Noest A J, van den Berg A V
Department of Medical and Physiological Physics, Utrecht University, The Netherlands.
Spat Vis. 1993;7(2):125-47. doi: 10.1163/156856893x00324.
Perceptual dissociation of moving plaid patterns into independently moving bar gratings occurs most readily when the grating signals are combined as if the bars were semi-transparent objects (Ramachandran, V. S. (1990) in: AI and the Eye. Wiley, Chichester, pp. 21-77. Stoner, G. R., Albright, T. D. and Ramachandran, V. S. (1990) Nature 344, 153-155). These and other examples of motion transparency are exploited to constrain the set of viable models for human motion processing. For example, one may exclude any fixed recombination of local motion signals into a plaid motion signal. Broad classes of linear and non-linear mechanisms for tracking blobs, corners, and other unambiguous plaid motion cues can also be ruled out because they fail to reproduce the experimental results even qualitatively. The shifting balance between the 'coherent plaid' and 'sliding gratings' percepts are attributed to processing stages before any integration or combination of local motion signals. The first essential stage is a roughly logarithmic nonlinearity before orientation filtering. In general, the resulting cross-products (at the intersections) code unambiguously for the true plaid motion vector, but these signals will be nulled for multiplicatively combined plaid components. Supporting evidence for this idea is obtained in our measurements of detection thresholds for the 'plaid' and 'sliding' percepts. The essential element of the second stage consists of 'end-stop' cells which detect the nullable intersection signal, and so produce a plaid-motion signal with the required characteristics. Finally, it is argued that the ecological role of the proposed mechanism lies in the ability to handle movement of patterned objects in lighting conditions dominated by complicated cast shadows.
当光栅信号组合起来就好像这些条纹是半透明物体时，移动的格子图案最容易被感知分离成独立移动的条形光栅（拉马钱德兰，V.S.（1990年），载于《人工智能与眼睛》。威利出版社，奇切斯特，第21 - 77页。斯托纳，G.R.，奥尔布赖特，T.D.和拉马钱德兰，V.S.（1990年），《自然》344卷，第153 - 155页）。这些以及其他运动透明度的例子被用来限制人类运动处理的可行模型集。例如，可以排除任何将局部运动信号固定重组为格子运动信号的情况。追踪斑点、角落和其他明确的格子运动线索的广泛线性和非线性机制类别也可以被排除，因为它们甚至在定性上都无法重现实验结果。“连贯格子”和“滑动光栅”感知之间变化的平衡归因于局部运动信号进行任何整合或组合之前的处理阶段。第一个关键阶段是在方向滤波之前的大致对数非线性。一般来说，由此产生的叉积（在交叉点处）明确编码真实的格子运动矢量，但对于相乘组合的格子分量，这些信号将为零。我们对“格子”和“滑动”感知的检测阈值测量获得了支持这一观点的证据。第二阶段的关键要素由检测可归零交叉信号的“终端停止”细胞组成，从而产生具有所需特性的格子运动信号。最后，有人认为所提出机制在生态方面的作用在于能够在由复杂投射阴影主导的光照条件下处理有图案物体的运动。
