10 December 2015
Ana Radonjić: Research Study Presentation on Color Constancy
On Thursday, December 10, 2015 Dr. Ana Radonjić, a Research Associate at the University of Pennsylvania discussed her research on the mechanisms underlying color and lightness constancy using naturalistic stimuli and tasks. It is known that color enables us to judge certain properties of an object. When we look at an object, color from that object is reflected and is projected towards the eye. The surface color of the object reflects some colors, and absorbs all of the rest, hence why we we are only able to perceive the colors that are reflected. Dr. Radonjić spoke of her work on how color guides selection in real-life tasks, as we often choose objects based on their color across a change in illumination (Radonjić, 2015).
There are two different types of photoreceptors located within the retina of the eye, rods which enable us to distinguish between light and dark, and cones which allow us to see color. When the perceived stimulus enters the visual field, the photoreceptors within the eye transduce the sensed stimulus into an electrical signal. The electric signal is directed from the optic nerve to the brain, where a more detailed version of the presented stimulus is perceived. The surface reflectants determine the objects color, however, reflected light is ambiguous in nature.
According to Dr. Radonjić, color is a proxy for achieving a goal. When we are faced with a task of choosing between a fresh piece of salmon and a spoiled piece of salmon, despite being able to smell the difference, we are able to visualize it as well. Color plays in a vital role in our everyday life tasks whether we know it or not. To validate this claim Dr. Radonjić asked subjects to recreate the arrangement of blocks shown in the room on the left, as closely as possible, by replacing the four black blocks shown in the middle room with the blocks chosen from the room on the far right (Figure 1). Subjects were asked to perform this task under a change in illumination. Dr. Radonjić found that similar to real-world tasks, subjects more often than not use the color of the blocks to recreate the arrangement, even though it is never explicitly referred to the subjects prior to performing the task. Dr. Radonjić’s findings suggest that as humans we use color constancy when performing naturalistic tasks (Radonjić et al., 2015).
Overall, I thought that Dr. Radonjić did a fantastic job presenting her research and proved herself to be well versed in the mechanisms of the visual system and how color is perceived. From her talk I learned how reliant upon color and consistent illumination we are as humans. Our visual system is dependent upon perception, however, our cognitive style differences and varying ratios of photoreceptors enable us all to see color differently.
Figure 1: Arrangement of Dr. Radonjić’s block copying task used to analyze color constancy in during naturalistic tasks .
Figure 1. (2015). Retrieved from http://www.sas.upenn.edu/~radonjic/research.html
Radonjić, A. (2015, December 10). Color Selection and Color Constancy. Lecture presented at
Research Presentation for the Faculty Position in Social Cultural in Life Sciences Center Room 134, Hartford, CT.
Radonjic, A., Cottaris, N., & Brainard, D. (2015). Color constancy in a
naturalistic, goal-directed task. Journal of Vision, 15, 3-3.