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Yaoda Xu; Neural fate of unattended features in object-based encoding. Journal of Vision 2008;8(6):552. doi: 10.1167/8.6.552.
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© ARVO (1962-2015); The Authors (2016-present)
Both behavioral and neuroimaging studies have shown that there exists an object-based encoding, such that when one object feature is attended, unattended features of the same object may also be automatically encoded. According to the perceptual load theory, however, unattended information is only processed when the central processing resources are unfilled. The question arises: Is object-based encoding always present regardless of processing load? Or is object-based encoding attenuated at high load according to the perceptual load theory? Response of the superior intra-parietal sulcus (IPS) has been shown to increase with increasing display set size and plateaus at the set size corresponding to the number of objects successfully retained in visual short-term memory (VSTM). A similar result for object shapes has been observed in the lateral occipital complex (LOC), an area participating in visual shape processing. Using these two brain areas as regions of interest, in this fMRI study, observers were presented with 1, 2 or 6 distinctive colored shapes and were asked to only encode the color of each shape in VSTM. Observers were able to retain maximally about 3 colors in VSTM. Corresponding to behavioral performance, superior IPS response was low for set size 1, medium for set size 2 and high for set size 6 displays. If object-based encoding exists regardless of processing load, the encoding of the unattended shapes by the LOC should show a response pattern similar to that of the superior IPS. However, if processing load modulates object-based encoding, LOC response pattern should be low for set size 1, high for set size 2, but low again for set size 6. The result is consistent with the second prediction. This finding indicates that object-based encoding only exists when the overall processing load is low and the central processing recourses are unfilled.
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