Levi D M, Waugh S J, Beard B L
College of Optometry, University of Houston, TX 77204-6052.
Vision Res. 1994 Dec;34(24):3315-33. doi: 10.1016/0042-6989(94)90067-1.
We used a masking paradigm to uncover the properties of the mechanisms engaged by the amblyopic visual system for vernier acuity and line detection. Line vernier and line detection thresholds were measured in the presence of one-dimensional noise masks varying in orientation, spatial frequency content or contrast. Our results reveal that in both normal and amblyopic eyes, there is a bimodal orientation tuning function for vernier acuity, i.e. vernier acuity is most strongly masked by mask orientations approx. +/- 10 deg on either side of the target lines. In contrast, in both normal and amblyopic eyes, line detection is most strongly masked when the mask and line target have the same orientation. In the normal fovea, the spatial frequency tuning is bandpass, with a peak spatial frequency of about 10 c/deg. In the amblyopic eyes, the spatial tuning is similar in specificity; however the peak is shifted to lower spatial frequencies, suggesting a shift in the scale of spatial processing of line stimuli. For all of the amblyopic eyes, the increased line detection thresholds are approximately proportional to the shift in spatial scale. In anisometropic amblyopes, the (unmasked) vernier threshold is elevated in proportion to the shift in spatial scale; however in some amblyopes with constant strabismus the shift in spatial scale is not sufficient to account for the degraded vernier acuity. The "extra" increase in vernier thresholds associated with strabismus may be a consequence of a high degree of positional uncertainty which adds noise at a stage following the combination of filter responses.
我们采用了一种掩蔽范式来揭示弱视视觉系统用于游标视力和线条检测的机制特性。在存在一维噪声掩蔽的情况下测量线条游标和线条检测阈值，这些噪声掩蔽在方向、空间频率内容或对比度上有所不同。我们的结果表明，在正常眼和弱视眼中，游标视力都存在双峰方向调谐功能，即游标视力在目标线条两侧约±10度的掩蔽方向下被最强烈地掩蔽。相比之下，在正常眼和弱视眼中，当掩蔽和线条目标具有相同方向时，线条检测被最强烈地掩蔽。在正常中央凹中，空间频率调谐是带通的，峰值空间频率约为10周/度。在弱视眼中，空间调谐在特异性上相似；然而峰值向较低空间频率移动，这表明线条刺激的空间处理尺度发生了变化。对于所有弱视眼，线条检测阈值的增加大致与空间尺度的变化成比例。在屈光参差性弱视患者中，（未掩蔽的）游标阈值与空间尺度的变化成比例升高；然而在一些恒定性斜视性弱视患者中，空间尺度的变化不足以解释游标视力的下降。与斜视相关的游标阈值“额外”增加可能是高度位置不确定性的结果，这种不确定性在滤波器响应组合后的阶段增加了噪声。
