The effect of change in US quality on the blocking effect

If one CS is paired with a US and then that CS together with a “redundant” stimulus is paired with the US, conditioning of that “redundant” stimulus is attenuated or blocked. The present experiment explores the effect upon this blocking of changing the quality of the US coincident with the introduction of the redundant stimulus. Changing US quality disrupted blocking only when the US potency was also increased. Quality changes in which the redundant stimulus was correlated with a lower potency US only increased blocking. These results are taken as supporting the conditioning model of Rescorla and Wagner but inconsistent with a casual informational model of conditioning.