Abstract
While effects of reward on conditioning have been extensively studied, its role in perceptual learning and memory is still unclear. Recently we have shown a case in which task-irrelevant stimuli were learned only if they were paired with reward (Seitz et al., 2009, Neuron). This result raises the possibility that reward enhances signals that are usually inhibited. Here, we test this hypothesis by applying Seitz et al. (2009)'s rewarding paradigm to retrieval-induced forgetting (RIF), in which a non-practiced item under the same category as a practiced item is inhibited from being retrieved (Anderson et al., 1994) The current experiment consisted of three phases; encoding, retrieval practice and memory-test phases. In the encoding phase, 91 participants tried to encode category-exemplar pairs (e.g, FRUIT-orange). Then, in the retrieval practice phase, they were presented with a category name and a two-letter word-stem (e.g, FRUIT-or) and were asked to complete an encoded word. When they completed correctly, drops of apple juice were delivered as rewards in the reward condition and a beep sound was presented instead in the control condition. In each trial of the memory-test phase, the participants were asked to report whether or not each exemplar had been presented in the encoding phase. If RIF occurs, in the memory-test phase, the exemplars that were not practiced in the retrieval practice phase under the same category as practiced exemplars are less likely to be retrieved than unpracticed exemplars not under the same category as the practiced exemplars. The results of the memory test indicated that RIF was eliminated in the reward condition, although RIF occurred in the control condition. These results suggest that the reward modulates inhibitory mechanisms of memory. Since the prefrontal cortex and/or hippocampus plays important roles in RIF (Kuhl et al., 2007), reward may modulate inhibitory processing in the area.
NIH R01 (EY015980, EY019466, AG031941, MH091801).