Department of Psychology, University of Fribourg, Fribourg, Switzerland.
Laboratory of Psychophysics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
Sci Rep. 2021 Apr 15;11(1):8212. doi: 10.1038/s41598-021-87620-1.
Human observers can accurately estimate statistical summaries from an ensemble of multiple stimuli, including the average size, hue, and direction of motion. The efficiency and speed with which statistical summaries are extracted suggest an automatic mechanism of ensemble coding that operates beyond the capacity limits of attention and memory. However, the extent to which ensemble coding reflects a truly parallel and holistic mode of processing or a non-uniform and biased integration of multiple items is still under debate. In the present work, we used a technique, based on a Spatial Weighted Average Model (SWM), to recover the spatial profile of weights with which individual stimuli contribute to the estimated average during mean size adjustment tasks. In a series of experiments, we derived two-dimensional SWM maps for ensembles presented at different retinal locations, with different degrees of dispersion and under different attentional demands. Our findings revealed strong spatial anisotropies and leftward biases in ensemble coding that were organized in retinotopic reference frames and persisted under attentional manipulations. These results demonstrate an anisotropic spatial contribution to ensemble coding that could be mediated by the differential activation of the two hemispheres during spatial processing and scene encoding.
人类观察者可以从多个刺激的集合中准确估计统计摘要，包括大小、色调和运动方向的平均值。统计摘要提取的效率和速度表明，存在一种超越注意力和记忆容量限制的自动集合编码机制。然而，集合编码在多大程度上反映了真正的并行和整体处理模式，或者是对多个项目的非均匀和有偏差的整合，仍在争论之中。在本工作中，我们使用了一种基于空间加权平均模型（SWM）的技术来恢复个体刺激在进行平均大小调整任务时对估计平均值的贡献的权重的空间分布。在一系列实验中，我们为在不同视网膜位置、不同离散度和不同注意力需求下呈现的集合导出了二维 SWM 图。我们的发现揭示了在集合编码中存在强烈的空间各向异性和左偏性，这些特性以视网膜参考系的形式组织，并在注意力操作下保持不变。这些结果表明，集合编码存在各向异性的空间贡献，这可能是由空间处理和场景编码过程中两个半球的差异激活介导的。
