Flanker Task

Version: v1 (current)

Overview

The Eriksen Flanker Task is a classic measure of selective attention and cognitive control. Participants see a row of arrows (or other directional stimuli) and must indicate the direction of the center arrow while ignoring the flanking arrows on either side.

On congruent trials, all arrows point the same direction (>>>>>), making responses fast and accurate. On incongruent trials, flankers point the opposite direction (<<><<), creating response conflict and slowing reaction times. The difference between these conditions, known as the flanker effect, quantifies how well participants can focus attention and suppress irrelevant information.

Scientific Background

The flanker task, developed by Eriksen and Eriksen (1974), is a cornerstone paradigm in attention research:

• Eriksen, B.A., & Eriksen, C.W. (1974). Effects of noise letters upon the identification of a target letter in a nonsearch task. Perception & Psychophysics, 16(1), 143-149.
• Kopp, B., Rist, F., & Mattler, U. (1996). N200 in the flanker task as a neurobehavioral tool for investigating executive control. Psychophysiology, 33(3), 282-294.

The task measures:

• Selective attention: Ability to focus on task-relevant information
• Response inhibition: Suppression of incorrect prepotent responses
• Conflict monitoring: Detection and resolution of response competition

The flanker effect typically ranges from 30-80ms in healthy adults, with larger effects indicating greater susceptibility to interference.

Why Researchers Use This Task

• Cognitive control assessment: Simple, robust measure of executive attention
• Developmental studies: Flanker effect decreases from childhood to adulthood
• Clinical applications: Sensitive to ADHD, anxiety, aging, and frontal lobe dysfunction
• Neuroimaging: Reliably activates anterior cingulate cortex (conflict monitoring)
• Training studies: Used to assess improvements in attentional control
• Individual differences: Correlates with other executive function measures

Task Parameters

Response Mode

Parameter	Type	Default	Description
Flanker Time Based	boolean	True	If True, trials auto-advance; if False, participant responds via button

Visual Configuration

Parameter	Type	Default	Description
Flanker Font Size (px)	number	72	Font size for arrow display (8-400)

Practice Trials

Parameter	Type	Default	Description
Flanker Practice Enabled	boolean	False	Enable practice trials with visual feedback
Flanker Practice Trials	array	[]	Array of practice trial configurations

Keyboard Shortcuts

Researchers can customize the keyboard bindings used during the task:

Parameter	Type	Default	Description
Show keyboard hint	boolean	True	Display an on-screen hint showing the configured keys
Left key	key	Arrow Left (←)	Key for left-pointing center arrow
Left action label	text	"Left"	Label shown in the keyboard hint for the left key
Right key	key	Arrow Right (→)	Key for right-pointing center arrow
Right action label	text	"Right"	Label shown in the keyboard hint for the right key

Trial Configuration

Each trial is defined in the Trials spreadsheet with the following columns:

Column	Description	Example
center	Center arrow character	>, <
flankers	Flanking arrow character	>, <
condition	Trial type	Congruent, Incongruent
expected_response	Correct answer	Left, Right
fixation_ms	Fixation cross duration	500
stimulus_ms	Arrow display duration	2000
block	Optional grouping label	Practice, Main, Block 1

Example Trials

| center | flankers | condition    | expected_response | fixation_ms | stimulus_ms | block |
|--------|----------|--------------|-------------------|-------------|-------------|-------|
| >      | >        | congruent    | right             | 500         | 2000        | main  |
| <      | <        | congruent    | left              | 500         | 2000        | main  |
| >      | <        | incongruent  | right             | 500         | 2000        | main  |
| <      | >        | incongruent  | left              | 500         | 2000        | main  |

Note: The task automatically builds the 5-arrow display: flankers + flankers + center + flankers + flankers

Participant Experience

Trial Sequence

1. Main Instructions: Explains to respond to the center arrow only
2. (Optional) Practice Instructions: If practice enabled
3. (Optional) Practice Trials: With visual feedback (green checkmark for correct, red X for incorrect)
4. (Optional) Trials Instructions: Shown before main trials
5. Main Trials: Each trial follows this sequence:
   • Fixation cross (+) appears (if fixation_ms > 0)
   • Arrow row appears (e.g., <<><<)
   • Participant presses left arrow key or right arrow key
   • Trial advances automatically (time-based) or after response (button-based)

Response Methods

Keyboard (recommended):

• Press Left Arrow Key (←) for left-pointing center arrow (default -- configurable by researcher)
• Press Right Arrow Key (→) for right-pointing center arrow (default -- configurable by researcher)

Buttons (if flanker_time_based: false):

• Click "Left" or "Right" button on screen

All keyboard bindings are configurable by the researcher in the study configuration. The keys listed above are the defaults.

Data Output

Markers and Responses

Markers (stimulus_shown):

{
  "type": "stimulus_shown",
  "ts": "2024-01-01T00:00:01.000Z",
  "hr": 1234.56,
  "data": {
    "trial_index": 1,
    "stimulus_id": "flanker_0_1",
    "row": "<<><<",
    "center": ">",
    "flankers": "<",
    "condition": "incongruent",
    "expected_response": "right",
    "block": "main"
  }
}

Response Data:

{
  "trial_index": 1,
  "stimulus_id": "flanker_0_1",
  "source": "keyboard",
  "raw_key": "ArrowRight",
  "row": "<<><<",
  "condition": "incongruent",
  "expected_response": "right",
  "response_value": "right",
  "correct": true,
  "latency_ms": 623,
  "ts": "2024-01-01T00:00:01.623Z",
  "hr": 1857.56
}

Summary Artifact

A JSON file (flanker_summary_<taskIndex>.json) with aggregated statistics:

{
  "task_kind": "flanker",
  "total_trials": 60,
  "overall": {
    "accuracy": 0.95,
    "mean_rt_ms": 542,
    "mean_correct_rt_ms": 531
  },
  "by_condition": {
    "congruent": {
      "accuracy": 0.98,
      "mean_correct_rt_ms": 487
    },
    "incongruent": {
      "accuracy": 0.92,
      "mean_correct_rt_ms": 575
    }
  },
  "flanker_effect_ms": 88,
  "trials": [ /* per-trial data */ ]
}

Key metrics:

• flanker_effect_ms: Difference between incongruent and congruent mean RTs (higher = more interference)
• accuracy: Overall proportion correct
• mean_correct_rt_ms: Average RT for correct responses only

Design Recommendations

Trial Design

Balanced design (recommended):

• 30 congruent trials
• 30 incongruent trials
• Randomize order to prevent anticipation
• Equal left/right responses in each condition

Minimum for reliable flanker effect:

• 20 congruent trials
• 20 incongruent trials

Timing Guidelines

Parameter	Standard	Fast	Slow
Fixation (ms)	400-600ms	200ms	800ms
Stimulus (ms)	1500-2000ms	1000ms	3000ms

Note: Most participants respond within 1000ms. Longer stimulus durations allow more time but may reduce time pressure.

Practice Trials

Include 8-16 practice trials:

• Mix congruent and incongruent (equal numbers)
• Provide feedback so participants learn the task
• Both left and right responses should appear
• Consider starting with all congruent, then introducing incongruent

Arrow Stimuli

Standard arrows (recommended):

• Left: <
• Right: >
• Builds 5-character display automatically

Alternative stimuli: You can use letters (H and S) or other directional characters, but arrows are most intuitive.

Common Issues and Solutions

No Flanker Effect

Problem: Incongruent RT not slower than congruent RT

Possible causes:

• Too few trials (high variability)
• Stimulus duration too long (no time pressure)
• Participants responding too slowly (speed-accuracy tradeoff)

Solutions:

• Increase trials per condition (minimum 20 each)
• Reduce stimulus_ms to 1500ms or less
• Emphasize speed in instructions ("Respond as quickly as possible")

High Error Rate (>15%)

Problem: Accuracy below 85%

Possible causes:

• Stimulus duration too short
• Participants not understanding "center arrow only"
• Keyboard confusion (arrow keys not working)

Solutions:

• Increase stimulus_ms to 2500-3000ms
• Extend practice with clearer feedback
• Test keyboard functionality before starting
• Add explicit examples in instructions

Keyboard Responses Not Working

Problem: Arrow keys don't register

Solutions:

• Ensure task window has focus (click on task area)
• Check browser compatibility (works best in Chrome/Edge/Firefox)
• Use button-based mode as alternative (flanker_time_based: false)

Example Study Configurations

Standard Adult Flanker

• 80 trials total (40 congruent, 40 incongruent)
• 500ms fixation, 1500ms stimulus
• Time-based mode with keyboard responses
• Practice: 12 trials with feedback
• Emphasize speed in instructions

Developmental Version (Children)

• Fewer trials (48 total: 24 per condition)
• Longer stimulus duration (2500ms)
• Larger font size (96px)
• Extended practice (20 trials)
• Button-based mode (easier than keyboard)

Clinical Assessment

• Moderate trial count (60 total)
• Longer stimulus duration (2000ms)
• Self-paced (button-based mode)
• Practice trials mandatory
• Multiple blocks with breaks

Within-Subjects Manipulation

Block 1: High congruency (80% congruent, 20% incongruent) Block 2: Low congruency (20% congruent, 80% incongruent)

This tests expectancy effects on the flanker effect.

References

• Eriksen, B.A., & Eriksen, C.W. (1974). Effects of noise letters upon the identification of a target letter in a nonsearch task. Perception & Psychophysics, 16(1), 143-149.
• Kopp, B., Rist, F., & Mattler, U. (1996). N200 in the flanker task as a neurobehavioral tool for investigating executive control. Psychophysiology, 33(3), 282-294.
• Fan, J., McCandliss, B.D., Sommer, T., Raz, A., & Posner, M.I. (2002). Testing the efficiency and independence of attentional networks. Journal of Cognitive Neuroscience, 14(3), 340-347.