Feature fusion reveals slow and fast visual memories

Although the visual system can achieve a coarse classification of its inputs in a relatively short time, the synthesis of qualia-rich and detailed percepts can take substantially more time. If these prolonged computations were to take place in a retinotopic space, moving objects would generate extensive smear. However, under normal viewing conditions, moving objects appear relatively sharp and clear, suggesting that a substantial part of visual short-term memory takes place at a nonretinotopic locus. By using a retinotopic feature fusion and a nonretinotopic feature attribution paradigm, we provide evidence for a relatively fast retinotopic buffer and a substantially slower nonretinotopic memory. We present a simple model that can account for the dynamics of these complementary memory processes. Taken together, our results indicate that the visual system can accomplish temporal integration of information while avoiding smear by breaking off sensory memory into fast and slow components that are implemented in retinotopic and nonretinotopic loci, respectively.