Desbordes Gaëlle, Rucci Michele
Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA.
Vis Neurosci. 2007 Mar-Apr;24(2):217-30. doi: 10.1017/S0952523807070460.
During visual fixation, small eye movements keep the retinal image continuously in motion. It is known that neurons in the visual system are sensitive to the spatiotemporal modulations of luminance resulting from this motion. In this study, we examined the influence of fixational eye movements on the statistics of neural activity in the macaque's retina during the brief intersaccadic periods of natural visual fixation. The responses of parvocellular (P) and magnocellular (M) ganglion cells in different regions of the visual field were modeled while their receptive fields scanned natural images following recorded traces of eye movements. Immediately after the onset of fixation, wide ensembles of coactive ganglion cells extended over several degrees of visual angle, both in the central and peripheral regions of the visual field. Following this initial pattern of activity, the covariance between the responses of pairs of P and M cells and the correlation between the responses of pairs of M cells dropped drastically during the course of fixation. Cell responses were completely uncorrelated by the end of a typical 300-ms fixation. This dynamic spatial decorrelation of retinal activity is a robust phenomenon independent of the specifics of the model. We show that it originates from the interaction of three factors: the statistics of natural scenes, the small amplitudes of fixational eye movements, and the temporal sensitivities of ganglion cells. These results support the hypothesis that fixational eye movements, by shaping the statistics of retinal activity, are an integral component of early visual representations.
在视觉注视过程中，微小的眼球运动使视网膜图像持续处于运动状态。已知视觉系统中的神经元对这种运动所导致的亮度时空调制敏感。在本研究中，我们考察了在自然视觉注视的短暂扫视间期，注视性眼球运动对猕猴视网膜神经活动统计特性的影响。当不同视野区域的小细胞（P）和大细胞（M）神经节细胞的感受野按照记录的眼动轨迹扫描自然图像时，对它们的反应进行了建模。注视开始后即刻，在视野的中央和周边区域，大量共同激活的神经节细胞集合扩展至数个视角范围。在这种初始活动模式之后，在注视过程中，P细胞对和M细胞对反应之间的协方差以及M细胞对反应之间的相关性急剧下降。在典型的300毫秒注视结束时，细胞反应完全不相关。视网膜活动的这种动态空间去相关是一种稳健的现象，与模型的具体细节无关。我们表明，它源于三个因素的相互作用：自然场景的统计特性、注视性眼球运动的小幅度以及神经节细胞的时间敏感性。这些结果支持了这样一种假说，即注视性眼球运动通过塑造视网膜活动的统计特性，是早期视觉表征的一个不可或缺的组成部分。
