Iconic Memory And How It Works
Updated December 11, 2018
Reviewer Wendy Boring-Bray, DBH, LPC
Iconic memory plays just one small part in your overall memory banks. Iconic memory is not something that is typically lost with memory loss, although its role in creating new memory is significant. Iconic memory lasts only milliseconds, but it plays an important role in procession what you see and using that information to form new memory.
What Is Iconic Memory?
Iconic memory is a form of sensory memory. Sensory memory is ultra-short-term memory that lasts only milliseconds for most people. Iconic memory is the sensory memory related to visual memory. It is called iconic because of icons, or pictures that your brain takes of things that you see.
Some people confuse iconic memory with photographic memory. While there is little evidence that photographic memory is real or how it works, iconic memory is definitive with a wide body of research. Photographic memory is the ability to see something and remember it from a brief image alone. Iconic memory is simply your brain's way of processing visual information.
Iconic memory does not last long, as is evidenced by many studies. You can see iconic memory at it's best through a simple exercise. Close your eyes for a few seconds. Open your eyes for one or two seconds just long enough to focus on an object then close them again. For a very brief time you will still see the image in your mind's eye. That is iconic memory at work.
There are three types of persistence that occur with visual stimuli. Neural persistence occurs when neural activity continues after the stimuli is gone. Visible persistence is when you continue to see the image after it is gone, such as with a bright flash of light. Informational persistence is when information about the visual stimuli is still available to the person for some time after the stimuli is gone.
Studies in the past have concluded that these three forms of visual persistence rely upon one another and is the source of visual information relayed after offset of stimulus in studies about visual persistence. However, new research has found that this is not the case.
According to newer studies, there are two phenomena that consistently occur with visual stimuli: The inverse duration effect, which is the longer a stimulus lasts, the briefer its persistence after offset; and, the inverse intensity effect, which is the more intense the stimulus the shorter the persistence lasts. These effects happen unless the stimuli are so intense that it produces after images. This is thought to occur in conjunction with neural persistence.
However, it is informational persistence that makes up iconic memory. It has distinctly different properties than visual or neural persistence. The study also concluded that iconic memory is not directly tied to the processes of the visual system. The study suggests that iconic memory is post-categorical, and occurs after stimulus identification. The stimulus identification is an automatic process but does not provide episodic properties.
In short, the new view is that physical stimulus must be temporarily attached to a representation of the visual stimulus in semantic memory. This temporarily attached information is what constitutes iconic memory.
Iconic memory decays rapidly after the visual stimulus is no longer present. Iconic memory is regarded by most to allow for perceptual integration of two or more images even if separated by a brief period of time. Many studies have been done to determine the duration of iconic memory, usually after the stimulus has been removed.
However, a new study has come to light in which it was hypothesized that iconic memory has a set temporal property starting from the onset of the visual stimulus, regardless of how long the stimulus is displayed. This would account for the inverse action of the iconic memory lasting for a briefer period of time with longer duration. The previous studies were measuring the duration of iconic memory from offset, but the new study measures it from onset.
The results of the new study seem conclusive, showing that regardless of how long visual stimulus is displayed iconic memory has a fairly set duration. Most often the duration of iconic memory is less than one second. Iconic memory is extremely brief. Only when iconic memory is put into context in the brain and relegated to short term memory does the information persist beyond a second.
One of the findings that has come up in repeated research about iconic memory is the inability to detect changes in a visual field. Many experiments have been done to determine the duration of iconic memory by doing change detection tests. The subject is given an array of items, then a brief time later given the same array slightly changed and asked to determine the change. In most cases, the subjects are unable to determine the change that was made.
A new study set out to determine why this happens. The common thought is that a serial search of all of the objects is necessary to determine the change, and the iconic memory of the first array fades before that can take place. However, the new study found that it is much more likely that iconic memory can only hold one array at a time. When the new array is presented, it overwrites the information from the first array.
Iconic memory is so brief and fleeting that it can only hold a small, limited amount of information for an infinitesimal amount of time. The only way to increase the memory of a visual array is to focus one's attention on the array, which moves the information from iconic memory to short-term memory.
Transfer To Durable Storage
Many studies have been done to determine the rate of transfer of information from iconic memory to durable storage, or short-term and long-term memory. Most studies have found that it takes significant attention to move information from iconic memory to durable storage. Without focused attention, the iconic memory fades rapidly and is not put into a context that commits it to more durable memory. The amount of information that can be moved from iconic memory to durable storage is limited by the capacity of the short-term memory.
Another study done by the NIH showed that iconic memory, with attention, could be transferred to a visual working memory that lasts several seconds. The visual working memory is a function of short-term memory. This memory in turn only lasts seconds, less than a full minute, without being transferred again to long-term memory.
The Brain And Iconic Memory
The primary part of the brain that is involved in iconic memory is the occipital lobe. It is responsible for processing and regulating visual information. The visual stimulus travels from the visual system of the eyes to the occipital lobe, where it is stored for mere milliseconds before being discarded or transferred to the temporal lobe. The hippocampus within the temporal lobe is primarily responsible for then converting that memory from short-term to long-term memory.
The Path Of Visual Memory
The path of visual memory is one that is travelled extremely quickly. Iconic memory, visual working memory, and short-term memory have limited capacities and brief temporal characteristics. Only by moving information all the way through the process to long-term memory can visual stimulus be remembered for more than a few minutes.
Presentation Of Stimuli
The first thing that must happen, of course, is for visual stimuli to be presented. Visual stimulus is processed by the visual system and the occipital lobe. Automatic recognition occurs, and it is then placed into iconic memory. This happens very quickly.
Once the stimulus has initially been presented, iconic memory begins. The automatic recognition of the visual stimulus is processed by the occipital lobe and transferred to iconic memory, where it remains for only milliseconds before being transferred to visual working memory or being discarded.
Visual Working Memory
From iconic memory, the information moves to visual working memory. This is like short-term memory for visual stimuli. Visual working memory can last for several seconds. In order for information to move to visual working memory, the subject must have focused attention on the visual stimulus and information.
Short Term Memory
The short-term memory lasts only a few minutes and has limited capacity. With focused attention and interrelated memories and thought, visual working memory can be transferred to short-term memory. There the information remains for several minutes before being discarded or in the moving on phase.
Long Term Memory
Long-term memory can be a confusing term. When most people think of long-term memory, they think of things that they remember for years. However, long-term memory doesn't necessarily last forever. It does decay over time, depending on how frequently you access the information. If information from iconic memory is to last beyond a few minutes, it needs to be stored in long-term memory.
Getting Help With Failing Memory
If you find that you can't remember things that you have seen, you might be suffering from early memory loss. Early memory loss usually begins with inadequate short-term memory. If you see something and within a few minutes have forgotten what you have seen, even if you paid close attention, there could be some problems with your short-term memory.
Memory loss is important to catch early, and there are a lot of things you can do to help make the process easier. Contacting a therapist or psychologist is your first step. They can give you a memory test to determine the depth of your memory loss. They can give you the next steps, and tell you what to watch for as your memory begins to fail.