The temporal trajectory of age-related decreases in executive function
Doreen Nessler¹, Ray Johnson, Jr.², Michael Bersick¹ and David Friedman¹
Task-switching studies indicate an age-related decrease in
working memory (or episodic memory [1]): Older adults’
reaction times (RTs) show a larger increase when
maintaining two task sets (in a mixed block) vs. one (mixing
costs). In contrast, age has a smaller impact on task-set
reconfiguration: The RT difference in mixed blocks between
task-set repetitions and switches to an alternative task
(switch costs) is age-invariant. However, these results vary
with the following task characteristics: switch frequency [2],
informative cue occurrence [3] and predictability [4]. Here,
we clarify the link between these characteristics and agerelated changes, and examine whether some aspects of
cognitive control, such as working memory and task-set reconfiguration, are compromised at an earlier age than others.
Methods
Participants:
15 Young (age 18 to 30); 15 Young-old (age 60 to 68); 15 Old-old (age 72 to 87)
Design:
Digit (not 5) required response: more/less than 5? or odd/even?
pure blocks: one task; mixed blocks: two tasks.
Factors: (1) Ratio of switch (S) to stay or repeat (R) trials
equiprobable; switch after 0, 1, or 2 trials: a-bb-aaa
rare switch 1:3; switch after 2, 3, or 4 trials: aaa-bbbb-aaaaa
(2) Cue-status: informative, uninformative;
(3) Predictability Status: predictable, unpredictable
Mixing costs = pre-switch RTs in mixed blocks - RTs in pure blocks
Switch costs = switch RTs – pre-switch RTs mixed blocks
Discussion
1
Target onset
300 800 1300
0
Cue onset
Baseline for
target-related ERPs
Informative Cue
400
300
200
100
0
2a
Young
Young-old
600
Old-old
400
300
200
Switch costs
100
400
300
200
100
0
0
2b
Young-old
Informative Cue
Old-old
3a Young
400
300
200
100
0
3b Young
Young-old
Old-old
1000 ms
Behavioral and ERP results indicate that the ability to
maintain two task sets in memory declines early in the aging
process (young-old), independent of task characteristics.
However, the ability to use working memory for advanced
task preparation when the upcoming task is predictable
remains intact until later in the aging process.
Task-set reconfiguration seems to be intact when task
demands are low, but compromised for rare, uninformed
switches for both groups of older adults. The age-related
decrease in the ability to reconfigure the task set could be due
to difficulties in 1) detecting the increased conflict and/or 2)
upregulating and increasing cognitive control.
Fz
7
Old-old
Cuerelated P3
Cz
4b
Old-old
target P3
Cz
Pure task
Pre-switch
Switch
Cz
Uninformative Cue
Cue
-1000
Cz
Cz
Target 1000 ms
Cz
Fig. 4a, b: The age-related increase in mixing cost (Fig. 2a, b) was
associated with a larger decrease in target P3 amplitude, most likely
reflecting task-set configuration processes that were not prepared
before target onset. (a) Despite age-invariant P3 amplitudes to the
cue, only older adults show a decrease in target P3 for pre-switch
and switch trials compared to pure trials. (b) Only the young show
a smaller decrease in the target P3 for pre-switch than switch trials.
Uninformative Cue
Fig. 3a, b: Similarly, for
young-old and old-old adults,
differences in switch costs
compared to the young were
only present for rare switches
after uninformative cues (see
arrows), which is when task
demands were highest.
Fz
Young-old
Young-old
4a
Fig. 2b: Young and youngold, but not old-old, adults
used predictability to decrease
mixing
costs
in
the
equiprobable, uninformative
switch condition (see arrows).
500
Young
Young
Fig.
2a,b:
For
all
manipulations, young-old and
old-old
adults
similarly
showed larger mixing costs
than the young.
Uninformative Cue
Young
500
Informative Cue
Equiprobable, predictable
Equiprobable, unpredictable
Rare switch, predictable
Rare switch, unpredictable
EEG recording:
62 sintered Ag/AgCl electrodes; ref.: averaged mastoids; continuous DC100Hz; 500 Hz sampling rate; Fig. 1: ERP epochs.
Baseline for cuerelated ERPs
Mixing costs
References
Introduction
¹ Cognitive Electrophysiology Laboratory, NY Psychiatric Institute, NY, NY; ² Department of Psychology, Queens College/ CUNY, Flushing, NY
Fz
baseline -200 200 400 ms
Response
MFN
Equiprobable, uninformative cue
Equiprobable, informative cue
Rare switch, uninformative cue
Rare switch, informative cue
Young-old
Old-old
Fig. 7: Response
conflict for older
adults, as indicated
by MFN amplitude,
was high regardless
of task demands.
The older adults’
impairment
in
detecting increased
conflict induced by
rare,
uninformed
switches may be due
to their having a
limit on the amount
of conflict that they
can detect (Fig. 3b).
[1] Mayr & Kliegl, 2000, JEP: Learning, Memory, and Cognition, 26, 1124-1140.
[2] Friedman, Nessler, Johnson, Ritter & Bersick, in revision.
[3] Kray, Li & Lindenberger , 2002, Brain and Cognition, 49, 363-381.
[4] Van Asselen & Ridderinkhof, 2000, Psychologica Belgica, 40, 259–273.
Fig. 5: For equiprobable, uninformed
items, the decrease
in target P3 was
smaller for predictable than for
unpredictable trials,
most likely reflecting advanced preparation (Fig. 2b),
for
young
and
young-old, but not
old-old adults.
Young
FCz
6
Young
Cz
Cz
0
5
0
Old-old
Cz
Pure task
Predictable trials
Unpredictable trials
500 1000 ms
(collapsed over pre-switch,
switch, post-switch)
Young-old
FCz
Young-old
Old-old
FCz
500 1000 ms
Pure task
Equiprobable, uninformative cue
Rare switch, uninformative cue
Fig. 6: The agerelated increase in
switch costs for
rare
uninformed
switches (Fig. 3b)
was associated with
the lack of a
significant decrease
in target P3.