Levi D M, Klein S A
University of Houston, College of Optometry, TX 77204-6052, USA.
Vision Res. 1996 Jul;36(14):2111-20. doi: 10.1016/0042-6989(95)00264-2.
Position judgements, which are exquisitely precise in the fovea, are markedly degraded in the periphery. In a recent article [Hess & Field (1993) Vision Research, 33, 2663-2670] argue that the poor representation of positional information in peripheral vision is a consequence of uncalibrated spatial disorder of cortical connections rather than due to undersampling of the retinal image. Specifically, Hess and Field argued that if positional uncertainty is due to undersampling, then because of univariance, there should be an associated contrast uncertainty. In this report we show that the univariance model is limited in its generality since: (1) the Hess and Field data in which contrast and position discrimination are decoupled do not preclude undersampling with large univariant filters: (2) aliasing can decouple position from contrast; (3) undersampling or noise at a second stage of processing can lead to selective losses of position information without any degradation of contrast information.
位置判断在中央凹处极为精确，但在周边区域则明显退化。在最近一篇文章中[赫斯和菲尔德（1993年）《视觉研究》，33卷，2663 - 2670页]认为，周边视觉中位置信息的不良表征是皮质连接未经校准的空间紊乱的结果，而非视网膜图像采样不足所致。具体而言，赫斯和菲尔德认为，如果位置不确定性是由于采样不足，那么由于单变量性，应该会有相关的对比度不确定性。在本报告中，我们表明单变量模型的普遍性有限，因为：（1）赫斯和菲尔德的数据中对比度和位置辨别解耦，并不排除使用大型单变量滤波器进行采样不足的情况；（2）混叠可以使位置与对比度解耦；（3）处理第二阶段的采样不足或噪声会导致位置信息的选择性丢失，而对比度信息不会有任何退化。
