fine distinctions

Human sensory systems are amazingly powerful at detecting differences. Many studies have show our senses operate near the limit of what is physically possible.  The "just noticeable difference" for many parameters is incredibly small. Overall, the performance of our senses is superb and much better than would be expected from the inherently noisy components that make up our bodies.

For complex stimuli our performance is often so good that it is hard or near impossible to match with sophisticated instruments and computing devices. When so-called pattern recognition is involved, humans beat every system that is out there today. One could say biology is exquisitely sensitive.

Yet there is something humans are not very good at, and that is absolute measurements. Some will call these "objective" measurements. It is rather easy even for untrained individuals to tell you which of two objects is heavier, or which of two sounds is louder, or whether two foods taste the same, or two perfumes smell alike. But it is very hard even for well trained individuals to tell you how heavy something is, how bright the light is, how loud the sound is, or what the pitch is.

One reason for this discrepancy is adaptation. Much like everything else, our sensory systems adapt to stimuli. Even though we can detect a few molecules that foul up a room full of air, if we stay in a smelly room for a short time we don't notice the offending smell anymore. If the first sunlight is too bright in the morning, soon we move around comfortably in light that is a few orders of magnitude brighter. If background noise stays constant, we tune it out. And if we suddenly go somewhere quiet, the absence of noise may create a strange "loudness" sensation.

Thresholds also adjust with internal states. When we are hungry the smell of food will be stronger and we are more likely to see the food items in a complex scene. If we are dehydrated, salty items will taste better. Studies have shown that messenger molecules released in our blood stream affect not just the threshold of our senses but also the interpretation of the stimuli. If one takes morphine painful stimuli will no longer be painful. If no help is forthcoming pain may become intolerable.

Adaptation is but one part of the process. The other part is context dependent understanding. Humans interpret stimuli in the context they are in. They set expectations and match new experiences to these expectations. If you eat from a big plate you will eat more. If you drink from a big cup you will drink more. And you will judge how much you ate or drank by what is left over. And if others are around you will unconsciously compare your performance to theirs.

There is evidence for imprinting or at the very least for very strong associative memories. Things that remind you of your childhood will often taste or smell better. Drinking water tests have revealed that individuals like water with additives that remind them of their childhood, even if such additives taste horrible to others. And to some extent, even if those additives are harmful. If a certain food makes us ill, the smell of it will cause nausea, sometimes for months to come.

All this shows why humans are very poor at objective judgments. And that is why you should be very suspicious of the "great experts." Experts in food, wine, and fine sound systems. Experts in anything that has to do with luxury life-style items. Every time such great experts are subjected to blinded tests, they fail miserably. While they may be able to detect differences, they cannot tell which is which. And that is exactly what we expect. Because the great experts are human too.