Jackson Stuart, Cummins Fred, Brady Nuala
Cognitive Science, UCD School of Computer Science and Informatics, University College Dublin, Belfield, Dublin, Ireland, UK.
PLoS One. 2008;3(12):e3982. doi: 10.1371/journal.pone.0003982. Epub 2008 Dec 18.
Certain visual stimuli can give rise to contradictory perceptions. In this paper we examine the temporal dynamics of perceptual reversals experienced with biological motion, comparing these dynamics to those observed with other ambiguous structure from motion (SFM) stimuli. In our first experiment, naïve observers monitored perceptual alternations with an ambiguous rotating walker, a figure that randomly alternates between walking in clockwise (CW) and counter-clockwise (CCW) directions. While the number of reported reversals varied between observers, the observed dynamics (distribution of dominance durations, CW/CCW proportions) were comparable to those experienced with an ambiguous kinetic depth cylinder. In a second experiment, we compared reversal profiles with rotating and standard point-light walkers (i.e. non-rotating). Over multiple test repetitions, three out of four observers experienced consistently shorter mean percept durations with the rotating walker, suggesting that the added rotational component may speed up reversal rates with biomotion. For both stimuli, the drift in alternation rate across trial and across repetition was minimal. In our final experiment, we investigated whether reversals with the rotating walker and a non-biological object with similar global dimensions (rotating cuboid) occur at random phases of the rotation cycle. We found evidence that some observers experience peaks in the distribution of response locations that are relatively stable across sessions. Using control data, we discuss the role of eye movements in the development of these reversal patterns, and the related role of exogenous stimulus characteristics. In summary, we have demonstrated that the temporal dynamics of reversal with biological motion are similar to other forms of ambiguous SFM. We conclude that perceptual switching with biological motion is a robust bistable phenomenon.
某些视觉刺激会引发相互矛盾的感知。在本文中，我们研究了生物运动中感知反转的时间动态，并将这些动态与其他运动产生的模糊结构（SFM）刺激所观察到的动态进行比较。在我们的第一个实验中，未经训练的观察者监测一个模糊的旋转行走者的感知交替，这个图形会在顺时针（CW）和逆时针（CCW）方向行走之间随机交替。虽然报告的反转次数在观察者之间有所不同，但观察到的动态（优势持续时间的分布、CW/CCW比例）与一个模糊的动态深度圆柱体所经历的动态相当。在第二个实验中，我们比较了旋转和标准点光行走者（即非旋转）的反转特征。在多次测试重复中，四分之三的观察者在旋转行走者的情况下平均感知持续时间持续较短，这表明添加的旋转成分可能会加快生物运动的反转速率。对于这两种刺激，试验和重复过程中交替率的漂移都很小。在我们的最后一个实验中，我们研究了旋转行走者和具有相似整体尺寸的非生物物体（旋转长方体）的反转是否在旋转周期的随机阶段发生。我们发现有证据表明，一些观察者在反应位置的分布中经历了相对稳定的峰值。利用对照数据，我们讨论了眼动在这些反转模式形成中的作用，以及外源性刺激特征的相关作用。总之，我们已经证明生物运动反转的时间动态与其他形式的模糊SFM相似。我们得出结论，生物运动的感知切换是一种稳健的双稳态现象。
