Dilating the pupils allow more quanta of light to impact the retina. Consequently, if one pupil is dilated with a pharmacological agent (Tropicamide), the brightness of a surface under observation should increase proportionally to the pupil dilation. Little is known about causal effects of changes in pupil size on perception of an object’s brightness. In a psychophysical procedure of brightness adjustment and matching, we presented to one eye geometrical patterns with a central square (the reference pattern) that differed in physical brightness within backgrounds of constant luminance. Subsequently, with the other eye, participants (n = 30) adjusted to the same luminance a similar pattern (target) whose central square luminance was randomly set higher or lower in brightness than the reference. As only one eye was treated with Tropicamide, we assessed whether the subjective brightness of the target square shifted in a consistent direction when viewed with the dilated pupil compared to the untreated (control) eye. We found that, as the pupil increased post drug administration, so significantly did the sense of brightness of the pattern (i.e., higher brightness adjustments followed viewing the reference pattern with the treated (Tropicamide) eye). A reversed effect was observed when the control eye viewed the reference pattern first. The results confirm that even slight pupil dilations can result in an enhanced perceptual experience of brightness of the attended object, corresponding to an average increase of 2.09 cd/m² for each 1 mm increase in pupil diameter.

扩张瞳孔可以让更多的光量子影响视网膜。因此，如果用药物（托吡卡胺）扩张一个瞳孔，被观察表面的亮度应与瞳孔扩张成正比。关于瞳孔大小变化对物体亮度感知的因果影响知之甚少。在亮度调整和匹配的心理物理学过程中，我们向一只眼睛呈现了具有中心正方形（参考图案）的几何图案，该图案在恒定亮度的背景下物理亮度不同。随后，用另一只眼睛，参与者 ( n = 30）将类似图案（目标）调整为相同的亮度，其中心正方形亮度随机设置为高于或低于参考的亮度。由于只有一只眼睛接受了托吡卡胺治疗，我们评估了与未治疗的（对照）眼睛相比，当用散瞳观察时，目标方块的主观亮度是否在一致的方向上移动。我们发现，随着给药后瞳孔增加，图案的亮度感也显着增加（即，在用治疗过的（托吡卡胺）眼睛观察参考图案后进行更高的亮度调整）。当对照眼睛首先查看参考图案时，观察到了相反的效果。结果证实，即使是轻微的瞳孔扩张也能增强对被照物体亮度的感知体验，瞳孔直径每增加 1 mm ²。