One distinction we usually make when talking about different human memory systems is between working memory and short-term memory.

In the existing literature, some authors consider short-term memory to be a subset of working memory, whereas others argue for the inverse relationship, and finallythere are those who use both terms interchangeablybecause they see both as the same memory system. Thus, there is no consensus in this ongoing theoretical debate [1].

In the clinical setting, however, we do make an explicit distinction between short-term memory spantests(or simple span tasks–for example,WAIS-IV “Digit Span Forward”) and working memory span tests (or complex span tasks–for example,WAIS-IV “Digit Span Backward” and “Digit Span Sequencing”).

So, what do we mean by short-term memory and working memory? What are the differences between the two?

Defining different types of memory: working memory and short-term memory

While the concept of short-term memory primarily refers to the capacity to hold information in mind in an active state for a brief period of time (30-40 seconds)[2], the concept of working memory or operative memory, by contrast, emphasizes the role of memory as a control system for information processing [1], and is defined as a memory system for the temporary storage and manipulation of information, that underlies more complex cognitive processes such as language comprehension, reading, and reasoning [2,]

Therefore, while both types of memory are characterized by temporary storage and activation of information in consciousness, working memory adds a manipulation component, that is, it transforms the information; working memory builds relationships between different data that it manages, and integrates these data with information stored in long-term memory, thereby enabling the performance of important cognitive processes such as language comprehension and reasoning.

The revised version of Baddeley’s working memory model

Probably, the most widespread working memory model nowadaysis the modelproposed by Baddeley in 2000.

As we all recall, this model consists of a central executive component (CE) and 3 subordinate systems that process different types of information: the visuospatial sketchpad, the phonological loop, and the episodic buffer[2].

• The phonological loop is the system that temporarily stores information inspeech-based form; this information is kept active by means of articulatory rehearsal, that is, viasubvocal speech: orofacial muscle movement occurs during rehearsal of information, as if the words were repeated out loud, but without generating any sound[2,3].

Here is a common exampleused to better understand this component. A person has just told you a number with various digits (a password, for example) and, as you search for a paper to record it, you repeat it to yourself subvocally so you do not forget it. If someone distracts you before writing it down, therehearsal is interrupted and you may no longer remember the number.

The phonological loop is responsible for the transient storage of verbal information (e.g.: reading), and for maintaining inner speech that is involved in short-term memory[3].

• The visuospatial sketchpad deals with visual and spatial information. This system temporarily holds and manipulates images, allowing us to create and usethese images and orient ourselves in space [2,3].
• The episodic buffersimultaneously stores phonological information from the loop and visual and spatial information from the sketchpad, in addition to integrating information from long-term memory, thereby creating a multimodal representation of the present situation [3].
• The central executive(CE) or supervisory attentional system (SAS) is a higher-order system responsible for the control, supervision, and selection of strategies; with information coming from the three previous subcomponents, the CE detects novel situations in order to respond to them by activating executive processes of anticipation, planning, and monitoring.

Working memory a.k.a.Attentional operative system

Tirapu-Ustárroz and Muñoz-Céspedes [3] stress that this latter component inBaddeley’s model, the CE or SAS, does not store information (it does not have a storage nature),and suggest that it carries out 6 interrelated sub-processes associated with executive functions:

1. Coding/maintenance of information that exceeds the capacities of the phonological loop and the visuospatial sketchpad.
2. Maintenance/updating: the ability of the CE/SAS to maintain and update information.
3. Maintenance and manipulation of information.
4. Dual-task:the ability to simultaneously work with the loop and the sketchpad.
5. Inhibition: the ability to inhibit irrelevant stimuli such as stimuli in Stroop paradigms.
6. Cognitive shifting: includes processes of maintenance, inhibition, and updating of mental sets.

In their review of the working memory concept and its relationship to executive functions[3], the authors also propose that the term working memory is inappropriate, since working memoryactually has more to do withan attentional system that works and operateswith the contents of memory activated, than with temporary memory storage, thereby defining working memory as “an attentional operative system that works with memory contents.”

Difference between working memory and short-term memory

In addition to the previously mentioned distinctions based on the definitions of working memory and short-term memory, differences between these two types of memory have been identified in relation to their different attentional demands.

As noted above[3,4], working memory is the system responsible for maintaining and manipulating information when the information to be maintained or the task to be performed is of such complexitythat the cognitive system becomes overloaded, so that short-term memory ends up being insufficient.

According to this,the activation of working memory ischallenging for our attentional resources; therefore, in high-load tasks such as carrying out an activity while simultaneously performing adistracting task, the subvocal rehearsalof the phonological loop is impeded by the attentional demand of the distracting task.In contrast, this does not occur in short-term memorytasks (e.g.:forward digit span).

In addition, working memory tasks positively correlate with measures of intelligence and executive function, whereas short-term memory tasks do not correlate very well.

NeuronUP has developed several exercises to train different working memory components, including verbal and visuospatial modalities, and specific exercises to train dual-task performance. If you are a neurorehabilitation professional and would like to try them out, ask for a free trial of the platform:

Bibliography

1. Ruiz-Vargas, J. M. (2010). La memoria a corto plazo. En: Manual de psicología de la memoria, pp. 147-179. Madrid: Síntesis.
2. Tirapu-Ustárroz, J. y Grandi, F. (2016). Sobre la memoria de trabajo y la memoria declarativa: propuesta de una clarificación conceptual. PanamericanJournal of Neuropsychology, 10 (3): 13-31.
3. Tirapu-Ustárroz, J. y Muñoz-Céspedes, J.M. (2005). Memoria y funciones ejecutivas. Revista de Neurología, 41 (8): 475-484.
4. Cowan, N. (2008). What are the differences between long-term, short-term, and working memory? Progress in BrainReserarch, 169: 323-338.