Effects of monochromatic rearing on spectral discrimination learning and the peak shift in chicks.

The team raised baby chicks under only one color of light.

Later they taught the birds to peck when they saw that color and not when they saw a new color.

They then tested if the chicks still showed the usual peak shift—responding most to a color even farther from the trained one.

The chicks learned the color rule just as fast as normal-reared birds.

Their peak shift was the same size too.

Early life under one color did not change later color learning or the shift effect.

Tracy (1970) saw a different story in ducklings.

Those birds raised under one color had flatter generalization curves and shifted color likes.

The ducklings looked at preference, not peak shift, so the two studies are not in true conflict.

Hawkes et al. (1974) later showed peak shift in pigeons still happens when reward amount changes.

Together the papers say: reward rules beat early light history in setting where birds peak.

For BCBAs, the message is simple: early limited sights did not lock in later stimulus control.

When you see odd generalization, look first at current reinforcement, not distant history.

This frees you to focus on today’s contingencies instead of digging into past events you cannot change.