There are many different assumptions about how human memory works, which often overlap. In recent years, research has clarified key aspects of sensory memory, one of the oldest concepts in scientific psychology applied to this basic process.
In this article, we will define the characteristics of the three main types of sensory memory which have been described to date: iconic, echoic and haptic memory, which function respectively with visual, sound and tactile stimuli.
What is sensory memory?
Sensory memory allows us retain information obtained by the senses for a short time; subsequently, these signals will be rejected or transmitted to other stores of longer term memory, working memory and long term memory, through which immediate stimuli can be actuated.
The concept of “sensory memory” was invented by Ulric Gustav Neisser in 1967. His model was based on basic research and defined sensory memory as a recording shortens the duration, Unlimited and pre-categorical capacity, that is to say prior to cognitive processing of information and consequently of others to conscious control.
Earlier, in 1958, Donald Eric Broadbent had proposed the existence of a perceptual system through which all sensory stimuli would pass before reaching short-term memory and being filtered for conscious processing of the most relevant elements.
In its original formulation Neisser considers that there are two types of sensory memory: The iconic, which processes visual information, and the economic, based on auditory and verbal stimuli. Subsequently, strong evidence was found to support the existence of haptic memory, related to touch and proprioception.
Types of sensory memory
Considering that there are probably short-lived mnemonic memories for all the senses, those which have been studied in more depth iconic memory, echo and haptics.
1. Emblematic memory
The most sought-after type of sensory memory is the iconic, which records visual information. The most relevant contributions to this phenomenon were made by George Sperling in the 1950s and 1960s, but later authors such as Neisser, Sakkit, and Breitmeyer updated the conception of iconic memory.
Through his pioneering tachistoscope studies, Sperling concluded that people we have the possibility to keep 4 or 5 elements simultaneously after looking for a while at a large set of stimuli. Other researchers have found that iconic memory persists for around 250 milliseconds.
In that case is called “icon” in the visual imprint that we keep in short-term memory. There is currently a debate as to whether this ICON is located in the central or peripheral nervous system; in any case, the predominant view is that iconic memory is fundamentally a laboratory artefact with no ecological validity.
Most likely, this phenomenon is related to the persistence of neuronal stimulation at the photoreceptor level located in the retina i.e. cones and rods. This system could have the function of allowing the processing of visual stimuli by the perceptual system.
2. Ecological memory
Similar to the iconic, echo memory has been defined as a pre-categorical, short duration, very large capacity recording. It differs from the iconic in that it deals with sound information rather than visual.
Ecological memory retains auditory stimuli for at least 100 milliseconds, Allowing us to distinguish and recognize sounds of all kinds, including those that make up speech, which can last up to 2 seconds; therefore, echogenic memory is fundamental in the understanding of language.
It is understood that this type of memory records auditory information in the form of a sequence, thus focusing on its temporal properties. In part, the time that the echo imprint is retained depends on stimulus properties such as complexity, intensity, and tone.
A notable phenomenon in relation to echo memory is the recency effect, which is specific to this type of memory. It is that we remember the last stimulus (or document) that we processed better than others that were presented immediately before.
Echo memory has been linked to the hippocampus and to different areas of the cerebral cortex: the premotor, the left posterior ventrolateral prefrontal, and the left posterior parietal. Injury in these areas results in deficits in the perception of visual stimuli and in the speed of reaction to them.
3. Haptic memory
This concept makes it possible to designate a mnemonic memory which functions with tactile information, and therefore with sensations such as pain, heat, itching, tingling, Pressure or vibration.
The haptic memory has a capacity of 4 or 5 elements, like the iconic, although the imprint stays longer, around 8 seconds in this case. This type of sensory memory it allows us to examine objects by touch and interact with them, for example to grab or move them correctly.
It is believed that there are two subsystems that make up haptic memory. On the one hand we find the skin system, which detects skin stimulation, and on the other hand proprioceptive or kinesthetic, Linked to muscles, tendons and joints. It is advisable to distinguish proprioception from interoception, which involves the internal organs.
Haptic memory has been defined more recently than iconic and echo, so the scientific evidence available around this type of sensory memory is more limited than it is on the other two we’ve described.
Haptic memory depends on the somatosensory cortex, Mainly regions located in the upper parietal lobe, which store tactile information. Likewise, the prefrontal cortex, fundamental for planning movement, also seems to be involved in this function.