This week, we were examinining color perception. We started out by testing our ability to discriminate between different hues. Both boys did well on this task!

The X-Rite Color Challenge
Kiosk Hue Test (we didn't do this one because of time constraints, but it's much harder!)

We learned about the two types of photoreceptors in the human retina: rods and cones (they actually look rod-like and cone-like). Humans have three different types of cones: one is sensitive to short wavelengths (blue-ish), one is sensitive to medium wavelengths (green-ish), and one is sensitive to long wavelengths (reddish). We covered opponent color theory, which suggests that cones are linked together to form three processing channels: one for blue vs. yellow, one for red vs. green, and one for black vs. white. Responses to one color in a channel inhibit responses to the other color in the same channel, which is why we don't see colors like reddish green or bluish yellow.

We explored afterimages, which are caused by overstimulation of photoreceptors. When photoreceptors adapt to overstimulation, they lose sensitivity (people use the analogy of cones getting "fatigued"). When a person is staring at a red square and then shifts their gaze to a white background, the cones that respond to red produce weaker signals than the cones that respond to blue and the cones that respond to green, which results in a cyan afterimage. The afterimage disappears when the cones recover.

We also learned about color constancy, which is the experience of perceiving the same color for objects even under different lighting conditions (e.g., sunny day vs. cloudy day). The visual system, when processing images, tries to take away the illumination (which it determines by registering the ranges of wavelengths of light reflected by objects in an image) to reveal the "true color", which is what we end up perceiving.

Here, because of color constancy, square A appears darker than square B when in fact they're both the same shade of gray. The boys covered up the squares and saw that they were in fact the same shade of gray.

We also talked about color blindness and examined how people with different types of color deficiencies see the world.

We ended by discussing how different cultures and languages label colors. English places red and pink into separate categories, but light green and dark green are considered to be part of the same category (green). In English, light blue and dark blue are in the same category, but Russian has different words for light blue and dark blue. Some other cultures like the Himba have very different color schemes. We'll discuss the influence of culture and language on cognition another time!