Iconic memory
Encyclopedia
Iconic memory is the visual sensory memory
(SM) register pertaining to the visual domain. It is a component of the visual memory
system which also includes visual short term memory
(VSTM) and long term memory
(LTM). Iconic memory is described as a very brief (<1000 ms), pre-categorical, high capacity memory store. It contributes to VSTM by providing a coherent representation of our entire visual perception
for a very brief period of time. Iconic memory assists in accounting for phenomena such as change blindness
and continuity of experience during saccades. Iconic memory is no longer thought of as a single entity but instead, is composed of at least two distinctive components. Classic experiments including Sperling's partial report paradigm as well as modern techniques continue to provide insight into the nature of this SM store.
who proposed that afterimages
were involved in the experience of a dream. Natural observation of the light trail produced by glowing ember at the end of a quickly moving stick sparked the interest of researchers in the 1700s and 1800s. They became the first to begin empirical
studies on this phenomenon which later became known as visible persistence
. In the 1900s, the role of visible persistence in memory gained considerable attention due to its hypothesized role as a pre-categorical
representation of visual information in VSTM. In 1960, George Sperling
began his classic partial-report experiments to confirm the existence of visual sensory memory and some of its characteristics including capacity and duration. It was not until 1967 that Ulric Neisser
termed this quickly decaying memory store iconic memory. Approximately 20 years after Sperling’s original experiments, two separate components of visual sensory memory began to emerge: visual persistence and informational persistence. Sperling’s experiments mainly tested the information pertaining to a stimulus, whereas others such as Coltheart performed directs tests of visual persistence. In 1978, Di Lollo proposed a two-state model of visual sensory memory. Although it has been debated throughout history, current understanding of iconic memory makes a clear distinction between visual and informational persistence which are tested differently and have fundamentally different properties. Informational persistence which is the basis behind iconic memory is thought to be the key contributor to visual short term memory as the precategorical sensory store.
. Neural persistence is generally represented by neuroscientific techniques such as EEG
and fMRI.
Different techniques have been used to attempt to identify the duration of visible persistence. The Duration of Stimulus Technique is one in which a probe stimulus (auditory "click") is presented simultaneously with the onset, and on a separate trial, with the offset of a visual display. The difference represents the duration of the visible store which was found to be approximately 100-200 ms. Alternatively, the Phenomenal Continuity and Moving Slit Technique estimated visible persistence to be 300 ms. In the first paradigm, an image is presented discontinuously with blank periods in between presentations. If the duration is short enough, the participant will perceive a continuous image. Similarly, the Moving Slit Technique is also based on the participant observing a continuous image. Only instead of flashing the entire stimulus on and off, only a very narrow portion or "slit" of the image is displayed. When the slit is oscillated at the correct speed, a complete image is viewed.
. Although activation in both rods
and cones
has been found to persist beyond the physical offset of a stimulus, the rod system persists longer than cones. Other cells involved in a sustained visible image include M and P retinal ganglion cells. M cells (transient cells), are active only during stimulus onset and stimulus offset. P cells (sustained cells), show continuous activity during stimulus onset, duration, and offset. Cortical persistence of the visual image has been found in the primary visual cortex (V1) in the occipital lobe
which is responsible for processing visual information.
(STS), a part of the ventral stream, was found to be active in macaques during iconic memory tasks. This brain region is associated with object recognition
and object identity. Iconic memory’s role in change detection has been related to activation in the middle occipital gyrus (MOG). MOG activation was found to persist for approximately 2000ms suggesting a possibility that iconic memory has a longer duration than what was currently thought. Iconic memory is also influenced by genetics and proteins produced in the brain. Brain-derived neurotrophic factor
(BDNF) is a part of the neurotrophin
family of nerve growth factors. Individuals with mutations to the BDNF gene which codes for BDNF have been shown to have shortened, less stable informational persistence.
has provided insight into the nature of the iconic memory store and its role in vision. Change blindness refers to an inability to detect differences in two successive scenes separated by a very brief blank interval, or interstimulus interval
(ISS). When scenes are presented without an ISS, the change is easily detectable. It is thought that the detailed memory store of the scene in iconic memory is erased by each ISS, which renders the memory inaccessible. This reduces the ability to make comparisons between successive scenes.
. These rapid eye movements occur in approximately 30 ms and each fixation lasts for approximately 300 ms. Research suggests however, that memory for information between saccades is largely dependent on VSTM and not iconic memory. Instead of contributing to trans-saccadic memory, information stored in iconic memory is thought to actually be erased during saccades. A similar phenomenon occurs during eye-blinks whereby both automatic and intentional blinking disrupts the information stored in iconic memory.
occurs. By 5 years of age, children have developed the same unlimited capacity of iconic memory that adults posses. The duration of informational persistence however increases from approximately 200 ms at age 5, to an asymptotic level of 1000 ms as an adult (>11 years). A small decrease in visual persistence occurs with age. A decrease of approximately 20 ms has been observed when comparing individuals in their early 20's to those in their late 60's. Throughout one’s lifetime, mild cognitive impairments
(MCIs) may develop such as errors in episodic memory
(autobiographical memory about people, places, and their contex), and working memory
(the active processing component of STM) due to damage in hippocampal and association cortical areas. Episodic memories are autobiographical events that a person can discuss. Individuals with MCIs have be found to show decreased iconic memory capacity and duration. Iconic memory impairment in those with MCIs may be used as a predictor for the development of more severe deficits such as Alzheimer’s disease and dementia
later in life.
became the first to use a partial report paradigm to investigate the bipartite model of VSTM. In Sperling's initial experiments in 1960, observers were presented with a tachistoscopic
visual stimulus for a brief period of time (50 ms) consisting of either a 3x3 or 3x4 array of alphanumeric characters such as:
Recall was based on a cue which followed the offset of the stimulus and directed the subject to recall a specific line of letters from the initial display. Memory performance was compared under two conditions: whole report and partial report.
Sensory memory
During every moment of an organism's life, sensory information is being taken in by sensory receptors and processed by the nervous system. Humans have five main senses: sight, hearing, taste, smell, and touch. Sensory memory allows individuals to retain impressions of sensory information after the...
(SM) register pertaining to the visual domain. It is a component of the visual memory
Memory
In psychology, memory is an organism's ability to store, retain, and recall information and experiences. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing memory....
system which also includes visual short term memory
Visual short term memory
In the study of vision, visual short-term memory is one of three broad memory systems including iconic memory and long-term memory. VSTM is a type of short-term memory, but one limited to information within the visual domain....
(VSTM) and long term memory
Long-term memory
Long-term memory is memory in which associations among items are stored, as part of the theory of a dual-store memory model. According to the theory, long term memory differs structurally and functionally from working memory or short-term memory, which ostensibly stores items for only around 20–30...
(LTM). Iconic memory is described as a very brief (<1000 ms), pre-categorical, high capacity memory store. It contributes to VSTM by providing a coherent representation of our entire visual perception
Perception
Perception is the process of attaining awareness or understanding of the environment by organizing and interpreting sensory information. All perception involves signals in the nervous system, which in turn result from physical stimulation of the sense organs...
for a very brief period of time. Iconic memory assists in accounting for phenomena such as change blindness
Change blindness
In visual perception, change blindness is a normal phenomenon of the brain which show in light that the brain does not have a precise representation of the world but a lacunar one, made of partial details...
and continuity of experience during saccades. Iconic memory is no longer thought of as a single entity but instead, is composed of at least two distinctive components. Classic experiments including Sperling's partial report paradigm as well as modern techniques continue to provide insight into the nature of this SM store.
Overview
The occurrence of a sustained physiological image of an object after its physical offset has been observed by many individuals throughout history. One of the earliest documented accounts of the phenomenon was by AristotleAristotle
Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...
who proposed that afterimages
Afterimage
An afterimage or ghost image or image burn-in is an optical illusion that refers to an image continuing to appear in one's vision after the exposure to the original image has ceased...
were involved in the experience of a dream. Natural observation of the light trail produced by glowing ember at the end of a quickly moving stick sparked the interest of researchers in the 1700s and 1800s. They became the first to begin empirical
Empirical
The word empirical denotes information gained by means of observation or experimentation. Empirical data are data produced by an experiment or observation....
studies on this phenomenon which later became known as visible persistence
Persistence of vision
Persistence of vision is the phenomenon of the eye by which an afterimage is thought to persist for approximately one twenty-fifth of a second on the retina....
. In the 1900s, the role of visible persistence in memory gained considerable attention due to its hypothesized role as a pre-categorical
Categorical perception
Categorical perception is the experience of percept invariances in sensory phenomena that can be varied along a continuum. Multiple views of a face, for example, are mapped onto a common identity, visually distinct objects such as cars are mapped into the same category and distinct speech tokens...
representation of visual information in VSTM. In 1960, George Sperling
George Sperling
George Sperling is an American cognitive psychologist. He is a Distinguished Professor of both Cognitive Science and Neurobiology & Behavior at the University of California, Irvine. Sperling documented the existence of iconic memory...
began his classic partial-report experiments to confirm the existence of visual sensory memory and some of its characteristics including capacity and duration. It was not until 1967 that Ulric Neisser
Ulric Neisser
Ulric Neisser is an American psychologist and member of the National Academy of Sciences. He is a faculty member at Cornell University. In 1995, he headed an American Psychological Association task force that reviewed The Bell Curve and related controversies in the study of intelligence. The task...
termed this quickly decaying memory store iconic memory. Approximately 20 years after Sperling’s original experiments, two separate components of visual sensory memory began to emerge: visual persistence and informational persistence. Sperling’s experiments mainly tested the information pertaining to a stimulus, whereas others such as Coltheart performed directs tests of visual persistence. In 1978, Di Lollo proposed a two-state model of visual sensory memory. Although it has been debated throughout history, current understanding of iconic memory makes a clear distinction between visual and informational persistence which are tested differently and have fundamentally different properties. Informational persistence which is the basis behind iconic memory is thought to be the key contributor to visual short term memory as the precategorical sensory store.
Components of Iconic Memory
The two main components of iconic memory are visible persistence and informational persistence. The first is a relatively brief (150 ms) pre-categorical visual representation of the physical image created by the sensory system. This would be the "snapshot" of what the individual is looking at and perceiving. The second component is a longer lasting memory store which represents a coded version of the visual image into post-categorical information. This would be the "raw data" that is taken in and processed by the brain. A third component may also be considered which is neural persistence: the physical activity and recordings of the visual systemVisual system
The visual system is the part of the central nervous system which enables organisms to process visual detail, as well as enabling several non-image forming photoresponse functions. It interprets information from visible light to build a representation of the surrounding world...
. Neural persistence is generally represented by neuroscientific techniques such as EEG
EEG
EEG commonly refers to electroencephalography, a measurement of the electrical activity of the brain.EEG may also refer to:* Emperor Entertainment Group, a Hong Kong-based entertainment company...
and fMRI.
Visible Persistence
Visible persistence is the phenomenal impression that a visual image remains present after its physical offset. This can be considered a by-product of neural persistence. Visible persistence is more sensitive to the physical parameters of the stimulus than informational persistence which is reflected in its two key properties.:- The duration of visible persistence is inversely related to stimulus duration. This means that the longer the physical stimulus is presented for, the faster the visual image decays in memory.
- The duration of visible persistence is inversely related to stimulus luminanceLuminanceLuminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square...
. When the luminance, or brightness of a stimulus is increased, the duration of visible persistence decreases. Due to the involvement of the neural system, visible persistence is highly dependent on the physiology of the photoreceptors and activation of different cell types in the visual cortexVisual cortexThe visual cortex of the brain is the part of the cerebral cortex responsible for processing visual information. It is located in the occipital lobe, in the back of the brain....
. This visible representation is subject to masking effects whereby the presentation of interfering stimulus during, or immediately after stimulus offset interferes with one’s ability to remember the stimulus.
Different techniques have been used to attempt to identify the duration of visible persistence. The Duration of Stimulus Technique is one in which a probe stimulus (auditory "click") is presented simultaneously with the onset, and on a separate trial, with the offset of a visual display. The difference represents the duration of the visible store which was found to be approximately 100-200 ms. Alternatively, the Phenomenal Continuity and Moving Slit Technique estimated visible persistence to be 300 ms. In the first paradigm, an image is presented discontinuously with blank periods in between presentations. If the duration is short enough, the participant will perceive a continuous image. Similarly, the Moving Slit Technique is also based on the participant observing a continuous image. Only instead of flashing the entire stimulus on and off, only a very narrow portion or "slit" of the image is displayed. When the slit is oscillated at the correct speed, a complete image is viewed.
Neural Basis of Visible Persistence
Underlying visible persistence is neural persistence of the visual sensory pathway. A prolonged visual representation begins with activation of photoreceptors in the retinaRetina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
. Although activation in both rods
Rod cell
Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than can the other type of visual photoreceptor, cone cells. Named for their cylindrical shape, rods are concentrated at the outer edges of the retina and are used in peripheral vision. On...
and cones
Cone cell
Cone cells, or cones, are photoreceptor cells in the retina of the eye that are responsible for color vision; they function best in relatively bright light, as opposed to rod cells that work better in dim light. If the retina is exposed to an intense visual stimulus, a negative afterimage will be...
has been found to persist beyond the physical offset of a stimulus, the rod system persists longer than cones. Other cells involved in a sustained visible image include M and P retinal ganglion cells. M cells (transient cells), are active only during stimulus onset and stimulus offset. P cells (sustained cells), show continuous activity during stimulus onset, duration, and offset. Cortical persistence of the visual image has been found in the primary visual cortex (V1) in the occipital lobe
Occipital lobe
The occipital lobe is the visual processing center of the mammalian brain containing most of the anatomical region of the visual cortex. The primary visual cortex is Brodmann area 17, commonly called V1...
which is responsible for processing visual information.
Informational Persistence
Information persistence represents the information about a stimulus that persists after its physical offset. It is visual in nature, but not visible. Sperling's experiments were a test of informational persistence. Stimulus duration is the key contributing factor to the duration of informational persistence. As stimulus duration increases, so does the duration of the visual code. The non-visual components represented by informational persistence include the abstract characteristics of the image, as well as its spatial location. Due to the nature of informational persistence, unlike visible persistence, it is immune to masking effects. The characteristics of this component of iconic memory suggest that it plays the key role in representing a post-categorical memory store for which VSTM can access information for consolidation.Neural Basis of Information Persistence
Although less research exists regarding the neural representation of informational persistence compared to visual persistence, new electrophysiological techniques have begun to reveal cortical areas involved. Unlike visible persistence, informational persistence is thought to rely on higher-level visual areas beyond the visual cortex. The anterior superior temporal sulcusSuperior temporal sulcus
The superior temporal sulcus is the sulcus separating the superior temporal gyrus from the middle temporal gyrus in the temporal lobe of the brain. The superior temporal sulcus is the first sulcus inferior to the lateral fissure....
(STS), a part of the ventral stream, was found to be active in macaques during iconic memory tasks. This brain region is associated with object recognition
Object recognition
Object recognition in computer vision is the task of finding a given object in an image or video sequence. Humans recognize a multitude of objects in images with little effort, despite the fact that the image of the objects may vary somewhat in different view points, in many different sizes / scale...
and object identity. Iconic memory’s role in change detection has been related to activation in the middle occipital gyrus (MOG). MOG activation was found to persist for approximately 2000ms suggesting a possibility that iconic memory has a longer duration than what was currently thought. Iconic memory is also influenced by genetics and proteins produced in the brain. Brain-derived neurotrophic factor
Brain-derived neurotrophic factor
Brain-derived neurotrophic factor, also known as BDNF, is a protein that, in humans, is encoded by the BDNF gene. BDNF is a member of the "neurotrophin" family of growth factors, which are related to the canonical "Nerve Growth Factor", NGF...
(BDNF) is a part of the neurotrophin
Neurotrophin
Neurotrophins are a family of proteins that induce the survival, development, and function of neurons.They belong to a class of growth factors, secreted proteins that are capable of signaling particular cells to survive, differentiate, or grow. Growth factors such as neurotrophins that promote the...
family of nerve growth factors. Individuals with mutations to the BDNF gene which codes for BDNF have been shown to have shortened, less stable informational persistence.
Role of Iconic Memory
Iconic memory provides a smooth stream of visual information to the brain which can be extracted over an extended period of time by VSTM for consolidation into more stable forms. One of iconic memory's key roles is involved with change detection of our visual environment which assists in the perception of motion.Temporal Integration
Iconic memory enables integrating visual information along a continuous stream of images, for example when watching a movie. In the primary visual cortex new stimuli do not erase information about previous stimuli. Instead the responses to the most recent stimulus contain about equal amounts of information about both this and the preceding stimulus. This one-back memory may be the main substrate for both the integration processes in iconic memory and masking effects. The particular outcome depends on whether the two subsequent component images (i.e., the “icons”) are meaningful only when isolated (masking) or only when superimposed (integration).Change Blindness
The brief representation in iconic memory is thought to play a key role in the ability to detect change in a visual scene. The phenomenon of change blindnessChange blindness
In visual perception, change blindness is a normal phenomenon of the brain which show in light that the brain does not have a precise representation of the world but a lacunar one, made of partial details...
has provided insight into the nature of the iconic memory store and its role in vision. Change blindness refers to an inability to detect differences in two successive scenes separated by a very brief blank interval, or interstimulus interval
Interstimulus interval
The interstimulus interval is the temporal interval between the offset of one stimulus to the onset of another. For instance, Max Wertheimer did experiments with two stationary, flashing lights that at some interstimulus intervals appeared to the subject as moving instead of stationary...
(ISS). When scenes are presented without an ISS, the change is easily detectable. It is thought that the detailed memory store of the scene in iconic memory is erased by each ISS, which renders the memory inaccessible. This reduces the ability to make comparisons between successive scenes.
Saccadic Eye Movement
It has been suggested that iconic memory plays a role in providing continuity of experience during saccadic eye movementsSaccade
A saccade is a fast movement of an eye, head or other part of an animal's body or device. It can also be a fast shift in frequency of an emitted signal or other quick change. Saccades are quick, simultaneous movements of both eyes in the same direction...
. These rapid eye movements occur in approximately 30 ms and each fixation lasts for approximately 300 ms. Research suggests however, that memory for information between saccades is largely dependent on VSTM and not iconic memory. Instead of contributing to trans-saccadic memory, information stored in iconic memory is thought to actually be erased during saccades. A similar phenomenon occurs during eye-blinks whereby both automatic and intentional blinking disrupts the information stored in iconic memory.
Development of Iconic memory
The development of iconic memory begins at birth and continues as development of the primary and secondary visual systemVisual system
The visual system is the part of the central nervous system which enables organisms to process visual detail, as well as enabling several non-image forming photoresponse functions. It interprets information from visible light to build a representation of the surrounding world...
occurs. By 5 years of age, children have developed the same unlimited capacity of iconic memory that adults posses. The duration of informational persistence however increases from approximately 200 ms at age 5, to an asymptotic level of 1000 ms as an adult (>11 years). A small decrease in visual persistence occurs with age. A decrease of approximately 20 ms has been observed when comparing individuals in their early 20's to those in their late 60's. Throughout one’s lifetime, mild cognitive impairments
Mild cognitive impairment
Mild cognitive impairment is a brain-function syndrome involving the onset and evolution of cognitive impairments beyond those expected based on the age and education of the individual, but which are not significant enough to interfere with their daily activities...
(MCIs) may develop such as errors in episodic memory
Episodic memory
Episodic memory is the memory of autobiographical events that can be explicitly stated. Semantic and episodic memory together make up the category of declarative memory, which is one of the two major divisions in memory...
(autobiographical memory about people, places, and their contex), and working memory
Working memory
Working memory has been defined as the system which actively holds information in the mind to do verbal and nonverbal tasks such as reasoning and comprehension, and to make it available for further information processing...
(the active processing component of STM) due to damage in hippocampal and association cortical areas. Episodic memories are autobiographical events that a person can discuss. Individuals with MCIs have be found to show decreased iconic memory capacity and duration. Iconic memory impairment in those with MCIs may be used as a predictor for the development of more severe deficits such as Alzheimer’s disease and dementia
Dementia
Dementia is a serious loss of cognitive ability in a previously unimpaired person, beyond what might be expected from normal aging...
later in life.
Sperling's Partial Report Procedure
In 1960, George SperlingGeorge Sperling
George Sperling is an American cognitive psychologist. He is a Distinguished Professor of both Cognitive Science and Neurobiology & Behavior at the University of California, Irvine. Sperling documented the existence of iconic memory...
became the first to use a partial report paradigm to investigate the bipartite model of VSTM. In Sperling's initial experiments in 1960, observers were presented with a tachistoscopic
Tachistoscope
A tachistoscope is a device that displays an image for a specific amount of time. It can be used to increase recognition speed, to show something too fast to be consciously recognized, or to test which elements of an image are memorable. Actual tachistoscopes use a slide or transparency projector...
visual stimulus for a brief period of time (50 ms) consisting of either a 3x3 or 3x4 array of alphanumeric characters such as:
- P Y F G
- V J S A
- D H B U
Recall was based on a cue which followed the offset of the stimulus and directed the subject to recall a specific line of letters from the initial display. Memory performance was compared under two conditions: whole report and partial report.