Does the Emergency Medical Hologram have (or could have) perfect recall of past events, as Commander Data apparently does, or are there indeed limits to his "memory"?

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    I would speculate there is minimal incentive to design an EMH to have the kind of recall Data has as it has a job to do and any memories would be towards that job. I speculate it would remember patient details but not the room's wall color for example. Further the first EMH holomatrix was notoriously only meant for short term use - so implicitly that means dont waste memory. See scifi.stackexchange.com/questions/27396/… . Voyager the series where the most interesting character is a hologram. Commented Jun 28, 2023 at 3:42
  • It's not enough to formulate an answer, but I think he has. He was programmed with extensive medical knowledge, there is no point in programming him with a feature that allows him forgetting. We never see him looking up medical files or any information that he already learned before. And the times where he does forget something are critical plot points.
    – Philipp
    Commented Jun 30, 2023 at 8:19

1 Answer 1


There are two episodes that suggest that the Doctor’s does not have perfect recall.

Season 3 episode 4 The Swarm deals with the doctor’s program degrading due to the memories and subroutines added over the 2 years it’s been active. His program deteriorates and he cannot even remember who Kes is.

But there is a later episode that deals more significantly with the doctor’s memory, season 5 episode 11 Latent Image, in which the doctor’s memory of an event 18 months ago has been blocked from him. There is a scene that tells us a bit about how the doctor’s memory works.

It comes after he has realised that he performed a procedure on Harry Kim that he does not remember, and goes to Seven for help. Someone erases his memory of the last hour in an attempt to keep him from investigating further:

EMH: Let's have a look at my program.

Seven: A deletion in your short term memory buffer.

EMH: Our chat in Astrometrics never got filed. That's why I can't remember it.

So this tells us that his program has a short term memory buffer that is processed in some way and then “filed” into long term storage.

Later in the same scene, Seven helps him access his memories of the event:

Seven: I've isolated your memory files from stardate 50979.

EMH: They weren't deleted?

Seven: No.

EMH: Then why can't I remember them?

Seven: The program was rewritten to deny you access to those memories. I'm trying to restore them.

And later:

Seven: The files are difficult to localise. The memories will be out of sequence.

This scene establishes that his long term memory is not optimised for “replay”, but, similar to our own memory, optimised for some other form of recall. The changes in his recall during The Swarm reinforce this idea.

Compare this to Data, whose memory was unable to be altered, even by himself, in the TNG episode S4E14 Clues, and thus he had to be ordered to keep a secret.

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    Hmmmm. If anything these two sequences suggest that his memory is usually perfect, except on a couple of occasions (one, a technical fault, the other an intentional deletion) where it isn't.
    – Valorum
    Commented Jun 28, 2023 at 7:18
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    @Valorum The dialog explicitly says that the memories are not deleted, but they are not perfect. We see them and they are blurry and have bad colour.
    – Ben Murphy
    Commented Jun 28, 2023 at 7:21
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    Because of the deletion and restoration process, presumably
    – Valorum
    Commented Jun 28, 2023 at 7:23
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    @Valorum as I said, seven says they weren’t deleted, only the permissions were changed.
    – Ben Murphy
    Commented Jun 28, 2023 at 7:24
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    We do see them better later in the episode once B’Elanna reversed the block, so I will concede he does have “good” recall, but I guess the key to my point was that he organises his memory like we do: “we had a surprise party”, “I took pictures”, and only with greater effort does he remember the rest. And still only (as far as we see), the key scenes.
    – Ben Murphy
    Commented Jun 28, 2023 at 7:43

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