Department of Neurobiology, Weizmann Institute of Science, Rehovot 76100, Israel; Gonda Multidisciplinary Brain Research Center, Bar-Ilan University, Ramat Gan 52900, Israel.
Department of Neurosurgery, Hofstra Northwell School of Medicine and Feinstein Institute for Medical Research, Manhasset, NY 11030, USA.
Curr Biol. 2017 Jan 23;27(2):155-165. doi: 10.1016/j.cub.2016.11.024. Epub 2016 Dec 29.
An inherent limitation of human visual system research stems from its reliance on highly controlled laboratory conditions. Visual processing in the real world differs substantially from such controlled conditions. In particular, during natural vision, we continuously sample the dynamic environment by variable eye movements that lead to inherent instability of the optical image. The neuronal mechanism by which human perception remains stable under these natural conditions remains unknown. Here, we examined a neural mechanism that may contribute to such stability, i.e., the extent to which neuronal responses remain invariant to oculomotor parameters and viewing conditions. To this end, we introduce an experimental paradigm in which intracranial brain activity, a video of the real-life visual scene, and free oculomotor behavior were simultaneously recorded in human patients. Our results reveal, in high-order visual areas, a remarkable level of neural invariance to the length of eye fixations and lack of evidence for a saccade-related neuronal signature. Thus, neuronal responses, while showing high selectivity to the category of visual images, manifested stable "iconic" dynamics. This property of invariance to fixation onset and duration emerged only in high-order visual representations. In early visual cortex, the fixation onset was accompanied with suppressive neural signal, and duration of neuronal responses was largely determined by the fixation times. These results uncover unique neuronal dynamics in high-order ventral stream visual areas that could play an important role in achieving perceptual stability, despite the drastic changes introduced by oculomotor behavior in real life.
人类视觉系统研究的一个固有局限性源于其对高度受控的实验室条件的依赖。现实世界中的视觉处理与这种受控条件有很大的不同。特别是在自然视觉中，我们通过可变的眼球运动不断地对动态环境进行采样，这导致光像的固有不稳定性。人类感知在这些自然条件下保持稳定的神经机制尚不清楚。在这里，我们研究了一种可能有助于这种稳定性的神经机制，即神经元反应对眼动参数和观察条件的不变程度。为此，我们引入了一种实验范式，在该范式中，同时记录了人类患者的颅内脑活动、现实生活视觉场景的视频和自由眼球运动行为。我们的结果揭示了在高级视觉区域中，神经元对注视长度具有显著的不变性，并且缺乏与扫视相关的神经元特征的证据。因此，神经元反应虽然对视觉图像的类别表现出高度选择性，但表现出稳定的“图标”动力学。这种对注视起始和持续时间不变性的特性仅出现在高级视觉表示中。在早期视觉皮层中，注视起始伴随着抑制性神经信号，而神经元反应的持续时间在很大程度上取决于注视时间。这些结果揭示了高级腹侧流视觉区域中独特的神经元动力学，这些动力学可能在实现感知稳定性方面发挥重要作用，尽管在现实生活中眼球运动行为会带来剧烈变化。
