The legacy of Guttman and Kalish (1956): Twenty-five years of research on stimulus generalization.
Stimulus-generalization research has refined testing procedures and revealed key factors like discriminability, inhibitory control, and attention that shape generalization gradients.
01Research in Context
What this study did
Wesp et al. (1981) looked back at 25 years of stimulus-generalization work that started with Guttman and Kalish (1956).
They traced how labs tested pigeons, rats, and later people with lights, tones, and line lengths.
The paper maps every twist: new measures, new schedules, and fights about what the curves mean.
What they found
The field moved from simple “peak” curves to fancy tools like self-timed viewing and inhibitory gradients.
Key drivers popped out: how easy the stimuli are to tell apart, how much training you give, and what schedule you use.
DRL and long VI schedules flatten the curve; extra discrimination sessions make it steep.
How this fits with other research
MORSE et al. (1958) first said reinforced and extinguished values sharpen the curve; Wesp et al. (1981) later showed that idea held up across dozens of labs.
Powell et al. (1968) and Snapper et al. (1969) both proved you need S+ vs S- training to get a strong inhibitory slope; the review bundles their finding as a rule.
Eilifsen et al. (2021) looks back again and notes the “mediated generalization” line had already died by the 1980s—confirming the 1981 map was right to leave it out.
Okouchi (2003) repeats the classic gradient with college students and gets the same asymmetric bump; the review predicted human data would mirror pigeons.
Why it matters
If a client’s correct responses spread too widely or too narrowly, tweak the training set, not the child. Add clear S- examples, run more discrimination trials, and pick schedules that sharpen control. These levers have worked since 1956 and still work in your clinic today.
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02At a glance
03Original abstract
This paper is a selective review of the methods, problems, and findings in the area of operant stimulus generalization over the 25 years since the publication of the original paper by Guttman and Kalish (1956) on discriminability and spectral generalization in the pigeon. The paper falls into five main sections, which encompass the main themes and problems stemming from the Guttman and Kalish work and its immediate successors. The first section addresses the relationship between stimulus generalization and stimulus control, as well as the variety of testing procedures and dependent variables used to measure generalization. The next section reviews the limited literature on the effects of early rearing on the generalization gradient. The relationship between discriminability among test stimuli and the slope of the spectral gradient is discussed in the third section, with emphasis upon recent reassessments of the pigeon's hue discriminability function. The fourth section reviews the topic of inhibitory stimulus control, one which developed with the discovery of the peak shift following intradimensional discrimination training. Problems of definition and measurement are discussed in conjunction with the gradient forms used to index inhibitory control. The last section is devoted to attentional effects and the two principal theories postulated to account for them. A survey of different attentional paradigms is provided and the possible role of constant irrelevant stimuli as a source of control is examined. A brief conclusion summarizes the contribution of the generalization technique toward an understanding of the nature and acquisition of stimulus control.
Journal of the experimental analysis of behavior, 1981 · doi:10.1901/jeab.1981.36-405