participle

1) I heard him discussing something
animatedly in the next room.

2) I saw my mother admitted into the room.

In first sentence -ing form has been used after the object 'him'. In second sentence past participial of verb 'admit' has been used after the object 'my mother'.

I don't know where present participle and, where past participle of verb will be used after object.

Please, explain it.

Thanks for your kind help.