Reading intervals

[outin]

I must be bored this morning because I started wondering about something...

When we read intervals on the staff, how do we adjust to the different key signatures? Do we somehow mentally add the flats or sharps to the notes on the staff while reading and change the intervals accordingly or are we able to adjust the intervals to the different keys on the keyboard because our hands are familiar with playing in a certain key? Or both? Or something else?

[dogperson]

This is difficult to answer because it's done so automatically....,but I think what I do is the recognize the interval but immediately mentally add in the sharp or flat  based on the key signature.  So the reading of the stave  is based on the pure interval with an immediate adjustment based on the signature. I know my mind does not think ' ah, this was a third  but is no longer a third based on the key signature or the accidental'. 

[outin]

This is difficult to answer because it's done so automatically....,but I think what I do is the recognize the interval but immediately mentally add in the sharp or flat  based on the key signature.  So the reading of the stave  is based on the pure interval with an immediate adjustment based on the signature. I know my mind does not think ' ah, this was a third  but is no longer a third based on the key signature or the accidental'. 

It is very difficult to analyze what I do...I don't have enough brain capasity to think about it when I'm doing it and afterwards I have no recollection of what I actually did

Probably it's like that for me too. But I wonder if I am actually reading the interval at all anymore but instead go back to the individual notes  with larger intervals... which makes me wonder if it would be useful to practice reading intervals in different keys as a separate exercise...

[j_tour]

Or, an alternative I sometimes have done, just re-write the score (if polyphonic material, usually putting the distribution to how I play it between the hands in more legible form than open-score), I just mark it up with reminders.

Kind of dumb, but I read a lot more stuff than I actually "know" by heart, so I like to make it easy on myself.

There's a lot of sh*t written in G-flat and (de jure) C-flat, though (well, maybe not a lot, but some) -- for that, I just deal with it and kind of curse under my breath.

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ETA I misread the OP.  Yeah, for that, just spot-reading, I just am used to it, so it seems natural, even if it's an abomination like reading in C# major (vs Db) or one of the odd ones like Cb major.  Meh, I don't know how or why, I just got used to it.