Photographic and Eidetic Memory

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The popular term photographic memory refers to the ability to capture and store an exact replicate of an image (like a photograph) in one’s brain and perfectly recall the image at a later time point.  This differs slightly from eidetic memory.  People with eidetic memory are able to reproduce a previously viewed image in their mind, maintaining general physical qualities such as spatial organization, color, and texture.  As described by Searleman (2007), a true eidetic image does not move when one moves their eyes.  Thus, an eidetic image is not simply an afterimage, which usually moves and is often different in color from the original image.  Eidetic images usually fade away involuntarily after a few minutes, and the image is lost upon blinking.  Once an eidetic image has faded away, it can rarely – arguably never – be retrieved.
However, an eidetic image is not unflawed.  As with all forms of memory, eidetic images are a construction of reality.  People with eidetic memory may alter physical features of an image or invent details during recall.  Searleman (2007) describes that eidetic images can be influenced by cognitive biases and expectations.  Therefore, eidetic images are not literally “photographic” representations of images, as implied by the popular term photographic memory.
Eidetic memory is extremely rare in the adult population.  However, research indicates that 2-15% of children possess eidetic memory.  A study by Ralph Haber in 1964 screened 500 elementary school-age children and found that as many as 50% of children possess eidetic memory (la Brecque, 1972).  Additionally, geriatric populations also demonstrate a higher frequency of eidetic imagery.  The tendency of eidetic memory to manifest in young and old populations is particularly interesting in light of research indicating that verbalization during the time that a person studies the original image interferes with eidetic image formation.  Therefore, it is plausible that the variation in frequency of eidetic imagery is due to dependence on linguistic ability.  While adults utilize abstract linguistic thought – and often have a hard time repressing this – children depend on visual stimuli while interacting with their surroundings.  Geriatric populations may also revert back to a similar approach as children, as the language centers in their brains begin to deteriorate.  Therefore, young and old populations are probably more likely to concentrate on visual details and less likely to verbalize while studying an image.  This is consistent with evidence suggesting that eidetic memory is more frequent in people with mental disabilities, such as autism.  One of the major characteristics of autism is delayed language and communication development.  Therefore, people with autism may depend on visual stimuli for much longer than other populations. 
            There are several methods of testing eidetic memory.  One is the Picture Elicitation Method, in which a picture is placed on an easel and studied by the subject for 30 seconds.  After the picture is removed, the subject continues to look at the easel and describes anything that they can observe.  A person with eidetic imagery acts as if they can still see the picture, as they scan the easel while answering questions.  Haber used this type of method in his study: children were identified as possessing eidetic memory if they moved their eyes in the appropriate direction while answering questions.  Haber also used another type eidetic imagery test that utilized superimposition of images.  Haber showed subjects two pictures, one at a time.  If the subject was able to retain the image of the first picture while visualizing the second, they would be able to see a third, composite image.  Although this type of test is normally effective, this particular test may not have been stringent because it has been suggested that the children could have guessed the composite image.
Although eidetic memory is a well documented phenomenon, the question exists whether photographic memory, as it is popularly defined, truly exists. The popular term photographic memory differs in two main ways from eidetic memory: it implies both a perfect and indestructible recall of images.  Photographic memory refers to the ability to essentially store a snapshot of an image in one’s head and accurately recall any detail of the image.  On the other hand, it is known that eidetic memory is often a flawed construction of reality.  Additionally, the term photographic memory implies that one can recall the image indefinitely, utilizing the image of a textbook perhaps during a test or of a map when navigating a new city.  However, as described above, eidetic images do not last for long periods of time, and one cannot chose what parts of an eidetic image fade away. 
Photographic memory, then, requires that one can store large amounts of unprocessed information in their brain for indefinite periods of time.  This raises the question of the efficiency of photographic memory.  It is uneconomical for the brain to store unprocessed information indefinitely.  As far as we know, the brain normally sifts through the sensory stimuli that one is exposed to and selects and stores useful information.  It is improbable that all details of an image would be deemed as useful information.  Additionally, there is a specific encoding process that moves information from short-term memory to long-term memory.  Long Term Potentiation describes the process of physical strengthening of neuronal connections that enable long-term retention of information.  Rehearsal and meaningful association of information are necessary for this process to occur.  However, photographic memory implies long-term storage of information without this specific encoding process.
The existence of this unusual type of memory could be rationalized if it has a specific adaptive purpose.  There is evidence to suggest that honeybees use this type of memory in order to recognize patterns.  Pattern recognition is an essential task for bees, as they must be able to identify specific flowers.  In a study by Giger and Srinivasan (1995) bees were exposed to patterned disks with nectar behind them; after a delay, the bees’ ability to identify the correct pattern (with nectar) was tested.  The authors concluded that although bees preferentially used orientational cues to recognize patterns, they used eidetic images when these were not available.  Although the authors call this eidetic imagery, they are likely actually referring to photographic memory, as the authors equate this pattern storage to a “snapshot” (Giger and Srinivasan, 1995).  Additionally, their experimental design required the bees to maintain the image for one hour.  However, this study provides weak evidence that bees are relying on photographic memory, because they rely only the bee’s ability to recognize different spatial intensity distributions in the patterns to determine that the bees are storing an exact replicate of the original pattern.  There may be several other memory mechanisms that the bees utilize to recognize different spatial intensity distributions that are not considered by the authors.  This type of faulty reasoning makes it clear that photographic memory may often be used as a default explanation for extraordinary memory abilities that we cannot explain.
Evidence for photographic memory in humans is primarily anecdotal, and documented cases are rare.  In 1970, Charles Stromeyer published an article indicating that a Harvard student named Elizabeth had photographic memory (Foer, 2006).  When Elizabeth’s right eye was exposed to a pattern of 10,000 random dots and her left eye was exposed to a different pattern of 10,000 random dots the following day, she was able to mentally fuse the two images into a three-dimensional image.  In order to complete this task, Elizabeth must have been able to store an exact replicate of the first dot pattern in her brain for an entire day.  However, even this remarkable case is tainted by the fact that Charles and Elizabeth got married, and her ability was never tested again.  Foer (2006) suggests that no one actually possesses photographic memory.  For example, in 1979, John Merrit published a photographic memory test in a magazine, hoping that he would find someone with photographic memory.  Although 30 people responded with the correct answer, none of these people were able to reproduce this ability when Merrit visited them at their homes.  Foer acknowledges that there are people with phenomenal memory abilities, but argues that there is always an underlying reason other than photographic memory.  For example, a Russian journalist was studied for three decades by a psychologist because of his amazing ability; however, it seems that he had mastered a set of mnemonic techniques that enabled his extraordinary feats.
We have a cultural tendency to label people with extraordinary memory abilities as possessing photographic memory.  For example, Stephen Wiltshire is a popular figure who has an extraordinary memory.  After taking one helicopter ride over Rome, he was able to draw a detailed and perfectly-scaled illustration of the city within three hours.  He has done the same with several other cities, including Tokyo and London.  The media refers to Wiltshire as “the human camera”, which refers to the assumption that he is able to create these illustrations from exact images of the cities in his head.  Wiltshire cannot be utilizing eidetic images, because they would not be retained for this long.  Despite the popular notion, Wiltshire also cannot simply be piecing together several photographic images, because he did not view every portion of the city from the same angle.  Instead, Wiltshire must reconstruct the images in his mind to account for the particular angle that he viewed each building from.  Therefore, it is likely that Wiltshire is not utilizing photographic memory but rather has exceptional memory abilities that we are not yet able to describe. 
There is a possibility, however, that Wiltshire has a photographic memory.  Wiltshire is autistic and has savant syndrome, a condition in which people with certain developmental disorders have incredible abilities.  It is possible that people with savant syndrome have disabled inhibitory mechanisms in the brain.  For example, the mechanism that inhibits most people from remembering all stimuli that they are exposed to may be turned off in people like Wiltshire.  According to this reasoning, Wiltshire may have a photographic memory because his brain does not sort for necessary information, but rather stores it all.  Interestingly, Wiltshire did not learn to use language effectively until he was nine years old, but instead relied heavily on visual information and drawing.  Wiltshire’s inability to verbalize at a young age may have contributed to his potentially photographic or eidetic ability.  However, the idea that disabled inhibitory mechanisms enable photographic memory is purely speculative, further demonstrating a desire to explain his extraordinary memory ability as photographic in nature.
The media’s attachment to the concept of photographic memory is clearly illustrated by its interpretation of scientific data.  A recent study by Lopez-Aranda et al. (2009) found that expression of the RGS-14 protein in layer 6 neurons of the V2 visual cortex in rats extended long-term object recognition memory from 45 minutes to many months.  This study may have been misinterpreted, as the authors defined object recognition by object exploration time and their results were contrary to the current multiple-domain model of visual memory.  Additionally, the original article does not mention photographic memory – it only comments on long-term visual memory; however, the media extrapolated from this article that the RGS-14 protein may be utilized to produce a photographic memory pill in the future (Smith, 2009).  Photographic memory is an appealing and magical concept – we want to believe in it because it is exciting.  However, there are few documented cases of photographic memory and its adaptive purpose is questionable.  Therefore, until there is further research proving the opposite, it can be concluded that photographic memory is simply a construct developed by our culture to explain extraordinary memory ability.
 
 
References
Foer, J. (2006, April). Kaavya Syndrome. Slate. Retrieved April 18, 2010, from    
http://www.slate.com/id/2140685
Giger, A. D., & Srinivasan, M. V. (1995). Pattern recognition in honeybees: eidetic imagery and  
orientation discrimination. J Comp Physiol A, 176, 791-795.
la Brecque, M. (1972). Photographic Memory. Leonardo, 5, 347-349.
Lopez-Aranda, M. F., Lopez-Tellez, J. F., Navarro-Lobato, I., Masmudi-Martin, M., Gutierrez,
            A., & Khan, Z. U. (2009). Role of Layer 6 of V2 Visual Cortex in Object-Recognition
            Memory.  Science, 375, 87-89.
Searleman, A. (2007, March). Is there such a thing as photographic memory? And if so, can it be 
learned?  Scientific American. Retrieved April 18, 2010, from         
http://www.scientificamerican.com/article.cfm?id=is-there-such-a-thing-as
Smith, D. (2009, July). Coming Soon: Photographic Memory in a Pill? Popular Science.   
Retrieved April 18, 2010, from http://www.popsci.com/scitech/article/2009-07/memory
problems-new-drug-could-give-you-photographic-memory.
Biography. The Stephen Wiltshire Gallery. Retrieved from
http://www.stephenwiltshire.co.uk/biography.aspx