Seifert Matthew, Hock Howard S
Department of Psychology, Florida Atlantic University, Boca Raton, FL, USA.
Department of Psychology, Florida Atlantic University, Boca Raton, FL, USA; Center for Complex Systems and Brain Sciences, Florida Atlantic University, Boca Raton, FL, USA.
Vision Res. 2014 May;98:61-71. doi: 10.1016/j.visres.2014.03.006. Epub 2014 Mar 21.
Motion perception is determined by changing patterns of neural activation initiated by spatiotemporal changes in stimulus features. Motion specified by 1st-order motion energy entails neural patterns that are initiated by spatiotemporal changes in luminance, whereas motion specified by counterchange entails oppositely signed changes in neural activation that can be initiated by spatiotemporal changes in any feature. A constraint in furthering this distinction is that motion energy and counterchange are co-specified by most visual stimuli. In the current study, counterchange was isolated for stimuli composed of translating subjective (Kanizsa) squares, surfaces created by the visual system. Motion energy was isolated for stimuli composed of sequences of luminance increments that spread across perceptually stationary, literal surfaces. Counterchange-specified motion was perceived over a wide range of frame durations, and preferentially for short motion paths. Motion specified by motion energy was diminished for relatively long frame durations, and was unaffected by the length of the motion path. Finally, it was found that blank inter-frame intervals can restore counterchange-specified motion perception for frame durations that are otherwise too brief for motion to be perceived. The results of these and earlier experiments suggest that 1st-order motion energy mechanisms, dedicated to the detection of changes in neural activation initiated by spatiotemporal changes in luminance, provide the basis for objectless motion perception (Wertheimer's phi motion). In contrast, counterchanging neural activation initiated by spatiotemporal changes in any feature, including features created by the visual system, provides a flexible basis for the perception of object motion (Wertheimer's beta motion).
运动感知由刺激特征的时空变化引发的神经激活模式的变化所决定。由一阶运动能量指定的运动需要由亮度的时空变化引发的神经模式，而由对比变化指定的运动则需要神经激活中具有相反符号的变化，这些变化可由任何特征的时空变化引发。进一步区分这两者的一个限制是，大多数视觉刺激同时指定了运动能量和对比变化。在当前的研究中，对于由平移的主观（卡尼萨）方块组成的刺激，即视觉系统创建的表面，分离出了对比变化。对于由亮度增量序列组成的刺激，这些序列分布在感知上静止的真实表面上，分离出了运动能量。由对比变化指定的运动在很宽的帧持续时间范围内都能被感知，并且在短运动路径上更受青睐。由运动能量指定的运动在相对较长的帧持续时间内会减弱，并且不受运动路径长度的影响。最后，研究发现空白的帧间间隔可以恢复由对比变化指定的运动感知，对于那些否则太短而无法感知运动的帧持续时间。这些以及早期实验的结果表明，一阶运动能量机制专门用于检测由亮度的时空变化引发的神经激活变化，为无物体运动感知（韦特海默的φ运动）提供了基础。相比之下，由任何特征（包括视觉系统创建的特征）的时空变化引发的对比神经激活，为物体运动感知（韦特海默的β运动）提供了灵活的基础。
