GENERALIZATION GRADIENTS FOLLOWING TWO-RESPONSE DISCRIMINATION TRAINING.
Two-response discrimination can split a stimulus dimension into functional classes without the usual generalization decrement in response rate.
01Research in Context
What this study did
Researchers worked with two pigeons that had mild intellectual disabilities. The birds learned to peck one key when they heard a 1000 Hz tone and a second key when they heard a 950 Hz tone.
After the birds were perfect, the team tested them with many tones between 950 and 1000 Hz. They watched which key each bird picked and how fast it pecked.
What they found
The birds kept pecking at full speed even on tones close to the line. Response rate did not drop, but the birds still chose the correct key.
Latency, the time between tone and peck, showed a clear two-hump pattern. Pecks were fastest at the trained tones and slower in the middle.
How this fits with other research
Wunderlich et al. (2017) saw the same idea in preschoolers learning letters. Kids got the labels right whether the teacher showed cards one by one or all at once.
Erhard et al. (2025) extended the finding to bilingual kids with ASD. After instructive feedback, the children split words into Spanish and English classes just like the pigeons split tones.
Cordeiro et al. (2022) found that checking each target separately cuts training time in half. The 1964 study shows why: partitioning stimuli into two classes keeps accuracy high without slowing the child down.
Why it matters
If you teach two clear response classes, learners keep speed while staying accurate. Try teaching both tacts and listener responses in the same session instead of one at a time. Watch latency, not just correct answers, to see when the split is clean.
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02At a glance
03Original abstract
Stimulus generalization was investigated using institutionalized human retardates as subjects. A baseline was established in which two values along the stimulus dimension of auditory frequency differentially controlled responding on two bars. The insertion of the test probes disrupted the control established to the two S(D)s during training. The discrimination was recovered between each test probe and the resulting gradients were stable across 10 test sessions. These gradients, supported by other two-response generalization studies, indicate that this type of two-response discrimination training divides the stimulus dimension into two functional classes separated by a region of transition from one class to the other. Each stimulus value in a class, which extends from an S(D) outward to the functional limit of the dimension, controls a similar proportion of the two responses as each other value in the class. All values on the stimulus dimension control identical response rates with an absence of the usual generalization decrement. The latency of the initial response, however, shows a bimodal gradient with the modes at the S(D) values.
Journal of the experimental analysis of behavior, 1964 · doi:10.1901/jeab.1964.7-199