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Alexander Huth, Claudia Wilimzig, Leif Zinn, Christof Koch; The indirect role of saliency in selection for short-term visual memory. Journal of Vision 2008;8(6):198. doi: 10.1167/8.6.198.
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The bottom-up processes that guide visual attention for the first few fixations following the presentation of a novel scene are reasonably well understood (Itti & Koch, 2001), but the processes guiding short term memory storage are not. Here we test whether a process responsible for directing early attention — visual saliency — also plays a role in short term memory storage. Seventeen subjects were shown a natural scene containing ten objects (VanRullen & Koch, 2002) for one second while having their eye movements recorded. They were then asked to recall as many objects as possible from an array of twenty object icons. We performed logistic regression to find that the best predictors of whether an object was recalled are relative eye position and object size. Saliency correlated strongly with eye position (as in earlier experiments), but was not itself a good predictor of recall. We found a strong recency effect among fixated objects that likely explains this discrepancy: more salient objects are fixated earlier, while a limited capacity short term memory queue reduces the probability of recalling objects at early fixations. This suggests that saliency has no direct effect on recall, but can influence it through fixation. The relative importance of eye position and object size suggests a cortical magnification effect wherein a larger representation in cortex leads to a higher probability of recall.
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