Glossiness perception and its pupillary response

Abstract

Recent studies have discovered that pupillary response changes depend on cognitive factors, such as subjective brightness caused by optical illusions and luminance. However, it remains unclear how the cognitive factor derived from the glossiness perception of object surfaces affects pupillary response. We investigated the relationship between glossiness perception and pupillary response through a gloss rating experiment that includes recording pupil diameter. For the stimuli, we prepared general object images (original) and randomized images (shuffled) that comprised of the same images with randomized small square regions. The image features were then controlled by matching the luminance histogram. The observers were asked to rate the perceived glossiness of the stimuli presented for 3,000 ms and changes in their pupil diameter were recorded. Consequently, if glossiness of the original images were rated as high, those of the shuffled were rated as low, and vice versa. High-gloss images constricted the pupil size more than the low-gloss ones near the pupillary light reflex. By contrast, the shuffled images dilated the pupil size more than the original image at a relatively later stage. These results suggest that local features comprising specular highlights involve the cognitive factor for pupil constriction, and this process is faster than pupil dilation derived from the inhibition of object recognition.