Peak shift following simultaneous discriminations.
Peak shift shows up even with side-by-side cues, so expect it in any discrimination lesson.
01Research in Context
What this study did
The researcher trained pigeons to peck one color and ignore another. Both colors appeared at the same time on the screen.
After the birds learned the rule, the team tested them with new colors that looked more or less like the trained ones.
What they found
Every bird showed peak shift. They pecked hardest at a color that was even further from the bad color than the one they were taught to pick.
Peak shift still happened even though the birds never saw the colors one after another.
How this fits with other research
Richardson (1973) used pigeons too, but tested paired-associate learning. Both studies show basic learning rules work the same across simple bird tasks.
Borrero et al. (2005) moved the idea to people. They added brain scans while adults picked money-linked pictures. Frontal-striatal areas lit up, proving the old pigeon rule still guides human brains.
LeFrancois et al. (1993) asked hens to work harder for each correct peck. They found FR 5-10 kept accuracy high. The 1975 paper kept the ratio easy at FR 1, showing peak shift needs no extra effort.
Why it matters
You now know peak shift will appear no matter how you set up the discrimination. Plan for it when you teach color, shape, or emotion cards. If the learner starts picking a 'stretched' version of the right answer, do not blame your teaching method. Just adjust the stimuli or add generalization probes early.
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02At a glance
03Original abstract
Pigeons were exposed to stimuli presented on two keys. For some birds, the stimuli varied in a dimension of visual flicker-rate, and for others they varied in visual intensity. During differential training, concurrent schedules operated, with one stimulus correlated with one schedule and another stimulus correlated with a second schedule that arranged a lower, or zero, rate of reinforcement. The stimuli were alternated randomly on the two keys. Generalization tests were given in which the original two, and seven other stimuli lying in the same dimension, were presented in pairs on the two keys in various combinations. In the generalization test given after differential training, each bird showed peak shift. The data did not support explanation for peak shift that gave critical emphasis to whether stimuli were presented simultaneously or successively during differential training.
Journal of the experimental analysis of behavior, 1975 · doi:10.1901/jeab.1975.24-303