Differential responding without differential reinforcement: Intensity difference, continuum position, and reinforcement density effects.

Raslear (1981) tested whether pigeons would peck two keys at different rates when the only cue was how loud the tone was.

Both keys paid off on the same schedule, so reinforcement stayed equal.

The birds simply heard a soft tone on one key and a loud tone on the other, with no extra rewards for choosing either side.

The louder tone made the birds peck faster, even though both keys gave the same amount of food.

When the volume gap was bigger, the difference in pecking grew.

Thicker reinforcement across the board boosted the effect, showing that stimulus intensity alone can steer behavior.

Badia et al. (1972) saw the opposite: when reinforcement stayed equal, birds never learned to tell tones apart by location.

The key difference is cue type. Location needs different payoffs to matter; intensity can matter on its own.

Lyons (1995) later explained that watching the cue, not just being paid for it, can build control. G’s data give that idea real feathers.

Hayes et al. (1975) also got different response rates without tying food to the bird’s choice, proving that non-contingent schedules can still sculpt gradients.

You can use salient sensory differences—brighter lights, louder clicks, bigger icons—to guide responding while keeping reinforcement flat. This is handy when you want steady pay rates but still need the client to notice which stimulus is on deck. Try pairing the target cue with a slightly stronger version of the same sense modality before you add extra rewards.