Pupillary evidence reveals the influence of conceptual association on brightness perception

Our visual experience often varies based on momentary thoughts and feelings. For example, when positive concepts are invoked, visual objects may appear brighter (e.g., a "brighter" smile). 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, 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 "brighter" responses after observers had evaluated the valence of a positive word. As pupillary light reflex is unlikely driven by voluntary control, these results suggest that the conceptual association between affect and luminance can modulate brightness perception.