Nawrot Mark, Stroyan Keith
Center for Visual Neuroscience, Department of Psychology, North Dakota State University, Fargo, ND 58108, USA.
Vision Res. 2012 Apr 15;59:64-71. doi: 10.1016/j.visres.2012.02.007. Epub 2012 Mar 1.
The perception of depth from relative motion is believed to be a slow process that "builds-up" over a period of observation. However, in the case of motion parallax, the potential accuracy of the depth estimate suffers as the observer translates during the viewing period. Our recent quantitative model for the perception of depth from motion parallax proposes that relative object depth (d) can be determined from retinal image motion (dθ/dt), pursuit eye movement (dα/dt), and fixation distance (f) by the formula: d/f≈dθ/dα. Given the model's dynamics, it is important to know the integration time required by the visual system to recover dα and dθ, and then estimate d. Knowing the minimum integration time reveals the incumbent error in this process. A depth-phase discrimination task was used to determine the time necessary to perceive depth-sign from motion parallax. Observers remained stationary and viewed a briefly translating random-dot motion parallax stimulus. Stimulus duration varied between trials. Fixation on the translating stimulus was monitored and enforced with an eye-tracker. The study found that relative depth discrimination can be performed with presentations as brief as 16.6 ms, with only two stimulus frames providing both retinal image motion and the stimulus window motion for pursuit (mean range=16.6-33.2 ms). This was found for conditions in which, prior to stimulus presentation, the eye was engaged in ongoing pursuit or the eye was stationary. A large high-contrast masking stimulus disrupted depth-discrimination for stimulus presentations less than 70-75 ms in both pursuit and stationary conditions. This interval might be linked to ocular-following response eye-movement latencies. We conclude that neural mechanisms serving depth from motion parallax generate a depth estimate much more quickly than previously believed. We propose that additional sluggishness might be due to the visual system's attempt to determine the maximum dθ/dα ratio for a selection of points on a complicated stimulus.
从相对运动中感知深度被认为是一个缓慢的过程，它会在一段时间的观察中“积累”起来。然而，在运动视差的情况下，由于观察者在观察期间进行平移，深度估计的潜在准确性会受到影响。我们最近提出的关于从运动视差中感知深度的定量模型表明，相对物体深度（d）可以通过视网膜图像运动（dθ/dt）、追踪眼球运动（dα/dt）和注视距离（f），利用公式d/f≈dθ/dα来确定。鉴于该模型的动态特性，了解视觉系统恢复dα和dθ并进而估计d所需的积分时间非常重要。了解最小积分时间可以揭示这一过程中存在的误差。我们使用了一项深度相位辨别任务来确定从运动视差中感知深度信号所需的时间。观察者保持静止，观看一个短暂平移的随机点运动视差刺激。每次试验中刺激持续时间不同。使用眼动仪监测并强制观察者注视平移刺激。研究发现，相对深度辨别可以在短至16.6毫秒的呈现时间内完成，仅两个刺激帧就能同时提供视网膜图像运动和用于追踪的刺激窗口运动（平均范围 = 16.6 - 33.2毫秒）。在刺激呈现之前眼睛处于持续追踪状态或眼睛静止的条件下均发现了这一结果。在追踪和静止条件下，一个大的高对比度掩蔽刺激会干扰持续时间小于70 - 75毫秒的刺激呈现的深度辨别。这个时间间隔可能与眼球跟随反应的眼动潜伏期有关。我们得出结论，用于从运动视差中感知深度的神经机制生成深度估计的速度比之前认为的要快得多。我们提出，额外的迟缓可能是由于视觉系统试图为复杂刺激上的一组点确定最大dθ/dα比率。
