Levi Dennis M, Klein Stanley A, Chen Inning
School of Optometry and Helen Wills Neuroscience Institute, UC Berkeley, Berkeley, CA 94720-2020, USA.
J Vis. 2008 Apr 4;8(4):1.1-23. doi: 10.1167/8.4.1.
Amblyopia results in a loss of visual acuity, contrast sensitivity, and position acuity. However, the nature of the neural losses is not yet fully understood. Here we report the results of experiments using noise to try to better understand the losses in amblyopia. Specifically, in one experiment we compared the performance of normal, amblyopic, and ideal observers for detecting a localized signal (a discrete frequency pattern or DFP) in fixed contrast white noise. In a second experiment, we used visibility-scaled noise and varied both the visibility of the noise (from 2 to 20 times the noise detection threshold) and the spatial frequency of the signal. Our results show a loss of efficiency for detection of known signals in noise that increases with the spatial frequency of the signal in observers with amblyopia. To determine whether the loss of efficiency was a consequence of a mismatched template, we derived classification images. We found that although the amblyopic observers' template was shifted to lower spatial frequencies, the shift was insufficient to account for their threshold elevation. Reduced efficiency in the amblyopic visual system may reflect a high level of internal noise, a poorly matched position template, or both. To analyze the type of internal noise we used an "N-pass" technique, in which observers performed the identical experiment N times (where N = 3 or 4). The amount of disagreement between the repeated trials enables us to parse the internal noise into random noise and consistent noise beyond that due to the poorly matched template. Our results show that the amblyopes' reduced efficiency for detecting signals in noise is explained in part by reduced template efficiency but to a greater extent by increased random internal noise. This loss is more or less independent of external noise contrast over a log unit range of external noise.
弱视会导致视力、对比敏感度和位置敏锐度的丧失。然而，神经损伤的本质尚未完全明了。在此，我们报告利用噪声进行实验的结果，以试图更好地理解弱视中的损伤情况。具体而言，在一项实验中，我们比较了正常观察者、弱视观察者和理想观察者在固定对比度白噪声中检测局部信号（离散频率图案或DFP）的表现。在第二项实验中，我们使用了可见度缩放噪声，并改变了噪声的可见度（从噪声检测阈值的2倍到20倍）以及信号的空间频率。我们的结果表明，在弱视观察者中，在噪声中检测已知信号的效率损失会随着信号的空间频率增加。为了确定效率损失是否是模板不匹配的结果，我们推导了分类图像。我们发现，虽然弱视观察者的模板向较低空间频率偏移，但这种偏移不足以解释他们的阈值升高。弱视视觉系统中效率的降低可能反映了高水平的内部噪声、位置模板匹配不佳，或两者皆有。为了分析内部噪声的类型，我们使用了一种“N次通过”技术，即观察者对相同实验进行N次（其中N = 3或4）。重复试验之间的不一致程度使我们能够将内部噪声解析为随机噪声和除模板匹配不佳导致的之外的一致噪声。我们的结果表明，弱视者在噪声中检测信号效率降低部分是由模板效率降低所致，但更大程度上是由随机内部噪声增加所致。在外部噪声的对数单位范围内，这种损失或多或少与外部噪声对比度无关。
