Abstract
Our visual experience often varies based on momentary thoughts and feelings. For example, when positive thoughts are invoked, visual objects may appear brighter. However, it remains unclear whether this phenomenological experience is driven by a genuine top-down modulation of brightness perception or by a mere response bias. To investigate this issue, here we use pupillometry as a more objective measure of perceived brightness. We asked participants to judge the brightness level of an iso-luminant gray color patch after evaluating the valence of a positive or negative word. We found that the gray color patch elicited greater pupillary light reflex and more frequent “bright” responses after observers evaluated the valence of a positive word. Furthermore, the pupillary light reflex effect was greater for words with more positive meanings. Collectively, the converging subject- and word-level findings suggest that the iso-luminant probe reliably looks brighter, manifested as larger pupil constriction, under positive thoughts. As pupillary light reflex is unlikely driven by voluntary control or response bias, these results suggest that positive concepts can genuinely modulate brightness perception.