It doesn't seem like I can reply to smtddr's sibling comment here (probably nested too deep?). So here's my two cents:
I agree that in context of memory, the brain's capacity does appear limitless. However, the brain's capacity to process all of the information that it's exposed to is quite limited. For example, for most people, working memory is limited to 7 items plus/minus 2. One part of a standard cognitive test is to expose the subject to a list of numbers, and after hiding the numbers, ask the subject to repeat them back to you (and again, but backwards). A similar test of memory is to ask a subject to remember a list of items, then ask a series of other questions, then ask the subject to repeat the same list some time later. Some people do pretty well at these tests; some don't (approximating a normal distribution in ). So while it's theoretically possible that all subjects do have all of the numbers stored in their brain, it's quite clear that there's differing capability at least in memory encoding and/or retrieval.
I guess I also wanted to mention the concept of saliency. Different people will pay attention to different things even if all of the people are exposed to exactly the same stimuli. This is important because the brain only encodes to memory what it finds particularly important and/or interesting (i.e. salient). This can be trained to a degree: more experienced or trained people will be able to detect what's important, like a soldier being better able to "sense" the presence of an IED in a warzone. So even if everyone has exactly the same memory capacity, there'd still be variation in how well the brain itself decides to use that capacity.
> It doesn't seem like I can reply to smtddr's sibling comment here (probably nested too deep?).
OT technical note.
The reason you do not see a "reply" link is because you viewed the comment within X minutes of its posting. HN disables the reply link for that period. However, if you click on the permalink (the "link" text), you will still get a usable text box for replying.
My strategy is generally to do this, but sometimes I actually just refresh to pick up any new contextual comments.
I agree that in context of memory, the brain's capacity does appear limitless. However, the brain's capacity to process all of the information that it's exposed to is quite limited. For example, for most people, working memory is limited to 7 items plus/minus 2. One part of a standard cognitive test is to expose the subject to a list of numbers, and after hiding the numbers, ask the subject to repeat them back to you (and again, but backwards). A similar test of memory is to ask a subject to remember a list of items, then ask a series of other questions, then ask the subject to repeat the same list some time later. Some people do pretty well at these tests; some don't (approximating a normal distribution in ). So while it's theoretically possible that all subjects do have all of the numbers stored in their brain, it's quite clear that there's differing capability at least in memory encoding and/or retrieval.
I guess I also wanted to mention the concept of saliency. Different people will pay attention to different things even if all of the people are exposed to exactly the same stimuli. This is important because the brain only encodes to memory what it finds particularly important and/or interesting (i.e. salient). This can be trained to a degree: more experienced or trained people will be able to detect what's important, like a soldier being better able to "sense" the presence of an IED in a warzone. So even if everyone has exactly the same memory capacity, there'd still be variation in how well the brain itself decides to use that capacity.