In music, subjective constancy is the identification of a musical instrument as constant under changing timbre or "conditions of changing pitch and loudness, in different environments and with different players." In speech perception this means that vowels or consonants are perceived as constant categories even if acoustically, they vary greatly due to phonetic environment (coarticulation), speech tempo, speaker's age and sex, speaker's dialect, etc.You know it's your dad's voice, whether he's in the room with you, on the phone, on tape, Skyping, or yelling over a hill.
Is there such a thing as memory constancy? Our recollections vary widely (wildly), changing shape and size, re-told and amplified, and though the essence of a memory might stay the same, the archetypal story that it tells, so many of the particulars fade and are replaced. A door doesn't have a story to tell; we have a story to tell about the door; the door remains a door no matter how it's perceived; a story of the door changes depending on when I'm telling it, to whom I'm telling it, and on what I need from the story. There's very little constancy in memory, it seems, apart from its obsessive nature.
I used to think that a .gif file was a good metaphor for memory. I'm less sure about that. True, a memory has no fixed start or finish, and a memory is an obsession in that it plays constantly as a .gif file does. But too much of a .gif remains too constant: the particulars remain the same as the story is told and re-told. That may be my past, but it's not my memory.