Here is a helpful summary of the problems which may arise with memory:

When memory serves as evidence, as it does in many civil and criminal legal proceedings, there are a number of important limitations to the veracity of that evidence. This is because memory does not provide a veridical representation of events as experienced. Rather, what gets encoded into memory is determined by what a person attends to, what they already have stored in memory, their expectations, needs and emotional state. This information is subsequently integrated (consolidated) with other information that has

already been stored in a person’s long-term, autobiographical memory.

What gets retrieved later from that memory is determined by that same multitude of factors that contributed to encoding as well as what drives the recollection of the event. Specifically, what gets retold about an experience depends on whom one is talking to and what the purpose is of remembering that particular event (e.g., telling a friend, relaying an experience to a therapist, telling the police about an event).

Moreover, what gets remembered is reconstructed from the remnants of what was originally stored; that is, what we remember is constructed from whatever remains in memory following any forgetting or interference from new experiences that may have occurred across the interval between storing and retrieving a particular experience.

Because the contents of our memories for experiences involve the active manipulation (during encoding), integration with pre-existing information (during consolidation), and reconstruction (during retrieval) of that information, memory is, by definition, fallible at best and unreliable at worst.

Mark L. Howe and Lauren M. Knott , “The fallibility of memory in judicial processes: Lessons from the past and their modern consequences” Memory, 2015, Vol. 23, No. 5, 633–656, http://dx.doi.org/10.1080/09658211.2015.1010709

First, let’s note the particulars of what is said:

“This is because memory does not provide a veridical representation of events as experienced.” Memory is not an objective recordation of a historical event. We know that even a photograph can be deceptive. We only see what is before the camera, not all of the things which remain outside of the photograph.  Look up the Beijing Olympics sky jump location: On television it appears to be a located on a snow covered mountain. But it was really an artificial structure in an industrial park next to what looks to be a nuclear reactor.

This example considers only one dimension of the problem: what can be seen. When it comes to reality involving human actors, the number of potential variables in play, sights, sounds, emotions, thoughts, et cetera, make a comprehensive “recording” of the event impossible. No one human being could possibly know everything was is present at any one time. Hence, our memory is not a complete recordation of the past.

So, the first limitation is attention: “Rather, what gets encoded into memory is determined by what a person attends to.”

Next, to be efficient, it will not be necessary for our memory to record everything taking place. Existing memories and expectations of what should occur can fill out what is actually recorded. The old Spiderman cartoons from the 1960’s repeatedly used certain elements as fillers (for instance, Spiderman swinging through some location). The stock segments were interspersed into the new episode. And so, memory depends upon “what they already have stored in memory, their expectations.”

The way in which the memory is taken down also depends upon our emotional state: this may effect the information we attend to as well as the way in which it is stored. For example, a particularly fearful event will be kept differently than an insignificant occasion. You can remember that time you almost died, but you have no idea what you saw on your way to work three years ago on a Tuesday in March.

Moreover, the information is then kept alongside of what you already known and have remembered: There is an integration of that information with your existing life:  “This information is subsequently integrated (consolidated) with other information that has

already been stored in a person’s long-term, autobiographical memory.” This can result in the information being smoothed out, accommodated into a consistent whole.

But memory only becomes functional (for purposes of testimony) when it is retrieved. There are a host of problems which can arise when it comes to “finding” the memory. And then, once it is found, not necessarily everything is retrieved: “What gets retrieved later from that memory is determined by that same multitude of factors that contributed to encoding as well as what drives the recollection of the event. Specifically, what gets retold about an experience depends on whom one is talking to and what the purpose is of remembering that particular event (e.g., telling a friend, relaying an experience to a therapist, telling the police about an event).”

The memory is recalled is not an exact reproduction of what was originally recorded. Due to the way in which memory is stored and encoded, the memory must “reconstructed”. This too can result in changes from the original event:

“Moreover, what gets remembered is reconstructed from the remnants of what was originally stored; that is, what we remember is constructed from whatever remains in memory following any forgetting or interference from new experiences that may have occurred across the interval between storing and retrieving a particular experience.”

Indeed, the process of reconstruction and then returning the memory can result in changes to the memory. The plasticity of memory itself a matter of research. This has been studied not merely to determine the extent to which memory is fallible or can be manipulated, but also as a means of therapy to help people who have suffered from traumatic memories and maybe suffering from the effects of such memory (for instance, what is often referred to as “PTSD”; this work focuses on something called memory “reconsolidation”).