A tone is followed by shock until the rat consistently responds to the tone. Then, the tone is accompanied by a light for several additional trials. In later test trials the tone or light is presented separately, the rat will show strong reaction to the tone and little or no reaction to the light. This phenomenon is called the

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The blocking effect occurs when a previously learned cue (in this case, the tone) prevents or "blocks" the learning of a new cue (the light) when the two are presented together. Since the rat already associates the tone with the shock, it does not learn to associate the light with the shock when the two stimuli are presented together.

A Tone Is Followed by Shock Until the Rat Consistently