Blocking the development of stimulus control when stimuli indicate periods of nonreinforcement.
First-trained cues can block later ones from controlling behavior, so always test new stimuli alone before counting on them.
01Research in Context
What this study did
The team worked with rats in a small lab cage. First, they taught each rat that a loud noise meant "no food now." The rat learned to stop pressing the lever when the noise came on.
Next, the noise was paired with a small light. Now both cues told the rat "still no food." The question: would the rat also learn to stop pressing when the light appeared alone?
What they found
The rats almost ignored the light. Because the noise already signaled "no food," the light never gained control over the lever pressing. This blocking effect showed that old cues can stop new cues from mattering.
How this fits with other research
Burgess et al. (1971) extended the idea. They asked what happens when two trained cues are shown together. The rats pressed at a speed halfway between the two original rates. Blocking says "first cue wins," while compound control says "cues average out."
Davison et al. (1991) moved the same rules to horses. The animals learned to tell colors apart and showed peak shift, proving that blocking and other stimulus-control laws work across species.
Baer (1974) added a twist: stimulus control can flip. In fixed-interval schedules, the same light slowed pressing early in the interval but sped it up later. Blocking is strong, yet context can still bend stimulus power.
Why it matters
When you add a new picture, word, or gesture to an already-working program, the learner may not notice it. Test the new cue alone to be sure it has power. If not, drop the old cue for a few trials and let the new one gain control. This simple check keeps your teaching lean and avoids hidden prompt dependence.
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02At a glance
03Original abstract
To learn whether prior discrimination training based on one stimulus would block learning about a subsequently added stimulus, rats were first trained to press a bar on a variable-interval schedule of food reinforcement. Occasional stimuli were presented during which no reinforcement was available. Responding became suppressed in the presence of these stimuli. Stimuli could be noise, light, or a compound of noise plus light. A group trained with noise in Phase 1, then trained with the compound in Phase 2, showed less suppression to light in a subsequent test than a group that had the same compound training in Phase 2 but only variable-interval training in Phase 1. This showed that prior training with noise blocked the development of control by light during compound training. Two further groups showed that noise training following compound training did not have the same effect on control by light.
Journal of the experimental analysis of behavior, 1969 · doi:10.1901/jeab.1969.12-767