He S, MacLeod D I
Department of Psychology, University of California at San Diego, La Jolla 92093-0109, USA.
J Opt Soc Am A Opt Image Sci Vis. 1996 Jun;13(6):1139-51. doi: 10.1364/josaa.13.001139.
Contrast sensitivity for orientation discrimination is limited to spatial frequencies below 50-60 cycles per degree by neural spatial integration, and we find that contrast sensitivity, measured using an orientation-discrimination criterion, declines sharply with increasing spatial frequencies in that range. Yet interference fringe patterns pulsed at constant mean luminance can be detected at spatial frequencies far above that resolution limit [D.R. Williams, Vision Res. 25, 195 (1985)]. This is due at least in part to aliasing by the receptor mosaic, but another possible cue is provided by nonlinear distortion, which can create spatially uniform temporal transients when a pulsed fringe pattern is presented. We investigated the contribution of these spatially unstructured distortion products to grating detection by superimposing the pulsed fringe patterns on a randomly flickering uniform field. This manipulation has almost no effect on contrast sensitivity well below the resolution limit. Just above the resolution limit, however, the random luminance mask greatly elevates the fringe pattern detection threshold, suggesting that spatially unstructured cues provide the basis for detection in this range. At still higher fringe pattern frequencies, which approximately match the cone mosaic, the random luminance flicker again becomes ineffective for some observers, creating a clear secondary peak in contrast sensitivity in the flicker mask condition, which is presumably due to spatially structured cues provided by aliasing with the cone mosaic. The aliasing peak is still more clearly demarcated if the subject sets contrast thresholds for the perception of pattern as such. The contrast sensitivity function then has a notch or gap between the normal sensitivity range and the aliasing range. Apparently, in the unmasked case, spatially uniform cues (changes in overall color and brightness) bridge this gap.
通过神经空间整合，用于方向辨别时的对比度敏感度在空间频率低于每度50 - 60周波时受到限制，并且我们发现，使用方向辨别标准测量的对比度敏感度，在该范围内随着空间频率的增加而急剧下降。然而，以恒定平均亮度脉冲的干涉条纹图案在远高于该分辨率极限的空间频率下仍可被检测到[D.R. 威廉姆斯，《视觉研究》25, 195 (1985)]。这至少部分归因于感受器镶嵌的混叠效应，但非线性失真提供了另一种可能的线索，当呈现脉冲条纹图案时，它可以产生空间均匀的时间瞬变。我们通过将脉冲条纹图案叠加在随机闪烁的均匀场上来研究这些空间无结构失真产物对光栅检测的贡献。这种操作对远低于分辨率极限的对比度敏感度几乎没有影响。然而，就在分辨率极限之上，随机亮度掩模大大提高了条纹图案检测阈值，这表明空间无结构线索为此范围内的检测提供了基础。在更高的条纹图案频率下，其大致与视锥镶嵌匹配，对于一些观察者来说，随机亮度闪烁再次变得无效，在闪烁掩模条件下对比度敏感度中产生一个明显的次峰，这大概是由于与视锥镶嵌的混叠效应提供的空间有结构线索。如果受试者设置图案感知的对比度阈值，混叠峰将更加清晰地划分出来。此时对比度敏感度函数在正常敏感度范围和混叠范围之间有一个缺口或间隙。显然，在无掩模的情况下，空间均匀线索（整体颜色和亮度的变化）弥合了这个间隙。
