Ghahghaei Saeideh, Walker Laura
The Smith-Kettlewell Eye Research Institute, San Francisco, CA, USA.
Envision Research Institute, Wichita, KS, USA.
J Vis. 2016 Sep 1;16(11):30. doi: 10.1167/16.11.30.
Crowding increases with eccentricity and is most readily observed in the periphery. During natural, active vision, however, central vision plays an important role. Measures of critical distance to estimate crowding are difficult in central vision, as these distances are small. Any overlap of flankers with the target may create an overlay masking confound. The crowding factor method avoids this issue by simultaneously modulating target size and flanker distance and using a ratio to compare crowded to uncrowded conditions. This method was developed and applied in the periphery (Petrov & Meleshkevich, 2011b). In this work, we apply the method to characterize crowding in parafoveal vision (<3.5 visual degrees) with spatial uncertainty. We find that eccentricity and hemifield have less impact on crowding than in the periphery, yet radial/tangential asymmetries are clearly preserved. There are considerable idiosyncratic differences observed between participants. The crowding factor method provides a powerful tool for examining crowding in central and peripheral vision, which will be useful in future studies that seek to understand visual processing under natural, active viewing conditions.
拥挤效应随离心率增加而增强，且在视野边缘最易观察到。然而，在自然的主动视觉过程中，中央视觉起着重要作用。在中央视觉中，由于这些距离较小，因此难以测量用于估计拥挤效应的临界距离。侧翼刺激与目标的任何重叠都可能造成叠加掩蔽混淆。拥挤因子法通过同时调节目标大小和侧翼刺激距离，并使用一个比率来比较拥挤和非拥挤条件，从而避免了这个问题。该方法是在外周视觉中开发并应用的（彼得罗夫和梅列什凯维奇，2011b）。在这项研究中，我们应用该方法来表征具有空间不确定性的旁中央凹视觉（<3.5视角）中的拥挤效应。我们发现，与外周视觉相比，离心率和半视野对拥挤效应的影响较小，但径向/切向不对称性明显保留。在参与者之间观察到了相当大的个体差异。拥挤因子法为研究中央和外周视觉中的拥挤效应提供了一个强大的工具，这将有助于未来旨在理解自然主动观看条件下视觉处理的研究。
