Dramatically Larger Flanker Effects
E81
Sarah Munro, Cecil Chau, Karine Gazarian, & Adele Diamond
3 mm
Sample
Stimulus
in Study 2
200
150
100
50
> or


OUTSIDE
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
>
<
OUTSIDE
>
Study 1: 96 young adults Study 2: 32 young adults
Both studies: 50% female; mean age 22 years
50% Chinese Canadians; 50% European Canadians
200
150
100
50
BLOCK BLOCK 3
1
(MIXED)
14 x larger in mixed block
123 msec difference
BLOCK BLOCK 3
(MIXED)
1
6 x larger in mixed block
74 msec difference
Out
Small
Study 2
250
NS
150
100
50
0
STUDY 1 STUDY 2
Large
Small
STUDY 1 STUDY 2
Small
Large
However, in the Mixed-task block, the Flanker
effect was much less sensitive to the size or
dispersion of the stimuli. There was no significant
difference in the size of the Flanker effect in the
Mixed block in Studies 1 or 2.
0.10
Smaller, Closer Stimuli (Study 2) Only
Studies 1 and 2 Combined
0.05
BLOCK BLOCK 3
(MIXED)
1
BLOCK BLOCK 3
1
(MIXED)
10 x larger in mixed block
SEPARATED
CUE
INTEGRATED
CUE
300
BLOCK 1
(Standard Flanker)
BLOCK 3
(MIXED)
250
NS
200
150
100
50
0
SQUARES ARROWS
SQUARES ARROWS
300
250
BLOCK 3
(MIXED)
BLOCK 1
(Standard
Flanker)
NS
BLOCK 5
(Standard
Flanker)
200
150
100
50
0
Squares Arrows
Squares Arrows
Squares Arrows
In the standard flanker condition, the type of stimulus used significantly affected the size of the Flanker
effect. The Flanker effect was much larger for Iconic Stimuli (Arrows) than for Symbolic Stimuli
(Squares). However, in the Mixed-task block, the Flanker effect was insensitive to stimulus type. There
was no significant difference in the size of the Flanker effect in the Mixed block whether arrows or
squares served as the stimuli.
250
NOT DUE TO PRACTICE EFFECTS
200
150
Flanker Effect by Block for Study 2 Non-Switch Trials Only
100
50
0
BLOCK BLOCK 3
(MIXED)
1
75 x larger in mixed block
213 msec difference
BLOCK BLOCK 3
1
(MIXED)
72 x larger in mixed block
144 msec difference
Regardless of whether the cue indicating which rule to follow (focus on central figure or flankers) was
part of the stimuli (their shape – the Integrated Cue condition) or external to the stimuli (the background
color – the Separated Cue condition), the Flanker effect was much larger in the Mixed Block than in the
Single Task Block. This was true for the standard flanker condition and for focus-on-the-flanker trials.
300
Block 1
Block 2
Block 3
(Mixed)
Block 4
Block 5
250
200
150
100
50
0
IN OUT
IN OUT
IN OUT
IN OUT
OUTSIDE
>

<


OUTSIDE
OUTSIDE
< OUTSIDE >
<
INSIDE
>
INSIDE
<
INSIDE
>
OUTSIDE
< OUTSIDE >
OUTSIDE
< OUTSIDE >
Mean RT for each Trial Type
for Inside, Non-Switch Trials in Study 2
505
495
485
475
465
455
445
435
425
415
BLOCK 1
(Standard Flanker)
BLOCK 3 (MIXED)
1050
1000
950
900
850
800
750
700
650
600
Cong No- Neu Incong
Cong No- Neu Incong
Dis
Dis
Congruent and No-Distractor trials were equally easy in the standard
Flanker task, but No-Distractor trials were far easier in the Mixed condition.
CONCLUSIONS
MAIN FINDINGS:
Squares vs. Arrows for Standard and Mixed Blocks Inside Non-Switch Trials
0.15
>
Order of trial types was counterbalanced within blocks.
Percentage of each trial type was: 43% Incongruent, 29% Congruent,
14% Neutral, and 14% No-Distractor trials.
RT in msec
Consistent with past studies, we found a larger
Flanker effect in the Standard Flanker task block
(Block 1) when the stimuli were smaller and
closer (Study 2) than when they were larger and
farther apart (Study 1). The Flanker effect was far
smaller with the larger stimuli.
BLOCK 3
(Mixed Block)
200
0.20
300
BLOCK 1
(Standard Flanker)
INSIDE

Large
Study 1
Small
Study 2
In
<

Out
In
INSIDE

Flanker Effect in msec
Relative Flanker Effect
INTEGRATED
CUE
300
Stimulus Size:
0.25
OUTSIDE
250
0
INSIDE
SEPARATED
CUE
Out
Larger, Farther Apart Stimuli (Study 1) vs. Smaller, Closer Stimuli (Study 2) for
Standard Flanker Blocks and Mixed Blocks (Inside Non-Switch Trials)
0.30
49 x larger in mixed block
16 x larger in mixed block
223 msec difference
Flanker Effect in msec
Flanker Effect in msec




>
The other 50% of subjects in Study 1
were tested with an Integrated Cue (the Stimulus Shape):
or >
Rules: If images are,
If images are,
or
focus on the INSIDE stimulus
focus on the OUTSIDE stimulus
<
0.35
0
BLOCK BLOCK 3
(MIXED)
1
STUDY 2
0.40
INSIDE
300
INSIDE
0.45
STUDY 1
Flanker Effect in Block 1 vs. Block 3 (Mixed Block) Non-Switch Trials
If pink background,
focus on the OUTSIDE stimulus
OUTSIDE
Relative RT difference: (I – C) / C
“Outside” Trials (ignore the center stimulus) also show a dramatic increase in the “Flanker” effect
between the Single-Task block (focus only on the Outside stimuli) and the Mixed-Task block (on some
trials focus on the Inside, on some trials focus on the Outside). This was true for both studies and for
both the absolute “Flanker” effect and correcting for longer RTs in the Mixed Block (right-hand figure).
All subjects in Study 2 and half the subjects in Study 1
were tested with a Separated Cue (the Background Color):
<
BLOCK BLOCK 3
1
(MIXED)
80 x larger in mixed block
227 msec difference
Half were tested with Symbolic Stimuli: e.g.,
or
Rules: For White, press Left. For Black, press Right.
OUTSIDE
STUDY 2
250
0
These are the stimulus parameters
used in most Flanker experiments.
>
3 x larger in mixed block
Flanker Effect in msec
300
STUDY 1
Large
Study 1
In
INSIDE
INTEGRATED CUE
Main Result, 2:
MORE ROBUST FLANKER EFFECT IN MIXED BLOCK
(Less sensitive to changes in stimulus size or dispersion)
BLOCK BLOCK 3
(MIXED)
1
Flanker Effect in msec
16 mm x 16 mm
INSIDE
3 x larger in mixed block
Relative Flanker Effect
8 mm
<
BLOCK BLOCK 3
1
(MIXED)
Both studies show a large increase in the Flanker effect between the standard Flanker condition (Block
1; focus on the Inside figure) and the Mixed-Task block (Block 3; on some trials focus on the Inside and
on some trials focus on the Outside).
RT was longer on all trials in the Mixed Block, but as the right-hand figure shows, the Flanker effect is
still much amplified in the Mixed Block when the effect is scaled to the baseline (Congruent) RT.
Flanker Effect in msec
In Study 1, the stimuli were larger & farther apart than in Study 2:
INSIDE
6x larger in mixed block
108 msec difference
Stimulus Size:
Out
>

14 x larger in mixed block
163 msec difference
In
0.05
0
BLOCK BLOCK 3
(MIXED)
1
0
0.10
RT Difference: Incongruent minus Congruent
Study 2 included single-task blocks of only Inside and only
Outside trials both before and after the Mixed block
(counterbalancing the order of the 2 single-task blocks).
Rules: If blue background,
focus on the INSIDE stimulus
BLOCK BLOCK 3
(MIXED)
1
0.15
50
INSIDE

50
0.20
100
<

100
0.25
150
INSIDE

150
0.30
STUDY 2:
Smaller,
Closer Stimuli
Block 1 vs. Block 3 (Mixed Block) Outside Non-Switch Trials Only
Study 1 included one block of each type, the single-task blocks
before the Mixed block.
Half the subjects were tested with Iconic Stimuli: <
Rule: Press where the stimulus is pointing
200
0.35
STUDY 1:
Large Stimuli,
Farther Apart
200
OUTSIDE
No Distractor
Neutral
Neutral

All subjects received 3 kinds of trial blocks:
Inside-Only
Outside-Only
Both Trial Types Intermixed
10 practice trials before each
16 practice trials
70 trials per block
180 trials
Half the subjects received Inside-Only first.
Half the subjects received Outside-Only first.
Sample
Stimulus
in Study 1
250
0
METHODS
36 mm x 36 mm
300
STUDY 2:
Smaller,
Closer Stimuli
STUDY 1:
Large Stimuli,
Farther Apart
Relative RT difference: (I – C) / C
250
INSIDE
No Distractor

Flanker Effect in msec
RT Difference: Incongruent minus Congruent
300
Block 3
(Mixed Block)
SEPARATED CUE

Our prediction was resoundingly confirmed. The Flanker
effect was dramatically larger in the mixed-condition than in
single-task blocks (in both cases comparing non-switch
incongruent and congruent trials). It was also much less
sensitive to variations in stimulus characteristics.
Block 1 (Standard Flanker) vs. Block 3 (Mixed Block) Inside Non-Switch Trials Only
Block 1
(Single-Task Block)
IN SUMMARY, regardless of
- stimulus size or the distance between stimuli
(Study 1 vs. Study 2),
- whether subjects had to focus on the Inside or
the Outside on a given trial,
- whether the cue was Integrated with the stimuli
or the color of the background, or
- whether the Flanker effect was calculated as
Incongruent minus Congruent RT or the ratio of
that to baseline (Congruent) RT,
the Flanker effect was dramatically larger when
subjects could not stay focused on just the
inside or just the outside, but had to periodically
switch the focus of their attention across trials.

We hypothesized that the reason for that is because subjects
can settle into concentrating on the central location.
We therefore predicted that if a switching component were
added, requiring subjects to sometimes focus on the flankers
and sometimes on the central stimulus, that the flanker effect
would be far larger and far more robust (less sensitive to
stimulus size or distance between stimuli).
Summary for Main Result, 1: Block 1 vs. Block 3 Non-Switch Trials
Flanker Effect in msec
The classic Flanker effect is highly replicable but relatively small
and fragile (i.e., very sensitive to stimulus characteristics).
Besides congruent and incongruent trial types, there
were also No-Distractor and Neutral trials:

Main Result, 1:
FAR LARGER FLANKER EFFECT IN MIXED BLOCK
Flanker Effect in msec
ABBREVIATED ABSTRACT
email: adele.diamond@ubc.ca

Department of Psychiatry, University of British Columbia, 2255 Wesbrook Mall, Vancouver, BC, Canada V6T 2A1
IN OUT
Early or late in the session, before or after the
Mixed Block, the Flanker effect was far
smaller when subjects did not have to change
the focus of their attention, whether they were
focusing on the center or on the outside.
The size of the flanker effect for inside-only
or outside-only trials was similar in Blocks 1,
2, 4, and 5. This also indicates that the size of
the Flanker effect was not affected by the
preceding block of trials.
The much larger Flanker effect in the Mixed
block cannot be explained by practice effects.
• When observers were allowed to consistently focus on a
specific area (either Inside-only or Outside-only), the Flanker
effect was much smaller than when subjects did not know in
advance whether the target would be in the center or the outside.
• The Flanker effect for Inside-only and Outside-only blocks
was very susceptible to disruption by increasing the size and
dispersion of the stimuli or by using stimuli less directly, automatically tied to the response.
• When observers had to randomly switch mindsets and the
focus of their attention across trials (Mixed block), the Flanker
effect increased dramatically in size and became significantly
more robust and resistant to disruption due to changes in the
physical
• The much larger Flanker effect in the Mixed block was true
regardless of stimulus type (iconic or symbolic), stimulus size or
spacing (large, farther apart or small, closer together), cue-type
(an integrated aspect of the stimuli themselves or the color of the
background), block order (whether preceded by a block where all
trials had the other rule, intermixed rules, or no preceding block),
whether early or late in a session, which rule was in effect (press
where the central stimulus tells you, or press where the outer
stimuli tell you), or how flanker effect was calculated (diffference
in absolute RT or that difference as a fraction of baseline RT).
• The dramatically larger Flanker effect in the Mixed block cannot
be attributed to practice effects or longer to RTs on all trials in the
Mixed block.
OTHER FINDINGS:
• Gender and age had no significant effect on RT or the Flanker
effect.
• Participants whose first language was Chinese showed larger
Flanker effects than non-Chinese participants for trials in which
the outer stimuli were the target.
This research was supported by an R01 grant from NIDA (#DA19685-16A2).