Contrast and stimulus generalization following prolonged discrimination training.
Steep stimulus generalization gradients can survive dozens of discrimination sessions, so do not bank on extended training alone to blunt emotional response drops.
01Research in Context
What this study did
Pigeons pecked a key for food. Colors on the key were the signals.
One color meant food was coming. Another color meant no food.
Training lasted 64 sessions. Then the birds saw many in-between colors to map how steep the generalization gradients were.
What they found
The gradients stayed steep. Excitatory and inhibitory control did not wash out.
Long training did not soften the emotional drop-off to the extinction color.
How this fits with other research
Reynolds (1966) reported that extended training erased contrast and peak shift. The new data say the emotional edge can stay sharp. The gap is timing: S ended earlier, so the fade may occur only after very long runs.
Locurto et al. (1980) later saw local contrast shoulders fade while gradients stayed steep. Together the three papers show: side lobes disappear, but the main slope does not flatten.
Harrison et al. (1975) switched to shock avoidance and still got steeper gradients with more training. The pattern holds across reinforcer types, strengthening the claim that prolonged discrimination tightens stimulus control.
Why it matters
If you think extra practice will automatically soften emotional responding to S-delta, think again. For learners with sharp discrimination, you may still see steep generalization. Plan for that when you probe novel stimuli or program gradual stimulus transfer.
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02At a glance
03Original abstract
Different groups of pigeons received discrimination training in which the reinforcement-associated and extinction-associated stimuli were respectively either (a) a line tilt vs a blank key, (b) a blank key vs a line tilt, or (c) two different line tilts. The high response rates that developed to the positive stimulus in all groups during discrimination learning were maintained over 64 sessions of training. After these sessions, all subjects were tested for stimulus generalization along the line-tilt dimension. Gradients of relative (per cent) generalization around the stimulus associated with reinforcement (so-called excitatory gradients) and around the stimulus associated with extinction (so-called inhibitory gradients) were as steep as they typically are after much briefer training periods. These results do not support several of Terrace's predictions on the basis of the hypothesis that emotional responses develop to the stimulus associated with extinction during discrimination learning with errors, but eventually dissipate after extended training.
Journal of the experimental analysis of behavior, 1971 · doi:10.1901/jeab.1971.15-355