Executive Function
An Overview of the Central Executive Component of Working Memory
Executive function is what controls the execution of complex, goal-directed activities. If a task requires numerous acts be taken in particular sequence in order to achieve success, executive function orchestrates that sequencing.
When executive function is compromised one may witness manifestations of forgetfulness, disorientation and agitation. Attention, on the other hand, is the cognitive ability to focus; to suppress extraneous stimuli and attend to that stimuli which is directly related to the task at hand.
Different Types of Executive Functioning
Research in the area of executive functioning has grown rapidly in recent years, both in the adult and developmental literatures. One of the key issues to emerge is the belief that executive functions represent not just a single type of skill, but a number of related skills (e.g. Miyake, Friedman, Emerson, Witzki, Howerter & Wager, 2000). Therefore, within the broad domain of executive functioning there are, nevertheless, separate abilities that can be distinguished.
A recent twin study has provided support for this viewpoint. Friedman, Miyake, Young, DeFries, Corley and Hewitt (2008) showed that executive functions draw on a common factor that is highly heritable, arguing that this is why different measures of executive functioning are related to each other. These authors also suggested that executive functioning is not simply another ability that can substitute for ‘intelligence.’ They have provided evidence that executive functions are not uniquely related to measures of intelligence, despite the fact that they are, nevertheless, responsible for much of what we might describe as ‘intelligent’ behavior (Friedman et al., 2006).
One of the sub-skills in the executive functioning ‘family’ of abilities has been identified as ‘working memory’, but the meaning of this term is rather specific. For example, Swanson (2006) defines working memory as:
a processing resource of limited capacity, involved in the preservation of information while simultaneously processing the same or other information. (p. 61)
There are several other skills believed to belong to the executive functioning family of abilities, and these will all be described in the remainder of this entry. However, an important point to reiterate before we do this relates to what brings together and unifies all executive functioning skills. This is that executive skills, regardless of their exact type, are used to deal with tasks that are novel; tasks that require new solutions outside routine behavior. As we have already pointed out, this is what the central executive is designed to do, so the concepts of ‘executive functioning’ and ‘central executive’ are at the very least highly overlapping, although there are uncertainties about exactly how these concepts interrelate.
In the literature on executive functioning, some authors (e.g. Pennington & Ozonof, 1996) have suggested that executive functioning can be divided into five or six discrete sub-skills. This division is often referred to as the ‘fractionation’ of executive functioning. Box 1-X describes the main areas of executive functioning identified in the literature.
| Box 1-X | Different Sub-areas of Executive Functioning |
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Other authors have suggested that there is good evidence for three sub-skills of executive functioning: inhibition, working memory and set shifting. There is a reasonable amount of evidence in children and adults for the existence of these factors (Bryson & Smith, 2008). However, not all of the evidence is entirely consistent, particularly for children. Another point to emphasize is that several of the aforementioned studies did not look for more than three factors, so this figure may be arbitrary.
Another key point that has emerged from the literature is that, whilst we can divide executive functioning into a number of distinct sub-skills, these skills are still loosely related to each other. Again, the evidence is not entirely consistent, but there is reasonably consensus that the sub-skills of executive functioning measure broadly the same types of abilities in relation to the control and regulation of behavior during complex, novel tasks (Miyake et al., 2000).
There are a wide range of tasks that have been used to assess executive skills. These areas include executive-loaded working memory, inhibition, set shifting, planning, fluency, dual-task performance and random generation. Some of these tasks have traditionally been used to study executive skills within the working memory domain, whereas others have been regarded as measuring executive functioning more broadly. This comprehensive approach has been taken to try to gain a greater understanding of executive control in typical and atypical development. However, please bear in mind that there are still uncertainties with respect to the relationships between the central executive and executive functioning in its widest sense. There is also the issue of exactly how these systems might be limited in terms of capacity, although it is clear that such capacity limitations do exist (e.g. Swanson, 2006).
The current view of the central executive has changed somewhat.
- First, the central executive is now not regarded as having any capacity for storage, rather, it is only responsible for the control and allocation of attention (Baddeley, 2000, 2007).
- Secondly, the link between the various working memory components Opens in new window and long-term memory Opens in new window is now via a new component known as the episodic buffer, which is discussed fully here Opens in new window.
Therefore, the core role of the central executive in the revised working memory model Opens in new window is in allocating attention within the working memory system, and this is done via focusing, dividing and switching attention.
Baddeley (1996) identified the following as the main functions of the central executive:
- switching of retrieval plans;
- timesharing in dual-task studies;
- selective attention to certain stimuli while ignoring others;
- temporary activation of long-term memory.
Smith and Jonides (1999) produced a somewhat similar list:
- switching attention between tasks;
- planning sub-tasks to achieve some goal;
- selective attention and inhibition;
- updating and checking the contents of working memory;
- coding representations in working memory for time and place of appearance.
Baddeley (2007) argues that there may be separate subcomponents for focusing and dividing attention, but he considers the evidence for a separate component for the switching of attention to be limited at present.
When the model of working memory was first presented (Baddeley & Hitch, 1974) little detail was given about the central executive.
Baddeley (1986) fleshed out the central executive by adopting the model put forward by Norman and Shallice (1986) of a supervisory attentional system (SAS). The SAS was responsible for intervening to direct behavior when new thought and planning was required.
In other words, this attentional system came into play when it was not possible to rely on well-learned patterns of responding. New ideas, new strategies and new plans to deal with new situations required a more demanding degree of attentional control, and this was provided by the SAS (Shallice, 1990).
Therefore, the central executive provides the higher levels of executive control that are required for carrying out novel tasks requiring new behavior or new approaches.
Box X-1 provides an example to illustrate how central executive resources may be used in novel situations.
| Box X-1 Using executive resources when things go wrong |
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| Think about driving to work using a well-known route on a day when nothing unusual happens. This probably does not require much in the way of central executive resources to focus, divide or switch attention. The route is familiar, driving is a routine process and nothing untoward occurs during the journey. However, imagine that, on a particular day, the usual route is blocked because of a burst water pipe. In this circumstance, the central executive must intervene to inhibit the well-learned behavior (i.e. following the familiar route) and work out a new plan that achieves the same goal of reaching the desired destination. Central executive resources may also be required to change the plan if other upsets occur such as traffic jams, to monitor progress, to check that the goal is being reached, and focus attention on negotiating an unfamiliar route. Note that satellite navigation systems remove much of the central executive burden from such tasks, which probably accounts for their popularity! |
Baddeley (1986) described the SAS as potential framework for the central executive because the job it does is very similar to his conceptualization of the role of the central executive.
Exeutive processes are likely to be strongly dependent upon frontal lobe functioning (Kane & Engle, 2002). For example, there is a large body of evidence from patients with frontal lobe damage showing that they often have difficulties with inhibiting well-learned patterns of behavior and arriving at new ways of solving problems Opens in new window.
They become trapped in repetitive cycles of well-learned behavior (known as perseveration) and lack the flexibility to change their behavior when novel situations arise. Baddeley refers to these general difficulties as the dysexecutive syndrome.
Therefore, it is increasingly helpful to view the central executive of working memory as a broad attentional control space. This type of system is likely to resemble very closely what many authors mean when they refer to executive functions Opens in new window. If we take a current definition of executive functions, ‘processes that control and regulate thought and action’ (Friedman, Miyake, Corley, Young, DeFries & Hewitt, 2006: 172), it becomes clear that the concepts of ‘central executive’ on the one hand, and ‘executive functions’ on the other, are very similar both in practical and theoretical terms.
Evaluation
Several findings that were hard to explain within previous versions of the working memory model are relatively easy to account for by assuming that people have an episodic buffer.
This suggests that the episodic buffer is a valuable addition to the model, and increases its ability to predict behavior in many situations. It remains for future research to clarify the processes determining what information is stored in the episodic buffer and how different kinds of information are integrated within the buffer.
See also:
- Adapted from:
- Working Memory and Academic Learning: Assessment and Intervention. A book by Milton J. Dehn.
- Cognitive Psychology: A Student's Handbook, by Michael W. Eysenck, Mark T. Keane
