Liu Tingting, Jiang Yi, Sun Xinghuai, He Sheng
Department of Ophthalmology, Eye and ENT Hospital, Fudan University, Shanghai 200031, China.
Curr Biol. 2009 Jan 27;19(2):127-32. doi: 10.1016/j.cub.2008.11.065. Epub 2009 Jan 8.
When embedded in adjacent distractors, a target becomes more difficult to perceive. The neural mechanism for this ubiquitous visual crowding effect remains unresolved. Stimuli presented on opposite sides of the vertical meridian initially project to different hemispheres, whereas stimuli with the same spatial distance but presented to one side of the vertical meridian project to the same hemisphere. Dissociation between visual spatial distance and cortical distance can also be found in V2 and V3 (quadrant representations of the visual hemifield) along the horizontal meridian. In the current study, we observed a strong crowding effect from spatially adjacent distractors with either Gabor or letter targets presented near the vertical or horizontal meridian. Interestingly, for a target presented near the vertical meridian, a distractor from the same side of the meridian (cortically near) had a significantly stronger crowding effect compared with an equidistant distractor presented on the opposite side (cortically remote). No such meridian modulation was observed across the horizontal meridian. These results constrain the cortical locus of the crowding effect to a stage in which left and right visual spaces are represented discontinuously but the upper and lower visual fields are represented continuously, likely beyond the early retinotopic areas.
当嵌入相邻的干扰项中时，目标物会变得更难被察觉。这种普遍存在的视觉拥挤效应的神经机制仍未得到解决。在垂直子午线相对两侧呈现的刺激最初投射到不同的半球，而具有相同空间距离但在垂直子午线一侧呈现的刺激则投射到同一半球。在沿水平子午线的V2和V3（视觉半视野的象限表征）中也能发现视觉空间距离和皮质距离之间的分离。在当前的研究中，我们观察到，当在垂直或水平子午线附近呈现带有Gabor或字母目标的空间相邻干扰项时，会产生强烈的拥挤效应。有趣的是，对于在垂直子午线附近呈现的目标物，与在子午线相对侧（皮质较远）呈现的等距干扰项相比，来自子午线同侧（皮质较近）的干扰项产生的拥挤效应明显更强。在水平子午线上未观察到这种子午线调制。这些结果将拥挤效应的皮质位点限制在一个阶段，在这个阶段中，左右视觉空间以不连续的方式表征，但上下视野以连续的方式表征，可能超出了早期视网膜拓扑区域。
