistently when the rate of reinforcement obtained from the variable component decreased from 30 to 0 reinforcers per hr. The rate of responding emitted during the constant component decreased when the rate of reinforcement obtained from the variable component increased from 30 reinforcers per hour to a higher rate. That is, negative but not positive behavioral contrast occurred. The failure to find positive contrast is consistent with one of the predictions of the additive theories of behavioral contrast. Finding negative contrast has ambiguous implications for the additive theories.
Journal of the experimental analysis of behavior, 1978 · doi:10.1901/jeab.1978.29-463