Rapid response learning in amnesia: delineating associative learning components in repetition priming.

Functional brain imaging studies of priming assume that the behavioral facilitation and activity reductions resulting from multiple repetitions reflect the continued tuning of processes engaged during the initial processing of items. Utilizing an object priming paradigm in which participants were asked to make relative size judgments about visually presented common objects, we tested an alternate hypothesis that states that with multiple repetitions participants come to rely on a more efficient response learning mechanism. In experiment 1, the decision cue was inverted such that previous judgments made either once or three times were rendered invalid. Decision inversion resulted in a reduction of all priming, but most critically, led to a reduction of multiple-repetition priming to the level of single-repetition priming. In experiment 2, patients with amnesia failed to show a priming advantage for multiple repetitions, indicating that response learning is dependent on the medial temporal lobes. Taken together, these results suggest that a different process increasingly mediates priming behavior as repetitions increase. With repeated exposure, behavioral facilitation rapidly comes to reflect a more efficient response learning mechanism rather than facilitated access to object knowledge.