Positional averaging explains crowding with letter-like stimuli
Positional averaging explains crowding with letter-like stimuli
复制标题
DOI：
10.1073/pnas.0901352106
复制
发表时间：
2009-08-04
影响因子：
11.1
通讯作者：
Dakin, Steven C.
中科院分区：
文献类型：
--
作者：
Greenwood, John A.;Bex, Peter J.;Dakin, Steven C.
视觉拥挤是发生在杂乱场景中的物体识别的故障，这是一个代表边缘视觉表现的原则限制的过程。当拥挤的物体被实验呈现时，一个关键的发现是观察者经常报告附近的侧翼物体而不是目标。这一观察结果导致了一种建议，即拥挤反映了物体位置编码中的噪音增加;尽管附近物体的存在如何破坏位置编码仍然不清楚。我们使用十字形刺激来量化这种破坏，观察者判断水平目标线是否位于刺激中点的上方或下方。总的来说，观察员在判断拥挤的侧翼存在的位置较差。然而，偏置水平线在侧翼也导致观察员报告说，水平线在目标被转移到同一个方向，一个效果，举行了阈下侧翼偏移。简而言之，拥挤诱导观察者的位置判断的随机和系统错误，有或没有检测到侧翼结构。计算建模表明，在侧翼存在下的感知位置遵循噪声目标和侧翼线位置的加权平均值，而不是如先前所提出的那样将侧翼特征替换成目标。总之，我们的研究结果表明，拥挤是一个预先注意的过程，使用平均规则化的嘈杂表示的位置在周边。
Visual crowding is a breakdown in object identification that occurs in cluttered scenes, a process that represents the principle restriction on visual performance in the periphery. When crowded objects are presented experimentally, a key finding is that observers frequently report nearby flanking items instead of the target. This observation has led to the proposal that crowding reflects increased noise in the positional code for objects; although how the presence of nearby objects might disrupt positional encoding remains unclear. We quantified this disruption using cross-like stimuli, where observers judged whether the horizontal target line was positioned above or below the stimulus midpoint. Overall, observers were poorer at judging position in the presence of crowding flankers. However, offsetting horizontal lines in the flankers also led observers to report that the horizontal line in the target was shifted in the same direction, an effect that held for subthreshold flanker offsets. In short, crowding induced both random and systematic errors in observers' judgment of position, with or without the detection of flanker structure. Computational modeling reveals that perceived position in the presence of flankers follows a weighted average of noisy target-and flanker-line positions, rather than a substitution of flanker-features into the target, as has been proposed previously. Together, our results suggest that crowding is a preattentive process that uses averaging to regularize the noisy representation of position in the periphery.