acts_as_ferret:: "field-restricted search" possible?

Can we tell acts_as_ferret
- to take up multiple search terms from a form, then
- use each term only on a specific column in the table to search?

- Model: User
- Attributes: firstname, lastname, location, favoritecolor
- Form fields: firstname, lastname, location, favoritecolor

-> Then let ferret search only in the "firstname column" using only
"firstname form field (entry)"
-> Do this for every form field entry
-> Compose the final search result list ?

Wikipedia seems to call that "Field-restricted search":
" Some search engines enable users to limit free text searches to a
particular field within a stored data record, such as "Title" or
"Author." "

As far as I have understood, acts_as_ferret takes multiple search terms
and uses them to search the *entire* created index (meaning all columns
specified in the model).

Is a "field-restricted search" possible (to speed up the query)? If yes,
what exactly would I have to do?

Thanks for your help!