Does updating a doc's non-indexed field cause any other indexes to udpate?

[Charlie]

I have a document structure similar to the below:

_id
authorId (objectid)
updated (date)
title (string)
content (string)
likes (number)
likers (array)

I have an index on 'authorId updated'.

The 'likes' and 'likers' fields are updated regularly so there is no index on them.

My question is, when the 'likes' field (or any other non-indexed field) is changed, does it trigger an update on any of the indexes, which would slow things down? Or, as I would imagine, does this only happen if 'authorId' or 'updated' are changed?