Date Published: May 9, 2019
Publisher: Public Library of Science
Author(s): Otmar Bock, Mathias Haeger, Claudia Voelcker-Rehage, Antonio Verdejo-García.
Using factor analysis, several studies reported that higher-order cognitive control involves separable executive functions. However, the number and definition of the purported functions differed between studies. One possible explanation for this discrepancy is that executive functions don’t exhibit a clear factorial structure, i.e., there is no clear dichotomy between executive function tests which are well-correlated (representing a common factor) and those which are poorly correlated (representing distinct factors). We scrutinize this explanation separately in data from young and from older persons.
Young and older volunteers completed cognitive tests of the purported executive functions shifting, updating, inhibition and dual-tasking (two tests per function). Confirmatory and exploratory factor analyses yielded, for either age group, factorial structures that were within the range reported in literature. More importantly, when correlations between tests were sorted in ascending order, and were then fitted them by piecewise linear regression with a breakpoint, there was no evidence for a distinct breakpoint between low and high correlations in either age group. Correlations between tests were significantly higher in older compared to young participants, and the pattern of test pairs with high and with low correlations differed between age groups.
The absence of a breakpoint indicates that executive function tests don’t segregate into well-correlated and poorly correlated pairs, and therefore are not well suited for factor analyses. We suggest that executive functions are better described as a partly overlapping rather than a factorial structure. The increase of correlations in older participants supports the existence of age-related dedifferentiation, and the dissimilarity of correlations in the two age groups supports the existence of age-related reorganization.
It has been proposed decades ago that human cognition is coordinated and supervised by a higher-order mechanism, probably residing in the frontal cortex [1,2]. This mechanism has later been formalized as “supervisory attention system”  or “central executive” . Later authors argued that a monolithic supervisory mechanism is nothing more than a “homunculus” with little explanatory value [5,6] and instead proposed the existence of multiple supervisory processes, often under the umbrella term ‘executive functions’. As an example, one of the most influential studies in this field stipulated three executive functions, ‘updating of working memory contents’, ‘shifting between tasks or mental sets’ and ‘inhibition of prepotent responses’ .
Table 1 lists the number of participants excluded from analysis. By far the most frequent reason for exclusion was random test performance by older persons. Fifty-nine young persons (23.15 ±2.91 years old, 20 males) and forty-two older persons (69.95 ±2.94 years old, 26 males) remained for further analyses. Table 2 summarizes the data collected from home-based questionnaires for those remaining participants: older persons were somewhat less physically active, less likely to suffer an accidental fall, less often sick, and more likely to drive car over longer distances.
The present study examined the structure of executive functions in young and older persons. We found that older participants performed less well than young ones on a range of executive function tests, that bivariate correlations between test pairs failed to segregate into relatively high and relatively low correlations in either age group, and that correlations were significantly higher in older persons than in young ones.