Chapter One
Working Memory Models

In their attempts to better understand the workings of the mind, psychologists develop explanatory models known as constructs. A hypothetical construct is inferred from data because it is not directly observable. For example, intelligence is a well-known and long-debated construct that cannot be directly observed or measured. This book is about working memory (WM), one of the most influential psychological constructs of the past 40 years. The behaviors associated with WM are measurable and real. However, the underlying construct associated with these behaviors remains hypothetical. Its exact nature, functioning, neurological structure, and even its name are still open to debate and refinement.

WM is the cognitive ability to briefly hold, maintain, or store information while processing the same or other information. Simply put, brief storage plus simultaneous cognitive processing equals WM. The brief storage aspect is commonly referred to as short-term memory (STM). Thus, the construct of WM includes STM, with WM having a supervisory role over the STM component (Baddeley, 1986). The supervisory role is just one of WM's executive functions. WM is complex; it has both cognitive and metacognitive dimensions (Dehn, 2014a).

Don't Forget

Working memory occurs whenever there is concurrent temporary storage and processing of information. Short-term memory provides the storage function. Thus, short-term memory is embedded within working memory. In this book, the term "working memory" includes short-term memory.

What makes WM so interesting and so influential is that it is very limited in humans, and these limitations have significant consequences for all sorts of human endeavors. Without keeping information refreshed in WM, it will be retained only for a few seconds. In the typical adult, only four to seven pieces of information can be maintained in WM during cognitive processing (Cowan, 2001).

Psychologists were measuring WM long before the construct was even proposed. The digit span test goes back more than 100 years. This test includes digits backward, which requires the examinee to reverse the sequence of orally presented digits. Digits backward is now recognized as a robust measure of WM. Prior to the 1990s, the widely used Wechsler Intelligence Scale for Children incorporated the digit span subtest into a composite score it called Freedom From Distractibility, a label that describes one of WM's key functions but gave psychologists little understanding of what they were actually measuring.

Caution

Despite working memory's wide-ranging influence, the definition of working memory should remain narrow. For example, reasoning and working memory are not the same thing, even though reasoning heavily depends on working memory capacity.

When defining WM and discussing the roles that it plays in cognitive functioning, it is important to consider how WM is typically measured. The usual task requires the maintenance of oral or visual stimuli while processing those stimuli in some manner. What is actually measured is not the processing but the number of sequential items (a span) that is retained. All of the empirical data on how WM is related with cognitive abilities, academic learning, and daily functioning is based on such traditional span measures of WM. Consequently, the definition and application of the WM construct should not go beyond how it is measured. For example, WM should not be equated with intelligence, general executive functioning, or all conscious mental activity. When the definition goes beyond the measurement of the construct, then WM becomes too inclusive and less meaningful. Also, very broad applications of the construct create false impressions that WM training should lead to improved functioning in psychological processes that may not really be WM.

Working Memory's Influence

Nearly all cognitive and metacognitive functions are closely interrelated with WM. For example, language expression, processing speed, reasoning, phonological processing, attentional control, and executive functions have high correlations with WM (see Chapter 2). Furthermore, nearly all aspects of learning, especially academic learning, depend on adequate levels of WM (see Chapter 4). Finally, performance and application of skills, as well as cognitively challenging daily activities, depend on WM. A short list of activities that are influenced by WM capacity includes:

• Keeping up with the flow of a conversation and remembering what one was going to say.
• Noticing errors that are contained in a written sentence one just produced.
• Keeping track of one's place while counting.
• Being able to take detailed notes while listening at the same time.
• Remembering multistep directions that were just presented or read.
• Completing a task in a time-efficient manner.
• Coping with distractions while thinking.
• Comprehending what is being said or read.
• Remembering what one was going to do next.
• Keeping track of subproducts while doing mental arithmetic.
• Being able to switch between mental tasks.
• Being able to reason, such as comparing and contrasting two concepts.
• Integrating visual and auditory information.
• Efficiently memorizing information.
• Consciously retrieving a name or word that does not come immediately.

Obviously, a normal WM ability is essential for all kinds of cognitive, learning, and daily activities (Engle, 2002). Consequently, unusual shortcomings or deficits in WM can lead to all kinds of problems. Such problems include forgetfulness, inattentiveness, difficulty following directions, difficulty completing tasks, difficulty communicating, and various types of learning disorders.

Baddeley's Working Memory Model

The predominant model of WM was originally proposed by Baddeley and Hitch in 1974 and later expanded by Baddeley (1986, 2000). The Baddeley model of WM is the theoretical basis of the majority of research on WM. This multicomponent model has been validated through neuropsychological research and has been operationalized in measurement instruments. Baddeley defines working memory as "a system for the temporary holding and manipulation of information during the performance of a range of cognitive tasks such as comprehension, learning, and reasoning" (1986, p. 34). The original multifaceted model was made up of three components: a phonological loop, a visuospatial sketchpad, and a central executive. In 2000, Baddeley added another component-the episodic buffer (see Rapid Reference 1.1). Baddeley's model is hierarchical, with the central executive as the top-level, domain-free facet that controls all of the subcomponents.

Rapid Reference 1.1 Baddeley's Working Memory Model

Figure 1.1 Baddeley's Working Memory Model

The Phonological Loop

What Baddeley refers to as the phonological loop is also known as auditory, phonological, or verbal short-term memory. (In this text, this aspect of WM will be called phonological short-term memory.) The phonological loop is a limited capacity component that briefly stores verbal information in phonological form. Baddeley (1986, 2003a) divides the phonological loop into passive storage and subvocal, articulatory rehearsal. The number of unconnected verbal items (such as words from a list) that can be retained in the phonological loop depends on the time it takes to articulate them (Baddeley, 2003a). Individuals can recall only a sequential span that they can articulate (aloud or subvocally) within 2 seconds (Ellis & Hennelley, 1980; Hulme & Mackenzie, 1992). For instance, if an individual's speech rate is two monosyllable words per second, his memory span will be about four monosyllable words. Thus, auditory STM span varies according to the length of the words and the individual's speech rate. Individuals with faster articulation rates can maintain more items than individuals who are slow articulators (Hulme & Mackenzie, 1992). Also, more monosyllable words can be retained than multisyllable words. For adults, normal phonological loop span is approximately seven monosyllable units.

Despite the strong evidence that word length and articulatory rehearsal speed determine auditory STM span, other influences also affect memory span. One influence is prior knowledge. Meaningful phonological information may activate relevant long-term memory (LTM) representations, which may then facilitate immediate recall from short-term storage. For instance, the average adult has a longer span for meaningful words than for pseudo-words. The degree of chunking or grouping of items into larger units also affects span. For example, the separate digits "five" and "eight" can be chunked as "fifty-eight." Also, individuals can remember sentences that take several seconds to articulate because the sentences can be chunked into meaningful phrases or ideas.

Subvocal rehearsal seems to largely determine verbal span because whenever individuals are prevented from rehearsing, performance is markedly impaired. The typical interference task prevents rehearsal by requiring the participant to engage in an unrelated attention-demanding task, such as counting. The impact of disrupting phonological short-term rehearsal...