Attention modulates the effects of stimulus brightness and contrast on time perception.

The perception of duration is influenced by various factors, including attention and the physical properties of stimuli. However, the interaction between these factors remains poorly understood. The present study investigated how covert visual attention, stimulus brightness, and contrast jointly influence time perception using a novel attentional temporal bisection task. Participants categorized the duration of a cued target stimulus as "short" or "long" while the brightness and contrast (relative to background) of the target and a distractor stimulus were systematically manipulated. Results showed that high-contrast targets were perceived as lasting longer than low-contrast targets. Surprisingly, brighter targets were perceived as shorter than dimmer targets. At the unattended location, the effects of distractor contrast and brightness were the mirror image, such that targets were perceived as longer in the presence of bright distractors and (though not reliably) low-contrast distractors. Taken together, the findings point to local encoding effects at the target (contrast lengthens; higher target brightness shortens) and a modest decisional/context bias from the distractor, consistent with partial competition across locations. Findings further indicate that contrast, rather than absolute brightness, is the primary determinant of perceived duration, with its effects mediated by attention. This study provides novel insights into how bottom-up stimulus properties and top-down attention jointly influence temporal processing, highlighting the need for more nuanced models of time perception that account for the complex interplay between attention, brightness, and contrast. Finally, the counterintuitive finding that increasing brightness can shorten perceived duration challenges the notion of a monotonic relationship between stimulus intensity and perceived time.