Maertens Marianne, Pollmann Stefan
New York University, NY, USA.
J Cogn Neurosci. 2007 Jan;19(1):91-101. doi: 10.1162/jocn.2007.19.1.91.
Our visual percepts are not fully determined by the physical stimulus input. That is why we perceive crisp bounding contours even in the absence of luminance-defined borders in visual illusions such as the Kanizsa figure. It is important to understand which neural processes are involved in creating these artificial visual experiences because this might tell us how we perceive coherent objects in natural scenes, which are characterized by mutual overlap. We have already shown using functional magnetic resonance imaging [Maertens, M., & Pollmann, S. fMRI reveals a common neural substrate of illusory and real contours in v1 after perceptual learning. Journal of Cognitive Neuroscience, 17, 1553-1564, 2005] that neurons in the primary visual cortex (V1) respond to these stimuli. Here we provide support for the hypothesis that V1 is obligatory for the discrimination of the curvature of illusory contours. We presented illusory contours across the portion of the visual field corresponding to the physiological "blind spot." Four observers were extensively trained and asked to discriminate fine curvature differences in these illusory contours. A distinct performance drop (increased errors and response latencies) was observed when illusory contours traversed the blind spot compared to when they were presented in the "normal" contralateral visual field at the same eccentricity. We attribute this specific performance deficit to the failure to build up a representation of the illusory contour in the absence of a cortical representation of the "blind spot" within V1. The current results substantiate the assumption that neural activity in area V1 is closely related to our phenomenal experience of illusory contours in particular, and to the construction of our subjective percepts in general.
我们的视觉感知并非完全由物理刺激输入所决定。这就是为什么即便在诸如卡尼兹三角错觉图这类视觉错觉中不存在由亮度定义的边界时，我们仍能感知到清晰的边界轮廓。理解哪些神经过程参与创造这些人为的视觉体验很重要，因为这或许能告诉我们在自然场景中是如何感知连贯物体的，自然场景的特征是物体相互重叠。我们已经通过功能磁共振成像研究表明[Maertens, M., & Pollmann, S. fMRI揭示知觉学习后V1区中虚幻轮廓和真实轮廓的共同神经基础。《认知神经科学杂志》，17, 1553 - 1564, 2005]，初级视觉皮层（V1）中的神经元会对这些刺激做出反应。在此，我们为“V1区对于辨别虚幻轮廓的曲率是必不可少的”这一假说提供支持。我们在对应生理“盲点”的视野部分呈现虚幻轮廓。对四名观察者进行了广泛训练，并要求他们辨别这些虚幻轮廓中的细微曲率差异。与在相同偏心率下将虚幻轮廓呈现于“正常”对侧视野相比，当虚幻轮廓穿过盲点时，观察到明显的表现下降（错误增加和反应潜伏期延长）。我们将这种特定的表现缺陷归因于在V1区内缺乏“盲点”的皮层表征时无法构建虚幻轮廓的表征。当前结果证实了这样一种假设，即V1区的神经活动尤其与我们对虚幻轮廓的现象体验密切相关，并且总体上与我们主观感知的构建密切相关。
