Executive functions in normal aging: the mediating effect of processing speed and attentional system

Objective
The normal aging is associated with decrease in executive functioning efficiency. However,
the source of these cognitive difficulties could reside in some factors that are not executive
per se. Therefore, this present study is aimed at determining whether speed of processing and
attentional variables would mediate the effect of age on the executive functioning.
Participants and Methods
Young (n = 104) and old (n = 63) participants were enrolled and carried out a large battery
made of 21 executive (inhibition, shifting, working memory updating, and double task
coordination), attentional (phasic alertness, selective attention, and sustained attention), and
processing speed tasks. Based on Baron & Kenny’s recommendations (1986), mediation
models of the age effect on the executive functioning were carried out with processing speed
and attentional system taken as mediators.
Results
Selective attention significantly mediated the effect of age on working memory updating [􀇻R2
= 7%, p < .001]. Moreover, processing speed significantly mediated the effect of age on
shifting [􀇻R2 = 7%, p < .001], working memory updating [􀇻R2 = 5%, p < .001], and double
task coordination [􀇻R2 = 14%, p < .001].
Conclusions
The mediating effect of age on most of the executive functions by measures of processing
speed is in agreement with the literature showing a major influence of the slowdown of the
processing speed on cognition (Salthouse, 1992; 2000; 2005). The age effect on inhibition did
not seem to be mediated neither by the attentional variables nor the speed variables, which is
in accordance with Zacks & Hasher’s hypothesis (1988). According to these authors,
inhibition would be the first cognitive function to decline with age.