Effects of variable-interval value and amount of training on stimulus generalization.
Extra training on a slow VI schedule flattens stimulus generalization, while faster VI rates keep the usual peaked curve.
01Research in Context
What this study did
The team asked: does the VI value you pick change how a stimulus generalizes? They ran three VI schedules: 30-s, 120-s, and 240-s. Pigeons pecked a key for food while the color or line angle on the key slowly changed.
After ten sessions they tested generalization by showing many stimulus values in extinction. A second group got extra sessions only on VI 240-s to see if longer training matters.
What they found
Ten sessions produced almost the same bell-shaped gradients no matter the VI value. Only the birds on VI 240-s that kept training showed a flatter, wider curve.
In plain words, a slow schedule does not reshape control early on, but keep it going and the peak spreads out.
How this fits with other research
Harrison et al. (1975) found more avoidance training sharpened gradients, while Bromley et al. (1998) now shows VI rate does not. The difference is the contingency: shock avoidance tightens control faster than food VI.
Touchette (1971) kept steep curves after 64 discrimination sessions, yet J et al. flattened them with extended VI 240-s. The key is task type: discrimination versus simple VI; discrimination keeps edges sharp, long VI blurs them.
Locurto et al. (1980) saw local contrast shoulders fade with more VI training, matching the later flattening seen here. Together they show extended VI smooths both small bumps and the whole gradient.
Why it matters
If you run thin schedules like VI 240-s for skill building, expect broader stimulus control after many sessions. This can help when you want flexible responding but hurts when you need tight discrimination. Check your gradient shape after extended training and tighten stimuli or add discrimination steps if the learner starts responding to the wrong cues.
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Join Free →After ten sessions on a lean VI, probe responding to three stimulus values around the trained one; if the gradient looks wide, add discrimination trials or tighten stimulus differences.
02At a glance
03Original abstract
In Experiment 1 pigeons pecked a key that was illuminated with a 501-nm light and obtained food by doing so according to a variable-interval (VI) schedule of reinforcement, the mean value of which differed across groups: either 30 s, 120 s, or 240 s. The pigeons in all three groups were trained for 10 50-min sessions. Generalization testing was conducted in extinction with different wavelengths of light. Absolute and relative generalization gradients were similar in shape for the three groups. Experiment 2 was a systematic replication of Experiment 1 using line orientation as the stimulus dimension and a mean VI value of either 30 s or 240 s. Again, gradients of generalization were similar for the two groups. In Experiment 3 pigeons pecked a key that was illuminated with a 501-nm light and obtained food reinforcers according to either a VI 30-s or a 240-s schedule. Training continued until response rates stabilized (> 30 sessions). For subjects trained with the 30-s schedule, generalization gradients were virtually identical regardless of whether training was for 10 sessions (Experiment 1) or until response rates stabilized. For subjects trained with the VI 240-s schedule, absolute generalization gradients for subjects trained to stability were displaced upward relative to gradients for subjects trained for only 10 sessions (Experiment 1), and relative generalization gradients were slightly flatter. These results indicate that the shape of a generalization gradient does not necessarily depend on the rate of reinforcement during 10-session single-stimulus training but that the effects of prolonged training on stimulus generalization may be schedule dependent.
Journal of the experimental analysis of behavior, 1998 · doi:10.1901/jeab.1998.70-139