Evidence for the innate basis of the hue dimension in the duckling.

Scientists trained ducklings to peck at one color of light for food. They then stopped giving food for that color and watched how the birds responded to nearby colors. The ducklings had never seen these exact lights before.

After extinction, the ducklings pecked most at a color slightly different from the one that had paid off. This “peak shift” matched the same pattern seen in adult pigeons and rats. The shift showed the birds treated wavelength as an ordered line, not just separate spots.

Crane et al. (2008) later saw a similar rebound in humans. When they extinguished the strongest cue, a weaker one took over—just as the ducklings moved to the next wavelength.

Weisman et al. (1975) worked with pigeons the same year. Both labs used extinction, but G asked why birds keep working during blackout while S asked where they aim next. Together they show extinction can both create new responses and redirect old ones.

Barnes‐Horowitz et al. (2025) warn that weak cues look “partially reinforced” instead of truly conditional. The ducklings’ neat peak shift may only appear when the color difference is big enough—an innate salience check built into the bird.

You now know peak shift is not a human-language trick; it is built into how nervous systems compare stimuli. When you run discrimination training, pick cues that line up on a clear physical dimension like brightness or size. After reinforcement stops, watch for the learner to shift toward the next step on that line—it tells you the dimension, not the label, is driving choice.