When stuff gets old: Material surface characteristics and the visual perception of material change over time

Materials’ surfaces change over time due to chemical and physical processes. These processes can significantly alter a material’s visual appearance, yet we can recognise the material as the same. The present study examined the extent of changes the human visual system can detect in specific materials over time. Participants (N = 5) were shown images of different materials (Banana, Copper, Leaf) from an existing calibrated set of photographs. Participants indicated which image pair (of the 2 pairs shown) displayed the largest difference. Estimated perceptual scales showed that observers were able to rank the images of aged materials systematically. Next, we examined the role that global and local changes in material surface colour play in the perception of material change. We altered the information about colour and geometrical distribution in the images used in the first experiment, and participants repeated the task with the altered images. Our results showed significant differences between individual observers. Most importantly, participants’ ability to rank the images varied with material type. The leaf images were particularly affected by our alteration of the geometrical distribution. Together, our findings show the factors contributing to the perception of material change over time.