The Scientific Indian

Is there a limit to human memory?

There is and there isn’t. The case for there is would go like this: let’s say, our brain can store 1000 doodles in each cell and a further 5000 doodles in each distinct connection (that is, the wiring itself as information). If we consider all the permutations and combination of cells and wiring, we get 10 raised to the power of some-doodillion. So there, that is the limit. Great. However, I think arriving at a number like this is questionable. It assumes that we have a valid definition of what memory is, which may not be true. (There are valid and verifiable definitions for computer memory but we are talking of human brain here).

To the next case: there is no limit to how much a human brain can store (and recall, because otherwise what’s the point). The case for this may be stated like this: What do we conceive of as unit memory? Let’s suppose that I don’t remember who I saw last month, but remember I did see someone whom I know. In this case how do I quantify this particular memory? Memory could be of real things and could be of other memories, it could be of memories of memories, and so on and so on – an infinite recursion like reflections between two mirrors. In this sense, there is no limit to our memory. I am, of course, being intentionally vague here. That’s because I am setting things up for the below.

There is a third case: the impossibility of quantifying memory. This can be stated in a more substantial and non-trivial way (and I will not be the one to do it, you give a try). The computational approach to memory – calculating storage space for unit memory, in my opinion, is misleading. Memory, it seems, needs characterization not quantification. But, what other approach is there? I don’t know. I am dissatisfied with all the ‘answers’ I’ve read on this. I was thinking about this yesterday night while going to sleep and confused myself terribly, once again.

Listen to Seth Lloyd for an overview of how one can frame a related question – that of processing limit.

Comments

  1. #1 Arby K
    February 2, 2009

    Just asking out of curiosity. Instead of trying to calculate it, can it inferred by how older ppl retain memory. If memory is limited, won’t there be symptoms of the same as ppl grow old, like forgetting stuff or incorrect recall etc.

  2. #2 greigos
    February 2, 2009

    You ask about the nature of memory, possibly in terms of units. That seems to assume memories are recorded in some discrete fashion. In other words, analogous to digital modes of memory used in today’s computers. More likely, I think, memory in biological brains is fixed using an analog model, perhaps by setting electrical potentials across synapses, like tuning a radio across a wide spectrum of frequencies. During recall the memory doesn’t come into focus unless all the appropriately set electrical potentials are reenacted and then the appropriate synapses fire. Quantifying all the permutations might be possible if the entire range of possibilities could be charted. Certainly down at the molecular level, electrical potentials become discrete again. (see http://www.refertogrey.com/index.php?showimage=38 for some related thoughts posted a while ago) Someone currently working in the field might be able to contradict or further illuminate.

  3. #3 Ashutosh
    February 2, 2009

    You would like Seth Lloyd’s book “Programming the Universe”

  4. #4 Mr Z
    February 3, 2009

    I’ve thought about memory for some time. Being involved with hobby robotics, memory is an essential future technology. Going on what I can find to read, what I have observed in animals and humans, and what I myself experience, I’ve begun thinking that memory is not a complete object retention/manipulation mechanism in humans and mammals in general. Rather it is much like some compression techniques that we see in video and telecommunications. My 5 senses are tied into my brain intricately, and sensory data usage is part of brain function. I think that in simplest terms, a group of look-up lists are stored in our brains. It’s easy to associate a small list of look-up values to sensory data. I.E. When you smell fresh pancakes, it can trigger a memory. Now, looking at all the state values of brain processes, our brains pre-fetch or look ahead mechanism is looking at those states and floating to the top of the stack any memory whose states match closely to those currently happening in real time. That is to say; the same pancake smell early in the morning while you still feel sleepy might always remind you of staying at your grandparents one summer as a kid, while the smell of pancakes in the afternoon always reminds you of funnel cakes at the amusement park. That is intentionally simplistic, and intended to demonstrate how one trigger can bring up multiple memories. When such strong memories arise in response, we are less likely to store new memories with higher precedence than those already stored. Make sense?

    The act of creating a memory and remembering one is similar in that the memory core has to see the same machine states to recall a vision or smell or sound (stored sensory data) as were active when it was stored.

    The process of trying to remember something that we can’t quite get is IMO a process of parsing through various thoughts, memories, and trigger states till the right memory is found. Try to recall your first grade teachers name right now. What visions, sounds, sensory data etc. went through your mind as you did that?

    I don’t think that we store memories, but the sensory states of memories that taken together pulls back all the bits and pieces into a coherent ‘memory’ experience. That is to say, the sensory inputs are replayed internally in a way that allows us to recall what we can put back together. Note that you may not remember everything. When I try to recall my first grade teacher’s name, I get the school name, it’s geographical location, my girlfriend’s name at the time, other big events that happened in that school, my teacher’s husband’s occupation, lots of things, but can’t get the teacher’s name yet. I can remember what my lunchbox looked like even… but not the teacher’s name. I recall playing king of the hill, first baseball games, tons of things from then, but not that teacher’s name.

    I think that this fits well with observed experiences of senility, drugged states, people in shock, intoxication, and basically every state that we can get into where sensory data processing is in some way impaired. There is anecdotal evidence to suggest that stored memories can be played back where the intoxicated (impaired processing) person perceives them as real: talking to walls or trees, seeing loved ones etc. Note also that several studies have been done on college students concluding that if you drink moderately as you study, you’re more likely to do well on the test if you are imbibing before or during, but only mild intake. With no alcohol intake before/during the test students who drank while studying did worse than those that did take some small amount of alcohol before the test. This adds to the notion that the mechanism states must be aligned to get best recall of a memory.

    I have looked for good evidence, but it is scarce to the amateur scientist, regarding whether people with congenital sensory defects remember things belonging to those senses. It would seem that people blind from birth do not remember in visions, nor dream in visions… at least not the way the rest of us do. The see only their internal visualization of sensory data, not what we would see. I have been looking for someone born blind and given sight as an adult to find out what changes. Haven’t found that yet.

    Well, that is how I perceive memories, or the short explanation.

  5. #5 Tim
    February 4, 2009

    There have been a few attempts at trying to quantify the capacity of human memory, most notably by Landauer and Dudai. They aren’t great, but they try to say something intelligent about how you might go about it:

    Landauer TK (1986) How much do people remember? Some estimates of the quantity of learned information in long-term memory. Cognit Sci 10:477– 493.

    Dudai Y (1997) How big is human memory, or on being just useful enough. Learn Mem 3:341–365.

    We’ve also thrown our hat into the ring recently with a paper where we make people remember details about thousands of objects with only a few seconds to encode each one. We have a very simple and quite silly model of how this relates to overall human memory capacity:

    T. F. Brady, T. Konkle, G. A. Alvarez & A. Oliva (2008). Visual long-term memory has a massive storage capacity for object details. Proceedings of the National Academy of Sciences, U. S. A., 105 (38), 14325-14329.

  6. #6 seer
    February 9, 2009

    Human memory should have a limit, afterall memory is just a part of our brain which is a completely a physical thing. also, human memory is analogous to a computer memory and the only difference is that there is a conscious memory for us humans.

    Its just that we dont use all our memory capacity, in case there comes a situation that we have used all our memory and the need arises for more, our brain might evolve further.

  7. #7 Rin
    February 11, 2009

    “What do we conceive of as unit memory? Let’s suppose that I don’t remember who I saw last month, but remember I did see someone whom I know. In this case how do I quantify this particular memory?”

    This concept is exactly why the term “recall” was formulated. Memory in and of itself is extremely vague and leaves for a lot of holes when attempting to gauge exactly how much the brain can hold. However, say you have a subject in the situation that you mentioned. Then you hold up a bunch of flashcards with the faces of all of the people they encountered during that month that they know or would possibly recognize. Their recall ability will be what is put to the real test when faced with this task and more likely than not, they’ll see the picture and the memory will be instantly revitalized as a full and coherent remembrance for that series of events that occurred where they saw that individual. The possibility of pinpointing that one memory out of a sea of faces doesn’t even seem feasible, but recall is amazing that way.

    Studies have also shown how inaccurate memory really is. I actually read an article where the subjects incorrectly identified past experiences pertinent to their own lives! Human memory by itself is flawed, but when looked at in it’s subdivisions (sensory, short and long-term, and then recall alone), only then can one even so much as attempt to test the limits.

    There are so many external factors to our memories that it’s near to impossible to tack a number onto how much one actually has held in their brain. Current science has only barely scratched the surface at attempting to understand this dauntingly impressive ability we possess.

  8. #8 Quan Duy
    October 20, 2009

    I think the human brain has to be limited. And the question here is what about the highest limitation of human brain?
    Can we find any brains which has a super power ?

  9. #9 Quan Duy
    October 20, 2009

    I think that there is surely a limit of human brain. But who can list some these limits which occur in real life ?
    Can these limits be higher in the future ?

  10. #10 Deepankar Pradhan
    October 26, 2009

    This question of Limit of a Human Brain has been puzzling me for a very long time. Im a II yr. Masters Chemistry student. And this question doesn’t have to do anything with my course, I guess. But, lets say why do old people forget things or say why do they have problem in recalling things. Is it because of their improper functioning of the brain due to old age or is it they have to much memory in their brain. So it gets entangled.
    I have this thought ki, more things you learn or more the knowledge you gather in ur memory, difficult the things will be for us to recall the things or it becomes more tangled up.
    For instance, there’s a 1000 sheets of paper in ur file and u require a particular paper, then in that case, more time and problem u face to get to that paper or take that sheet of paper out. In contrast, lesser will be the case when the mass nos. are less.
    I exactly dont know what am I talking about. I hope someone will write to me explaining exactly what is it.
    And also is memory related to quantum? Is a single memory like a quanta of light?
    I hope my queries will be answered.

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