can vs can't

[keannu]

Learning from a video lesson about difference between can and can't, I found the following.
1. It's hard to tell the difference between a and b as glottal stop sounds just like a mute pause. Can native speakers tell the difference between a and b easily?
2. In c, I was surprised to find /kɪn/ as I have never seen it. Maybe I took /kən/ for /kɪn/ as the former sounds similar to the latter. And I learned /kən/ instead of /kɪn/, so do I have to abandon /kən/ from now on?

**This had better be learned on an online chatting program like Paltalk with native English teachers, but I don't think it's easy for them to make an appoinment with me.

Lesson 11b - CAN/ CAN'T - English Pronunciation - YouTube
a. I can't come - /kӕn+glottal stop/

b. If you can, please come. - /kӕn/

c. Can you come? She can see well. - /kɪn/ or /ken/

[birdeen's call]

As you know, I'm not a native speaker, but I want to say something about your first question. There was more difference between her "can" and "can't" than just the glottal stop at the end of the latter. The intonation was also different.

Unfortunately, that isn't always the case. Also, not every American will be kind enough to throw in a glottal stop there, which as you say is not that easy to catch anyway. I know from Americans that it does happen that "can" and "can't" confuse them (when stressed). These words can be indistinguishable even to native American speakers.

[Chicken Sandwich]

In BrE the disctinction between "can" and "can't" is quite noticible as the "a" sounds differently.

[I'm With Stupid]

Americans will typically have a shorter a sound that British speakers in can't. Americans will use /ӕ/ whereas Brits will use /a:/. But both will say /kən/ for can in most cases.

I can see how in American English, it would be difficult to tell the difference if they were stressing can or can't in the sentence.

"I can do it" or "I can't do it." Especially in this example, because the /d/ sound that follows is exactly the same mouth position as the /t/ at the end of "can't."

[I'm With Stupid]

Learning from a video lesson about difference between can and can't, I found the following.
1. It's hard to tell the difference between a and b as glottal stop sounds just like a mute pause. Can native speakers tell the difference between a and b easily?

Yes. The giveaway is the length of the vowel sound. Can has a short vowel even when it's stressed: /kӕn/. Can't has a long vowel sound /ka:nt/ (the t can be replaced with a glottal stop).

2. In c, I was surprised to find /kɪn/ as I have never seen it. Maybe I took /kən/ for /kɪn/ as the former sounds similar to the latter. And I learned /kən/ instead of /kɪn/, so do I have to abandon /kən/ from now on?

No. That's a very particular pronunciation. I've heard it before, but most people say /kən/.

[5jj]

Americans will typically have a shorter a sound that British speakers in can't. Americans will use /ӕ/ whereas Brits will use /a:/. But both will say /kən/ for can in most cases.

The giveaway is the length of the vowel sound. Can has a short vowel even when it's stressed: /kӕn/. Can't has a long vowel sound /ka:nt/ (the t can be replaced with a glottal stop).

You appear to be contradicting yourself there.

The second quote is true for most speakers of BrE but not, as you pointed out in the first quote, for most speakers of AmE.

[I'm With Stupid]

What can I say? I usually speak to British people.

[keannu]

This can probably be best answered by Americans. In my experience, I really had a hard time distinguishing "can" and "can't" when "can" was "stressed". As you said, /kən/ seems to be more common for "can", but if they stressed it, I had no way to tell as I didn't even know about glottal stop.

If this is so hard, how do Americans tell these two confusing sounds? Do they have a secret like context or gesture- I even heard from Americans that they sometimes tell from facial expressions or gestures? But this won't apply in other cases as sometimes I have to practice taped listening tests, which has no clue of such things.

...I can see how in American English, it would be difficult to tell the difference if they were stressing can or can't in the sentence...

[Chicken Sandwich]

Context can tell us a lot.

[konungursvia]

I think it's the reverse. Unvoiced consonants are nearly always preceded by shorter vowels, with voiced ones following longer vowels. "Can" to me sounds 20% longer than "can't."