Sometimes I'll be singing a song, and then I'll play a recording and discover I was singing in the same key. Does this mean I have perfect pitch?
The Levitin Effect
The ability to intuitively sing a song in the key your originally heard it is known as the Levitin Effect.1 It is a cognitive ability separate from absolute (perfect) pitch insofar as the latter does not seem to be a prerequisite for the former.
As stated in the Wikipedia article, the first description of the phenomenon is credited to Daniel Levitin in his 1994 article "Absolute memory for musical pitch: Evidence from the production of learned melodies". Reproduction of the effect was confirmed in a 2012 study, "Comparative replication studies of the "Levitin Effect" in five laboratories". Further research can be found in the 2013 paper "The Influence of Music-Elicited Emotions and Relative Pitch on Absolute Pitch Memory for Familiar Melodies".
To test yourself for perfect pitch, ask someone to play some pitches for you, and see if you can name them (no peeking, of course). Also, see if you can name the individual notes in a chord. Of course, you cannot know the names of any pitches during the test. Good relative pitch would allow you to name any notes played after one pitch is identified.
1 Note that the Levitin Effect does not require the exact pitch. It includes pitches within two semitones of the original. See his 1994 paper, linked above.
Forty percent of the subjects sang the correct pitch on at least one trial; 12% of the subjects hit the correct pitch on both trials, and 44% came within two semitones of the correct pitch on both trials.
- Do I have perfect pitch? (#1)
- Do I have perfect pitch (#2)
- Do I have perfect pitch or good pitch memory?
- Able to recall music in its correct key, but don't have perfect pitch — what is it called?
- Detecting absolute pitch by ear
Thanks to @Athenasius for pointing out that the Levitin Effect allows for two semitones difference from the original pitch and for advice on how to test for Absolute Pitch.
@Aaron 's answer is astonishing. Besides, I also have absolute pitch and I can say it is something to be developed, not accomplished. You can either develop the Absolute Pitch you have or lose it partially if you don't practice. It can work faster or take longer to recognize the notes or even start failing sometimes. Absolute Pitch is not a dead-end: it can become better or worse in a matter of time.