Penfield also worked with a colleague, Phanor Perot, to look separately at stimulation that invoked complex visual experiences. In research published in 1963,6 they found that when part of the brain (the parietotemporal cortex) was activated, patients seemed to relive entire scenes from their lives. This effect, however, only happened when the right hemisphere was activated, which was taken to mean that perhaps visual memories were stored primarily on the right side of our brains. These recollections could often be confirmed as real memories, since they mapped onto documented experiences or everyday encounters in these individuals’ lives.
The team thought they had found the neural substrate of past experience – the singular location in the brain that stored all our memories. According to Brenda Milner,7 one of Penfield’s former colleagues, this led Penfield to ‘postulate that somewhere in the brain of each of us there is a continuous, ongoing record of the stream of consciousness (of everything we attend to, not of things we are not attending to) from birth to death’. A built-in tape recorder. A tiny webcam in our brains that is always on.
When questioned by Milner about this notion, which she had difficulties accepting as an experimental psychologist, Penfield apparently replied: ‘Of course this is not memory as you psychologists understand the term when you refer to the variability of memory, with its abstractions, generalizations and distortions. In ordinary remembering we do not have direct access to the record of past experience in our brain.’ So his idea was that not only did we have a tiny 24/7 camera that recorded this stream of consciousness, but also that this braincam stored its files in a secret location.
In his early work, Penfield speculated that this hypothetical storehouse of our memories might be in the temporal lobes; he later thought it might reside in the higher brainstem, then finally settled back on the temporal lobes. Like many other researchers at the time, he suspected that the hippocampus acted as the intermediary, allowing us to access, or not access, certain memories from this stream of consciousness storehouse. He therefore called the hippocampus the ‘key of access’ and sketched it in personal correspondence to Brenda Milner in December 1973. He claimed to have come up with the idea when he was studying a patient with postoperative memory loss. According to Milner:
In his diagram Penfield was saying that the two hippocampi must play a crucial role in scanning, or retrieving, from that hypothetical record of the stream of consciousness … he was suggesting that if you are trying, for example, to remember something about John Jones, who was your friend between 1950 and 1960, then in some way, via the interpretive cortex of the temporal lobes, the hippocampi give you ‘keys of access’ to those past recorded experiences.
If Penfield was right, then everything we remember is stored away somewhere in our brains, and the abilities of HSAMs could be explained as their somehow having a more direct access to this information.
However, in spite of its intuitive appeal, the tape-recorder model of memory has lost scientific traction. Today the consensus is that there is no evidence of any such secret storage facility; there is no conspiracy whereby the hippocampus is restricting access to your full memory potential. In search of another explanation of exceptional memory, some people turn to yet another related concept: photographic memory.
Photographic memory
So, maybe we don’t have a secret tiny braincam that records everything, but what about the ability to perfectly snap up individual moments? Perhaps we are able to make perfect engrams of, say, a particular scene. That seems like not too much to ask. A life-selfie. This one is going into the memory bank. Snap. A way to capture special moments in our lives. The scientific term that comes closest to describing the popular conception of photographic memory is eidetic memory, and the researchers who study it explore the limits of our ability to remember visual information.
The most popular way to study ‘eidetikers’, the term for people with eidetic memory, is through something called the picture elicitation method. Professor Alan Searleman from St Lawrence University, has described the testing process:8 an unfamiliar picture is shown to participants on an easel for 30 seconds – researchers often call that ‘unlimited viewing time’, because most people neither continue encoding details nor care to after 30 seconds looking at the same picture. Try it – 30 seconds feels really long when you are stuck with a single image.
After the image has been removed the person is instructed to continue looking at the easel that it was on. They are then asked to describe everything they can about the picture. People who have eidetic memory will report that they can still see the picture, that they can scan and examine their personal memory of the image as if it were still in front of them. They generally use the present tense when describing a recently removed photo and can report a tremendous amount of detail.
Of course, most of us do not have eidetic memory, and never will. Searleman has summarised the research in one of the leading textbooks in this field, Memory from a Broader Perspective,9 and suggests that eidetic images are different from other kinds of visual images people may encounter. The experience is not simply an after-image – the kind of lasting visual stimulation that happens when we stare at something for too long, or when a bright flash goes off and taints our vision temporarily. Those are the result of the way the cells in our eyes were stimulated. After-images are purely responses by these cells. After-images move with your eyes, and they are the opposite colour or shade to original stimulation. The aftermath of a white flash might be a dark circle right in the middle of your vision; the aftermath of red might be a light green. An eidetic image is different from this – it does not move with your eyes and remains the same colour as the original image.
Eidetic images are also different from regular visual memories which can arguably last forever; they fade away involuntarily and can last only a couple of minutes. Apparently the images usually fade away piece by piece rather than as a whole, and the eidetiker has no control over which components remain in place the longest. Eidetic images represent a moment of amazing memory that cannot last. But, while much better than other kinds of visual memories, even they are still prone to manipulations, omissions and false inclusions – the same kinds of distortions as any other kind of memory. According to Searleman, even eidetikers can misremember entire objects and forget pieces of scenes; it seems their exceptional memories for a particular image can still have some flaws.
What is more, as far as we can tell this kind of memory really only exists in children. In one of the few reviews of the literature on this topic, dated all the way back to 1975, researchers Cynthia Gray and Kent Gummerman10 estimated that 5 per cent of children have eidetic memory, and 0 per cent of adults do. It seems eidetic memory is quite possibly non-existent in adults.11
The rate of incidence is higher among children with developmental disabilities, particularly brain injuries, jumping to 15 per cent. These kinds of findings are what have led some researchers, such as Enrol Giray and colleagues,12 to wonder whether eidetic memory is actually an immature version of memory, one that is used before we are able to think about and encode experiences in a more abstract manner. This could also mean that a child’s eidetic memory is actually a sign of developmental problems, rather than developmental advantages. So, the ability closest to the popular conception of photographic memory is not actually all that impressive or common. It really is quite amazing that although by the late 1970s researchers essentially considered the existence of photographic or eidetic memory a myth (except as an incredibly short-lived and rare occurrence in children), the idea is still such a frequent misconception in society today.
So, how does this link back to our HSAMs? Well, on proper analysis, it doesn’t. It might be tempting to draw a link to our HSAMs, but their memories are actually the result of a different process entirely. HSAMs are adults who may certainly appear to have photographic memories – their memories seem to remain in perfect, detailed, multisensory condition. However, they seem to experience their memory di
fferently from eidetikers – not as a vivid and temporary visual echo, but as something more long-term. In 2013, Lawrence Patihis and his team from the University of California published the results of research13 in which they had set out to examine just how perfect the memories of HSAMs actually are. Or, rather, how error-prone they are. The team asked ‘Are people with HSAM abilities vulnerable to the same kinds of distortions and errors that others are, or do their abilities protect them in some way from suggestive influences?’ To attempt to answer this question, they conducted three false memory experiments on 20 verified HSAMs.
In the first experiment, the HSAMs were given what is called the DRM14 (Deese–Roediger–McDermott) test. In this test, participants are read a list of related words and asked to remember as many of them as possible. For example, they might be told to remember night, dream, pillow and dark. When they are tested later, most participants will recall other items that are conceptually related but which were not actually mentioned in the list; so if given the list just mentioned they might, for example, also include the word sleep. When asked about any of the false words they have recalled, participants often claim to be certain that it was originally mentioned, making this inaccurate word recall a tiny false memory. It turns out that in this task, HSAMs were as likely to misremember the non-mentioned words as control participants.
The second part of the study involved a classic ‘misinformation’ task. In this task, participants were shown two slideshows, each consisting of 50 photos. The first included a sequence of photos showing a man pretending to help a woman while actually stealing her wallet. The second showed a man breaking into a car and stealing money and necklaces. Later, the participants were given two narratives about the slide shows, each 50 sentences long. In each passage, six pieces of information were incorrect. So when the man had put his hands in his jacket pockets, the text claimed he had put his hands in the pockets of his trousers, for example. The researchers wanted to see whether the participants would report these inaccurate details when their memories of the slideshow events were tested. Contrary to what we might expect, HSAMs were actually significantly more likely to incorporate such incorrect details into their descriptions than non-HSAMs.
Finally, in the third experiment, HSAMs were questioned about whether they had seen particular footage of one of the 9/11 plane crashes, specifically United Airlines Flight 93, which crashed in a field in Pennsylvania. Here is an excerpt from one HSAM’s quite detailed response:
Interviewer: … a witness on the ground in Pennsylvania took some video of the plane crashing and it has been widely shown on TV news and the internet in the months and years since the attack. Do you remember seeing that footage?
HSAM: Yes, but a couple of days later.
Interviewer: OK, Can you tell me what you remember about the footage?
HSAM: Uh, I saw it going down. I didn’t see all of it. I saw, uh, a lot of it going down, uh, on air.
Interviewer: OK, do you remember how long the video is?
HSAM: Just a few seconds. It wasn’t long. It just seemed like something was falling out of the sky. It was probably was really fast, but I was just, you know, kind of stunned by watching it you know, go down.
Interviewer: OK, so here is the last question, I would like for you tell me how well you can remember having seen the video on the scale from 1 to 10, where 1 means no memory at all and 10 means a very clear memory?
HSAM: I’d say about 7.
Of course, as this was a false memory study, the video was invented by the researchers and never actually existed – this type of study is referred to as the non-existent news paradigm, and interestingly HSAMs and non-HSAMs scored more or less equally poorly on it, with 20 per cent of HSAMs and 29 per cent of non-HSAMs reporting that they had seen the video and offering at least one or two details. It appears our memory unicorns may not be so magical after all; not even the best rememberers on the planet can have an absolutely perfect memory.
Picking up the memory-braincam analogy from earlier, in the 21st century digital photos, like our memories, can be quite easily shared and edited by ourselves and others. Even if photographic memory were to exist – and it seems doubtful that it truly does – it appears that memory Photoshop would exist right beside it. Along with advances in actual photography, our memory-photo analogy may need a similar upgrade. We no longer use Polaroid cameras, and we should no longer be calling memories photographic, at least not in a way that implies perfection and permanence.
Spreading activation
However, perhaps we can still find a way to explain why HSAMs may innately have far better autobiographical memory than other people, while still being prone to false memories. The most popular current explanation, much in line with the associationist model of memory that was discussed in Chapter 4, is that HSAMs have particularly strong connections between pieces of their memories, making for strong neural networks. More specifically, it seems that an enhanced version of something called the spreading activation model, as proposed by memory researchers Allan Collins and Elizabeth Loftus in 1975,15 may best explain the process that happens in the brains of HSAMs. What this model suggests is that when we are looking for something in our brains, we send out an electrical signal searching for an idea, a piece of knowledge or an event that is related to whatever it is we are currently thinking about.
Let’s say that we wanted to recall an event from our childhood. We might already be thinking ‘I want to remember the family cottage.’ Then, from the location in the brain of that initial piece of memory, the concept of your family cottage, we send out an electrical signal which disperses along the web of all those neurons connected to the initial memory. The memory engram of the family cottage will be connected to other engrams. As the neuroscientist Dean Buonomano at the University of California Los Angeles explains16, ‘An item is stored in relation to other items, and its meaning is derived from the items to which it is associated.’
It might help to understand the process if you picture a giant spider’s web, with your initial search going out from the middle. In our hypothetical web, the things that are most strongly related to the concept are along the first, closely knit, threads, and they will be activated strongly and quickly. Then, as the signal progresses further from the centre, concepts further out – not as strongly related – can be triggered too. Of course in your actual brain the proximity of neurons to one another has little to do with how strongly connected they are, but a web of dissipating strength can help us to picture what is going on.
Spreading activation
So we might go from the family cottage engram, to the nearby lake, to the related concept of kayaking, to the yet physically further and more weakly related concept of islands, which then may make us spiral off and think about the unrelated concept of the Cayman Islands. The further out we go on our hypothetical web, the weaker the connection with the original concept, and the more likely we are to encounter topics that are not relevant to our original search. If this happens we can back up and restart our search from a more closely related topic. The process actually seems very similar to mind mapping, the activity sometimes used in educational and occupational settings where you write down ideas and concepts as an interconnected web spreading out from a main concept.
Let’s return to this idea as it relates to HSAMs. AJ has previously described the subjective experience of her recall of events as a kind of cascade of memories that trigger one another. Fortunately, or unfortunately, her memories trigger one another automatically, rather than intentionally. She claims she is powerless to control this reaction, so she often activates too many memories at once. According to her, ‘It’s like a split screen; I’ll be talking to someone and seeing something else.’17 In the early stages of research on the issue, which is where we find ourselves right now, it seems that HSAMs may just have far more efficient, but not perfect, spreading activation in their brains. This could result in their being able to quickly search their memory banks and find the
information they need in a way that is faster and more accurate than the rest of us.
Island of genius
Now let us explore another subject that is commonly associated with exceptional memory – autism. I bet right there you thought, yes, Rain Man. The movie Rain Man won an Oscar in 1988, and it depicts a grown man with autism who is very low-functioning, with severe social and cognitive deficits, but with an exceptional memory. A real person named Kim Peek originally inspired the movie.
So, would Rain Man be classified as an HSAM today? The answer is, probably not. He is certainly an individual with an innate ability to remember a tremendous amount of information, but his memory is largely for facts and numbers, rather than being autobiographical in nature (the A in HSAM). He is certainly, however, a superior memory individual. And he is not the only autistic individual to have such an amazing memory.
Approximately one in ten of those diagnosed with autism have exceptional skills related to memory. Such people are known as savants. According to psychiatrist Darold Treffert, who in 2009 summarised current understanding of the phenomenon,18 individuals are referred to as savants if they have a serious developmental disability, due to conditions such as autism or brain lesions, but simultaneously excel at something, such as being exceptional at remembering certain kinds of facts. Their abilities range from splinter skills, where the individual has specific skills that stand out in relation to their disability (but which are not necessarily exceptional in relation to the general population), all the way to prodigious savants, who display such brilliance at something that it would be considered amazing even for an individual without cognitive deficiencies.
The Memory Illusion Page 10