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  • Title: Human cortical responses to contrast modulations of visual noise.
    Author: Calvert J, Manahilov V, Simpson WA, Parker DM.
    Journal: Vision Res; 2005 Aug; 45(17):2218-30. PubMed ID: 15924937.
    Abstract:
    We studied visual evoked potentials (VEPs) elicited by second-order contrast modulations of binary dynamic noise and first-order luminance modulations. Using a 3-point Laplacian operator centred on Oz, we found that contrast modulations of both low and higher spatial frequencies elicited a negative component whose latency was about 200 ms. The latency of this component was significantly longer than that of the early Laplacian components to first-order luminance modulations. These findings could be due to slower first-stage linear filters and additional processing stages of the second-order pathway. The topographical analysis of scalp recorded VEPs to central and half-field stimulation has suggested that the responses to second-order patterns are likely to be generated by neuronal structures within the primary visual cortex which may have inputs from extrastriate neurons via feedback connections.
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