There is a complex functional adaptation in humans for recognizing human faces- to function, we need to be able to tell each other apart. Faces seem so natural to us that we forget how tiny the differences we’re detecting are. The difference between the facial expressions for “happy” and “angry” is less than two centimeters, yet most people can detect these expressions from over five meters away. People without this adaptation have to use their general image-processing machinery for faces; “identifying a person” falls into the same mental category as “identifying a sheep”. Most of us couldn’t keep track of one specific sheep even if we had to. It would certainly be much harder than keeping track of one specific person, or even one specific car- sheep just all look alike.
The information required, in terms of entropy or Kolmogorov complexity, to specify a facial expression is roughly the same for humans, sheep, and most other mammals. Sheep faces, for the most part, act like human faces- they have the same basic layout and are deformed in the same manner. The input to the brain is similar in both cases. The difference in perception arises when the information is processed; the sheep-face information just gets thrown on the garbage heap, while the human-face information is relayed to other systems. Even if your frontal cortex knows you are supposed to remember this particular sheep, the message isn’t automatically relayed to the rest of the brain. The visual cortex evolved in an environment where you couldn’t make conscious decisions, so the only built-in way to adapt to new tasks was Pavlovian conditioning- if you see the sheep over and over again, it’s probably important. Because conscious decision-making is so new, this limitation applies to most of our brain functions; you can’t just decide to make your memories of “playing a game” or “researching relativity” available, you have to train yourself.
Once you have enough training for a basic familiarity with something, your brain will start to dissect it into its component building blocks. These building blocks are not necessarily physical; they are made up of the concepts that associate to our memories. A car, once you first encounter it, may be just “a thing that takes people places”; as you gain more experience, you associate it to smaller-scale concepts like “gasoline” and “exhaust”, as well as larger-scale concepts like “traffic jam” and “rules of the road”. The things we think about in our everyday life- the things we are most familiar with- may have hundreds of different building blocks, all stored in our subconscious ready for use. If you light up a map of thingspace with the stuff we think about in our everyday lives, the stuff that glows most brightly will bleed into adjacent regions. I, personally, have never seen a car that makes toast, but I can easily imagine one by stacking “toaster” on top of “car”, inserting a toaster into the list of other car building-blocks like “dashboard” and “cup holder”. But if you try to stack two new concepts, like “tangent vectors” and “directional derivatives”, you run into a roadblock- you haven’t built up the network of associations up yet, and so the ways in which they are connected are still hidden and non-obvious.
Following the inference chain backwards, there should be a strong correlation between how much detail we observe (or, equivalently, how much variability there is in the category, or how many bits of information we process) and how closely something is related to our everyday life. Most of us see cars every day, and so we can readily distinguish between a Ford and a Ferrari. When we see a car, we instantly notice what color it is, what condition it’s in, how many people it seats, roughly what the mass is, and how much it would cost to buy. Trains, a much less frequent mode of transportation, have fewer details attached; I’d only know the mass of a train, or how many people it sits, or how powerful the engine is to within an order of magnitude, even if I studied it for a few minutes. When you get to totally obsolescent forms of travel, such as the horse-and-buggy, you don’t pick up any details at all- I have no clue what the defining characteristics of a particular horse-and-buggy setup are, they all look the same. Remember, though, that the variation is there regardless of whether you perceive it. People had ways of telling horse-and-buggy setups apart back in the olden days, but if you rattled them off to me, I’d instantly forget them; it would just bounce off a brick wall, as if you were describing the intricacies of a particular can of garbage.