We remember color patterns when we don't know we're doing it

Take a look at the image below. Your job is to find the T among the sea of Ls. If you're like most people it will take just a second or two.

Figure 1:

If you repeat this task several dozen times, each time with a new set of Ls and T in different colors, positions, and orientations, you'll get quicker at the task. Try this one -- again, look for the T.

Figure 2:

But what if a pattern was repeated later on? Would you remember it? Would you be quicker? Take a look at this figure; again, look for the T:

Figure 3:

Here, the pattern of colors is the same as in Figure 1, and the T is in the same location, but the orientation of the Ls and T is different. Most people are quicker finding the T in this case, even after seeing dozens of different pictures.

Liquan Huang showed sets of 24 pictures like this to volunteers. The first set was completely composed of new pictures, but after that, in each set 12 of the pictures were new and 12 followed the same color pattern as one of the pictures in the first set, but the orientation of the Ls and T were different, as in Figure 3 above. Here are the results:

So viewers gradually become faster at finding the T in cases where they've seen the same color pattern, even though the orientation of the letters is different every time.

But what is it about the colors that we remember? Are we remembering the location of the colors, or just the pattern formed by the colors? For example, in Figure 2, we might recall the fact that there's a backwards "L" formed by the three red Ls in the middle of the figure, and not remember the specific color. To test this possibility, Huang repeated the experiment where each letter could be displayed in any of hundreds of different colors, so that there was no possibility of distinct patterns involving particular colors. Viewers still found the T faster when they had seen the same color pattern before.

In another experiment, Huang repeated the initial task, but at the end specifically asked viewers whether they had seen each display before. Even though they located the T faster in previously-viewed figures, they did not accurately recall whether they had seen any given figure previously.

In further experiments, Huang found that hue and luminance differences could independently invoke the same effect.

Most fascinating is the fact that all of the memory phenomena in Huang's experiments are unconscious. Indeed, these unconscious memories are different from conscious visual memories, because in conscious memory, the location of an object and its surface properties are often processed independently, whereas here, the color and location of an object are processed simultaneously.

Huang, L. (2006). Contextual cuing based on the spatial arrangement of color. Perception & Psychophysics, 68(5), 792-799.