can and could 5: with see, hear, etc

1 see, hear, feel, smell, taste
When these verbs refer to perception (receiving information through the eyes, ears etc), we do not normally use progressive forms. To talk about seeing, hearing etc at a particular moment, we often use can see, can hear etc (especially in British English).
I can see Susan coming, (NOT I’m seeing …)
Can you hear somebody coming up the stairs?
What did you put in the stew? I can taste something funny.
Suddenly she realised she could smell something burning.
In American English, I see/hear etc are common in this sense.
2 guess, tell
Can and could are often used with guess and with tell (meaning see, know). Can!could are not normally used with know in the sense of ‘find out’
(see know.5).
I could guess what she wanted.
You can tell he’s Irish from his accent, (NOT You can know-…)
3 understand, follow, remember
Canlcould is often used with these verbs too. It does not always add very much to the meaning.
I can’t/don’t understand what she’s talking about.
Do/Can you follow what he’s saying?
I (can) remember your grandfather.

For more information consult a good dictionary like Langman, Oxford, Merriam Webster, or Collins.