'seeing' in the progressive?

Question

I put the same question up on EL&U a few other forums, but I don't get it well yet.
So I'm putting it up again with some touches.

I really want to know the meanings of the verb 'see' and 'hear' in the progressive
except for the cases (and there will be more cases with changing their meanings)-

    a) hallucination:
        : I'm seeing stars.
    b) meeting someone:
        : I'm seeing the doctor in the afternoon.
    c) listening to people giving their opinions:
       What are you hearing from people there?

Now here are the examples I've collected until now.

1.a. I can't believe what I'm hearing here!
1.b. I can't believe what I (can) hear here!

: I found 1.a. when I was watching an America drama.
  'hear' doesn't go with the progressive in the meaning of sounds coming through the ear, AFAIK.
  I still feel 1.b. is more natural and I can't seem to find the difference between 1.a. and 1.b.
  Is there any good reason for the hearing in 1.a?

2.a. I've been seeing the dark entity that haunts your house and your land.
2.b. I've seen the dark entity that haunts your house and your land.

: 2.a is a line from an America horror movie, and the female main actor did see
  the ghost hanged from a tree just one time. 2.b. is more natural to me and I don't know why 2.a was said.

3.a. Can you see what I'm seeing?
3.b. Can you see what I see?

: It might have been 'do you see...?', but I'm not sure. I heard 3.a when I was playing a computer game.
  Isn't it good enough to say 3.b.?

4.a. Why am I seeing this?
4.b. Why do I see this?

: 4.a is a message box popping up in Windows to ask if you want it to remember passwords.
  4.b sounds better to me. Is there any reason for 4.a.?

5.a. What are we supposed to be seeing here?
5.b. What are we supposed to see here?

: Here's the context. There is a man in the living room with his friends,
  and he shows them a video. But they don't seem to understand what the video is,
  and one of them says, "What are we supposed to be seeing here?"
  What is the effect of saying 5.a. instead of 5.b.?

Is there any reason for the above uses of the progressive? any effect?

---

I was reading a grammar and found this explanation, which I'm not clear on:

... it's difficult to catch oneself in the middle of a single act of seeing or hearing.
(though for a scientist not impossible) To see or to hear is to receive a sensory impression.
The reception of the impression is an involuntary act:
we cannot normally prevent the completion of it.
Thus, as we commonly say in English, you see - or you don't see. (fine so far...)
Yet sometimes it's possible for us to perceive the reception of a visual image in an unfinished state.
Wearing the wrong spectacles or having dined not wisely but too well, I might be seeing double.
Such occurrences of see in IU (single act / uncompleted) may be rare, but they help to explain
why see is normally found only in the completed aspect.
Yet in SU (series of acts / uncompleted) see would occur as frequently as any other verb,
since we have no difficulty in imagining an uncompleted series of the acts of perception;
e.g. “I'm seeing too many pictures,” said Sue at the exhibition. “I can't look at any more.”
(I'm completely lost here...)

Could you elaborate on this and tell me your opinions?

Answer 1

I think that perhaps your native language is making you 'feel' that some things are unnatural - in all instances, the 'original', progressive phrase is the one you should use.

The reasons for this is subtle and the distinction between the two not always obvious. When using 'see' or 'hear' in the active form, it refers to a sudden, instantaneous moment in time.

"I heard something!" shrieked Jane

Usually, this is not the case. For all examples,

1. The soap character is probably hearing some bad news, and uses this phrase halfway through the conversation. He/she does not know whether the conversation is over at that point. Alternatively, he/she is hearing strange sounds, and expects them to continue after he/she mentioned this.
2. This is actually questionable. You say that she has only seen the entity once, in which case 2b would actually be correct. In using 2a, she implies that she's seen the entity more than once - perhaps glimpses or the results of his haunting? Perhaps she pretends it was more than once to convince the others?
3. A good example sentence would be 'Can you see what I'm currently seeing?' The question 'Can you see what I see' would mean if the two of you are sharing a pair of eyes. One would ask the latter question if you were both logged on to the same security camera.
4. Again, this sentence is actually 'Why am I currently seeing this?' - the error message hasn't disappeared yet, you are in the middle of the act of seeing it. If the error message is gone, you would say 'Why did I just see that?', or if the error message is frequent, you can say 'Why have I been seeing this?'
5. When using 5a, you are referring to a part or the entire video. When using 5b, you are referring to a specific point in the video, or a specific part of the image - a part could be obscured due to a faulty camera.

Do note however that not everything in English has a reason - the simple fact is that the English like to use 'see' and 'hear' in combination with another verb:I can't see the traffic lights., I'd like to see that happen., and rarely use it on it's own. Then, it's usually used idiomatic: 'I see your point, but..', 'I hear what you're saying, but...