Bipolar control in fixed interfood intervals.
Within fixed schedules, the same cue can punish early and reinforce late, so timing matters more than the cue itself.
01Research in Context
What this study did
Palya (1993) worked with pigeons on a fixed-time food schedule. Every 60 seconds the birds got grain no matter what they did.
During each minute the chamber lights changed four times. These colors marked early, middle, and late parts of the wait.
The team asked: will the birds treat early cues differently from late cues?
What they found
The pigeons learned to work to turn off early-period lights. They pecked to remove the red that came right after food.
The same birds worked to keep on the lights that showed up just before the next meal. Early cues acted like bad news; late cues acted like good news.
Response rates lined up in smooth curves, proving the stimuli had become true reinforcers with opposite signs.
How this fits with other research
Davidson et al. (1992) had already shown that schedule-induced hopping can be punished with a setback. Their pigeons slowed down when extra pecks delayed food. Palya (1993) now shows the flip side: cues inside the same interval can act as rewards or punishers depending on when they appear.
O'leary et al. (1969) used brief food-paired stimuli under second-order schedules and saw orderly response ramps. Palya (1993) sharpens that picture by mapping the whole minute and finding the crossover point where function switches from negative to positive.
Iversen et al. (1984) found visual cues control schedule-induced activity better than auditory ones. Palya (1993) keeps the visual cue advantage and adds the new twist: the exact moment within the interval decides whether the same cue helps or hurts.
Why it matters
For BCBAs running token boards or DRO timers, the lesson is clear: a stimulus is not just "neutral." Early signals can feel like losses; late signals feel like gains. Place your praise, tokens, or chimes closer to the reinforcer delivery and you may boost their value. If you must mark the start of a long wait, pair that cue with an easy way to remove it so it does not become a tiny punisher.
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02At a glance
03Original abstract
The ability of stimuli correlated with successive periods in a fixed interfood interval to support a response that produced or removed them was examined using pigeons. The degree to which those correlated stimuli elicited directed key pecks was also obtained. Stimuli early in the interval functioned as negative reinforcers, and stimuli late in the interval functioned as positive reinforcers. Stimuli correlated with successively later portions of the second half of the interval supported successively higher rates of elicited pecking and, with the exception of the final stimulus, supported successively higher rates of stimulus production. Stimuli in successively earlier portions of the first half of the interval supported successively higher rates of correlated-stimulus removal. This effect occurred in spite of the addition of a conjoint variable-interval dependency for food. An ogive fit to the mean normalized response distributions resulted in r(2)s demonstrating that most of the variance in the temporal organization of the behavior was accounted for. The findings were taken to indicate that fixed interfood intervals establish bipolar control.
Journal of the experimental analysis of behavior, 1993 · doi:10.1901/jeab.1993.60-345