Responding of pigeons under variable-interval schedules of signaled-delayed reinforcement: effects of delay-signal duration.
A longer bridge during delayed reinforcement speeds responding, but the effect is stronger when you add time than when you take it away.
01Research in Context
What this study did
Schaal et al. (1990) worked with pigeons on a variable-interval 60-second schedule. The birds pecked a key for grain, but the grain always arrived 10 seconds after the peck.
A colored light filled the 10-second wait. The team changed how long that light stayed on. They wanted to see if a longer bridge changed how fast the birds pecked before the delay.
What they found
Longer bridge lights pushed the birds to peck faster before the delay started. The effect was not the same going up and down. Raising the signal length raised rates more than lowering it cut them.
In plain words, the direction of your change matters. Stretching the signal boosts responding, but shrinking it does not fully reverse the gain.
How this fits with other research
Hamm et al. (1978) ran a similar VI set-up but left the delay dark. They saw short unsignaled delays lift rates, while long ones kill them. Adding the signal in Schaal et al. (1990) keeps the lift even when the delay itself stays long.
Davidson et al. (1992) later kept the brief signal and varied the VI value. When the schedule paid every 20 s, a 20-s signaled delay hurt rates. Together the two W papers show: keep the signal short next to the time between pays.
Guest et al. (2013) stretched the idea to ratio schedules. Brief unsignaled delays helped VI birds but did nothing for VR birds. The signal trick works for interval work, not for piece-rate style schedules.
Why it matters
If you run token boards, delayed praise, or cash-in times longer than a few seconds, give a clear bridge—points, lights, or words—through the whole wait. Keep the bridge brief relative to the average time between rewards. Watch for asymmetry: clients may speed up when you add the bridge, but they might not slow back down when you fade it. Plan extra teaching to thin the signal later.
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02At a glance
03Original abstract
Two experiments with pigeons examined the relation of the duration of a signal for delay ("delay signal") to rates of key pecking. The first employed a multiple schedule comprised of two components with equal variable-interval 60-s schedules of 27-s delayed food reinforcement. In one component, a short (0.5-s) delay signal, presented immediately following the key peck that began the delay, was increased in duration across phases; in the second component the delay signal initially was equal to the length of the programmed delay (27 s) and was decreased across phases. Response rates prior to delays were an increasing function of delay-signal duration. As the delay signal was decreased in duration, response rates were generally higher than those obtained under identical delay-signal durations as the signal was increased in duration. In Experiment 2 a single variable-interval 60-s schedule of 27-s delayed reinforcement was used. Delay-signal durations were again increased gradually across phases. As in Experiment 1, response rates increased as the delay-signal duration was increased. Following the phase during which the signal lasted the entire delay, shorter delay-signal-duration conditions were introduced abruptly, rather than gradually as in Experiment 1, to determine whether the gradual shortening of the delay signal accounted for the differences observed in response rates under identical delay-signal conditions in Experiment 1. Response rates obtained during the second exposures to the conditions with shorter signals were higher than those observed under identical conditions as the signal duration was increased, as in Experiment 1. In both experiments, rates and patterns of responding during delays varied greatly across subjects and were not systematically related to delay-signal durations. The effects of the delay signal may be related to the signal's role as a discriminative stimulus for adventitiously reinforced intradelay behavior, or the delay signal may have served as a conditioned reinforcer by virtue of the temporal relation between it and presentation of food.
Journal of the experimental analysis of behavior, 1990 · doi:10.1901/jeab.1990.53-103