When I refer to “sense data”, I mean information that’s conveyed in one of several ways, either through one of our many senses (of which there are more than the five Aristotle counted), or by whatever other means information makes its way into our stream of consciousness (for example, the introspection that allows us to carry on inner soliloquies). Philosophers sometimes use the term “qualia” to refer to “the introspectively accessible, phenomenal aspects of our mental lives”, but “sense data” emphasizes the informational aspect of our experience. I also think it’s appropriate to think of our conscious experience as a whole. The term “data”, understood as a collective noun, emphasizes what’s often called “the unity of consciousness”.
A term that could be used is in place of “sense data” is “sensorium”. Wikipedia cites the Oxford English Dictionary:
A sensorium is the sum of an organism’s perception … where it experiences and interprets the environments within which it lives…. In medical, psychological, and physiological discourse it has come to refer to the total character of the unique and changing sensory environments perceived by individuals. These include the sensation, perception, and interpretation of information about the world around us by using faculties of the mind such as senses, phenomenal and psychological perception, cognition and intelligence.
As David Chalmers put it in the article I quoted a few days ago: “What unites all of these states is that there is something it is like to be in them. All of them are states of experience.”
So what is sense data? From what is ordinarily called the “mental” point of view, sense data is information expressed as sights, sounds, smells, feelings, thoughts and so on. Although a computer can run a program perfectly well with one source of information (the data stored as tiny magnetic regions on a hard drive, for example), creatures like us need more. We require lots of information about the world in order to survive and it’s beneficial to collect that information in more than one way (echolocation would be especially handy at night).
Hence, we evolved with various capacities for collecting information about the world inside and outside our bodies. If the information we collect is accurate, it will generally allows us to maneuver successfully and avoid difficulties. If it’s garbled, incomplete, hard to understand, illusory or even hallucinatory, it will tend to be less helpful.
From what is ordinarily called the “physical” perspective, however, sense data is activity in our brains. Scientists, of course, can only detect what’s happening in our brains up to a point, since the technology is so new. We, however, have a front row seat, metaphorically speaking. In fact, we each have a metaphorical theater to ourselves. We each experience some of the activity in our brains as sense data, i.e. sights, sounds, smells, feelings, thoughts and otherwise. Nobody understands how this works yet – how or why particular kinds of activity are experienced in particular ways – but that seems to be only a matter of time.
Among professional philosophers, the idea that sense data or conscious experience is brain activity is controversial, although not so much among scientists who study the brain. The so-called “identity theory” has been debated for decades and various alternatives have been offered. Nevertheless, it still seems to me that mental activity is brain activity, somewhat like heat is the motion of atoms or molecules, a cloud is water vapor and a squirrel is a collection of cells.
One big objection to the identity theory that seems very wrong is that it leaves no room for minds or mental activity. Many philosophers used to believe that the mind is a mental substance that’s somehow attached to the physical substance of the body (and that made sense if a person’s mind or soul was supposed to float away post mortem). Very few philosophers think that today. Yet there are still those who believe that mental properties are very different from physical properties. Property dualism, in particular, is the idea that consciousness is a fundamental property not reducible to physical properties.
I don’t see any good reason to believe that. The simple, most plausible explanation for why so-called mental events or properties seem different from so-called physical events or properties is this: when we’re conscious, we experience some physical events in our brains as mental events (what I’m calling “sense data”), but we never experience other physical events, either in our bodies or outside them, in the same way. The traditional way of describing this distinction is to say that we have direct experience of what’s happening in our conscious minds and indirect experience (via our eyes and ears, for example) of everything else.
Consider what we know about perception and feelings like pain or hunger. Stimuli of various kinds come in contact with specialized cells in the body. Electrical impulses make their way via the nervous system to the brain. A tiny number of these impulses are combined with the brain’s own contributions, resulting in conscious experience. It’s the activity in the brain itself that ultimately counts.
You really could be a brain in a vat and have a vivid mental life, assuming the technology existed to allow your brain to receive the necessary stimuli (and thus the necessary information to process) and to react accordingly (by seeking new stimuli, for example, as in “Hey, what’s that noise over there?”). Using the traditional terminology, It’s the end product (the sense data) that you are “directly” aware of. So long as that information kept arriving and your brain could react appropriately, your world would seem the same.
It’s the things that information is about, whether it’s the sunburn on your back, a band playing in the park or your daughter’s first day at school, that we are “indirectly” aware of (again using the standard terminology). But all of it is (or was or will be) physical stuff, whether it’s the band in the park, the electrical stimuli or the brain’s own activity. It’s all ultimately composed of things like quarks and bosons (and maybe some dark matter or dark energy, whatever those are).
But the direct vs. indirect distinction can be misleading in at least two ways. First, calling our awareness of things outside our brains “indirect” suggests that there could be a more direct way of being aware of such things. But how could that possibly be? How could I possibly be more aware of the chair I’m sitting in than by sitting in it, looking at it, measuring it, touching it and so on? Experiencing something outside of us isn’t and cannot be the same as experiencing the brain activity that’s part of us. Nevertheless, using our senses to gain knowledge about such things is the ideal, most direct way there could possibly be.
Second, saying that we are directly aware of sense data may suggest that our awareness is complete. It’s sometimes said that we have “privileged access” to our sense data. That’s certainly true, since nobody else has the same access to our sense data that we do. Similarly, the Stanford Encyclopedia article on sense data lists this as the third defining feature of traditional sense data theories: “Sense data [has] the properties that perceptually appear to us”. That’s usually understood to mean that we can’t be mistaken about what our sense data is. We may interpret our sense data incorrectly, but if you have blue sense data, your sense data is definitely blue, even if the thing your sense data is about (the wall in front of you, for example) isn’t blue at all. It could be a different color, as we usually describe such things. In reality, it’s got no “color” (the blueness you actually see) in itself at all.
This doesn’t mean that we can always accurately describe what our sense data is or even know what we’re sensing. Data, after all, is sometimes vague, incomplete, too complex to understand and even inconsistent. (Imagine seeing an object directly in front of you that isn’t there when you try to touch it.) It’s reasonable to say that sense data always has the properties that perceptually appear to us, so long as we don’t take that to mean we are always clear about what those properties are.
The most popular objection to sense data theories is that they break the link between us and the external world. If we’re only aware of sense data, how do we know that anything outside our own minds even exists? How do we know that there is a physical world at all? Or perhaps you and I are like Keanu Reeves before he was unplugged.
Given the sense data I’ve had over the years and am still having, I’m very sure that there is a physical world outside my mind that contains New York City, our cat, Rice Krispies and aluminum siding. But am I absolutely, completely, 100% certain beyond any doubt whatsoever? Not really. I could get an extremely, extremely big surprise one day.
But so what? I’m not absolutely, completely, 100% certain that the world wasn’t created 10 seconds ago, with geological strata and historical records in place and all of us enjoying false memories of years gone by. Being able to conceive of a very different world doesn’t make that very different world plausible. Philosophers (some of them) are paid to worry about these things, and many have tried to prove beyond any possible doubt things we and they already know to be true. But the quest for absolute certainty on this or almost any other topic is a waste of time. It’s impossible to achieve and wouldn’t be of any use if it was.
In conclusion, I should mention that, in a 2009 survey of philosophy professors, graduate students and others who follow academic philosophy, only 19% of the respondents accepted or leaned toward “sense-datum theory” or “qualia theory” in the philosophy of perception. However, applying simple labels to philosophical theories is extraordinarily difficult. The most popular answer was “other” with 43%, but coming in second was “representationalism” with 26%. Another article in the Stanford Encyclopedia describes representationalism or representative realism as follows:
… our immediately experienced sense-data, together with the further beliefs that we arrive at on the basis of them, constitute a representation or depiction of an independent realm of material objects — one that we are, according to the representationalist, justified in believing to be true.
I couldn’t (and didn’t) say it better myself.
PS — It’s very difficult to contract Ebola in a country with a decent public health system, so please don’t worry. It’s not spread like a cold or the flu. If you’re in a country with a poor public health system and people are getting the disease, please don’t expose yourself to the bodily fluids of someone who has a high fever, body aches, etc. You can only get it from the bodily fluids of someone who already has symptoms.