Sensory memory

Key takeaways

Sensory memory belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Sensory memory to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sensory memory from memory before moving on to harder problems.

Reference excerpt

During every moment of an organism's life, sensory information is being taken in by sensory receptors and processed by the nervous system. Sensory information is stored in sensory memory just long enough to be transferred to short-term memory. Humans have five traditional senses: sight, hearing, taste, smell, touch. Sensory memory (SM) allows individuals to retain impressions of sensory information after the original stimulus has ceased. A common demonstration of SM is a child's ability to write letters and make circles by twirling a sparkler at night. When the sparkler is spun fast enough, it appears to leave a trail which forms a continuous image. This "light trail" is the image that is represented in the visual sensory store known as iconic memory. The other two types of SM that have been most extensively studied are echoic memory, and haptic memory; however, it is reasonable to assume that each physiological sense has a corresponding memory store. For example, children have been shown to remember specific "sweet" tastes during incidental learning trials but the nature of this gustatory store is still unclear. However, sensory memories might be related to a region of the thalamus, which serves as a source of signals encoding past experiences in the neocortex.

Characteristics SM is considered to be outside of cognitive control and is instead an automatic response. The information represented in SM is the "raw data" which provides a snapshot of a person's overall sensory experience. Common features between each sensory modality have been identified. However, as experimental techniques advance, exceptions and additions to these general characteristics will surely evolve. The auditory store, echoic memory, for example, has been shown to have a temporal characteristic in which the timing and tempo of a presented stimulus affects transfer into more stable forms of memory. Four common features have been identified for all forms of SM:

The formation of a SM trace is only weakly dependent on attention to the stimulus. The information stored in SM is modality specific. This means, for example, that echoic memory is for the exclusive storage of auditory information, and haptic memory is for the exclusive storage of tactile information. Each SM store represents an immense amount of detail resulting in very high resolution of information. Each SM store is very brief and lasts a very short period of time. Once the SM trace has decayed or is replaced by a new memory, the information stored is no longer accessible and is ultimately lost. All SM stores have slightly different durations which is discussed in more detail on their respective pages. It is widely accepted that all forms of SM are very brief in duration; however, the approximated duration of each memory store is not static. Iconic memory, for example, holds visual information for approximately 250 milliseconds. The SM is made up of spatial or categorical stores of different kinds of information, each subject to different rates of information processing and decay. The visual sensory store has a relatively high capacity, with the ability to hold up to 12 items. Genetics also play a role in SM capacity; mutations to the brain-derived neurotrophic factor (BDNF), a nerve growth factor, and N-methyl-D-aspartate (NMDA) receptors, responsible for synaptic plasticity, decrease iconic and echoic memory capacities respectively.

Types

Iconic memory The mental representation of the visual stimuli are referred to as icons (fleeting images.) Iconic memory was the first sensory store to be investigated with experiments dating back as far as 1740. One of the earliest investigations into this phenomenon was by Ján Andrej Segner, a German physicist and mathematician. In his experiment, Segner attached a glowing coal to a cart wheel and rotated the wheel at increasing speed until an unbroken circle of light was perceived by the observer. He calculated that the glowing coal needed to make a complete circle in under 100ms to achieve this effect, which he determined was the duration of this visual memory store. In 1960, George Sperling conducted a study where participants were shown a set of letters for a brief amount of time and were asked to recall the letters they were shown afterwards. Participants were less likely to recall more letters when asked about the whole group of letters, but recalled more when asked about specific subgroups of the whole. These findings suggest that iconic memory in humans has a large capacity, but decays very rapidly. Another study set out to test the idea that visual sensory memory consists of coarse-grained and fine-grained memory traces using a mathematical model to quantify each. The study suggested that the dual-trace model of visual memory out-performed single-trace models.

Echoic memory

Echoic memory represents SM for the auditory sense of hearing. Auditory information travels as sound waves which are sensed by hair cells in the ears. Information is sent to and processed in the temporal lobe. The echoic sensory store holds information for 2–3 seconds to allow for proper processing. The first studies of echoic memory came shortly after Sperling investigated iconic memory using an adapted partial report paradigm. Today, characteristics of echoic memory have been found mainly using a mismatch negativity (MMN) paradigm which utilizes EEG and MEG recordings. MMN has been used to identify some of the key roles of echoic memory such as change detection and language acquisition. Change detection, or the ability to detect an unusual or possibly dangerous change in the environment independent of attention, is key to the survival of an organism. One study focusing on echoic sensory changes suggested that when a sound is presented to a subject, it is enough to shape an echoic memory trace that can be compared to a physically different sound. Change-related cortical responses were detected in the superior temporal gyrus using EEG. With regards to language, a characteristic of children who begin speaking late in development is reduced duration of echoic memory. In short, "Echoic memory is a fast-decaying store of auditory information." In the case of damage to or lesions developing on the frontal lobe, parietal lobe, or hippocampus, echoic memory will likely be shortened and/or have a slower reaction time.

Haptic memory

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Sensory memory

Start with the simplest possible case. Write down what Sensory memory claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sensory memory before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sensory memory ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sensory memory

In research: Sensory memory appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Sensory memory in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Sensory memory is common in secondary-school and first-year university syllabi. It links to neighbouring topics Memory, Senses, so understanding it makes those chapters shorter.
In everyday life: Look for Sensory memory outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Sensory memory in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sensory memory means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Sensory memory out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sensory memory in simple terms?

During every moment of an organism's life, sensory information is being taken in by sensory receptors and processed by the nervous system. Sensory information is stored in sensory memory just long enough to be transferred to short-term memory.

Why does Sensory memory matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sensory memory?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sensory memory.