Additive summation following intradimensional discrimination training.

Scientists trained rats to press a lever for food when they saw colored lights.

Each light color was first taught alone. Then two colors were shown together.

The team wanted to know if the combined light would create stronger control than each color by itself.

The double-color light made the rats press faster than either single color.

This proved that stimulus elements within one sense channel add up, a rule called additive summation.

Thomas et al. (1968) saw the opposite: when two lights signaled different types of food, the rats pressed at a middle speed, not faster. The clash disappears when you notice the 1968 study mixed reinforcers while J et al. kept them the same.

Lattal (1974) backs the new rule: light-plus-tone also boosted pressing even when shock was added, showing the summation effect survives mixed consequences.

Podlesnik et al. (2017) took the same add-stimuli idea into human relapse prevention: combining a therapist stimulus with extinction cut problem responding more than extinction alone.

When you build a discriminative stimulus, stacking related visual cues inside one modality can strengthen control. Think color plus brightness of a token board, or two pictures on a choice card. Keep the reinforcer the same and the cues will pool their power, giving you sharper, faster learner responses without extra reinforcement.