Ruff Douglas A, Brainard David H, Cohen Marlene R
Department of Neuroscience and Center for the Neural Basis of Cognition, University of Pittsburgh , Pittsburgh, Pennsylvania.
Department of Psychology, University of Pennsylvania , Philadelphia, Pennsylvania.
J Neurophysiol. 2018 Nov 1;120(5):2296-2310. doi: 10.1152/jn.00906.2017. Epub 2018 Aug 15.
The way that humans and animals perceive the lightness of an object depends on its physical luminance as well as its surrounding context. While neuronal responses throughout the visual pathway are modulated by context, the relationship between neuronal responses and lightness perception is poorly understood. We searched for a neuronal mechanism of lightness by recording responses of neuronal populations in monkey primary visual cortex (V1) and area V4 to stimuli that produce a lightness illusion in humans, in which the lightness of a disk depends on the context in which it is embedded. We found that the way individual units encode the luminance (or equivalently for our stimuli, contrast) of the disk and its context is extremely heterogeneous. This motivated us to ask whether the population representation in either V1 or V4 satisfies three criteria: 1) disk luminance is represented with high fidelity, 2) the context surrounding the disk is also represented, and 3) the representations of disk luminance and context interact to create a representation of lightness that depends on these factors in a manner consistent with human psychophysical judgments of disk lightness. We found that populations of units in both V1 and V4 fulfill the first two criteria but that we cannot conclude that the two types of information in either area interact in a manner that clearly predicts human psychophysical measurements: the interpretation of our population measurements depends on how subsequent areas read out lightness from the population responses. NEW & NOTEWORTHY A core question in visual neuroscience is how the brain extracts stable representations of object properties from the retinal image. We searched for a neuronal mechanism of lightness perception by determining whether the responses of neuronal populations in primary visual cortex and area V4 could account for a lightness illusion measured using human psychophysics. Our results suggest that comparing psychophysics with population recordings will yield insight into neuronal mechanisms underlying a variety of perceptual phenomena.
人类和动物感知物体亮度的方式取决于其物理亮度以及周围环境。虽然整个视觉通路中的神经元反应会受到环境的调节，但神经元反应与亮度感知之间的关系却鲜为人知。我们通过记录猴子初级视觉皮层（V1）和V4区域中神经元群体对在人类中产生亮度错觉的刺激的反应，来寻找亮度的神经元机制，在这种错觉中，圆盘的亮度取决于其所处的环境。我们发现，单个神经元编码圆盘及其环境的亮度（或者对于我们的刺激来说，对比度）的方式极其多样。这促使我们思考V1或V4区域中的群体表征是否满足三个标准：1）圆盘亮度被高保真地表征；2）圆盘周围的环境也被表征；3）圆盘亮度和环境的表征相互作用，以产生一种亮度表征，这种表征以一种与人类对圆盘亮度的心理物理学判断一致的方式依赖于这些因素。我们发现，V1和V4区域中的神经元群体都满足前两个标准，但我们不能得出这两个区域中的两种信息以一种能清晰预测人类心理物理学测量结果的方式相互作用的结论：我们对群体测量结果的解释取决于后续区域如何从群体反应中读出亮度。新内容及值得注意之处视觉神经科学中的一个核心问题是大脑如何从视网膜图像中提取物体属性的稳定表征。我们通过确定初级视觉皮层和V4区域中神经元群体的反应是否能解释使用人类心理物理学测量的亮度错觉，来寻找亮度感知的神经元机制。我们的结果表明，将心理物理学与群体记录进行比较将有助于深入了解各种感知现象背后的神经元机制。
