What happens when "eyes glaze over"?

We’ve all seen it or at least heard about it–someone speaks at length about a topic that is boring, incomprehensible, or long-winded, and the audience’s “eyes glaze over.” What is the physical configuration of the eyeball that causes us to perceive this?

Is it the focus point? People have a highly evolved ability to read the movement and positioning of eyes to be able to tell what someone is looking at. It’s obvious enough that an eye is looking in one direction or another, but I’m not sure that we can tell whether it is focused on the object that it appears to be aimed at. We do talk about people “staring off into space,” but I’m not sure how we distinguish between that and “staring at something.” Do we subconsciously read the convergence point of the two eyes to deduce this?

Or perhaps it is a general perception that is based on the whole of body language, including the areas surrounding the eyes, and it’s not an eyeball phenomenon at all.

I think it’s the result of people tuning out the external and daydreaming or thinking about the hottie one row over, or next week’s vacation or the like. The face goes slack and the eyes become dull, as opposed to when you are engaged, focused and animated.

There is this … there is also a video below

This is the crux of my question. What does that really mean? Eyes are just wet blobs of jelly. How can they look “dull” as an indication of the mood of the owner?

Guessing that the eyes stop tracking anything and remain more or less fixed in one place (I know that eyes are never completely stationary, assuming you are conscious) rather than tracking the other person’s body movements, movements of other objects, etc.

This comes up in one of “Lazlo Toth”'s letters to journalist James J. Kilpatrick:

The slackness of the face, as mentioned, and the unfocused look, also mentioned. When someone says that a person has expressive eyes, what they really mean is that the person is very animated in his facial expressions and is intent on what others are saying.

I think it’s what a person looks like just before they fall asleep. :o

It is a metaphor and is not meant to be taken literally.

But, basically, you’re usually thinking about something other than what’s going on, so you aren’t focusing on the person speaking, but either at something in the distance or nearby.

Teachers can easily tell when the class is attentive and listening to a lecture. An experienced teacher can also tell when they’ve lost the classes attention. It’s a combination of things. Body language, vacant expressions on faces, fidgeting and even sleeping. Eyes gaze over is all of that.

I’ve been in lectures where the teacher would drop a heavy book or make some noise to startle everyone and wake them up. Some material is just so dry that even the teacher has trouble working up any enthusiasm for it.

Beyond what Chefguy said in post two, surely the main thing would be that that the listener’s eyes would no longer be looking at the speaker (or any visual aids the speaker might be using) most of the time.

For a fully “glazed over” effect, the eyes would not be looking at anything in the current environment. If the person is daydreaming, the eyes will be moving in a way that would be appropriate to exploring the environment being imagined in the daydream (as opposed to exploring the environment they are actually in. As the OP mentioned, we have a highly evolved ability to (mostly unconsciously) read other people’s eye movements, and can generally tell quite well from this whether someone is paying attention to their current environment, or to some other place that they are imagining.