Abstract
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.