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Jessie J. Peissig, Keisuke Kawasaki, David L. Sheinberg; Long-term familiarity as measured by visual evoked potentials in the monkey. Journal of Vision 2004;4(8):94. doi: 10.1167/4.8.94.
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Holscher et al., 2003 reported that over the course of several days, familiar stimuli show a higher level of activation in the perirhinal cortex than unfamiliar stimuli. Their study did not address whether familiarity with a category of objects might affect the familiarity response to new exemplars from that category. Thus, for a familiar category of objects will the first learned exemplars always maintain an advantage over those learned later, or does the number of repetitions alone define familiarity? We used event-related potentials to explore familiarity over the course of several days with two categories of objects learned at the basic level (prior studies explored familiarity at the subordinate level). The monkey was initially trained with eight exemplars from each category. Subsequently, the monkey was trained with new sets of exemplars for each category, added at three different points in time. The monkey was able to immediately generalize the correct category response to new exemplars. In contrast, we found a significantly larger event-related potential for familiar stimuli than for novel stimuli (starting at approximately 140 ms after stimulus onset); this difference persisted for several blocks of training. The difference between novel and familiar exemplars was significantly reduced once the monkey was given an equivalent number of repetitions for each stimulus. The familiarity effect did not weaken as the monkey gained experience with a category of objects, suggesting that this measure of familiarity is at the level of the exemplars, not at the category level.
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