Some determiners of attention.

Johnson et al. (1968) worked with pigeons in a small lab chamber.

First the birds learned to peck when only one color or shape was shown.

Later the team presented two-part pictures (color + shape). They counted how much the birds pecked at each part.

Birds pecked most at the part they had already been taught to notice.

Early discrimination training made that part grab almost all of their attention.

The other part was mostly ignored, even when both appeared together.

Snapper et al. (1969) ran the same setup one year later and saw the same split of attention. This direct replication shows the effect is reliable.

Pisacreta (1982) moved the picture around the screen every half-second. The pigeons still followed the part they knew, proving strong stimulus control survives motion.

Williams et al. (2002) cut viewing time to only two seconds. Birds chose correctly, showing that brief exposures are enough once the stimulus already controls behavior.

Peterson et al. (1971) switched from birds to preschool children. Experimenter presence alone changed whether kids copied actions, extending the same stimulus-control rule to humans.

If a client has already learned to discriminate a cue, that cue will overshadow new ones paired with it. Probe each element separately to be sure the right one is driving the response. When you add new targets, first teach them alone, then blend them in. This guards against accidental stimulus overselectivity in your programs.