如果你在看完电影后走到阳光下，或是盯住一部照相机的闪光灯，这时你的瞳孔将会收缩。
日前，发表在美国《国家科学院院刊》（PNAS）网络版上的一项研究结果称，如果你仅仅是观看一个明亮物体的图像，也会出现同样的结果，即瞳孔也会收缩。
研究人员要求志愿者凝视一系列视觉错误图像——包括成圆圈向内排列的泪珠要比向外排的泪珠，在中心上看起来更亮一些（如图所示），随后测量这些受试者的瞳孔发生了哪些变化。
挪威奥斯陆大学的Bruno Laeng和Tor Endestad发现，物体看起来越亮，瞳孔收缩得也就越厉害。在最初的收缩之后，瞳孔会逐渐放大，以反射到达眼睛的实际数量的光线。
这一研究与之前的成果结合在一起，表明当观看一些吸引我们或让人感兴趣的事物时，我们的瞳孔会扩张，这意味着所谓的瞳孔光反射并不仅仅是一种下意识的反应（就像你的手会从热火炉上抽走一样）。相反，更高级的大脑功能的输入——例如负责解释我们所看到的事物——在其中也扮演了一个重要角色。（生物谷Bioon.com）
doi:10.1073/pnas.1118298109
PMC:
PMID:
Bright illusions reduce the eye's pupil
Laeng, Bruno; Endestad, Tor
We recorded by use of an infrared eye-tracker the pupil diameters of participants while they observed visual illusions of lightness or brightness. Four original illusions {based on Gaetano Kanisza's [Kanizsa G (1976) Subjective contours. Sci Am 234:48–52] and Akiyoshi Kitaoka's [Kitaoka A. (2005) Trick Eyes (Barnes & Noble, New Providence, NJ).] examples} were manipulated to obtain control conditions in which the perceived illusory luminance was either eliminated or reduced. All stimuli were equiluminant so that constrictions in pupillary size could not be ascribed to changes in light energy. We found that the pupillary diameter rapidly varied according to perceived brightness and lightness strength. Differences in local contrast information could be ruled out as an explanation because, in a second experiment, the observers maintained eye fixation in the center of the display; thus, differential stimulation of the fovea by local contrast changes could not be responsible for the pupillary differences. Hence, the most parsimonious explanation for the present findings is that pupillary responses to ambient light reflect the perceived brightness or lightness of the scene and not simply the amount of physical light energy entering the eye. Thus, the pupillary physiological response reflects the subjective perception of light and supports the idea that the brain's visual circuitry is shaped by visual experience with images and their possible sources.
