Michigan College of Optometry, Ferris State University, Big Rapids, Michigan.
Optom Vis Sci. 2022 Jul 1;99(7):547-559. doi: 10.1097/OPX.0000000000001907. Epub 2022 Apr 13.
Binocular summation is a sensitive metric of binocular integration. As such, characterization of the mechanisms underlying binocular summation is a key step in translating and applying this knowledge to abnormal binocular systems afflicted with strabismus and amblyopia.
Computational models of binocular summation have advocated the operation of mechanisms sensitive to the interocular phase disparity of first-order carrier gratings. This study investigated if such generalization depended on carrier spatial frequency and orientation.
Monocular and binocular contrast detection thresholds were measured in nine observers with normal binocular vision. Stimuli comprised Gabor targets presented with one of three spatial frequencies (1, 3, and 9 cycles per degree [cpd]), two orientations (horizontal and vertical), and five interocular phase disparities (0, ± π /2, ± π radians). Horizontal and vertical fixation disparities were measured for each binocular threshold condition. Binocular summation ratios were computed by dividing the mean monocular detection threshold by the respective binocular detection threshold.
Binocular summation ratio varied significantly with interocular phase disparity for the 1- and 3-cpd horizontal and vertical gratings. Phase dependency was reduced with the 9-cpd horizontal grating and absent for the 9-cpd vertical grating, even though binocular summation ratio exceeded predictions of probability summation. Computational modeling that incorporated the variability of fixation disparity into a vector summation model predicted a reduction in peak binocular summation ratio with increasing carrier spatial frequency but did not account for the reduction of phase sensitivity noted with the 9-cpd stimulus.
Binocular summation magnitude is less dependent on interocular phase disparities for carrier spatial frequencies that exceed 3 cpd, especially with vertical gratings. Although vergence variability due to fixation disparities contributes to the overall reduction in binocular summation magnitude with increasing carrier spatial frequency, it does not provide a complete account for the lack of interocular phase disparity tuning noted with high grating spatial frequencies.
双眼总和是双眼整合的一个敏感指标。因此，描述双眼总和背后的机制是将这一知识转化并应用于斜视和弱视等异常双眼系统的关键步骤。
双眼总和的计算模型提倡使用对一级载波光栅的眼间相位差敏感的机制。本研究探讨了这种泛化是否依赖于载波空间频率和方向。
在 9 名具有正常双眼视觉的观察者中测量了单眼和双眼对比检测阈值。刺激包括以 3 种空间频率（1、3 和 9 周/度）、2 种方位（水平和垂直）和 5 种眼间相位差（0、±π/2、±π 弧度）呈现的 Gabor 目标。对于每个双眼阈值条件，都测量了水平和垂直的双眼固视差异。双眼总和比通过将平均单眼检测阈值除以相应的双眼检测阈值来计算。
1- 和 3-cpd 水平和垂直光栅的双眼总和比随眼间相位差显著变化。相位依赖性随着 9-cpd 水平光栅而降低，并且即使双眼总和比超出了概率总和的预测，9-cpd 垂直光栅也不存在。将固视差异的可变性纳入向量总和模型的计算模型预测，随着载波空间频率的增加，峰值双眼总和比会降低，但无法解释在 9-cpd 刺激下观察到的相位敏感性降低。
对于超过 3 cpd 的载波空间频率，双眼总和的幅度对眼间相位差的依赖性较小，尤其是垂直光栅。尽管由于固视差异导致的聚散度变化会导致随着载波空间频率的增加，双眼总和幅度总体降低，但它不能完全解释在高光栅空间频率下观察到的眼间相位差调谐缺失。
