Task-dependent pupillary responses to glossiness and attractiveness judgments

Human pupillary responses are influenced by not only low-level visual properties but also cognitive and affective factors related to task demands. Nevertheless, how the temporal dynamics of pupil modulation differ across evaluative tasks in the context of material perception remains unclear. In this study, we investigated how pupillary responses vary when observers evaluate the same set of object images for either glossiness or attractiveness. These two perceptual attributes were selected to represent distinct cognitive demands: Glossiness is more closely related to lower-level visual processing, whereas attractiveness involves higher-level evaluative processing. The stimuli included 60 grayscale object photographs selected from the THINGS database, representing common real-world items without social or facial content. Low-level image statistics were controlled using histogram matching to equalize luminance and contrast across all the stimuli. Participants viewed each image for 3,000 ms while maintaining central fixation and rated its glossiness or attractiveness on a 7-point scale in separate task blocks. Grand-average waveforms revealed task-dependent modulations of pupil size across rating levels, which is consistent with previous reports that pupillary responses vary with evaluative context even for identical stimuli. Furthermore, temporal principal component analysis and generalized additive modeling revealed that higher glossiness ratings were associated with greater pupil constriction at early, light reflex-like latencies, whereas higher attractiveness ratings elicited greater pupil dilation at later time points. These findings suggest that distinct temporal profiles of pupil size reflect task-specific processing demands in material perception, which is potentially consistent with differences in temporal weighting between visual and affective evaluations.