Doppelganger:
You can measure light waves or sound waves, but you cannot measure sound or color and there is no place that either sound or color itself exists outside of its perception.
You can measure color in the sense that you can measure the wavelength of light. You can measure sound in the sense that you can measure the vibration of air particles. In other words it is possible to detect colors and sounds using instruments. Cameras and microphones are good at these things.
"What instrument measures "taste" for example?"
Taste is a combination of sensory molecules on the tongue and in the nose. If one could build a machine sensitive to the molecules that our tongues and noses can detect, then you could reconstruct taste. Some progress has been made in this regard (e.g., the OLFACT).
I rather get the feeling, though, that you aren't really talking about color, sound, and taste as they are commonly defined, but as the subjective human perception of these things. I would put subjective human perceptions in the same category as concepts: they are constructions of the mind that don't have any direct physical manifestation. In fact, they are symbols that represent reality, much like language, which I discuss further below.
You're sure the common noun "chair" is not an abstraction? What is a common noun? What do common nouns do? By what process does something become signified by the classifier "chair"?
Ah, my apologies. I misunderstood you. Language is a set of concepts, namely symbols that allow us to describe our surroundings, our feelings about them, etc. So no, the common noun "chair" has no physical existence. It is simply a symbol that is associated with a certain class of physical object.
I'm not a language expert, so I can't say too much about how something becomes signified by a particular symbol. I would imagine that the common experience (via the senses) of chairs by speaking humans, and the need of these humans to communicate about chairs, leads them to agree on verbal and written symbols that signify that object.
So if a rock is on the edge of a cliff and the wind blows hard against it (input) and the rock begins rolling over the ledge (output), is that a "decision"?
Yes. And you could say that the laws of physics provide the algorithm. The algorithm consists of Newton's laws of motion, and takes as input the position of the rock, it's weight, the speed of the wind, etc., and gives as output the trajectory of the rock.
Of course, in this case there is no intention involved: the decision is not being made according to some predetermined requirements, it is simply made as an inevitable unfolding of the laws of nature.