Ro Tony, Breitmeyer Bruno, Burton Philip, Singhal Neel S, Lane David
Department of Psychology-MS 25, Rice University, 6100 Main Street, Houston, TX 77005, USA.
Curr Biol. 2003 Jun 17;13(12):1038-41. doi: 10.1016/s0960-9822(03)00337-3.
It has traditionally been assumed that processing within the visual system proceeds in a bottom-up, feedforward manner from retina to higher cortical areas. In addition to feedforward processing, it is now clear that there are also important contributions to sensory encoding that rely upon top-down, feedback (reentrant) projections from higher visual areas to lower ones. By utilizing transcranial magnetic stimulation (TMS) in a metacontrast masking paradigm, we addressed whether feedback processes in early visual cortex play a role in visual awareness. We show that TMS of visual cortex, when timed to produce visual suppression of an annulus serving as a metacontrast mask, induces recovery of an otherwise imperceptible disk. In addition to producing disk recovery, TMS suppression of an annulus was greater when a disk preceded it than when an annulus was presented alone. This latter result suggests that there are effects of the disk on the perceptibility of the subsequent mask that are additive and are revealed with TMS of the visual cortex. These results demonstrate spatial and temporal interactions of conscious vision in visual cortex and suggest that a prior visual stimulus can influence subsequent perception at early stages of visual encoding via feedback projections.
传统上人们认为，视觉系统内的处理过程是以自下而上、前馈的方式从视网膜传导至更高层次的皮层区域。除了前馈处理外，现在很清楚的是，对于感觉编码也有重要贡献，这依赖于从更高视觉区域到更低视觉区域的自上而下的反馈（折返）投射。通过在元对比掩蔽范式中利用经颅磁刺激（TMS），我们探讨了早期视觉皮层中的反馈过程是否在视觉意识中发挥作用。我们发现，当视觉皮层的TMS时机设定为对作为元对比掩蔽的环带产生视觉抑制时，会促使原本无法察觉的圆盘恢复可见。除了产生圆盘恢复外，当圆盘先于环带出现时，TMS对环带的抑制作用比单独呈现环带时更大。后一个结果表明，圆盘对后续掩蔽的可感知性有累加效应，并且通过视觉皮层的TMS得以显现。这些结果证明了视觉皮层中意识视觉的空间和时间相互作用，并表明先前的视觉刺激可以通过反馈投射在视觉编码的早期阶段影响后续感知。
