The 3 types of sensory memory: iconic, echoic and haptic

There are many different hypotheses about the functioning of human memory that often overlap with each other. In recent years, research has shed light on key aspects of sensory memory, one of the oldest concepts in the field of scientific psychology applied to this basic process.

In this article we will define the characteristics of the three main types of sensory memory that have been described to date: iconic, echoic and haptic memory, which work with visual, sound and tactile stimuli, respectively.

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What is sensory memory?

Sensory memory allows us retain information obtained through the senses for a short period; later, these signals will be discarded or will be transmitted to other memory stores of longer duration, the working memory and long-term memory, through which it will be possible to operate on stimuli immediate.

The term "sensory memory" was coined by Ulric Gustav Neisser in 1967. His model was based on basic research and defined sensory memory as

a short-lived record, of unlimited and precategorical capacity, that is, prior to the cognitive processing of information and consequently beyond conscious control.

Previously, in 1958, Donald Eric Broadbent had proposed the existence of a perceptual system through which all sensory stimuli before reaching short-term memory and being filtered for conscious processing of larger items relevant.

In its original formulation Neisser considered that there are two types of sensory memory: the iconic, which processes visual information, and the echoic, based on auditory and verbal stimuli. Subsequently, solid evidence has been found in favor of the existence of haptic memory, related to touch and proprioception.

Sensory memory types

Although it is considered that there are probably short-term memory stores for all the senses, those that have been studied in greater depth are iconic, echoic and haptic memory.

1. iconic memory

The most researched type of sensory memory is iconic, which records visual information. The most relevant contributions regarding this phenomenon were made by George Sperling in the 50s and 60s, but later authors such as Neisser, Sakkit and Breitmeyer have updated the conception of memory iconic.

Through his pioneering tachistoscope studies, Sperling concluded that people we have the capacity to simultaneously retain 4 or 5 items After fixing your gaze for an instant on a wide stimulating set. Other researchers found that iconic memory persists for about 250 milliseconds.

In this case the visual trace is called “icon” that we hold 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 conception that iconic memory is fundamentally a laboratory artifact with no ecological validity predominates.

Most likely, this phenomenon is related to the persistence of the neural stimulation in photoreceptors located in the retina, that is, the cones and rods. This system could have the function of allowing the processing of visual stimuli by the perceptual system.

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2. echoic memory

In a similar way to the iconic memory, echoic memory has been defined as a precategorical record, of short duration and with a very high capacity. It differs from the iconic one in that it processes sound information instead of visual information.

echoic memory retains auditory stimuli for at least 100 milliseconds, allowing us to discriminate and recognize sounds of all kinds, including those that make up speech, which can last up to 2 seconds; therefore, echoic 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 length of time that the echoic imprint is retained depends on stimulus properties such as complexity, intensity, and pitch.

A remarkable phenomenon in relation to echoic memory is the recency effect, which is specific to this type of memory. It consists of the fact that we remember the last stimulus (or item) that we have processed better than others that have been presented immediately before.

Echoic memory has been associated with the hippocampus and with different areas of the cerebral cortex: the premotor, the left posterior ventrolateral prefrontal, and the left posterior parietal. Lesions in these regions cause deficits in the perception of visual stimuli and in the speed of reaction to them.

3. haptic memory

This concept is used to designate a memory store that works with tactile information, and therefore with sensations such as pain, heat, itching, tickling, pressure or vibration.

The haptic memory has a capacity of 4 or 5 items, like the iconic one, although the trace is maintained for a longer time, about 8 seconds in this case. This type of sensory memory allows us to examine objects by touch and interact with them, for example to pick them up or move them properly.

It is believed that there are two subsystems that make up haptic memory. On the one hand we find the cutaneous system, which detects the stimulation of the skin, and on the other the proprioceptive or kinesthetic, related to muscles, tendons and joints. It is convenient to distinguish proprioception from interoception, which involves internal organs.

Haptic memory has been defined more recently than iconic and echoic, so scientific evidence available around this type of sensory memory are more limited than those around the other two we have discussed. described.

haptic memory depends on the somatosensory cortex, especially from regions located in the superior parietal lobe, which store tactile information. Likewise, the prefrontal cortex, essential for movement planning, also seems to be involved in this function.