Tuesday, September 01, 2009

What Is It Like to Feel Sleepy?

Here are three types of conscious experience, or "phenomenology", that it's difficult to deny:

(1.) sensory experience (like the experience of redness produced by looking at a red object, like the taste of saltiness in one's mouth),
(2.) imagery experience (like a picture in one's mind's eye of the Taj Mahal, or a tune or sentence running silently through one's head), and
(3.) emotional experience (the rush of anger, the shock of sudden fear).

Some scholars think one or more of these reduces to or is a variant of another (maybe emotional experience is just sensory experience of the body [as William James says], maybe imagery experience is just a faint version of sensory experience [as David Hume says]). But clearly we have all three types of experience.

It's sometimes argued that we also have other types of experience, but there has never been a consensus on what the other types are. Imageless thought or "cognitive phenomenology" is one suggestion, which has been getting a lot of attention recently (e.g., by Charles Siewert, David Pitt, and Russ Hurlburt) -- the supposed experience we have of thinking something which is not just a matter of having images or emotional experiences of a certain sort, but which has its own irreducible phenomenology. Early in the 20th century, E.B. Titchener argued against the existence of such cognitive phenomenology, suggesting that it mostly reduces to visual images, inner speech (both forms of imagery), and the like. More recently, William Robinson and Jesse Prinz have argued similarly against it.

How about the experience of feeling sleepy? I can't recall any good discussions of this in the philosophical or psychological literature. (If I've missed something, please let me know!) Is that reducible to one or more of those three types of experience?

Maybe it's a type of sensory experience? To think clearly about this, we need first to think about what other kinds of experiences are sensory -- for the categories above are clearly incomplete unless we have a fairly broad notion of "sensory", such that pains count as sensory experiences and feelings of muscular tension and limb position and feelings of fullness or discomfort in the alimentary canal. Is feeling sleepy sensory in the same way these other experiences are -- a matter of experiencing how things are going in your body?

As it happens, I'm sleepy right now. (Hence the inspiration for this post.) This slight headache, this feeling that I'm tempted to describe as a heaviness near my eyes -- those seem like sensory experiences. But there's more to sleepiness than that. A lassitude in my limbs? Is that sensory? But could I have this very same heaviness and lassitude and not feel sleepy? Or feel sleepy without this heaviness and lassitude? My guess is -- but it's only a guess -- that there's something more.

Also: Sleepiness is as much a state one one's brain as of one's body. I can understand how detecting the condition of one's body is, in an appropriately broad sense, sensory; but is detecting the condition of one's brain also sensory? That doesn't seem right. The brain does all kinds of self-monitoring and engages in all kinds of feedback loops; would those, too, be "sensory"?

So maybe sleepiness is, experientially, an emotion? It has a valence, like emotion (negative, usually), and perhaps a typical facial posture. But it doesn't appear on most psychologists' lists of emotional states (sadness, happiness, fear, anger, surprise...). It doesn't seem to arise, usually, as a reaction to how things are going for you and those you care about, for example in response to a change for better or worse in one's condition, as emotions typically do. But maybe not all emotions are like that? (Is surprise even like that?) What is an emotion, exactly? Well, we won't solve that question today.

Or is the experience of sleepiness sui generis, just its own unique sort of thing? And if so, then the feeling of being well-rested, too? And who knows what all else? Feeling energetic? Competent? Lusty? Healthy? The boxes in which we're supposed to fit things, the categories of experience -- their borders seem no longer clear, or they won't stand still....


  1. I don't have an immediate feeling about the thesis, but are you leaving out one option, that the 'feeling' of sleepiness is a cluster or pattern in one's other sensations and thoughts (if those have a distinct phenomenology)? Or perhaps we partially self-attribute sleepiness on the basis of yawning, slowness of thoughts, and so on, not phenomenology per se. We feel various things in our eyes, limbs, head, none of which are individually necessary or sufficient for "sleepiness".

  2. Thanks, Justin. You're right that I didn't fully canvas the options -- especially blends like what you mention.

    What I find most interesting it that it's not at all obvious -- to me, at least!

  3. Feeling sleepy is probably a qualitative experience in its own right although an intermediate one.

    It´s a sensory experience because it produces distortions (hypnagogic hallucinations)of our phenomenology.

    But the point is what difficult seems to sharp the boundaries among experiences, particularly those transitional states (in media res)

  4. Depending on how one answers this question, the possibility of gradations of "sleepiness" might follow. Perhaps this will line-up with a gradation in the causal effects of sleepiness, on other aspects of one's experience. For instance, when one is beginning to feel somewhat sleepy, one's conscious thoughts start to become affected. When one is bordering on falling asleep, one's thoughts can feel somewhat hallucinatory.

  5. There is nothing it is like to feel sleepy, just as there is never anything it is like to get sleepy; there is nothing it is like to V more generally (Hacker). Although there is always something it is like to be me while Ving at time t (and hence Hacker's dispute with all this 'what it is like' language fails). The question, then, is, what is it like to be S - trans-sensory unity and all that - when getting sleeping at time t? Shoot if I know. Although, I do know what it is like to be me right now getting sleepy - as far as this sort of knowledge goes - but the specificity of this occurrence makes it "its own unique sort of thing." Good thing words do not create category boxes but rather cue the right sort of specific yet different simulation in me when S says, "And then I got sleepy". No?

  6. Thank you for the new thought that you have introduced me to. I don't know, but it is going to be fun thinking about it.

  7. Hi Eric, are you familiar with Proust's meandering description of sleepiness in the opening scene of In Search of Lost Time? I can think of no better phenomenological description of the experience of falling asleep in the literature. K

  8. Thanks for reminding me of that, Kevin. I remember loving the beginning of Proust's Remembrance when I read it, many years ago. I'll go back and refresh myself!