Cristina Menchaca 2007-49018

Favorite colors are so not a human thing.

Well, they're not exclusively human.

Two years ago, Wells, McDonald and Ringland conducted experiments to determine the color preferences of two species of ape (Gorilla gorilla gorilla and Pan troglodytes). Color affects us humans in many ways. it can affect our moods and physiological reactions, cognitive functioning, and emotional well-being. We even favor colors. Cool colors, such as blue, green and violet, promote tranquility and calm, increase our intention to purchase things, and improve performance in computer-based challenges. Warm colors, such as yellow, red and orange, on the other hand, are what we perceive less positively. They heighten arousal, stress, excitement, and in terms of competition, increase strength and result in better performances in sports. Animals have also been shown to have color preferences, and in many cases, similar to us humans. Moths, bumblebees and robins have a preference for the color blue, while chickens, pigeons and mice have been shown to be aversive to the color red.

Now what about the apes? Just like humans, apes and Old World monkeys have a trichromatic color vision. There has been much debate on the origins of this visual trait, evolutionary speaking. The most likely answer is the combination of two suggestions: first, the ability to discriminate between red and green allowed for a detection of food from afar (discriminating fruit from leaves). Once this was developed, it drove the evolution of red skin and hair, because of sexual selection. This has to do with the second suggestion (or the second part of combined explanation), which has to do with communication in a sociosexual context. Rhesus macaques, for example, have been found to be more attracted to the opposite sex if their anatomical features (male face, female hindquarters), were digitally manipulated to be a redder version.

Few research has been done on determining color preferences of primates. Rhesus macaques have been found to prefer blue over red lighting, and orangutans have been found to prefer colored than non-colored food. The researchers thus sought to explore color preferences of monkeys and gorillas, mostly because of their similar visual system to us humans. It is possible then, that they perceive things just as we do, maybe even react to colors, and prefer colors, like we do.

A total of 12 apes were involved in the study, six gorillas (three males, three females) and six chimps (two males, four females). The apes were shown three types of stimuli: cotton cloths, cardboard boxes, and transparent sheets of acetate. Each stimulus was available in the color red, blue or green (colors that hominoids can perceive). Colors for each stimulus varied slightly in brightness and saturation between the three types of stimuli but this was not a conspicuous difference. The stimuli were also notably chosen for safety and health reasons, ease of availability, and for long-term use in the zoo environment. The two species of ape experienced similar conditions in the zoo: housing, cleaning, viewing, mealtimes, etc.

Each animal was exposed to a series of five preference tests per stimulus. Fresh stimuli were always used on each day of testing. Each stimulus was presented for five separate days, with a control period (no exposure to any stimulus) of two days between each stimulus. A Latin square design was used to randomize the order of presentation of the stimuli among the animals so that an order effect could be avoided. Color preferences were assessed by recording the amount of interest directed at the stimulus (touching the box or cloth, or looking at the acetate sheets). The animals were observed unobtrusively and from different points of view. Finally, all animals were studied at the exact same time of day. The two groups were tested on separate days, each observed by one researcher. A pretest was made so that interrupter reliability could be obtained among the two (and it was a 100% agreement). During the study itself, the primary researcher would make periodic checks between the two researchers to ensure reliable recording of data. Although the two species of ape do not make use of color as cues in sexual signaling, detection of red and yellow fruit made the researchers hypothesize that red would be more biologically relevant to the apes.

Data was analyzed in terms of the two groups separate or combined. Researchers also analyzed the stimuli separately and together. Tests were also conducted to see if preferences were correlated with sex. Overall, the gorillas and chimpanzees showed a significant evidence for color preferences. Whether analyzed by species or as a group, red was given a less amount of preference compared to green and blue, no matter what stimulus was used. Green and blue had no significant differences, and sex of the ape had no significant effect on color preference either. This study is similar to the finding on the preference of rhesus macaques for blue more than red colored light. More interestingly, the study also shows that the color preferences of apes are similar to humans. As our closest living relatives, this could possibly tell us that we may, evolutionary speaking, be predisposed to prefer certain colors over others.

Why did the apes prefer blue and green over red if red is an important biological signal in nature (male dominance, sexual selection, food selection)? Perhaps it has to do with the type of stimulus. For example, in a natural environment, species of ape consume a substantial proportion of leaves, shrubs, and herbs, which consist of the cool colors. Thus, such colors would be more relevant to them. Perhaps it could have to do with the nature of the stimuli. Male rhesus macaques for example, look longer at reddened hindquarters of females, but not reddened faces. Maybe if the stimuli used were more biologically meaningful, a different result would have occurred. Finally, maybe it has to do with the aversion of animals to red. The aversion to red could be because dusk or dawn are times when predators are out, or because of other arousing stimuli such as fire or blood, or simply because bright colors like red and yellow act as warning signals. Red has been shown to have to do with dominance, superiority, and threat.

Why no difference between green and blue? Perhaps such similar reactions are because both are colors are for similar edibles found in the environment. It is suggested though, that more color contrasts be used for future study, so that possible explanations could be narrowed down. How about the lack of difference between sexes? Humans, after all, have been found to have a wide variety of individual differences when speaking of color. Females have a greater preference for red than males, adults have a stronger liking for green than kids, and introverts prefer darker colors more than extroverts. Considering the small sample size, it is still highly possible that differences in age, background, etc. of apes could cause individual differences for color preference.

Color has a big effect on humans to the point that color therapy is even being used in treating depression and anxiety. For all we know, color could have the same effect on animals, and finding out how color affects their moods may play a role in more "positive" (emotionally speaking) housing strategies, etc. For now, the study has shown that animals can indeed discriminate between color features in the environment. Also, not only do animals have preferences like we do, but our closest primate species actually prefer colors similar to our preferences. And so we ask, is there an innate relationship between color and physiological reaction? Does the exposure to specific colors translate to general psychophysical effects?

I found this study very interesting because it wasn't just a study on the perception of color but on the perception of color of animals. We've taken up a chapter on color recently after all, and it talked about how colors are not arbitrary but are created by our nervous systems. I thus felt that animals perceived things differently, and then was shocked to find out that our closest primates, the apes, also have a trichromatic color vision. Now I wonder how far this processing extends. I also wonder how researchers figured out the color vision of animals in the first place, when they don't talk. It's a humbling experience, realizing that we humans are similar to some types of animals, such as when perceiving color.

I liked that the study was well-planned out. Once again, I'm amazed with the fact that all the journal articles I've been encountering include studies that think of every single detail. The researchers made use of an unobtrusive viewpoint so that the responses of the animals would not be affected. They made use of different viewpoints while observing so that their data would be more holistic. They even conducted a pretest before the actual study, to make sure that one observer's data gathering would be the same as the other's. They also thought of making sure no order effects would get in the way of true scores, and they made sure to have "rest periods" in between stimuli. They also had a very specific way of taking note of the data (called the scan-sampling technique). Even their data analysis was very meticulous. They looked at the data in so many ways. Per species, as a whole, per stimulus, per color, based on sex. They also used different statistical tests to get results, including post hoc tests. I was seriously boggled with all the numbers and z's, d's, p's, x2's, etc.

I actually wondered why the researchers didn't consider other types of stimuli like yellow, orange, etc. I'm guessing that maybe they were playing it safe and trying not to avoid making assumptions. After all, color is indeed created by the nervous system. Even if they do see colors red, blue and green, maybe they see orange and other colors differently than we do. However, we can look at it another way. We're not trying to find out if they see other colors like we do after all, but which one they prefer most. My only suggestions for this study is to have more researches with a bigger sample, more hues per stimuli, and different natures of stimuli. A bigger sample would allow us to see if animals have any individual differences like we humans do when it comes to color preferences. We could also find out if background, such as captive born or wild born, would have any effect on their preferred colors, just as we have seen in other topics in class that experience-dependent plasticity has an effect on things we perceive quicker. The question then would be, would they prefer something they are used to seeing, or something novel but not used to perceiving? Of course, a bigger sample would also allow us to compare across age. I also recommend looking at different hues of the colors red, blue and green, so that we can be more sure of the generalizability of results. Also, make use of other colors, and make use of other types of stimuli. After all, just as was brought up when we discussed grandmother cells, it is possible that the stimuli were so limited that results were 'clumped together'. What if, when we use different hues, we find out that their preference for blue or green was only for some stimuli? What if, when we use another type of stimuli, they end up preferring another color? Finally, maybe after such studies, researchers can also look into other animals. Then we can find out how far back in evolution trichromatic color vision goes.

There is still so much that can be manipulated for us to be sure of the results and to be more confident in narrowing down our explanations behind the origin of color and other things. Still, I'm impressed with what this study has brought about. It makes us ask more questions, sure, but how exciting is it to find out that we humans aren't alone when it comes to our color processing, and that other animals have trichromatic color vision too? How far does it extend? What ideas can we extrapolate from such a find? What's interesting about this study is that it doesn't just look at psychophysical properties of color for humans and animals, but it's also intertwined with evolution, origins, and our similarities with other species.

Source:

Wells, D., McDonald, C., & Ringland, J. (2008). Color preferences in gorillas (Gorilla gorilla gorilla) and chimpanzees (Pan troglodytes). Journal of Comparative Psychology,122(2), 213-219.