In my last post I started to explain why our perception of reality isn’t a faithful representation of the real world. If you haven’t already, go read that post to learn about how we only perceive a small part of the world, and what we do perceive is highly distorted.

This follow-up post discusses another way that our brains fool us: categorization. There are a lot of things in the world that lie along a continuous spectrum, like colors and sounds. Our brains tend to divide those things up into specific categories, which helps us make sense of them.

This may be useful, but it totally changes our perception of the world. We see things in black and white when the real world is shades of grey.

Seeing color

Let’s start with the example of color. As I mentioned last time, we perceive different wavelengths of light as different colors—from red with the longest wavelength (700 nm) to violet with the shortest (390 nm). Even though different wavelengths of light vary along a continuous spectrum, we define specific categories of wavelengths as distinct colors, like red, orange, yellow, green, blue, and violet.

 

These boundaries between colors are arbitrary divisions that humans have made up. And we don’t always agree where they are, which you’ve probably noticed if you’ve argued with someone about whether your new t-shirt is actually blue or green. But it’s all just semantics, right?

Turns out, no. The way we categorize and name colors actually affects how we see them.

Here’s the experiment: ask people to distinguish a pair of colors that differ by a fixed amount, say 20 nm. (Remember, different colors are just different wavelengths of light, so they can all be quantified as a number.) You’d think our ability to distinguish two colors simply depends on how far apart they are in the color spectrum. If they’re farther apart, we can distinguish them more easily. Red and yellow look way more different than red and reddish-orange.

It’s true that we can tell colors apart better if they’re farther apart on the spectrum, but this isn’t all that matters. We’re way better at distinguishing a pair of colors from different categories (like red vs. orange) than colors within the same category (like different shades of red)—even if they’re exactly the same distance apart on the spectrum.

This is really weird, guys. It’s like if you precisely measured out two different mile-long courses with exactly the same terrain, and then found that you could consistently run twice as fast on one of them.

What’s even more interesting is that different societies draw color boundaries at different places, and that affects how they perceive color. For example, there’s a stone-age tribe in Papua New Guinea called the Berinmo tribe that defines different color categories than English-speakers.

 

The Berinmo people do not draw an explicit boundary between blue and green, like we do, and studies have shown that they’re not as good as us at distinguishing colors from these two categories.

But the tribe does draw a clear boundary between two different types of green: “wor”, which is more yellow-green, vs. “nol”, more of a bluish green. And as you might expect, the tribespeople do better than us at distinguishing colors from these two green categories.

All of this means that our perception of colors, which are well-defined features of light that can be precisely quantified by their wavelength, is totally subjective.

Instead of faithfully telling you which wavelength of light you’re seeing, your brain categorizes that wavelength into a group with a specific name. Your brain lumps different hues of red together in the same group, making it harder for you to tell which is which, even though your eyes are perfectly capable of doing so.

This isn’t some accident or flaw in our biology. This is your brain deciding (over millions of years of evolution) that distinguishing red and orange is important for your survival, but distinguishing different hues of red isn’t as important as knowing they’re all red. Everything is a tradeoff. Being better at telling things apart might make us worse at grouping them together.

Sound barriers

Your brain performs this kind of categorization for all of your senses, not just vision. It intentionally discards information in order to emphasize what’s most important.

Categorization in hearing, for example, is a critical part of understanding speech. There are plenty of sounds that gradually differ along a continuum, just like the light spectrum, but we learn to draw boundaries to separate them into distinct categories.

One example is the “ba” vs “pa” sound. You’re probably thinking that “ba” and “pa” sound totally different. But they’re actually very similar. They both involve opening your lips while vibrating your vocal cords. The only difference is that “ba” involves generating the vibration around the same time you open your lips or just after, while for “pa” you first open your lips and then wait slightly longer before vibrating your vocal cords. And by “slightly longer” I mean like one-twenthieth of a second.

(If you’re sitting at your desk right now repeating the syllables “ba” and “pa” and hoping no one notices, I feel you.)

The longer the delay between your lips opening and your vocal cord vibration, the more the syllable will sound like “pa” instead of “ba”. But we draw an arbitrary boundary right around 25 milliseconds. Any sound with a delay less than that sounds like a “ba”, no matter what the delay actually is, and any sound with a longer delay sounds like a “pa”.

Studies show that we’re really good at distinguishing between the two categories, but we’re terrible at distinguishing different “ba” or “pa” sounds within each category. We’ve lost the ability to keep track of what the sound actually sounds like in favor of just picking out what we need to know.

This is true for almost all sounds—they fall along some kind of spectrum, but we’ve created artificial boundaries to categorize them. And again, like with colors, different societies draw different boundaries, which make people actually perceive sounds differently.

That’s why native Japanese speakers often have trouble distinguishing “r” and “l”—a boundary that’s important in English, but not Japanese. Language differences also explain why most of my friends can’t understand why my parents’ native language, Telegu, has 16 vowels and 41 consonants—apparently a bunch of the sounds sound the same to non-native speakers.

Tasting the world

Let’s discuss one final example: taste. Taste is how we sense chemicals on our tongue. There are millions of chemical compounds in the world. Do you think our brains are capable of identifying and distinguishing all of those different chemicals?

Not even close. Lots of chemicals are tasteless, meaning they’re invisible to our sense of taste. And our brain categorizes the rest into just five groups: sweet, salty, savory, sour, and bitter.

Like many features of sensory systems, this is really strange when you think about it. It’s not like all the chemicals in the world naturally fall into these five groups. It’s just that these five categories represent types of chemicals that are critically important for us to either eat or avoid eating.

For example, sweet taste is the taste of various sugars, like sucrose and fructose. Sugars are a good energy source, so our nervous systems have evolved to detect sugar and perceive it as yummy, which entices us to eat it. (Usually too much of it, nowadays.)

Same for salt. Ingesting salts like sodium is critical for the function of various organs, including the brain, so we’ve evolved to find salt almost as yummy as sugar. That’s right, we’re basically hardwired to spend our nights binging on potato chips and ice cream.

Conversely, some chemicals are harmful to ingest—maybe even fatal. We’ve evolved so that these chemicals taste really bad, which discourages us from eating them. Most of these chemicals fall into the category of “bitter”. Bitter is kind of a catch-all taste that encompasses many different types of chemicals.

 

Most of these bitter chemicals are nothing alike in the real world. They have very different molecular structures and chemical properties. But we perceive them as being exactly the same: “bitter”. Yet again, our brains are arbitrarily lumping things together.

It’s not actually arbitrary, of course. The chemicals we lump together as “bitter” may be very different, but they have a similar meaning to our lives. They’re chemicals we need to avoid ingesting.

It’s like if you snooped around my childhood memorabilia box and found my random assortment of movie ticket stubs, high school musical programs, name badges from spelling bees, a leaf from the tree I studied for my 6^th grade science project, and a piece of the wooden board I successfully broke during my Taekwondo black belt test. These items have no similarity in the real world, but they’re grouped together because they share a common significance in my life.

That’s essentially what our brains are doing all the time—grouping and organizing things based on their relevance to our lives, not their intrinsic properties.

Creating order from chaos

So now you’ve seen myriad examples of how we lump things together that aren’t always that similar, and we draw boundaries between things that hardly differ at all. This means we aren’t perceiving the world as it really is. Our perception of reality is a construct of the brain.

But don’t be mad about it. Our brains are simply trying to collect and categorize the information that’s relevant for our survival. Sometimes this means distorting reality to make things simpler for us to recognize or understand. The world is a messy place, and your brain is doing the best it can to make sense of it.