Executive functions and frontal lobe tasks - Miyake et al., - 2000 - Article

Introduction

People with frontal lobe damage seem to have serious problems controlling their behavior and have problems functioning on a daily basis. They seem to have impairments on several complex frontal lobe tasks. Executive functions (or frontal lobe tasks) are general-purpose control mechanisms that modulate the operation of various cognitive sub-processes and thereby regulate the dynamics of human cognition. Unfortunately, there is not yet a decent theory that can explain how these are organized and what their role is in complex cognition. The scientific world lacks research on how specific cognitive processes are being controlled and coordinated during the performance of complex cognitive tasks.

In this research the focus is on three executive functions (or frontal lobe tasks), namely the shifting of mental sets, monitoring and updating of working memory representations and inhibition of prepotent responses.

Baddeley’s multicomponent model of working memory

Baddeley’s model has three components. One component is specialized in maintaining speech-based, phonological information, also called the phonological loop. A second component maintains visual and spatial information, also called the visuospatial sketchpad. The third component is the central executive, which controls and regulates cognitive processes. It is this third component which is often linked to frontal lobe functioning.

This research

Here will be researched to what extent different functions that are often attributed to the frontal lobes or to the central executive, can be considered unitary in the sense that they are reflections of the same underlying mechanism or ability. There are many correlational, factor-analytic studies that theorize about the organization of frontal lobe tasks. However, there are many problems with these studies. A new and more promising approach is latent variable analysis.

This research

The focus lies on the three frontal lobe tasks, and the extent of unity or diversity of these functions at the level of latent variables will be examined. They will statistically extract what the functions have in common, in order to tap a putative executive function. They will use that latent variable factor to examine how different frontal lobe tasks relate to one another.

The study is meant to provide a stronger assessment of the relationships between the three frontal lobe tasks. The two goals are specifying the extent to which the three executive functions are unitary or separable, and specifying their relative contributions to more complex tests that are often used to evaluate executive functioning.

Shifting between tasks or mental sets

This function concerns shifting back and forth between multiple tasks, operations or mental sets. A very simplistic interpretation of this function is the disengagement of an irrelevant task and changing to active engagement of a relevant task. This function will be referred to as “shifting”.

Updating and monitoring of working memory representations

This function has been chosen due to its supposed association with the working memory and therefore its connection to the prefrontal cortex. The function concerns monitoring and coding incoming information for relevance to the task at hand, and then correctly revising the items that are being held in the working memory by replacing the old and no longer relevant information with newer, more relevant information. It is not passively storing information, but actively manipulating relevant information in the working memory. This function will be referred to as “updating”.

Inhibition of dominant or prepotent responses

This function concerns someone’s ability to deliberately inhibit dominant, automatic or prepotent responses when necessary.

Results

First goal: the extent to which the three executive functions are unitary or separable

The results are very clear: the full three-factor model in which the correlations among the three frontal lobe tasks were allowed to vary freely, was a significantly better fit to the data than any other model that assumed total unity among two or all three of the latent variables. However, the tasks do have something in common, because they are not completely independent. They are indeed separable, but also moderately correlated constructs. This result points to unity

Second goal: specifying the relative contributions of the frontal lobe tasks to more complex tests that are often used to evaluate executive functioning

The results for the second goal are less clear. The frontal lobe tasks that are often used in scientific research are not completely homogeneous, in the sense that the different tasks contribute differentially to performance on these tasks.

Conclusion

Both unity and diversity of frontal lobe tasks should be taken into consideration when developing a theory of executive functions. The results have shown that the tasks are separable, but they also share some underlying commonality. What that commonality might be has to be focused upon in future research. Here, two possible explanations are given.

Common task requirements

It is possible that the different tasks shared some common task requirements, for instance the maintenance of goal and context information in working memory.

Inhibitory operation processes

A second possibility is that the tasks all involve some sort of inhibitory processes to operate properly. In one task for instance, one has to ignore irrelevant incoming information. In another task, one has to forget information which is no longer relevant. Even though these are not conceptually the same, this type of inhibition may be related to more controlled and deliberate inhibition of the prepotent responses. This could possibly explain the moderate correlations between the tasks. Further research is necessary to find out what this inhibition really entails.